Radio / SDR

Current radio propagation conditions:

Recently, dipped my toes back into Software Defined Radio. Using a DVB-T dongle I had lying around, I got to tuning some local FM radio stations using zadig and hdsdr software on the laptop, and it piqued my interest for sure..

I now have a decent quality RTL-SDR dongle (820T2 tuner) with the associated antenna kit in addition to three DVB dongles with FC0012 and E4000 tuners. I’ve been able to tune in a lot of different things.. From medium wave radio through the various HAM bands, through broadcast radio, through aircraft VHF, through maritime VHF, through DAB digital radio, through digital TV signals, through seeing my car unlock signals from the keyfob, to picking up and plotting ADSB signals from planes. A huge world of signals out there, and it’s really interesting to be able to see that much of the spectrum on the screen at any one time.

Currently I have Raspberry Pis serving radio signals across my network. One Raspberry Pi is serving FM signals via rtl_sdr from the RTL-SDR dongle, and another RPi is serving the HF spectrum via the SDRPlay RSP1a and rsp_tcp application. The Pi can supply ~2048 kHz of radio bandwidth across the network which is generally good enough. I do get more consistent behaviour when using 1Mhz instead.

To get decent HF signals I took a 10m length of parallel speaker cable, split the two conductors, and attached one end of each cable to the connectors on a co-ax connector, and connected both of those in a coupler. That gave me a centre-fed dipole, with fairly good connectivity end-to-end. That co-ax connector feeds the core of a 50m co-ax cable. The screen of the cable is earthed just outside the house and also just near the antenna. The core and sheath are connected indoors to the stubs of the dipole antenna supplied with the RTL-SDR dongle. This gives me a horizontal dipole antenna with a total length of ~20m. It’s currently extended across the end of the lawn, and gives some pretty good results.

I’ve been able to tune and decode some DRM (Digital Radio Mondiale) signals from the shortwave bands such as Radio Nigeria and Kuwait radio. Another DRM station is a radio station from Bulgaria. On ordinary AM, I’ve been able to receive BBC World Africa from Ascenscion Island, and Voice of America as transmitted from Botswana – a straight line of almost exactly 9000km, and very clear. I can also pick up DCF77 and MSF60, and I’ve picked up a Russian time signal that was clearly distorted by multipath routes. The RSP1a device is actually really good for browsing HF..

My current issue is to chase down why I have such high levels of RFI from 7Mhz downwards at my PC. If I connect my laptop and SDR device in the lawn, I have lovely clear and quiet conditions with a clean MW range. On the Pis or PCs in the room in the house, I have a huge amount of noise. I’m suspecting the UPS..

In the post I have a number of interesting toys on the way. I have some low noise amplifiers, an FM broadcast block, an amplified powered mini-whip antenna, and another RTL-SDR dongle with HF antenna kit. I also have an Airspy R2/Spyverter R2 combination inbound as well, as I recently received the RSP1a. Those receivers can show me 10Mhz of the spectrum at the same time, which is an upgrade from the current ~2Mhz that the RTL-based dongles can show.

All in all, it’s an interesting return to a hobby I’ve skirted around for years me. Maybe it’ll lead on to getting a HAM license?

Some useful links:

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