Thursday, 6 March 2014

Receiver Woes! Dongle not Antenna!

Oh flippin' heck!

As well as the ground plane antenna, I decided to knock up a colinear, to try and increase receive aperture and get better ADS-B signals. This being nothing more than some strategically bent wire, took little time to create. The most effort was drilling a small bit of PCB material to mount the socket and radials on. A bit of nylon cord was attached to hang it up for testing

I tried this antenna with the modified RTL dongle - nothing! No matter what I did, neither the GP or the colinear would give me any usable decodes.

I started thinking then it must be a software config issue. But try as I might, nothing could be found amiss with the software. I even tried different software, I tried the firewall settings, I tried Telnet (on the main PC, the Vista laptop was told to enable the Telnet client about 2h ago and is still trying!). I could not get any received data. Looking at the spectrum on SDR#, I was only seeing occasional pulsed of ADS-B at 1.09GHz, surely theres more planes within range than that!?

Suspicion began to fall on the receiver...

By a lucky chance, the postie came with a couple of parcels, one of which was - my second RTL dongle! I set the software back to SDR#, put the cheap and tacky stock mag-mount on the new dongle, plugged it in and started the software...

Blimey! A MASSIVE column of ADS-B bursts at incredible strength filled the screen! Switching to ADSB#, and starting ADSBscope, and a few seconds later this was my laptop screen

Dozens of aircraft! So the problem lies in the RTL receiver stick, or the antenna modifications. I have one adapter for the MCX connection, but I also have the MCX plug and a bit of coax cut from the first dongles stock antenna, so I will find make up some sort of adaptation for the TNC connectors on the antennas.

I wonder if the problem is down to the way I just patched my 50 ohm coax across the 75 ohm MCX antenna?

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