Antenna on roof, what cable to use?

lsusb -v will give details on power use.
My FA devices and airspy seem to want 500ma each.

I don’t have any RTL-SDR plugged in at the moment to check.

I tried the link to the one that you said you used second and got good results, but I did not get anything. Could you please check the hyperlink. THanks.

I was just a link to a picture of it, but I ordered this one: … UTF8&psc=1

Please note; everything I do is still testing and finding out what’s what so no guarantees. But when I replaced the previous flat cable with this one results were better.

I put an USB amp meter in between the power supply and the Raspberry at this moment.
When booting the draw goes to about 0.7-0.8A and after a while it settles around 0.6A total.

lsusb -v says indeed the FA Pro Stick draws 0.5A.

So just something random; yesterday I broke the 800.000 total reports barrier.
I hit 819.409 total reports received. Maybe not that much compared to other sites but it’s kinda cool to break this barrier.

With the summer season only just begun; maybe I’ll hit the 900.000 barrier sometime this summer? :mrgreen:
FlightAware total reports record by Iemand91, on Flickr

I have something I can’t explain related to this. When I connect an antenna directly to my SDR or with a very short cable I get no planes, but when I add a 10’ cable in the middle I get lots of planes. I’ve tried multiple antennas, in the same rooftop location. So far, despite all knowledge saying this is wrong, a longer (20’) cheap cable tv antenna works better than thicker short cables and way better than a simple male to male sma adapter (which receives absolutely nothing). Yet that same adapter is fine if connected to a longer cable.
I can’t figure it out.

So either your SDR / RPi / power supply is noisy and feeding noise into the antenna.

Or alternatively the attenuation is reducing some foreign interference. Above a certain threshold interference will obliterate your reception. Attenuating everything in this context can improve reception because the SDR isn’t overloading anymore.

So try a filter?

One possible cause may be the short cable and connectors. I helped someone with a cable with the reverse polarity connectors, and the center conductor of the cable never touched the receiver dongle. The male cable connectors must have a center pin to work. Just a thought.

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I have a flightaware pro and a pro plus. The pro plus has the filter on it. It still won’t work with a short cable, but does improve the message rate on a long cable slightly. I also tried swapping the power supplies and the whole raspberry pi’s. The only variable that makes it work is the long cable.

@astrodeveloper described the most probable cause (it’s caught out more than a few people).

It’s not that, I’ve used the same adapters as I mentioned. I’ve also tested resistance to the antenna and ground and found no loss.

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Sorry - cant see it. What adapters are you using?
It’s the plugs on each end of the short cable @astrodeveloper was referring to.

What antenna are you using and what reading do you get?

With the RP-SMA connectors, the center pin of the male connector is a socket instead of a pin. You need to measure the resistance of center pin at the SDR dongle to the center pin of the antenna connection. This needs a low resistance, (not 50 ohms, as that is the impedance of the coax and not DC resistance). RP-SMA connectors do not provide the connectivity on the center pins, thus no signal arrives at the SDR dongle. No idea why anyone ever designed the RP-SMA connectors, as they mess up many installations. If this is your situation, you can do a fairly easy patch by using a 1/2 inch (10-12 mm) wire inside the RP-SMA connector. Cheap and easy, though the real connector is a better thing to use. Hope you get your system up and running well soon. Best wishes. I am an old ham radio / USAF retired electronics guy, just pushing electrons around in interesting projects.



Insert a piece of wire in the hole to act as a pin

RP-SMA Worksround


I do know what RP connectors are and I’m not using any. Let me try to illustrate what’s happening since you all seem very confused.

RP-RTLSDR-XXAntenna - I get 5-10 messages per second / 1-2 aircraft
RP-RTLSDR-6m cable-XXAntenna - I get 250+ messages per second / 50+ aircraft

Same device, same power supply, same RTLSDR, same antenna. Putting a long cable between them has astronomical improvement in performance.

It doesn’t make sense. And yet there is is.

Even though you say you are using the same connectors adapters for both, if you could provide pics of the cables/adapters you are using for at least 1, both ends, that might help.

Other possibility already mentioned is you are getting some massive noise when the short connection is used so close to your pi.
You could run a freq scan for both setups and post those pics too.

Yes I can do that.

By frequency scan do you mean hook it up to like airpspy or some other radio software on a computer?

I was trying to make another pi with sdr software and was using a generic rtlsdr but haven’t really gotten it working well yet. So I’d probably have to use a laptop to do that.

I did try using the flightaware pro plus with the 1090mhz filter as mentioned and that didn’t make a difference with no cable or a short cable. I’m not sure how effective that filter is. It did boost performance slightly with the long cable.

Does anyone know where to get a 978mhz filter that doesn’t cost more than the whole usb setup?

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At this point, I believe you on your connectors. I have had bad cables not working and with poor connectivity for some reason. In the end, I cut the cable in two pieces and threw both away. I made a new cable and things worked well then. I suspect some non-visible flaw in the cable or connectors is messing you up. Perhaps using an ohm meter measure connectivity of the center pins and then shields. Both should be near zero as this is a DC resistance. Should be open between center pin and shield. Hope you can get it worked out. Might want to flex the cable as you make the measurements, as that will help find mechanical flaws. Good luck.

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Spectrum scan

At the risk of stating the obvious, there is something wrong with your cable.
If you can’t find the problem, follow this recommendation and replace it.

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