Helping a friend diagnose issues with interference on 123.000Mhz causing both installed radios to break squelch (roughly -77db on v16 display) and even a handheld in or near the cockpit to break squelch. We tracked it down to the A16 unit as both radios would no longer show constant RX when A16 power was disconnected. Using a spectrum analyzer we observed a spike on 123mhz that went away when A16 was shut down.
We pulled the unit and tested with just power connections (see video link) and same spike showed. https://youtu.be/zmXKiN1EVmk?si=eYO3DfHUplnHV7bP
A shop nearby had an A16 to test, so we flew over and tested and it did the same thing.
Has this been seen before? Don’t think it’s a one off situation as two units tested both show same RF noise output.
A16 Generating RF Noise
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Re: A16 Generating RF Noise
Not sure where that comes from - there is no signal source in the A16 at the frequency or anything lower that would create a harmonic at that frequency. The images below show a A16 taken out of its housing (so no shielding at all) with just power connected.
You can see the typical wideband antenna used for EMI measurements at that frequency range in front of it (less than a meter distance) connected to a spectrum analyzer showing the range from zero to 500Mhz. The green marker is at 123Mhz. You can see the FM band with many stations to the left of that and to the right cable leakage from the signal generator below which is set to 127Mhz coming through - further to the right you see mostly TV stations.
There is no difference to the image whether the A16 is plugged in or not.
You can see the typical wideband antenna used for EMI measurements at that frequency range in front of it (less than a meter distance) connected to a spectrum analyzer showing the range from zero to 500Mhz. The green marker is at 123Mhz. You can see the FM band with many stations to the left of that and to the right cable leakage from the signal generator below which is set to 127Mhz coming through - further to the right you see mostly TV stations.
There is no difference to the image whether the A16 is plugged in or not.
Re: A16 Generating RF Noise
Here is another one - this time concentrating around 123Mhz with narrow bandwidth and a 100Khz span. This gets us down to -100dbm from the antenna. There is no visible emission from the A16. As test to verify the setup I took the picture below - here my Adret super accurate and high quality signal generator is set to produce 123Mhz CW at 0dbm. The ouput is left unconnected (open). What you see here is the small amount of leakage escaping the signal generator and picked up by the antenna.
The only signal that is produced by the A16 that is close to 123Mhz is one of the slower bus clocks inside the CPU chip that runs as 120Mhz (the core runs at 480Mhz and most of the other busses at 240Mhz). However even at 120Mhz nothing is visible on the spectrum analyzer.
The only signal that is produced by the A16 that is close to 123Mhz is one of the slower bus clocks inside the CPU chip that runs as 120Mhz (the core runs at 480Mhz and most of the other busses at 240Mhz). However even at 120Mhz nothing is visible on the spectrum analyzer.
Re: A16 Generating RF Noise
Any chance failed power supply components could cause this? It seems a little high frequency and narrow band for that type of issue.
It is strange that two units did the same thing. I believe my friend said his was produced in October of 2020, but wasn’t used until a few weeks ago. Similar case with the second unit we tested, bought for a project that hadn’t been completed.
Any chance that any unconnected wires could cause such an issue? The video is pretty clear that the noise on 123mhz is only when the a16 is powered.
We are in the US and my friend submitted a ticket to Michigan Avionics, maybe they will have a newer production unit we can swap and try.
Thanks
Joe
It is strange that two units did the same thing. I believe my friend said his was produced in October of 2020, but wasn’t used until a few weeks ago. Similar case with the second unit we tested, bought for a project that hadn’t been completed.
Any chance that any unconnected wires could cause such an issue? The video is pretty clear that the noise on 123mhz is only when the a16 is powered.
We are in the US and my friend submitted a ticket to Michigan Avionics, maybe they will have a newer production unit we can swap and try.
Thanks
Joe
Re: A16 Generating RF Noise
There has not been an update to the A16 since release - same hardware.
Yes 123Mhz is a bit too high for the switch mode power supplies - not impossible but we on purpose use quite ancient switch mode chips - the L5973 which is a low frequency chip and quite bullet proof. I can't tie 123Mhz to anything on the board.
Are you using the A16 with a Razor display ? Perhaps it's the razor radiating - that's got a LCD display - LCD displays like radiating...
I can see some bursts in the 2.4Ghz area - that's from the bluetooth transmitter.
Rainier
Yes 123Mhz is a bit too high for the switch mode power supplies - not impossible but we on purpose use quite ancient switch mode chips - the L5973 which is a low frequency chip and quite bullet proof. I can't tie 123Mhz to anything on the board.
Are you using the A16 with a Razor display ? Perhaps it's the razor radiating - that's got a LCD display - LCD displays like radiating...
I can see some bursts in the 2.4Ghz area - that's from the bluetooth transmitter.
Rainier
Re: A16 Generating RF Noise
The video in original post does the A16 removed from aircraft with only power pins connected and a Tiny SA centered on 123mhz.