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Equipment / NDB DXing with the Malachite SDR
« on: June 04, 2022, 1805 UTC »
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
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
