Receiver Spec vs. ATP, a few Suggestions and a Question or Two
John,
I took a few minutes to look over your new specs and compare them against the Acceptance Test Procedure. I've got a number of tests in the ATP for which there are no specs:
* Image rejection
* Internally generated spurs
* Local oscillator leakage
* Input and Output VSWR
Items that need to be addressed that aren't in either document:
* EMI conducted susceptibility
* EMI radiated susceptibility
* Short and long-term frequency stability
I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature.
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Rather than worry about trying to conduct heat through a PCB why not just go to externally mounted regulators for the CAN-Do and the Receiver right on the case itself. We're not that pressed for space. That eases the heat sink and the associated thermal gap filler issues. EMI will still be an issue, but only for external sources instead of one that is inside the enclosure itself. That strikes me as a huge bonus. Why not design a single-sided PCB with the regulators hanging over the edge and the whole assembly, PCB and regulators, mounted directly to the enclosure. Stick it in with the CAN-Do module in a separate cell. Filter all the signal and power through the common bulkhead.
I'm also curious as to why you are specifying two different types of SMA connectors.
73,
Juan - WA6HTP
Juan:
From a practical aspect, the hanging of electronics on the outside of an E05
20 module is rather implacable as there is no place to put them. The thin metal cover is not a place as the heat would not be spread out for dissipation, and the cover would not be "divorceable" from the rest of the module. You would not want to place them on the front connector bracket as you are already scrambling for space for connectors. Those are the only areas that are open to the outside world.
We already have solutions for the mounting of these electronics on the inside of the module, where they belong, so I do not see where you otherwise plan to place these power conditioning electronics?
Dick Jansson, KD1K
mailto:kd1k@amsat.org kd1k@amsat.org
mailto:kd1k@arrl.net kd1k@arrl.net
From: eagle-bounces@amsat.org [mailto:eagle-bounces@amsat.org] On Behalf Of Juan Rivera Sent: Saturday, 28 July, 2007 05.23 To: 'John B. Stephensen' Cc: David Smith; Dave Black (Work); Dave Black (Home); eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: [eagle] Receiver Spec vs. ATP, a few Suggestions and a Question or Two
John,
I took a few minutes to look over your new specs and compare them against the Acceptance Test Procedure. I've got a number of tests in the ATP for which there are no specs:
. Image rejection
. Internally generated spurs
. Local oscillator leakage
. Input and Output VSWR
Items that need to be addressed that aren't in either document:
. EMI conducted susceptibility
. EMI radiated susceptibility
. Short and long-term frequency stability
I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature.
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Rather than worry about trying to conduct heat through a PCB why not just go to externally mounted regulators for the CAN-Do and the Receiver right on the case itself. We're not that pressed for space. That eases the heat sink and the associated thermal gap filler issues. EMI will still be an issue, but only for external sources instead of one that is inside the enclosure itself. That strikes me as a huge bonus. Why not design a single-sided PCB with the regulators hanging over the edge and the whole assembly, PCB and regulators, mounted directly to the enclosure. Stick it in with the CAN-Do module in a separate cell. Filter all the signal and power through the common bulkhead.
I'm also curious as to why you are specifying two different types of SMA connectors.
73,
Juan - WA6HTP
Dick,
I know this is an unpleasant subject and I apologize, but I don’t think the existing enclosure is going to satisfy the real-world requirements for SMT PCB flex. I’m basing this on several things. The first is a paper written by AVX (see below), one of the largest surface mount capacitor manufacturers in the world. They recommend a maximum PCB flex specification based on bend radius to prevent component cracking. It works out to 0.0084” in any 1-inch segment. They also caution against placing any components near mounting screw holes as they are areas of especially high stress. As you know, this board has ceramic chip capacitors (the most brittle components on the board) extremely close to the heat sink mounting hardware. This imposes even more need for absolute rigidity and flatness across the entire mounting surface. Given the current expectation to cold soak this Receiver down to -60C it places almost impossible demands on the PCB, the components, and the enclosure. Coefficient of thermal expansion mismatches between these items is aggravated by this huge ∆T the receiver is expected to survive. I have yet to find anyone who has experience with a payload that was expected to survive repeated excursions down to -60C.
Next is my experience with this prototype enclosure. Yesterday I disassembled the PCB and heat sinks and took a few measurements. Here’s what I found:
Heat Sink No.
Minimum Dim.
Maximum Dim.
1
0.183”
0.186”
2
0.181”
0.185”
3
0.185”
0.189”
As you can see, the tolerances on the heat sink thickness are pretty bad. I’m not able to measure the standoffs because of the material extending out the opposite side of the base plate. I checked the parts list for this chassis and those standoffs are not listed so I don’t know what the manufacturer’s tolerance is on height.
I also found that seven out of the ten PEM standoffs are loose and can be rotated with your fingers. This raises a concern over grounding. But the main problem is that the enclosure is flexible and warped. I think there are several reasons for this. The sheet metal base might have been slightly bowed to start with and then the large amount of work that is done to it (34 PEM standoffs and captive nuts) might have aggravated the warp. And of course milling holes in the base to gain access to the connectors might have contributed to this. I also notice that the base becomes more warped after the front connector panel is attached. I inspected this closely and found that some of the PEM captive nuts that are applied from the bottom are not completely flat on the top surface. When the connector plate is drawn down to the base plate the base plate is flexed over those protruding PEM nuts causing more warp. This changes the dynamics of the enclosure. Attaching the lid and finally mounting the enclosure to the satellite frame will all cause the PCB mounting surface to shift, tilt, and bend in unpredictable ways.
