Why is my 1090 range limited to <40 nmi?

I stood up my site only two days ago, but I’m already seeing something that I can’t explain. (I was on the FAA industry ADS-B team for a few years so I think I might still know something about this stuff.) My “coverage graph” indicates that I’ve forwarded 5,497 position reports at that range but none in any range bin over 40. That can’t be right. I’m about 15 mi SE of KBWI, so between being under the localizer for 33L and generally in the midst of the global crossroads stretching between IAD and BOS, I should be receiving a boatload of reports.

Could it be that, because this area is already paved with receiver sites, the FlightAware system has set a range filter in my PiAware installation? Sorta seems like they have.

My installation is a 50 MHz - 3 GHz discone on a mast up 30’ and fed with 50’ of LMR-400 coax. I’m using an RTL-SDR v3 dongle fed through the FlightAware 1090 filter. ( I have a UHF TV transmitter nearby. )

Any help will be appreciated.

BRgds… Frank / WA3NHK

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That doesn’t look right to me too. I get more range when I had a tiny antenna on my basement window bars.
Can you check your gain settings? They may be too low.
Have you tried this setup with a known antenna connected directly the the RTL-SDR Dongle.
A Discone is a very wide band antenna. Tuned antennas, like Flightawares, DPDs and others, do provide a little out of band filtering. The coax is great. If you use N connectors, ensure they are the same impendence(one has a thinner pin). If you use SMA connectors, double check you don’t have the RP (Reverse Polarity) version on one end. Ensure that one end has a pin and the other doesn’t. It is possible to get two that will happily mate together and neither has a pin (one SMA and the other SMA-RP).
Given that you’re an Extra(Me too), I suspect most of this has already been done.
I am in NYC and had to use cavity filters on all of my antennas 144Mhz up to 1090Mhz because there was so much noise in the area. Look at the posts for do I need a filter. These show you how to run a scan to see how much noise your antenna is receiving. They should also show your FA filter is working. If possible, try the setup without the filter.

Hi Jon,

Thanks much for the quick reply.

How do I check my gain settings? Is there a CLI that I can telnet into for doing command line stuff?

Roger on the connectors. I definitely have the right connectors. All of my antennas use N connectors and appear in my N patch panel. So I just run a patch cable over to my bench and use an Nf-SMAm adapter. I’ve used the discone before for other things so I know it’s good but I’ll check it again. And I’m definitely using the proper SMA type at the input to the filter. Yep, it’s broadband but you’d think the filter would compensate for that.

I"ll take a look at those posts tomorrow but I should tell you that my performance was identical before I installed the 1090 filter, so at the moment the filter appears to have no effect. Just to check every base I’ll put the antenna feed into my SpecA tomorrow and have a look at the debris coming in. There’s always a chance that the TV broadcast transmitter down the road is putting some transmitter noise right on 1090, in which case the best filter in the world won’t help. I’ll also put the filter on my VNA to see how good it is.


No, we don’t do that in the stats display.

What does your local data (i.e. SkyAware) look like?

The SDR frontends are very broadband and are very susceptible to out of band interference (the filter will help but it’s common to need the filter even with a 1090-tuned antenna)

Make a quick (vertical) dipole/monopole for comparison? Doesn’t need to be on the mast – you should hear plenty of traffic with a simple antenna in a window, and if it is an interference problem then not being on the mast will probably help with that.

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The DisCone is a (very) broad-band scanner antenna. And it has low gain. Basically it receives everything badly (that’s quite uncharitable, but serves for this argument).

Given your location, you’ll be receiving a lot of very strong (in band) signals, so you’ll want:
A purpose built antenna
(yet to be determined) a filter
edit your piaware-config file and add “adaptive-burst yes” and “adaptive-dynamic-range yes” - then play with them and see what works for you.

Hi obj,

Thanks for the reply. I’m starting to realize that my discone isn’t as good as I thought it was. So yesterday I moved the antenna feed to my 440 MHz 9 dBi ham antenna. Definitely not optimum for 1090 but it definitely picks up more traffic than the discone. (See SkyAware screen capture below.) The range limit is the same, but definitely more traffic. So I’ve ordered the Signalplus 12 dBi vertical. (Probably not 12 dBi gain but at one meter in length it should be better than an isotropic.)

I looked at the 1090 neighborhood on my SpecA. There’s no indication of any co-channel transmitter noise from the TV down the road, but it’s entirely possible that the ADC is being saturated by the primary carrier.

I’ll do those piaware edits. thanks.

Thanks, gecko.

I’ll try those settings at my next opportunity. Also, I ordered a proper 1090 antenna today. It’s one meter tall so I have to assume there are collinear elements inside because their gain guess is 12 dBi. Performance improved on my 9dBi 440 MHz vertical but still not what it should be.

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Try this easy DIY Antenna

QUICK SPIDER - No Soldering, No Connector








Pigtails to connect QuickSpider’s RG6 F-connector to SDR’s SMA Connector

pigtail-F-female to SMA-male- RG316



Tnx. If I weren’t so lazy (and preoccupied with my dogs) I’d give this a try. So instead I just received the SignalPlus 12 dBi vertical from Amazon. Even though it’s only 8’ above the ground and blocked by my house and trees I’m still seeing A/C 72 nmi away vice the 20 nmi limit with the discone. Now I have to revamp the installation to get the antenna higher and improve on the 17 dB of feedline loss that I have now. Theoretically, if I get the feedline loss down to about 5 dB I should see my range extend by a factor of four.