DARC 10m Contest 2021

This year i spent quite some time in preparation of the 10m contest. Already a year ago i bought some fishing rods with the plan to make a Moxon antenna. This antenna was realized now. The transceiver was my HiQSDR again driving a R155 PA. In order to improve sensitvity i connected a wideband LNA from Funkamateur. The LNA was switched on and bypass by one of my sequencer PCBs. Quisk SDR forwarded 192kHz IQ samples to skimmer and from there the decodes went to the bandmap of tlf log. I started in CW and worked quite some multies. After one hour i changed to SSB which was a likely a fault because the activity in phone was low. The last 30 minutes were spent in CW again.
The map below shows the locations of the stations worked. They were taken from internet and might be incorrect. The map shows that i mainly had the moxon to north and west direction.

stations worked in 10m contest 2021 – maps by openstreetmap and opentopo contributors via DL4MFM edi analyzer

The most heavy part of the moxon is the mounting plate. The fishing rods are snapped to the plate and then fixed with U brackets. There are 16 wing nuts to fix.

10m moxon antenna under test indoor

Getting the antenna outside is not that easy. It needs to be mounted outside and there was little space because of a chimney nearby.

Moxon antenna mounted outside the roof window

It you do not take care everything will end up in a big mess.

Gordons knot – wires of the moxon

The software did cosist of Quisk, skimmer and tlf log.

SDR software just before the contest

The R155 PA can generate 100W with 5W input. Unfortunately it seems not very robust against some RF nearby. The linear power supply i tried to use before went unstable in SSB. Therefore i had to swap the supplies.

PA and power supply

HiQSDR is quite unsensitive on 10m. I used a LNA from Funkamateur which has bypass relais for TX. I had to replace the transistors because both where faulty.

HiQSDR and preamp

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 dh5ym@darc.de

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 www.drm.org

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.