And lastly, we may need to split the enclosure into two compartments with the CAN-Do module and other switching power supply components in the front and analog circuitry in the back. This may be necessary to resolve radiated EMI issues.
So there are my concerns and findings. To me they all point to the need for a milled enclosure. Such an enclosure would have a flat plate on top as a cover. A milled enclosure would allow the power supply regulators to be mounted on the inside surface of one of the walls, greatly improving and simplifying heat dissipation. Most importantly, all of the heat sink and PCB mounting surfaces would be part of the same block of aluminum as the enclosure itself and would be very rigid and flat.
Here’s a link to the AVX paper I mentioned --> http://www.avxcorp.com/docs/techinfo/smzero.pdf (see page 4)
73,
Juan – WA6HTP
_____
From: Dick Jansson-rr [mailto:rjansson@cfl.rr.com] Sent: Saturday, July 28, 2007 5:26 AM To: juan-rivera@sbcglobal.net; 'John B. Stephensen' Cc: 'David Smith'; 'Dave Black (Work)'; 'Dave Black (Home)'; eagle@amsat.org; 'Samsonoff@Mac. Com'; 'Juan.Rivera (Work)' Subject: RE: [eagle] Receiver Spec vs. ATP, a few Suggestions and a Question or Two
Juan:
From a practical aspect, the hanging of electronics on the outside of an E05 20 module is rather implacable as there is no place to put them. The thin metal cover is not a place as the heat would not be spread out for dissipation, and the cover would not be “divorceable” from the rest of the module. You would not want to place them on the front connector bracket as you are already scrambling for space for connectors. Those are the only areas that are open to the outside world.
We already have solutions for the mounting of these electronics on the inside of the module, where they belong, so I do not see where you otherwise plan to place these power conditioning electronics?
Dick Jansson, KD1K
kd1k@amsat.org
kd1k@arrl.net
From: eagle-bounces@amsat.org [mailto:eagle-bounces@amsat.org] On Behalf Of Juan Rivera Sent: Saturday, 28 July, 2007 05.23 To: 'John B. Stephensen' Cc: David Smith; Dave Black (Work); Dave Black (Home); eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: [eagle] Receiver Spec vs. ATP, a few Suggestions and a Question or Two
John,
I took a few minutes to look over your new specs and compare them against the Acceptance Test Procedure. I've got a number of tests in the ATP for which there are no specs:
* Image rejection
* Internally generated spurs
* Local oscillator leakage
* Input and Output VSWR
Items that need to be addressed that aren’t in either document:
* EMI conducted susceptibility
* EMI radiated susceptibility
* Short and long-term frequency stability
I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature.
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Rather than worry about trying to conduct heat through a PCB why not just go to externally mounted regulators for the CAN-Do and the Receiver right on the case itself. We’re not that pressed for space. That eases the heat sink and the associated thermal gap filler issues. EMI will still be an issue, but only for external sources instead of one that is inside the enclosure itself. That strikes me as a huge bonus. Why not design a single-sided PCB with the regulators hanging over the edge and the whole assembly, PCB and regulators, mounted directly to the enclosure. Stick it in with the CAN-Do module in a separate cell. Filter all the signal and power through the common bulkhead.
I’m also curious as to why you are specifying two different types of SMA connectors.
73,
Juan – WA6HTP
Juan:
I do not know how you can be concerned with storage temperatures of -60°C when you have just soldered a PCB with temperatures of from two to a a few hundred degrees! It seems to me that the stress of soldering would vastly exceed those of a low storage temperature. The thermal excursions of soldering considerably exceed those of the storage situation.
73,
Dick Jansson, KD1K
mailto:kd1k@amsat.org kd1k@amsat.org
mailto:kd1k@arrl.net kd1k@arrl.net
From: eagle-bounces@amsat.org [mailto:eagle-bounces@amsat.org] On Behalf Of Juan Rivera Sent: Saturday, 28 July, 2007 05.23 To: 'John B. Stephensen' Cc: David Smith; Dave Black (Work); Dave Black (Home); eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: [eagle] Receiver Spec vs. ATP, a few Suggestions and a Question or Two
John,
· (snip)
I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature.
(snip)
73,
Juan WA6HTP
Isn't the issue the rate of change of the temperature of the baseplate?
The minimum storage temperatures for most components is -65 C and the SAW filters are -40 C.
73,
John KD6OZH ----- Original Message ----- From: Dick Jansson-rr To: juan-rivera@sbcglobal.net ; 'John B. Stephensen' Cc: 'David Smith' ; 'Dave Black (Work)' ; 'Dave Black (Home)' ; eagle@amsat.org ; 'Samsonoff@Mac. Com' ; 'Juan.Rivera (Work)' Sent: Saturday, July 28, 2007 18:32 UTC Subject: RE: [eagle] Receiver Spec vs. ATP, a few Suggestions and a Question or Two
Juan:
I do not know how you can be concerned with storage temperatures of -60°C when you have just soldered a PCB with temperatures of from two to a a few hundred degrees! It seems to me that the stress of soldering would vastly exceed those of a low storage temperature. The thermal excursions of soldering considerably exceed those of the storage situation.
'73,
Dick Jansson, KD1K
kd1k@amsat.org
kd1k@arrl.net
From: eagle-bounces@amsat.org [mailto:eagle-bounces@amsat.org] On Behalf Of Juan Rivera Sent: Saturday, 28 July, 2007 05.23 To: 'John B. Stephensen' Cc: David Smith; Dave Black (Work); Dave Black (Home); eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: [eagle] Receiver Spec vs. ATP, a few Suggestions and a Question or Two
John,
· (snip)
I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature.
