Antenna Update

Last year I logged around 500-600K positions daily. Then, around Jan of 2022, the numbers dropped to around 150K and stayed that wat. I was using the higher priced stick antenna FlightAware sells. I thought water got in the coax or the antenna was no good. I explored several options including homebrew spider, 1090Mhz stick from Aliexpress, 50 to 75 ohm coax, and nothing worked. So I put it all back up like originally had it. Over the past month, the postions suddenly rose back up to around 500K. The only explanation - propagation. The 2M band has been wide open in the midwest. As of today, the numbers, like the band opening, are starting to drop

ADS-B is on 1.09GHz, 2 meters is on 144-148MHz, so it’s doubtful that 2m VHF propagation conditions would have any effect on line-of-sight UHF. In any event it would perhaps affect your range rather than the number of positions. It’s more likely that there was a noise or interference source that was causing the issue. Search the board for do I need a filter to find out how to check.

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Do I Need A Filter?


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Mobile / Cell Phone Frequencies close to ADS-B Frequencies ES 1090 MHz and UAT 978 MHz - Regional Deployment Designated by the ITU (International Telecommunication Union) for the operation of GSM mobile phones and other mobile devices.


Mobile Cell Phone Frequencies Close to 1090 and 978 MHz


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Don’t rely on FA stats is the first thing to do.
For one, looking at FA anywhere skews the numbers massively.

Also the reporting rates could be changed.

Thanks. Should have said propagation in general. I had 2 meters on the brain. The range has been effected with more reports coming on 50-100 whereas 150-200 dropped significantly. Live in rural area. Will check out info on filters.

Interesting. I live in a rural area so I can’t imagine too much cellular interference. I do have a police scanner antenna mounted close by. Those freqs are in the 700mhz range.

The Dongle’s R820T tuner chip has a frequency range of 24MHz to 1760 MHz. Therefore any strong RF signal within this frequency range (including 700 MHz) can overload the front end of the receiver (Dongle) and make it deaf to weak signals from distant planes.

The method given in the How-To " Do I Need A Filter? " scans RF signals in frequency range 800 MHz to 1200 MHz, so it wont show your Police Scanner.

There is another How-To which scans FULL frequency range of the Dongle, and is pretty fast too.


Spektrum - How-to Speedily Scan RF Noise in band 24MHz ~ 1800MHz












It would have to be very strong indeed to overload the radio when it’s tuned to a completely different frequency, and when its antenna’s not resonant at the frequency of the interfering station.

Unless you’re transmitting on 700MHz that antenna has noting to do with anything.

The R820T tuner chip is the front-end chip to which antenna input is connected. It is a highly integrated silicon tuner that has build-in low noise amplifier (LNA), mixer, fractional PLL, VGA, & voltage regulator.

The built-in LNA of the tuner chip R820T gets the signal from antenna before the tuning stage, and hence handles signals of all frequencies. Tuning takes place on the output of builtin LNA of R820T chip. It is this built-in LNA which gets overloaded by a strong RF signal of any frequency within 24 ~ 1760 MHz band.






So the FA antenna could be receiving the scanner 700mhz signal in addition to position reports? The scanner antenna is mounted 2 ft from the FA antenna. Not sure why is worked for a year, then position reports dropped

Additionally, I have an APRS 144.390 antenna in the same vicinity as well as another 2M antenna for aircraft voice traffic.

Would not expect interaction between 2m freq and ads-b.
I have a triband diamond v2000 antenna (2m, 6m, 70cm bands ) mounted 1 meter over my 2 ads-b antennas.
Also have a carolina windom off center fed HF antenna approx 2 meters below the ads-b antennas.
Have not encounteted issues over the past many years.

Also would not anticipate issue with your 700mhz receive-only antenna.
If it were TX, that might be a whole other story…

Why? Why did you post these diagrams and overexplain them?

Do you not read the posts that you are responding to?

He has a police scanner antenna nearby. That’s a receiver.

Which @jaymot pointed out.

So here’s my question - based on your diagrams, at what power level is it safe to continue to NOT TRANSMIT on your receiving antenna if you want to avoid interference with your ADSB receiver dongle?

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Max input power is +10dBm. You can calculate when you get that level in your antenna, but depends on so many factors, that is easier to actually measure it with a good RF meter.
Same considerations apply for a filtered LNB first stage (before filtration). But those have usually better specs.

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What you have shown is the reference design, not necessarily anything you can actually buy.

Have you considered the filter (L7/C9) shown? It is before the R820t input and therefore “before the tuning stage”.

I have wondered about that document also. It’s preliminary information. For one thing, it says the tuning range is 42 to 1002 MHz – so it doesn’t cover 1090 MHz ? However, I would expect that the basic architecture is correct. That is, there is an LNA followed by a mix to a low IF. That LNA sees the full tuning range. Regarding the maximum input level of +10 dBm – that’s probably the level above which damage could occur. It’s not an operational level.

Regarding whether a receiving antenna nearby can be a problem – there’s a possibility that LO leakage from the other receiver could interfere with the ADS-B receiver. But not likely.

Edit: I see the data sheet says +10 dBm with QAM64 at 7/8 code rate. So I guess it could operate at that high a level.

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I believe that to be correct. I’m going back to my original theory of propagation. LOS whether vhf or uhf is affected by propagation and the band/s have seen some significant opening recently. Now, that opening is starting to wane

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The freq range specified is the range for which the other specifications are valid. So if you are operating outside the freq range, the performance parameters are not guaranteed.
Fortunately for us, the 820t’s PLL will still lock well out of range - unlike the FC0012 which has similar spec. but won’t go to 1090MHz.

Yes, but …
As we all know, 10dBm is equal to 0.7VRMS which is the voltage D6 will clamp the input - the result is you’d have to try pretty hard to overload the input to the point of damage.