I found the source of the 10.7 MHz spur. It's being generated inside the
receiver itself. This is the first spur I have found that is not caused by
switching power supplies.
The origin appears to be in the 10 MHz reference area. I turned off and
unplugged the SDR-IQ and fed the IF output from the 70 cm Receiver to my
TS-2000. The spur is still there.
Next I connected the RF input to my sniffer loop and moved it around the PCB
surface. I get the strongest signal near the long trace between the two
Freq inputs to U4 and U9, the two phased-locked loops.
The source of the spurs in the 70 cm prototype receiver is the CAN-Do
This is the receiver IF output as designed
(powered from pins 39 and 40 of the CAN-Do Module)
This is the receiver running off of a separate power source
(bypassing the CAN-Do Module +13 volt output on pins 39 and 40)
This is the same configuration as above, but with the CAN-Do module shut
>From the above it appears that:
1. The CAN-Do module is the source of all the spurs that I see
2. None of the spurs are being generated by the receiver's internal power
3. Some, but not all, of the noise is entering the receiver via the
switched +13 volt CAN-Do output on pins 39 and 40
4. The remainder of the noise could be entering the receiver on other
CAN-Do pins, or being radiated to receiver components or traces in close
See my log for all the intermediate steps I took to reach these conclusions.
Remaining RF issues:
1. Phase noise
John & Juan:
Your EMI problems certainly do present considerable difficulties. Your
suggestions of placing connectors on multiple faces of a module run
counter to the whole module mounting plan for Eagle. The modules are
mounted with only about 1.5mm clearance at the flanges and only about
16mm clearance on the sides. The "rear end" of the module is also
difficult as there is just not that much space for cabling and
connector access. Mechanical designers in the past have been raked over
the coals for not providing sufficient connector access. The curren
plan allows about 100mm (I don't have the drawings with me at the
moment) of space between facing columns of modules for the cabling and
connector access. This is a plan that is pretty basic to the whole
wiring plan for Eagle, and it is a result of a lot of experience with
While the basic module design for Eagle, unlike P3D, does not provide
for the stacking of modules, a small CAN module placed on top of the
URx, could be considered. Wiring to this sub-module would be by means
of jumper leads from its connector face into the URx.
I caution that there currently is not planned for much space above the
rows of modules as the current spaceframe plan has the modules placed
fairly closely under the solar panels. This concept is part of the need
to keep the mass moment of inertia, Izz, high. This is NOT just a
desirable feature, but a necessary, MUST need for the spin stability of
the spacecraft. So any top-mounted sub-module would have to not be very
All of these issues arise from the practical considerations of the
overall mission of the spacecraft. Unfortunately for the EMI and
other "local" issues, we cannot design the spaceframe only for EMI, but
must solve other mission requirements, too.
I am not trying to be unmovable on the design if the URx, but I am
trying to explain how we can have a successful mission.
I don't want to tear into the CAN-Do module. I feel like it is a loaner and
not mine to modify. It would be interesting to disconnect the switch and
the current monitor from the CAN-Do power input and move it to those user
pins as you suggest. That might just work, but I also know they don't want
to have multiple versions of the module floating around and this would be
We also can't loose sight of the radiated noise from that inductor. I can
see signs of EMI if it gets within 2 inches of the sensitive areas of the
From: Chuck Green [mailto:[email protected]]
Sent: Sunday, June 17, 2007 9:18 AM
Subject: Re: [eagle] 70 cm Receiver IF Spurs - Problem Solved
I am impressed with your testing and analysis.
I find it curious that you were unable to filter the power from the
CAN-Do! . But switching noise is notorious for being difficult to
filter. So maybe that is something to just forget. But in a total
system (satellite) it may not be possible to forget. We may need to
find a way to filter the power for sensitive modules even if not using
power from the CAN-Do! ; in which case, such a filter may also filter
the noise from the CAN-Do! .
If your analysis is correct, and it certainly seems to be, then it would
also seem possible to remove the switch from the CAN-Do! (not just
bypass it) and rout your clean power source through the CAN-Do! current
measurement circuit thus saving having to do this in the module.
Great work! And thanks.
Juan Rivera wrote:
> Hi Chuck,
> Bad news I'm afraid. See my report for details... I've sent out a link
> the group.
> -----Original Message-----
> From: Chuck Green [mailto:[email protected]]
> Sent: Saturday, June 16, 2007 8:57 AM
> To: juan-rivera(a)sbcglobal.net
> Cc: eagle(a)amsat.org; David Smith; Dave Black (Work); Dave Black (Home);
> [email protected] Com; Juan.Rivera (Work)
> Subject: Re: [eagle] 70 cm Receiver IF Spurs - Problem Solved
> Hi Juan,
> This is fantastic!
> Please try one more experiment. Pass the module current through the
> current measuring circuit on the CAN-Do! while bypassing the switch
> transistor (you could just short across the switch transistor) and see
> if the problem reappears.
> If you end up having to use the user pins, you will need to add current
> measuring circuitry to your module. While this is no big deal, its one
> more thing you might not have to do.