(snip)
73,
Juan - WA6HTP
On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Hrm. What makes you say "a slight efficiency hit"?
Doing this on one or two modules that are particularly susceptible to noise *may* make sense (and I'm certainly open to considering this as an alternative), but we're already on our second power supply design on the CAN-Do! because the original switcher, which was more efficient than a linear regulator, was deemed too inefficient to fly on P3E by our AMSAT-DL friends.
Bdale
Bdale,
It would be a trade-off. I've put out all the information I have and everyone knows my opinions. I think someone else is supposed to be looking into this but I forgot who it is since nothing has been posted. I'd like to see some alternative suggestions from the experts on the CAN-Do, the enclosure, and the EMI situation in general.
By the way, do I have a prototype CAN-Do module or was the intent to fly this version with the dead-bug step-down converter hanging by three leads and a few wires?
Juan
-----Original Message----- From: Bdale Garbee [mailto:bdale@gag.com] Sent: Saturday, July 28, 2007 2:41 PM To: juan-rivera@sbcglobal.net Cc: 'John B. Stephensen'; David Smith; Dave Black (Work); Dave Black (Home); eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: Re: [eagle] Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Hrm. What makes you say "a slight efficiency hit"?
Doing this on one or two modules that are particularly susceptible to noise *may* make sense (and I'm certainly open to considering this as an alternative), but we're already on our second power supply design on the CAN-Do! because the original switcher, which was more efficient than a linear regulator, was deemed too inefficient to fly on P3E by our AMSAT-DL friends.
Bdale
Hi Juan,
I think the reason you have not seen much regarding the CAN-Do redesign is that, as far as I know, no one has stepped up to do the power supply redesign. Until that happens, not much else will happen.
I'm not thrilled with the idea of giving up the switching power supply. Remember that the efficiency hit must be multiplied by 10-15, the number of CAN-Do's on the satellite.
The "dead-bug" modification is intended to fly. Those who were not around in the early days have no idea what loose wires have flown successfully in the past. That's not to say we should encourage such things, just that it's not as ugly to those of us who have seen much worse in the past as you might think. Because of the IC's mass (very small) it is probably very secure just the way you see it. But we will also epoxy a radiation shield to it and then conformal coat the whole thing with a heave conformal coating which will make it very difficult for anything to move.
I'm ready to start a new design (layout) just as soon as someone gives us a new power supply design that is quieter, and hopefully, more efficient than the 90% we now have.
Chuck
Juan Rivera wrote:
Bdale,
It would be a trade-off. I've put out all the information I have and everyone knows my opinions. I think someone else is supposed to be looking into this but I forgot who it is since nothing has been posted. I'd like to see some alternative suggestions from the experts on the CAN-Do, the enclosure, and the EMI situation in general.
By the way, do I have a prototype CAN-Do module or was the intent to fly this version with the dead-bug step-down converter hanging by three leads and a few wires?
Juan
-----Original Message----- From: Bdale Garbee [mailto:bdale@gag.com] Sent: Saturday, July 28, 2007 2:41 PM To: juan-rivera@sbcglobal.net Cc: 'John B. Stephensen'; David Smith; Dave Black (Work); Dave Black (Home); eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: Re: [eagle] Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Hrm. What makes you say "a slight efficiency hit"?
Doing this on one or two modules that are particularly susceptible to noise *may* make sense (and I'm certainly open to considering this as an alternative), but we're already on our second power supply design on the CAN-Do! because the original switcher, which was more efficient than a linear regulator, was deemed too inefficient to fly on P3E by our AMSAT-DL friends.
Bdale
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
Linear regulators would add 1-1.6 W of power consumption depending on battery voltage.
73,
John KD6OZH
----- Original Message ----- From: "Chuck Green" greencl@mindspring.com To: juan-rivera@sbcglobal.net Cc: "'Dave Black (Work)'" dblack@mail.arc.nasa.gov; "'Dave Black (Home)'" dblack1054@yahoo.com; "'David Smith'" w6te@msn.com; eagle@amsat.org; "'Samsonoff@Mac. Com'" samsonoff@mac.com; "'Juan.Rivera (Work)'" Juan.Rivera@gd-ais.com Sent: Saturday, July 28, 2007 22:30 UTC Subject: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
Hi Juan,
I think the reason you have not seen much regarding the CAN-Do redesign is that, as far as I know, no one has stepped up to do the power supply redesign. Until that happens, not much else will happen.
I'm not thrilled with the idea of giving up the switching power supply. Remember that the efficiency hit must be multiplied by 10-15, the number of CAN-Do's on the satellite.
The "dead-bug" modification is intended to fly. Those who were not around in the early days have no idea what loose wires have flown successfully in the past. That's not to say we should encourage such things, just that it's not as ugly to those of us who have seen much worse in the past as you might think. Because of the IC's mass (very small) it is probably very secure just the way you see it. But we will also epoxy a radiation shield to it and then conformal coat the whole thing with a heave conformal coating which will make it very difficult for anything to move.
I'm ready to start a new design (layout) just as soon as someone gives us a new power supply design that is quieter, and hopefully, more efficient than the 90% we now have.
Chuck
Juan Rivera wrote:
Bdale,
It would be a trade-off. I've put out all the information I have and everyone knows my opinions. I think someone else is supposed to be looking into this but I forgot who it is since nothing has been posted. I'd like to see some alternative suggestions from the experts on the CAN-Do, the enclosure, and the EMI situation in general.
By the way, do I have a prototype CAN-Do module or was the intent to fly this version with the dead-bug step-down converter hanging by three leads and a few wires?
