Hello Bill,
I have been keeping logs on the 70 cm receiver construction and testing as we progress from the first prototype to the first set of non-flight units. Lot's has happened in the past few months. You can find them all on EaglePedia if you'd like some light reading.
We now have one prototype running in my shop, with a few remaining problems to fix. Then John is going to redesign the radio and my group will fabricate four units. We are getting close to that point now. John has released a new preliminary specification which is on Eaglepedia for review and comments. There is nothing in this new spec about EMI. Based on what I'm seeing I think this needs to be hammered out before we start ordering parts. I just went back and revised my last log to include a few links to EMI surface mount filters in automotive applications. This might be a good place to start looking for a fix.
Anyway, the main issue at hand right now, in my humble opinion, is this: The CAN-Do module, which is to be an integral part of every payload on Eagle, and mounted INSIDE the payload chassis, ON THE PCB, produces copious quantities of radiated and conducted noise. I had to move the receiver PCB 2-1/4 inches away from the CAN-Do module to escape the radiated noise, and run independent power around the CAN-Do module's normal switched +14 to escape the conducted noise. This is not a good thing! I think that bad boy needs to be quieted down somehow.
If you can come up with an interface control document that addresses these issues I think that would be an excellent step in the right direction!
73,
Juan
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From: Bill Tynan [mailto:[email protected]] Sent: Sunday, June 17, 2007 2:56 PM To: [email protected]; 'Bdale Garbee' Cc: 'David Smith'; 'Dave Black (Work)'; 'Dave Black (Home)'; [email protected]; 'Samsonoff@Mac. Com'; 'Juan.Rivera (Work)' Subject: Re: [eagle] Re: 70 cm Eagle Receiver - Final Spur Report (at least fortoday...)
Right On Juan:
Here is where an interface document is a nesessity. That's what I told Jim I would undertake. But, I have been out of the Eagle loop for months and thus didn't know that such issues were now coming up.
An interface document should spell out power, including power quality, not mere pin connections and physical fit data.
I have a lot of catching up to do but will need a lot of help to get started.
73,
Bill Tynan, W3XO
----- Original Message -----
From: Juan mailto:[email protected] Rivera
To: 'Bdale Garbee' mailto:[email protected]
Cc: 'David Smith' mailto:[email protected] ; 'Dave mailto:[email protected] Black (Work)' ; 'Dave Black (Home)' mailto:[email protected] ; [email protected] ; 'Samsonoff@Mac. mailto:'Samsonoff@Mac.%20Com' Com' ; 'Juan.Rivera (Work)' mailto:[email protected]
Sent: Sunday, June 17, 2007 12:58 PM
Subject: [eagle] Re: 70 cm Eagle Receiver - Final Spur Report (at least fortoday...)
Bdale,
I certainly wouldn't suggest that no one in AMSAT understands power distribution. I just can't find any detailed requirements. What I have found was a spreadsheet (click http://www.amsat.org/amsat-new/eagle/EaglePedia/uploads/1/14/Wiring.xls here) that lays out all of Eagle's wiring. There is no mention of shielding or twisted pairs for the power. Both are important to reduce radiated noise.
As a newcomer I am wary of aural tradition and informal meetings as good tools for development of complex systems. I think everything needs to be written down in unambiguous requirements documents, starting at the top level. This current exercise with the 70 cm receiver is a good test of the current processes and procedures.
I've glanced at John's new receiver specifications and I don't see any reference to input power or the EMI environment that the receiver must work in. How can it be designed or tested if that environment has not been specified as a requirement? It's not John's fault. He has nothing to base it on. That's where the top level requirements would give him something to work with. Everything needs to start at the top and work down. Not from the bottom up.
73,
Juan
-----Original Message----- From: Bdale Garbee [mailto:[email protected]] Sent: Sunday, June 17, 2007 10:04 AM To: [email protected] Cc: [email protected]; David Smith; Dave Black (Work); Dave Black (Home); Samsonoff@Mac. Com; Juan.Rivera (Work) Subject: Re: [eagle] 70 cm Eagle Receiver - Final Spur Report (at least fortoday...)
On Sun, 2007-06-17 at 08:48 -0700, Juan Rivera wrote:
I've completed my testing and analysis of the spurs that appeared in
the IF output of the 70 cm Eagle Receiver prototype. I believe I know
the source and the cause of all of them and how they can be eliminated
or rendered harmless.
Nice work.
Reading your report, two things strike me, neither of which I consider
myself an expert on in AMSAT or elsewhere, but both of which I'll
mention to help motivate the review of power system requirements you
clearly hope comes next/soon.
The first is that I think AMSAT does understand most if not all of the
issues you're warning against regarding DC distributiong wiring. Some
care was taken, for example, in planning pinouts of the 15-pin connector
on the spacecraft bus side of the CAN-Do! widget, and in the proposed
wiring harness design from the Black Forest meeting.
The second is that I think more work is going to be required to ensure
receivers behave reasonably in the presence of supply noise. For
various reasons, as others have already alluded, I wouldn't count on the
Eagle power bus being very quiet.
Bdale, from Edinburgh
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