> Juan Rivera wrote:
>> The 70 cm Receiver spur problem has been solved. Click here
>> for details.
>> Via the Eagle mailing list courtesy of AMSAT-NA
I've started a new log here
I've repeated some preliminary phase noise tests using a simulated PAVE PAWS
signal, along with a simulated Ham uplink signal. In the process of looking
at those signals with the SDR-IQ I discovered another spur directly in the
middle of the IF. I don't know the exact source but it is generated inside
the receiver, and definitely not from the CAN-Do module.
I've also come to one general conclusion that I would like to bring up for
discussion... I believe all switching power supplies on Eagle should be
running at frequencies as high as possible - around 1 MHz would be a good
ball park. That would put most spurs outside the passband of the payloads,
and make EMI filtering much easier. The 5 kHz CAN-Do switching power supply
needs to be completely redesigned in my opinion. I believe that if it is
not cleaned up the impact will be devastating, and the full scope will
likely not be known until integration and test when it is too late to do
anything about it.
Having said all that, I also believe that we need to come up with EMI
standards for everything on Eagle. Specifically we need:
1) A definition of the noise amplitude and spectral content to be
expected from the Eagle power distribution point
2) A repeatable way to reproduce that noisy DC source in our labs for
3) A simple and effective way to test to the spec that we create
I think the way to make this work is to create a noise source that consists
of several representative switching power supplies that are intended to be
flown on Eagle. The exact makeup of this test fixture would be specified in
the EMI requirements. Then, all payloads would need to be designed to
operate without impairment while powered by this noisy power source. The
EMI requirement would also spell out exactly what constituted impairment.
They also need to keep conducted noise leaving the payload down to some
specified level. More on that in a minute...
Here's a possible layout for a noise source:
The one ohm resistors account for lead resistance and allow the three
switching power supplies to all modulate the power bus, along with whatever
conducted EMI comes back from the devise under test (your payload.) It
would be easy to crank out three or four of these noise sources for
distribution to groups that need them. That way everyone would be testing
using the same conducted EMI.
The gold standards for EMI are MIL-STD-461 and -462. They break EMI into
* CS - Conducted Susceptibility (the 70 cm Receiver suffers from
* RS - Radiated Susceptibility (the 70 cm Receiver suffers from
* CE - Conducted Emissions (The CAN-Do Module is guilty of this)
* RE - Radiated Emissions (The CAN-Do Module is guilty of this)
This noise source would provide a way to test for compliance with our CS
requirement. RS and RE can be dealt with by shielding. That leaves CE.
We'd need a way to insure that noise coming out of a payload is within spec.
We'd need another test fixture for this.
I hope this stimulated some discussion. I'm eager to hear what you all
Juan - WA6HTP
The second call for Symposium papers has been issued.
As I said a while back, it is EXTREMELY important that Eagle have a lot
to say and show at Symposium. Each TEAM should publish SOMETHING. I'd
prefer team leads to present, but anyone on the team is fine with me.
Or, if you have something to present, but can't make it, I'll do it, or
get someone to. (This is a last resort, I want the presentations to be
about what YOU are doing, not me. But I'd rather get the info out....)
Please get your abstracts in to Dan NOW, so he can start planning. To
that end, Tom Clark, has agreed to write, have peer reviewed and PUBLISH
IN THE PROCEEDINGS the collected thoughts regarding phased array.
We have advertised the ACP as a key part of Eagle, the PRIMARY payload
in the eyes of some. Yet, we've said little about it, since publishing
the minutes of the San Diego meeting, which was held a year ago. Now is
the time. We need to say a LOT about ACP: modulation schemes, digital
protocols, multiplexing techniques, link budgets (in terms of how many
watts I need on uplink, how big an antenna, and how good a preamp) etc.
Yes, much of that can be gleaned from the SD meeting, but much is not
yet defined. It's time to define it, and publish what is at least our
current thinking. At least one ACP presentation needs to be for the
general user, who is not a digital communications geek. We need to
convince him what ACP will do, the benefits to HIM, and why he should
buy the equipment when we make it available. Think of this one as a
sales pitch. THIS IS IMPORTANT.
Similarly, we need to publish some RESULTS from the power system
Juan Rivera has agreed to something on all the efforts and results of
the project Oscar team with the U-band RX. Juan, you and I have
corresponded about which topic, I sent you suggestions, please choos and
send in the abstract soonest. Writing the paper can come as it evolves.
Guys, this is important, please make the commitment and take a few
minutes to do the abstract. Dan needs it for planning, and Patti and
Kevin need it for purposes of marketing Symposium. They are working
hard on local educational connections, but that can only go so far
without at least a list of content.
I apologize for my low profile lately. The last two weeks have been
brutal at work, included a long trip to VA (spoke at a retirement, went
to a wedding, and happened to be in town when my grandson was born 5
weeks early), a 27 hour power outage (now have a 5500 watt generator)
and I did take time out for Field Day. I'm going to continue to be low
profile, as I leave in an hour or so for a meeting in DC which will be
gruelling. Back here Sunday, probably a day or so to recover, then back
in the saddle. Despite all this, I have managed to provide answers Juan
needed to continue working, and have corresponded with a couple of others.
