Does ARF module decrease ADSB sensitivity?

[captchaos]

Probably showing my ignorance but here goes. Whilst I was waiting for regulator, etc. I got the unit working without the ARF installed and was happily picking up ADSB traffic as verified on flightradar 24. Built the ARF bit when the components arrived and checked soldering seemed OK with mulitmeter.

Booting unit up and things seemed to be normal but I wasn't seeing traffic so removed ARF from GPIO and traffic started appearing as before.

Added the ARF back again and after a while picked up some traffic which was virtually overhead.

I am running current minus version of the software, original digole set up, all components as specified and have tried with both mains USB power and also Aukey battery pack.

I am running indoors so don't expect massive range but there definitely seems a loss of sensitivity with the ARF running.

Any ideas appreciated.

[onkelmuetze]

From the little I know about antennas, receiving of two antennas side by side is not an issue.

But you can run into problems when one of them starts sending, because it couples in on the other one, and will thereby decrease range of the passive one.

I will talk to one of my colleagues who is our antenna/wireless-guy at work later, what he thinks about its. maybe he can do some measurements i he has the time to.

From my personal experience with the PA-unit, I did not recognize any problems. Indoors I have a range of 20-30 NM on the ADS-B with no dropouts, but I can't tell what the P3i side does, because there has not been any othe P3i device in range so far.

[onkelmuetze]

my colleague said reception of the receiving antenna/module might get blocked while the other one is sending, if both are more or less on the same frequency (within or close to the bandwith of the transceived signal)

But there should not be a problem as 868 MHz (P3i) and 978/1090 MHz (ADS-B) are far enough away from each other.

Maybe your problem is more due to power loss at the DVB-T-Stick, as power consumption of the ARF increases when transmitting?

[captchaos]

Not sure if it is a power thing or not. With the ARF it seems to take a lot longer to start showing traffic. It was working quite well for a time today but then the collisonaware stopped linking.

I am trying the newest patched release to see if that helps.

[trapdoor]

The data burst from the ARF is pretty brief (a few tens of milliseconds) and only a max of 0.5W ERP whilst it is possible to overload the front end of a poorly designed receiver (and I'm assuming that these Chinese dongles aren't exactly 'top notch' design) which will desensitise or block the received wanted signal I can't say that I have noticed any kind of degradation. The ARF P3i data burst only occurs every second (or more - not sure what determines the frequency, Lee may be able to enlighten) so it's really not going to be a problem.

You stand more chance of overloading it with the aircraft transponder & DME which will be 'on frequency' and in the order of up to a couple of hundred watts or your aircraft VHF which is a few tens of watts. That may indeed happen with some people - I have yet to run any tests. If I get any time at the weekend (unlikely, but can hope) I may setup my sig gen to sweep a range of aviation frequencies and see if it has any noticeable effect on the DVB-T dongle.