Juan
-----Original Message----- From: Bdale Garbee [mailto:bdale@gag.com] Sent: Saturday, July 28, 2007 2:41 PM To: juan-rivera@sbcglobal.net Cc: 'John B. Stephensen'; David Smith; Dave Black (Work); Dave Black (Home); eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: Re: [eagle] Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Hrm. What makes you say "a slight efficiency hit"?
Doing this on one or two modules that are particularly susceptible to noise *may* make sense (and I'm certainly open to considering this as an alternative), but we're already on our second power supply design on the CAN-Do! because the original switcher, which was more efficient than a linear regulator, was deemed too inefficient to fly on P3E by our AMSAT-DL friends.
Bdale
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
All,
Let's consider the trade-offs...
If the CAN-Do module used a linear regulator the EMI problem (from the CAN-Do module only) would completely disappear. That would mean there would probably be no need to consider a two-compartment enclosure to provide shielding. But the power consumption would increase.
If we were to go to the switching step-down converter I'm thinking of at 400 kHz then the EMI would be pushed out of the passband of the 70 cm Receiver. If the PCB were laid out per the manufacturer's recommendations instead of dead-bug as is the case now, and if the inductor was shielded, then the EMI from the CAN-Do module should be greatly reduced. Since I don't believe the existing converter is operating properly this converter might actually result in a slight reduction in power consumption. Filtering conducted EMI at 400 kHz will require relatively small components, saving weight.
If you go with what you have now I think you'll be flying a module with a poorly functioning, motorboating, step-down converter and the enclosure will need to be divided into two compartments for shielding. You'll also need more bulky filtering to get rid of the conducted EMI at 5 kHz. Switching to a shielded inductor might help the radiated EMI but that won't resolve the problems with the poor layout of the circuit.
I know Chuck says the dead bug installation is intended to fly, but my concern is not only for the mechanical integrity of the wiring but mostly for the EMI implications. Bear with me for a few days and I'll try to get my write-up out as soon as I can. My conclusion is that the CAN-Do module PCB layout needs to be revised per the Maxim recommendations to get the existing converter to stop motorboating. If you accept that conclusion then you might as well switch from a 5 kHz converter to one that switches at 400 kHz.
73,
Juan
-----Original Message----- From: John B. Stephensen [mailto:kd6ozh@comcast.net] Sent: Saturday, July 28, 2007 4:10 PM To: Chuck Green; juan-rivera@sbcglobal.net Cc: 'Dave Black (Work)'; 'Dave Black (Home)'; 'David Smith'; eagle@amsat.org; 'Samsonoff@Mac. Com'; 'Juan.Rivera (Work)' Subject: Re: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
Linear regulators would add 1-1.6 W of power consumption depending on battery voltage.
73,
John KD6OZH
----- Original Message ----- From: "Chuck Green" greencl@mindspring.com To: juan-rivera@sbcglobal.net Cc: "'Dave Black (Work)'" dblack@mail.arc.nasa.gov; "'Dave Black (Home)'" dblack1054@yahoo.com; "'David Smith'" w6te@msn.com; eagle@amsat.org; "'Samsonoff@Mac. Com'" samsonoff@mac.com; "'Juan.Rivera (Work)'" Juan.Rivera@gd-ais.com Sent: Saturday, July 28, 2007 22:30 UTC Subject: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
Hi Juan,
I think the reason you have not seen much regarding the CAN-Do redesign is that, as far as I know, no one has stepped up to do the power supply redesign. Until that happens, not much else will happen.
I'm not thrilled with the idea of giving up the switching power supply. Remember that the efficiency hit must be multiplied by 10-15, the number of CAN-Do's on the satellite.
The "dead-bug" modification is intended to fly. Those who were not around in the early days have no idea what loose wires have flown successfully in the past. That's not to say we should encourage such things, just that it's not as ugly to those of us who have seen much worse in the past as you might think. Because of the IC's mass (very small) it is probably very secure just the way you see it. But we will also epoxy a radiation shield to it and then conformal coat the whole thing with a heave conformal coating which will make it very difficult for anything to move.
I'm ready to start a new design (layout) just as soon as someone gives us a new power supply design that is quieter, and hopefully, more efficient than the 90% we now have.
Chuck
Juan Rivera wrote:
Bdale,
It would be a trade-off. I've put out all the information I have and everyone knows my opinions. I think someone else is supposed to be looking into this but I forgot who it is since nothing has been posted. I'd like
to see some alternative suggestions from the experts on the CAN-Do, the enclosure, and the EMI situation in general.
By the way, do I have a prototype CAN-Do module or was the intent to fly this version with the dead-bug step-down converter hanging by three leads and a few wires?
Juan
-----Original Message----- From: Bdale Garbee [mailto:bdale@gag.com] Sent: Saturday, July 28, 2007 2:41 PM To: juan-rivera@sbcglobal.net Cc: 'John B. Stephensen'; David Smith; Dave Black (Work); Dave Black (Home); eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: Re: [eagle] Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Hrm. What makes you say "a slight efficiency hit"?
Doing this on one or two modules that are particularly susceptible to noise *may* make sense (and I'm certainly open to considering this as an alternative), but we're already on our second power supply design on the CAN-Do! because the original switcher, which was more efficient than a linear regulator, was deemed too inefficient to fly on P3E by our AMSAT-DL friends.
Bdale
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
Hi Chuck,
I don't think that existing supply is running at 90% efficiency. I'll have to solder it back together to take a few measurements but the manufacturer's specs don't claim quite that much and this one isn't running properly. I've got a bit more data in my symposium presentation and I hope to complete that in the next few days and get it out.
I found a step-down converter that's designed to supply a maximum of about 100 mA and it runs at 400 kHz with automotive temp range. If no one else steps up I'll put out some info on this one.
