NDB DXing with the Malachite SDR

[AlanC]

I thought this might be of interest to someone...

For my birthday in April I treated myself to a Malachite receiver - it's a Chinese clone, the one that says 'Malahit-DSP SDR Radio' on it and comes with 1.10a firmware registered. This little box is a bit of a steep learning curve initially, but once you get it set up something like and get used to it, it starts to put a smile on your face and you can get really good results from it. I'm using my homebrew miniwhip antenna. This is a 30cm length of wire as a pickup, with a FET and bipolar transistor as source follower and emitter follower respectively to drive the coax. There is a lot written about these elsewhere on the web. Mine is simply powered at the antenna by a 9V battery. On HF, you can get surprising results even with the antenna indoors but on MF and LF noise is your enemy. It simply blanks everything out. So this afternoon I took it outside in the garden here in suburban Sheffield, UK and attached the miniwhip to our decking parasol and had a tune around the NDB band - one of my favourites!

I had already experimented with the AM mode and various filter widths to try to optimise NDB reception, though with only average results. Eventually I hit on an idea that makes the Malachite super sensitive for NDB DXing. Since most of the NDB's here in the UK are AM with 400Hz tone modulation, I use the Malachite on USB mode with the narrow filter configured to give a passband from 250 to 550Hz - i.e. 400Hz, +/- 150Hz. You can then position the red tuning line on the carrier, and you will hear just the upper modulation sideband in the centre of the filter. If there is QRM here you can tune down 800Hz and listen to the lower sideband of the NDB instead, which in a noisy situation might just be enough for you to ID it.

The real downside to the Malachite is the spurious responses which although not a problem on HF, down here are fairly numerous. You will immediately spot them because they tune in the opposite direction, and at a higher rate, than wanted signals. Also there is QRM on some frequencies from the radio itself; it's from the display actually, you can quick-press the power button to turn it off.

So to the results. This is what I achieved, between 15:00 and 16:00 today Saturday June 4th. There was plenty of lightning static around from storms in northern France which made copying the weaker signals a bit challenging.

Freq kHz ID   Location     Distance km
332.5    CAM  Cambridge   170
335      WCO  Westcott    169
337      WTN  Warton      101
338      FNY  Finningley  34
340      HAW  Hawarden    105
342.5    NWI  Norwich     199
349.5    LPL  Liverpool   90
352      NT   Newcastle   188
353.5    EME  East Mids   60
365      KIM  Humbs Apt   78
378      KLY  Killiney    307
368.5    WHI  Whitegate   78
393      EMW  East Mids   57
385      WL   Walney Is   145
402.5    LBA  Leeds/Brfd  59
406      BHX  Birmingham  100
421      BUR  Burnham     211
433.5    HEN  Henton      183

The best DX was clearly Killiney in Eire, at 307km which is a new one for me. And it was nice to get re-acquainted with some old friends as well; in fact it's good to see so many NDB's still on the air.

Cheers
Alan

[JustGreg]

I glad you are enjoy yours.  I have one and found the spurious responses were a problem.  Using mine with a 66 wire shortwave antenna resulting in hearing WBCQ in the AM broadcast band.  You also have to watch the RF gain.  I had a local FM station show up in the shortwave band.  A FM band reject filter eliminated that problem.  But, I will say the Malachite works well in the FM band and for NOOA weather stations.  It is a quirky little receiver, but, it does work if you take the time to learn how to use it.