What should I see/hear tuned to 869.525Mhz with a Software Defined Radio?

[RichardGriffiths]

The background to this query:  I'm updating the Rosetta in a shared aircraft.  For a while it has not been showing up on Vector plots, although the SkyEcho we also carry has.  After a lot of mucking about, I finally looked at the set hex ID; someone had set it to a random number, so It wouldn't be recorded against this aircraft.  I did look at Vector for that number, but nothing recorded.  So, even if the hex ID was wrong, it still looks like no P3i is being transmitted.  (but then I'm not sure how long ago the PA was used.

As I had a leftover DVB-T USB Receiver Dongle from upgrading from the Classic to Rosetta, I set it up as a SDR and listened on 869.525Mhz while the PA Rosetta was operating near by.  I appeared to get nothing, though there is certainly a lot of transmissions on nearby frequencies.  Nothing changes PA on or off.

Is that a legit test of the P3i broadcast?

[JCurtis]

The transmissions are a few milliseconds every second or so.  An SDR probably can pick them up, if you have a waterfall plot you may be able to see it pulsing.  It won't transmit if it doesn't have a GPS fix, though.  It won't give you an accurate power output, but it should at least show some activity.

I test PAW Bridge RF output with a real-time spectrum analyser.  The only way to be able to determine the effective transmitted power coming out of the SMA connector on the bridge.  This also verifies the frequency is correct too.  I do this on any PAW bridge I fix the SMA connector on to verify the repair.  Only takes a few mins to run the tests, if you're near Cambridge happy to test it.

[RichardGriffiths]

Thanks for that info.  I guess I need to investigate further.  Unfortunately not near Cambridge; down on the South Coast.

P.S., We have one of your excellent chargers fitted to our aircraft. 

Richard

[JCurtis]

Excellent in the charger!
Your welcome to post it, the only “fee” is the return shipping. Take so very little time to actually test it.

[RichardGriffiths]

I'd like to take you up on that.  I took the bridge off and examined it for physical damage; it looks perfect.  Reinstalled it and had another go, transmit speed set to 0kts, and GPS locked on: nothing in the waterfall.  It would be good to have its u/s status confirmed before I source another bridge.
Presumably I just post the bridge?

[JCurtis]

Ideally, the whole thing, unless Lee can sort me out a temp licence for a spare Pi to install PAW onto? 
I borrowed the Pi from my previous test bench to fix something else that had an "accident" during some development work...

Drop me a PM here or send me a mail to the address on the Charge4 website and I'll give you the address, or take it from the invoice from your charger purchase.  Return shipping would be £12 + VAT.

Lee, I have a spare Pi 3 Model B v1.2 is that suitable? Would I just need to send you the MAC address from the PAW status page on it?  The Host ID of my spare Pi is B827EB23B6C6 

[RichardGriffiths]

To conclude this thread for subsequent readers:

I sent the bridge PCB to Jeremy for testing and he confirmed that transmit was not functioning.  I purchased a new bridge from PA and installed it.  Now when I use the SDR to listen on 869.5 MHz I hear bursts of activity approximately once per second..  Curiously they don't show up on the SDR software waterfall; I guess I haven't selected the precise enough settings.