73,
Juan
-----Original Message----- From: Chuck Green [mailto:greencl@mindspring.com] Sent: Saturday, July 28, 2007 3:30 PM To: juan-rivera@sbcglobal.net Cc: 'Bdale Garbee'; 'David Smith'; 'Dave Black (Work)'; 'Dave Black (Home)'; eagle@amsat.org; 'Samsonoff@Mac. Com'; 'Juan.Rivera (Work)' Subject: Re: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
Hi Juan,
I think the reason you have not seen much regarding the CAN-Do redesign is that, as far as I know, no one has stepped up to do the power supply redesign. Until that happens, not much else will happen.
I'm not thrilled with the idea of giving up the switching power supply. Remember that the efficiency hit must be multiplied by 10-15, the number of CAN-Do's on the satellite.
The "dead-bug" modification is intended to fly. Those who were not around in the early days have no idea what loose wires have flown successfully in the past. That's not to say we should encourage such things, just that it's not as ugly to those of us who have seen much worse in the past as you might think. Because of the IC's mass (very small) it is probably very secure just the way you see it. But we will also epoxy a radiation shield to it and then conformal coat the whole thing with a heave conformal coating which will make it very difficult for anything to move.
I'm ready to start a new design (layout) just as soon as someone gives us a new power supply design that is quieter, and hopefully, more efficient than the 90% we now have.
Chuck
Juan Rivera wrote:
Bdale,
It would be a trade-off. I've put out all the information I have and everyone knows my opinions. I think someone else is supposed to be
looking
into this but I forgot who it is since nothing has been posted. I'd like
to
see some alternative suggestions from the experts on the CAN-Do, the enclosure, and the EMI situation in general.
By the way, do I have a prototype CAN-Do module or was the intent to fly this version with the dead-bug step-down converter hanging by three leads and a few wires?
Juan
-----Original Message----- From: Bdale Garbee [mailto:bdale@gag.com] Sent: Saturday, July 28, 2007 2:41 PM To: juan-rivera@sbcglobal.net Cc: 'John B. Stephensen'; David Smith; Dave Black (Work); Dave Black
(Home);
eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: Re: [eagle] Receiver Spec vs. ATP, a few Suggestions and
aQuestion
or Two
On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Hrm. What makes you say "a slight efficiency hit"?
Doing this on one or two modules that are particularly susceptible to noise *may* make sense (and I'm certainly open to considering this as an alternative), but we're already on our second power supply design on the CAN-Do! because the original switcher, which was more efficient than a linear regulator, was deemed too inefficient to fly on P3E by our AMSAT-DL friends.
Bdale
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
Hi Juan,
My use of the value 90% (efficiency) is based on your measurements of current supplied and my previous measurements of power consumed. But it really doesn't matter how good this figure is, I think we can do a little better.
I really suspect the existing regulator is running normally. It is likely in a very low power mode and therefor not running at the 100 kHz + speed it can run at. But I'm not defending it. If there is something better (more suitable for our current needs), great! You may very well have found such a device. However, since it would be running at 10-15% of capacity it may also switch to a more efficient mode (slower switching speed).
Given the switching speed the regulator is running at now, I doubt the layout has much to do with the issues you have uncovered. But that really doesn't matter because we certainly wouldn't design a new board to install the device dead-bug stile. However, you might want to experiment with the new device as a direct replacement on the board which would likely mean dead-bug stile. The topology of switching supplies are often very much alike so it may well be that you could do this as a first experiment.
And I wouldn't give up on your idea of an analog supply. Just because one or two of us are not excited about this doesn't mean it isn't the right thing to do. It's a system level issue of power management. But I still want to encourage experimenting with a new switching supply to see if it can resolve the problem.
Chuck
Juan Rivera wrote:
Hi Chuck,
I don't think that existing supply is running at 90% efficiency. I'll have to solder it back together to take a few measurements but the manufacturer's specs don't claim quite that much and this one isn't running properly. I've got a bit more data in my symposium presentation and I hope to complete that in the next few days and get it out.
I found a step-down converter that's designed to supply a maximum of about 100 mA and it runs at 400 kHz with automotive temp range. If no one else steps up I'll put out some info on this one. 73,
Juan
-----Original Message----- From: Chuck Green [mailto:greencl@mindspring.com] Sent: Saturday, July 28, 2007 3:30 PM To: juan-rivera@sbcglobal.net Cc: 'Bdale Garbee'; 'David Smith'; 'Dave Black (Work)'; 'Dave Black (Home)'; eagle@amsat.org; 'Samsonoff@Mac. Com'; 'Juan.Rivera (Work)' Subject: Re: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
Hi Juan,
I think the reason you have not seen much regarding the CAN-Do redesign is that, as far as I know, no one has stepped up to do the power supply redesign. Until that happens, not much else will happen.
I'm not thrilled with the idea of giving up the switching power supply. Remember that the efficiency hit must be multiplied by 10-15, the number of CAN-Do's on the satellite.
The "dead-bug" modification is intended to fly. Those who were not around in the early days have no idea what loose wires have flown successfully in the past. That's not to say we should encourage such things, just that it's not as ugly to those of us who have seen much worse in the past as you might think. Because of the IC's mass (very small) it is probably very secure just the way you see it. But we will also epoxy a radiation shield to it and then conformal coat the whole thing with a heave conformal coating which will make it very difficult for anything to move.
I'm ready to start a new design (layout) just as soon as someone gives us a new power supply design that is quieter, and hopefully, more efficient than the 90% we now have.