Thanks for all your efforts. We are a few short months from Symposium,
please make the push.to publish. This is an opportunity we must fully
Thanks & 73,
PS Grandson is fine, just tiny. He may even leave hospital this week.
A few photos at www.wb4gcs.org
I'm not trying to beat this to death but I want to make sure I fully
understand what I'm looking at here...
I spent some time this evening looking at the spectrum between the 10.7 MHz
IF output and zero Hertz. I did this because I believe it may be a
significant area of interest since the receiver will feed an analog to
digital converter. The A/D converter is not a tuned stage so it will
digitize baseband noise along with the IF signal. I've been told that the
impact of noise in the baseband is to reduce the dynamic range in the
digital domain. I'd appreciate an explanation since I am woefully ignorant
in this area.
I posted my results in the usual area. Just scroll down till you come to
In an 8-hour period I have received five of these messages, which means
that someone (always with the same IP address) has tried to guess my
TeamSpeak password 25 times today.
Anyone else seeing this?
> From: TeamSpeak <forum(a)goteamspeak.com>
> To: n1al(a)cds1.net
> Subject: Account on TeamSpeak locked out
> Date: Wed, 20 Jun 2007 03:44:48 +0000
> Dear alan_bloom,
> Your account on TeamSpeak has been locked because someone has
> tried to log into the account with the wrong password more than
> 5 times. You will be able to attempt to log in again in another
> 15 minutes.
> The person trying to log into your account had the following
> IP address: 22.214.171.124
> Don't forget that the password is case sensitive. Forgotten your
> password? Use the link below:
> All the best,
Good morning Stephen,
I do have a few questions. Thanks for asking!
1) What if the CAN-Do module suffers a failure that causes a current
overload? Is it protected by a fuse? The next generation receiver should
continue to function as long as it has power. An overload in either unit
should not cause the other to fail.
2) Do you have any information of previous efforts to reduce CAN-Do
noise by either shielding the module or replacing the inductor with a
3) Do you have a shielded inductor that I could swap for the existing
one if that proved necessary?
4) Have you designed a circuit that would allow temperature to be
determined inside the receiver PCB itself, and not just on the CAN-Do
module? This will be important, especially if the receiver is split into
two separate enclosures.
My plan is to desolder the CAN-Do module from the receiver PCB today and
move the receiver PCB to the enclosure's rear set of mounts. This will put
about 2-inches of space between the two. I'll make up two interconnecting
cables - one just long enough to attach the two while in the case, and one
that is a foot or two long, assuming that I can find the parts I need and
don't have to solder the cable to the two units. I can use that long cable
to try some troubleshooting. I'll use that CAN-Do's noisy inductor as the
noise source and move it around over the receiver to see what affect it has.
Perhaps I can find the area that is the most susceptible to noise that way.
I think the next receiver could use the entire available board space to:
1) Put distance between the two modules
2) Further isolate the CAN-Do module with a shield if necessary
3) Add power supply input filtering and input current overload
4) Include CAN-Do data line filtering if that turns out to be necessary
5) Add a temperature sensor in the vicinity of the SAW filters, and
another on the second PCB if it gets split into two sections
One last question. How do I reduce the heartbeat timing below three
seconds? I couldn't find any way to do that using the net controller. I'd
like to confirm that the jump in frequency I see in the CAN-Do module's 5
kHz noise every three seconds goes away.
From: smmoraco(a)gmail.com [mailto:[email protected]] On Behalf Of Stephen
Sent: Tuesday, June 12, 2007 7:21 PM
To: Juan Rivera; Juan Rivera
Cc: Jim Sanford; Bdale Garbee
Subject: late to tonight's meeting
Sorry I missed your presentation/discussion tonight.
Any questions/issues for me re: CAN Do! ?
I dug into the CAN-Do circuitry today. The CAN-Do module uses a Maxim
max1836 switching down-converter. I found the following quote in the spec
sheet, "Commonly, instability is caused by excessive noise on the feedback
signal or ground due to poor layout or improper component selection. When
seen, instability typically manifests itself as 'motorboating,' which is
characterized by grouped switching pulses with large gaps and excessive
low-frequency output ripple during no-load or light-load conditions."
It reminded me of the waveform I captured earlier from CAN-Do inductor, L3.
(See the waterfall display below.) Those are definitely grouped pulses with
large gaps. Notice also that there is tremendous splatter over a large
bandwidth that can just be seen as faint horizontal lines.
I'd like to propose an alternative - Move the switching down-converters out
to the power distribution and management area and feed DC to the payloads at
an appropriate voltage so switching power supplies can be removed from all
analog payloads. This would go a long way towards cleaning up what is
shaping up to be a nasty situation. It's just not good design practice to
bundle switching supplies with low-level analog signals.