Searching for some FreeDV QSO partner on VHF

Since i use Quisk for my HiQSDR i found it interesting to experiment with FreeDV again. Quisk can directly support using the FreeDV API and work in this digital mode without building lots of cables. Since i wanted to try the latest mode 700C i had to compile the library from the scratch and add the mode to the configuration of quisk. Below you can find recordings of my CQ call in the modes 1600 and 700C which were made loopback.
Now i search for a QSO partner preferably on 2m somewhere in the area around JO61. I can work relatively well direction southeast. So east OK might be good.

Mode 1600

Mode 700C

Please remember the 700C mode uses only 1kHz of bandwidth.
If you are interested in some tests just send me a email to

WSPR and 10m Aircraft Scatter


A evening of TX. The picture was made by DK1RS in a distance of 80km and shows my signal (horizontal line) during about half an hour. The crossing lines are reflections from aircraft +- Dopplershift. So far signal raises about 10dB compared to the direct path between Rainer and myself. WSPR cannot decode if the Aircraft Reflection is present because it cannot deal with the Doppler drift.


HiQSDR repaired…

A while ago i destroyed the RX input amplifier of my HiQSDR. Last weekend i replaced the two hittide switches and the differential amplifier of that circuit. Now its fully operational again. On the photo you see the backside of the HiQSDR enclosure as well as my antenna tuner and the SWR/Power meter. The transceiver itself does not have any human interface. It just has inputs for power, RF, key and PTT and outputs for RF, PTT and some control signals.
The digital baseband goes via UDP connection to the SDR PC. Usually i use my Laptop connected via Wifi.

KBS from Sofia in DRM/AM Simulcast

The korean national service KBS is currently testing DRM-AM simulcast. This means the same service is transmitted side by side on co channels. One channel contains the service broadcasted in DRM mode, the next channel contains the same service via AM. This gives the opportunity for some nice comparisons between DRM and AM stability and audio quality. Find two audio snippeds below.
The transmissions will be every evening from 19UTC to 20UTC on 5875kHz (DRM) and 5885kHz (AM) – source

The screenshot shows a part of the radio band yesterday evening. Unfortunately the conditions to Sofia had been really poor. You can see the both signals of KBS and some much stronger signals from other broadcasters.
Obviously the DRM signal was suffering from sideband lobes falling into the DRM spectrum limiting the SNR because at the end when the modulation was already switched off the DRM SNR increased rapidly.


Voice audio snipped – first DRM, then switching to AM

Music audio snipped – first DRM, then switching to AM

The DRM audio was transmitted in AAC+ Mono with 18kBit/s. It gives a rather nice sound compared to other DRM broadcasts that can be received at the moment.