Chuck
Juan Rivera wrote:
Bdale,
It would be a trade-off. I've put out all the information I have and everyone knows my opinions. I think someone else is supposed to be
looking
into this but I forgot who it is since nothing has been posted. I'd like
to
see some alternative suggestions from the experts on the CAN-Do, the enclosure, and the EMI situation in general.
By the way, do I have a prototype CAN-Do module or was the intent to fly this version with the dead-bug step-down converter hanging by three leads and a few wires?
Juan
-----Original Message----- From: Bdale Garbee [mailto:bdale@gag.com] Sent: Saturday, July 28, 2007 2:41 PM To: juan-rivera@sbcglobal.net Cc: 'John B. Stephensen'; David Smith; Dave Black (Work); Dave Black
(Home);
eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: Re: [eagle] Receiver Spec vs. ATP, a few Suggestions and
aQuestion
or Two
On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Hrm. What makes you say "a slight efficiency hit"?
Doing this on one or two modules that are particularly susceptible to noise *may* make sense (and I'm certainly open to considering this as an alternative), but we're already on our second power supply design on the CAN-Do! because the original switcher, which was more efficient than a linear regulator, was deemed too inefficient to fly on P3E by our AMSAT-DL friends.
Bdale
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
Hi Chuck,
I found the device I was thinking of. It's an Analog Devices ADP3000AR-5. Here's the link --> http://www.analog.com/UploadedFiles/Data_Sheets/ADP3000.pdf
Its operating temp range is -40C to +85C in an 8-lead SOIC style package.
Here's the block diagram:
Unlike most of these step-down converters, this one switches around 400 kHz regardless of the load. A wider temp range would be nice. I'll keep looking...
73, Juan
-----Original Message----- From: Chuck Green [mailto:greencl@mindspring.com] Sent: Sunday, July 29, 2007 7:28 AM To: juan-rivera@sbcglobal.net Cc: 'Bdale Garbee'; 'David Smith'; 'Dave Black (Work)'; 'Dave Black (Home)'; eagle@amsat.org; 'Samsonoff@Mac. Com'; 'Juan.Rivera (Work)' Subject: Re: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and aQuestion or Two
Hi Juan,
My use of the value 90% (efficiency) is based on your measurements of
current supplied and my previous measurements of power consumed. But it
really doesn't matter how good this figure is, I think we can do a
little better.
I really suspect the existing regulator is running normally. It is
likely in a very low power mode and therefor not running at the 100 kHz
+ speed it can run at. But I'm not defending it. If there is something
better (more suitable for our current needs), great! You may very well
have found such a device. However, since it would be running at 10-15%
of capacity it may also switch to a more efficient mode (slower
switching speed).
Given the switching speed the regulator is running at now, I doubt the
layout has much to do with the issues you have uncovered. But that
really doesn't matter because we certainly wouldn't design a new board
to install the device dead-bug stile. However, you might want to
experiment with the new device as a direct replacement on the board
which would likely mean dead-bug stile. The topology of switching
supplies are often very much alike so it may well be that you could do
this as a first experiment.
And I wouldn't give up on your idea of an analog supply. Just because
one or two of us are not excited about this doesn't mean it isn't the
right thing to do. It's a system level issue of power management. But
I still want to encourage experimenting with a new switching supply to
see if it can resolve the problem.
Chuck
Juan Rivera wrote:
Hi Chuck,
I don't think that existing supply is running at 90% efficiency. I'll
have
to solder it back together to take a few measurements but the
manufacturer's
specs don't claim quite that much and this one isn't running properly.
I've
got a bit more data in my symposium presentation and I hope to complete
that
in the next few days and get it out.
I found a step-down converter that's designed to supply a maximum of about
100 mA and it runs at 400 kHz with automotive temp range. If no one else
steps up I'll put out some info on this one.
73,
Juan
-----Original Message-----
From: Chuck Green [mailto:greencl@mindspring.com]
Sent: Saturday, July 28, 2007 3:30 PM
To: juan-rivera@sbcglobal.net
Cc: 'Bdale Garbee'; 'David Smith'; 'Dave Black (Work)'; 'Dave Black
(Home)';
eagle@amsat.org; 'Samsonoff@Mac. Com'; 'Juan.Rivera (Work)'
Subject: Re: [eagle] Re: Receiver Spec vs. ATP, a few Suggestions and
aQuestion or Two
Hi Juan,
I think the reason you have not seen much regarding the CAN-Do redesign
is that, as far as I know, no one has stepped up to do the power supply
redesign. Until that happens, not much else will happen.
I'm not thrilled with the idea of giving up the switching power supply.
Remember that the efficiency hit must be multiplied by 10-15, the number
of CAN-Do's on the satellite.
The "dead-bug" modification is intended to fly. Those who were not
around in the early days have no idea what loose wires have flown
successfully in the past. That's not to say we should encourage such
things, just that it's not as ugly to those of us who have seen much
worse in the past as you might think. Because of the IC's mass (very
small) it is probably very secure just the way you see it. But we will
also epoxy a radiation shield to it and then conformal coat the whole
thing with a heave conformal coating which will make it very difficult
for anything to move.
I'm ready to start a new design (layout) just as soon as someone gives
us a new power supply design that is quieter, and hopefully, more
efficient than the 90% we now have.
Chuck
Juan Rivera wrote:
Bdale,
It would be a trade-off. I've put out all the information I have and
everyone knows my opinions. I think someone else is supposed to be
looking
into this but I forgot who it is since nothing has been posted. I'd like
to
see some alternative suggestions from the experts on the CAN-Do, the
enclosure, and the EMI situation in general.
