Saturday, May 14, 2016

40m doublet antenna - excellent

This weekend some antenna work. I've put up an open wire fed "doublet" antenna for 40m and of course all bands up from that. The centre insulator is made from a piece of perspex.

The open wire ladder line runs down to the shed and terminates to a 4:1 balun I previously used for an off centre fed antenna. From the balun it goes into a transceiver with internal tuner that is able to tune it on all bands from 40m up.

The tree holds a few other antennas including an inverted L for 80m, and one end of a half G5RV.

So far my observation is that noise is low and signals are big, it's great to have the flexibility of multiple bands in one simple antenna.

Monday, May 02, 2016

Fifi SDR control app for MacOS

One of the intriguing things about the Fifi SDR is that as well as I/Q output via an in-built USB sound device it also has the ability to demodulate built right in and that audio output appears as an additional sound device.

The Fifi SDR can be controlled using the same API as a Softrock so I've started work on a native MacOS app that can control the frequency, bandwidth, demodulation mode and play through the audio. It's pretty rough so far but looks like this:

The code is based on rockprog and Apples AVRecorder sample.

So with just the Fifi box and this software you have a simple radio that tunes all of HF and plays through your Mac's audio. If you want the full, waterfall style, experience then I recommend DSP Radio which also supports Fifi.

You can download the alpha app here. As I haven't signed it you will need to right click (control click) and choose Open the first time to open it.

Be careful not to choose built-in audio from the input device and turn up the volume or you'll get feedback. Speaking of feedback, let me know if you find this useful.


Build 2 has the following improvements:

  • Automatically selects the FiFi audio device if found
  • A button to set the frequency directly
  • A tuning slider - I'm still experimenting to get this working nicely.
On my device anyway, the frequency is off. I'll have to look at how to fix this.