DC – 2MHz Waterfall
We’ve added 10KHz – 2MHz receive capability to the SUWS Farnham WebSDR.
You can access the WebSDR at: http://websdr.suws.org.uk/
This frequency band is received by an Active Antenna developed by Martin G8JNJ, which is fed into an R820T2 RTL-SDR running in Direct Sampling mode on the ‘Q’ ADC Input.
The current antenna is a prototype, and is mounted only a few meters up the mast. We are planning to fit a notch filter to reduce intermodulation distortion from the onsite DMR repeater before installing the antenna at the top of the mast, which should significantly reduce electrical noise from the ground and increase sensitivity.
I’m giving your SDR a mention in the LF column in the next Radcom as it’s unusual in the UK for a web SDR to cover 136 and 472kHz.
Having been involved with the Derby web-SDR (www.1942khz.net) I know how difficult it is to get a quiet receive aerial at a comms site. We eventually went for a flat-top dipole as its lack of a vertical element made it more immune to local noise. The site we are on has kiloWatts of band 2 causing active loops to curl up and die but maybe a Wellbrook or similar would work at your site and could be rotated to minimise the noise?
Good luck with your interesting project!
Dave G3YXM
Hi Dave,
Thanks for giving us the mention!
Most of the noise we’re encountering is either in the shack directly below the mast, or on the mast itself. It would also be nice to maintain omnidirectional reception.
Martin G8JNJ has now completed the build of the new Active LF antenna, this contains a Low-Pass filter at 3MHz, as well as notch filters for the broadcast band segments to make the most of the RTL-SDR’s limited dynamic range. This will also be mounted about 20m higher than the existing LF antenna.
We’ve now just got to find a time to head up there and install it, hopefully should be soon!
73s,
Phil M0DNY
Hi Phil.
I tried the LF and MF bands last night looking for WSPR signals.
After routing the audio through to a copy of WSJT-X I was unable to see any activity on the waterfall or decode anything. After switching to The SW-UKSDR (KiwiSDR) I could see 8 stations on MF, 6 of which had very strong signals. Do you know if the active antenna is working or if there is some other problem with LF/MF reception?
Hi David,
Unfortunately the LF/MF reception is not as good as it could be, mostly due to the high local noise level on site (a PC recycling center.) We’ve notched out all the large sources and believe that we’re doing the best we can at this site.
We are currently evaluating another (far more remote) unique site, so stay tuned!
Phil M0DNY