By the way, do I have a prototype CAN-Do module or was the intent to fly
this version with the dead-bug step-down converter hanging by three leads
and a few wires?
Juan
-----Original Message-----
From: Bdale Garbee [mailto:bdale@gag.com]
Sent: Saturday, July 28, 2007 2:41 PM
To: juan-rivera@sbcglobal.net
Cc: 'John B. Stephensen'; David Smith; Dave Black (Work); Dave Black
(Home);
eagle@amsat.org; Samsonoff@Mac. Com; Juan.Rivera (Work)
Subject: Re: [eagle] Receiver Spec vs. ATP, a few Suggestions and
aQuestion
or Two
On Fri, 2007-07-27 at 21:23 -0700, Juan Rivera wrote:
I have a few thoughts... The CAN-Do switching step-down converter is
only supplying 11 milliamps. If we take a slight efficiency hit we
could just go to a simple linear regulator and completely eliminate
the radiated and conducted EMI emission problem from CAN-do. That
eases the EMI filtering and shielding requirements for every single
payload. That seems like a good trade-off to me.
Hrm. What makes you say "a slight efficiency hit"?
Doing this on one or two modules that are particularly susceptible to
noise *may* make sense (and I'm certainly open to considering this as an
alternative), but we're already on our second power supply design on the
CAN-Do! because the original switcher, which was more efficient than a
linear regulator, was deemed too inefficient to fly on P3E by our
AMSAT-DL friends.
Bdale
Via the Eagle mailing list courtesy of AMSAT-NA
Eagle@amsat.org
I'll add a specification for spurs such that that they don't exceed the noise level in the text-mode uplink bandwidth.
Maximum VSWR can be calculated given the I/O impedances specified in the document. I could reword this as minimum return loss in a 50 ohm system.
The image is at 833-836 MHz and this frequency range is allocated to "Public Mobile" or cell phones. There is no system-level requirement, but I could create one by assuming that the maximum interfering signal level will be 1 kW EIRP plus a path loss 6 dB greater than that at 435 MHz plus at least a 6 dB loss in the antenna. This makes the interferer 18 dB stronger than a 1 W text-mode uplink so 24 dB of image rejection should be adequate.
LO leakage is at 634-637 MHz and won't interfere with on-board systems. This range is allocated to terrestrial TV broadcasting so it would take a very strong signal to cause interference. We can set the allowed level to 1 mW.
I have a long-term frequency stability requirement when the internal reference is used. Otherwise, it's determined by the external frequency reference. The short-term stability could be added. This would be determined by the requirements for the ranging system. Who knows what's required there?
The power system designers should come up with a conducted EMI number. I'd guess that it won't exceed 1 Vrms over a range of 0.01-100 kHz and 0.1 Vrms above 100 kHz but I could be wrong.
The receiver should be tested for susceptibility to the three transmitters. The 70 cm antenna will be effective at picking up the 2 m transmitter. Since no one has simulated the antenna coupling, it's hard to guess signal levels. Measuring the response to 2 W at 145.8-146 MHz might be a good test. The third harmonic needs to be attenuated as much as possible and 80 dB should be acheivable so testing with 20 nW (-47 dBm) at 437.4-438 MHz should be adequate. Note that the uplinks have to be in the lower half of the band, or 435-436.5 MHz, as with previous P3 satellites.
The interference levels from the S1 and C downlinks should be lower so testing with 200 mW signals at 2400-2402 MHz and 100 mW signals at 5830-5850 MHz should be adequate. This assumes a 20 dB loss between the transmitting antennas and the receiving antenna.
I didn't realize that I specified two types of SMA connectors. I should have specify\ied gold-plated brass bodies with gold-plated contacts for all connectors. This makes soldering easier.
73,
John KD6OZH ----- Original Message ----- From: Juan Rivera To: 'John B. Stephensen' Cc: eagle@amsat.org ; Bill Ress ; Dave Black (Home) ; Dave Black (Work) ; Dave hartzell ; David Smith ; Don Ferguson ; Juan. Rivera (Home) ; Juan.Rivera (Work) ; Samsonoff@Mac. Com Sent: Saturday, July 28, 2007 04:23 UTC Subject: Receiver Spec vs. ATP, a few Suggestions and a Question or Two
John,
I took a few minutes to look over your new specs and compare them against the Acceptance Test Procedure. I've got a number of tests in the ATP for which there are no specs:
· Image rejection
· Internally generated spurs
· Local oscillator leakage
· Input and Output VSWR
Items that need to be addressed that aren't in either document:
· EMI conducted susceptibility
· EMI radiated susceptibility
· Short and long-term frequency stability
I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature.
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Rather than worry about trying to conduct heat through a PCB why not just go to externally mounted regulators for the CAN-Do and the Receiver right on the case itself. We're not that pressed for space. That eases the heat sink and the associated thermal gap filler issues. EMI will still be an issue, but only for external sources instead of one that is inside the enclosure itself. That strikes me as a huge bonus. Why not design a single-sided PCB with the regulators hanging over the edge and the whole assembly, PCB and regulators, mounted directly to the enclosure. Stick it in with the CAN-Do module in a separate cell. Filter all the signal and power through the common bulkhead.
I'm also curious as to why you are specifying two different types of SMA connectors.
73,
Juan - WA6HTP
Hi John,
That all sounds good. Once you revise the requirements let me know and I'll bring the ATP into alignment.
