Two out of two isn’t bad.
The front end, especially for receiving, is open to interpretation.
I’m not convinced the differential input has much impact on the noise immunity and SNR but that would be an interesting study.
The differential is more for transmitter PA matching than high performance receiving.
Hopefully the regulator will be in tomorrow and I can resume testing of the modified circuit.
Jim McCullers
WA4CWI
All,
Reviewing the boards this morning all four of the receivers have the same inductor. There could be a difference in tolerance creating different values in the registers. This could be checked by swapping the inductors. The traces on the board are similar in two cases and slightly different in two others.
I now feel the issue with the two receivers that are not working is the matching circuit. I essentially had four different matching circuits on the board for testing. Two of the circuits are working and two are not. May be able to get the two non-working units up by changing the components or restructuring the interface. This would allow testing with all four Rx devices.
My original idea was to experiment with differential inputs to try and improve noise immunity and increase SNR.
Bob
Oops. Well I got 91 and nano right.
73,
AMSAT(R) Engineering -- Flight Software
On Mon, May 6, 2024 at 11:12 PM Bob Stricklin via pacsat-dev <[email protected]> wrote:
Jim,
This could be an issue. I will look at it more.
Sorry you having trouble with the voltage regulator. Hope you get it fixed without much trouble.
I am keeping the PCB in the 3D printed case with the covers off for probing here and have not had any issues here so far. I take the board out to solder if needed.
L301 on receiver 2, L201 on receiver 1.
I was half paying attention this afternoon, read the 91 and kept going.
It’s 91nf and something is required there for VHF, the actual value will determine the range which I believe to be the weakest idea on the chip. I assume they had reason. For higher frequencies like 70cm the inductor can be shorted.
My belief is the problem is in the front end circuit and I had completed modifying receiver 2 and headed for the test bench when I bonked the regulator.
Should be in Wednesday as I bought it a higher class ticket.
I thought it would not range at 2m without the capacitor. But I'm far from an expert!
AMSAT(R) Engineering -- Flight Software
On Mon, May 6, 2024 at 10:16 PM Bob Stricklin via pacsat-dev <[email protected]> wrote:
Burns,
I do not have a 91nF cap around the Rx devices. Perhaps this is used on another project?
I will look at the clock input on each of the Rx devices with a scope to see if there is any issue with clocking inputs.
The clocks are all being feed from a buffer driver with a 16 MHz clock with Clock 1 signal being feed to two Rx devices one of which is working and one not.
I’m not certain how the ranging process works as to what it leaves in the PLL values but it is affected by the range capacitor (91nF or whatever) as well as board and circuit stray capacitance so that is a possibility.
The purpose of ranging is to align the PLL correctly.
I spent time this weekend doing what Bob did, taking measurements and reviewing the circuits.
Part of the time was using a $29 eBay phase detector I purchased to measure the actual phase out of the transformers.
At the moment no ready to give it a 5 out of 5 and am struggling for a 1. It uses a Analog Devices chip that apparently goes to 2.8g but the device appeared to struggle at 146mhz and no phase change from input to no input.
I find it difficult to think it is in the code as it’s all load and go but ….
And in the process of moving the board between the work bench and the test stand I banged the LM1117 regulator and broke a lead at the body.
Digi-Key has one on the way.
I do solemnly swear to never work on this board on a Saturday night. That’s two for two power supply problems and I know the source for at least one if not the other.
I’ve done my verification work and have a couple ideas to try when the chip arrives (I bought two to quell the demons).
Is it possible that this relates to differences in the 91nF capacitors? E.g. that either the caps differ or there is some different capacitance in in the area on the board or something? I just remember that the ranging seemed to differ some from board to board. Maybe from chip to chip too?
AMSAT(R) Engineering -- Flight Software
On Mon, May 6, 2024 at 2:44 PM Bob Stricklin via pacsat-dev <[email protected]> wrote:
I went through a series of test using the instructions provided by Bruns for hanging the frequency.
When i placed 3 of the four AX5043 devices on 145.840 MHz I could mostly only copy signals on Device 2. Occasionally Device 3 would come through also but it is supposed to be set on 145.870 MHz.
Then I placed all four devices on 145.840 and again mostly only Device 2 is copied but occasionally Device 3 would be copied.
Then I moved the frequency setting on device 2 and 3 off of 145.840 to 145.890. At that point occasionally Device 3 would copy the signals.
Using a spectrum analyzer I checked the signal coming into each one of the AX5043 inputs and found the levels to be about the same on all devices.
May need to do more testing by forcing interrupt on the parts not responding if possible. I think I recall Chris indicating he did see interrupts coming back from all four devices.
With the AX5043 devices all set at 145.840 I see different values in the PLL registers. This seems odd to me.
I am attaching logs for my testing this morning.
I plan to spend some time looking over the layout for each AX5043 to make sure they all match except for Device 2.
When I first started this morning the frequency for one of the devices was 145.860 MHz. I did change the values in config.h file and I had issues an "init new proc" and a "pre flight init" yesterday trying to get the config.h frequencies in place.
There are some minor issues which may be addressed later but not a problem on debug. There may be a bug in the AX5043 code however.
Bob
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