Audio Digital Signal Processors and radio interference suppression

This quest all started when Horst VK5HY) was having trouble with solar inverter noise from houses near him middle of 2015. He remembered he had a quite old JPS NIR10 DSP device which he had put away years ago and forgotten about.

He rummaged through his shack and found the thing. Hooked it up and we were amazed at what it did to interference. He even turned on the BFO on a AM signal and the NIR10 all but chopped out the resulting whistle !!!

It was then I remembered I had been given a similar device from a deceased estate collection, a TimeWave DSP 9+ and written on it was US. When I got it I plugged in 12 Volt and no LED's, no sign of life so into the bottom of the junk pile it went.

Encourged by the success Horst had, I rummaged around and found the TimeWave unit. I soon discovered the problem was a shorted 5 Volt regulator driving the processors.

At that time I was listening to a European net on 14.307 late afternoons on a Heathkit SB-300 (all tubes) Ham Band receiver and so I plugged the little black box into the speaker output and a speaker into the output of the box and I was getting a noticable lowering of noise. My next thought was if I can drive the DSP-9+ from accross the volume control I can see how much it does by winding up either the valve rigs volume control or the DSP's volume control. This was complicated by the DSP having low impedance solid state input and the tube rig having a 500K pot. Another tube socket on the chassis provided a cathode follower and the problem was solved.

Have a look here:

Conditions on the BA net have been difficult the last couple of months so I put an advert in VKHAM for a DSP box. I got two replies, one of the fellows had a BHI AMEN he was not using and so that was soon on its way to me.

I also got a reply from VK5AKK who had a later version of the one Horst has, A JPS NIR12, and even more professional unit intended for professional audio processing. After four days of searching we had to give up on that one, he thinks he may have sold it some years ago.

Trevor VK5ATQ must have also been reading VKHAM and a few days later he turned up at my place with two more DSP boxes he was not using and was willing to sell. Modern rigs have these things built in so these old DSP units are only any use to BoatAnchor folks like me perhaps. The DSP in the IC-756 ProII sold me on this technology. I was fixing this rig for VK5NAQ and one night when the BA net was realy bad I put that on the air and wow, what a difference. When I handed the rig back to Peter the next week I said, if you ever want to sell that thing, give me first refusal !!! It took a year but Peter upgraded to a newer Icom and the 756 come back to me after an exchange of money.

From Trevor I now have a BHI NEIM 1031, similar to the BHI AMEN I got from the fellow in NSW but with actual controls instead of just a couple of buttons. This same "insides" are also available as a tiny module to fit to FT-817's etc.

The fourth one is a Timewave DSP 599ZX, an amazing thing with lots of switches, knobs and even an LCD display. It is dual channel and was often used to fix audio signals in studios or signals on two radio receivers in communication installations. Must get some time to try that one out soon. I suspect it will not do any better than the BHI units as these make bad siganls readable and that is all I want to be able to do.

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Written by and Copyright, Phil. Storr © Last updated 30th January 2017