73,
Juan
_____
From: John B. Stephensen [mailto:kd6ozh@comcast.net] Sent: Saturday, July 28, 2007 4:01 PM To: juan-rivera@sbcglobal.net Cc: eagle@amsat.org; Bill Ress; Dave Black (Home); Dave Black (Work); Dave hartzell; David Smith; Don Ferguson; Juan. Rivera (Home); Juan.Rivera (Work); Samsonoff@Mac. Com Subject: Re: Receiver Spec vs. ATP, a few Suggestions and a Question or Two
I'll add a specification for spurs such that that they don't exceed the noise level in the text-mode uplink bandwidth.
Maximum VSWR can be calculated given the I/O impedances specified in the document. I could reword this as minimum return loss in a 50 ohm system.
The image is at 833-836 MHz and this frequency range is allocated to "Public Mobile" or cell phones. There is no system-level requirement, but I could create one by assuming that the maximum interfering signal level will be 1 kW EIRP plus a path loss 6 dB greater than that at 435 MHz plus at least a 6 dB loss in the antenna. This makes the interferer 18 dB stronger than a 1 W text-mode uplink so 24 dB of image rejection should be adequate.
LO leakage is at 634-637 MHz and won't interfere with on-board systems. This range is allocated to terrestrial TV broadcasting so it would take a very strong signal to cause interference. We can set the allowed level to 1 mW.
I have a long-term frequency stability requirement when the internal reference is used. Otherwise, it's determined by the external frequency reference. The short-term stability could be added. This would be determined by the requirements for the ranging system. Who knows what's required there?
The power system designers should come up with a conducted EMI number. I'd guess that it won't exceed 1 Vrms over a range of 0.01-100 kHz and 0.1 Vrms above 100 kHz but I could be wrong.
The receiver should be tested for susceptibility to the three transmitters. The 70 cm antenna will be effective at picking up the 2 m transmitter. Since no one has simulated the antenna coupling, it's hard to guess signal levels. Measuring the response to 2 W at 145.8-146 MHz might be a good test. The third harmonic needs to be attenuated as much as possible and 80 dB should be acheivable so testing with 20 nW (-47 dBm) at 437.4-438 MHz should be adequate. Note that the uplinks have to be in the lower half of the band, or 435-436.5 MHz, as with previous P3 satellites.
The interference levels from the S1 and C downlinks should be lower so testing with 200 mW signals at 2400-2402 MHz and 100 mW signals at 5830-5850 MHz should be adequate. This assumes a 20 dB loss between the transmitting antennas and the receiving antenna.
I didn't realize that I specified two types of SMA connectors. I should have specify\ied gold-plated brass bodies with gold-plated contacts for all connectors. This makes soldering easier.
73,
John
KD6OZH
----- Original Message -----
From: Juan mailto:juan-rivera@sbcglobal.net Rivera
To: 'John B. mailto:kd6ozh@comcast.net Stephensen'
Cc: eagle@amsat.org ; Bill Ress mailto:bill@hsmicrowave.com ; Dave Black mailto:dblack1054@yahoo.com (Home) ; Dave Black (Work) mailto:dblack@mail.arc.nasa.gov ; Dave hartzell mailto:hartzell@gmail.com ; David Smith mailto:w6te@msn.com ; Don Ferguson mailto:kd6ire@sbcglobal.net ; Juan. mailto:juan-rivera@sbcglobal.net Rivera (Home) ; Juan.Rivera (Work) mailto:Juan.Rivera@gd-ais.com ; Samsonoff@Mac. Com mailto:Samsonoff@Mac.%20Com
Sent: Saturday, July 28, 2007 04:23 UTC
Subject: Receiver Spec vs. ATP, a few Suggestions and a Question or Two
John,
I took a few minutes to look over your new specs and compare them against the Acceptance Test Procedure. I've got a number of tests in the ATP for which there are no specs:
* Image rejection
* Internally generated spurs
* Local oscillator leakage
* Input and Output VSWR
Items that need to be addressed that aren't in either document:
* EMI conducted susceptibility
* EMI radiated susceptibility
* Short and long-term frequency stability
I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature.
I have a few thoughts... The CAN-Do switching step-down converter is only supplying 11 milliamps. If we take a slight efficiency hit we could just go to a simple linear regulator and completely eliminate the radiated and conducted EMI emission problem from CAN-do. That eases the EMI filtering and shielding requirements for every single payload. That seems like a good trade-off to me.
Rather than worry about trying to conduct heat through a PCB why not just go to externally mounted regulators for the CAN-Do and the Receiver right on the case itself. We're not that pressed for space. That eases the heat sink and the associated thermal gap filler issues. EMI will still be an issue, but only for external sources instead of one that is inside the enclosure itself. That strikes me as a huge bonus. Why not design a single-sided PCB with the regulators hanging over the edge and the whole assembly, PCB and regulators, mounted directly to the enclosure. Stick it in with the CAN-Do module in a separate cell. Filter all the signal and power through the common bulkhead.
I'm also curious as to why you are specifying two different types of SMA connectors.
73,
Juan - WA6HTP
On Saturday 28 July 2007 00:23:00 Juan Rivera wrote: [snip]
I also take issue with the -60C minimum power-down temperature. I think this is unrealistic just from a CTE mismatch perspective. The reliability of anything subjected to that wide a temperature spread is going to suffer. A way must be found to raise that temperature.
As I understand this the low temp came from the combination of the need to heat sink the receiver and the long eclipses. If, during the redesign, John could find a way to avoid needing the heat sink then the temp swings would be much less.
73, Lee-KU4OS
Hi Jim,
Fine on the paper edits.
Did you get any response to your CAN-Do/EMI recruiting post on the AMSAT-BB???
Regards...Bill - N6GHz
participants (7)
-
Bdale Garbee -
Bill Ress -
Chuck Green -
Dick Jansson-rr -
John B. Stephensen -
Juan Rivera -
Lee McLamb