VK5SRP LF/VLF experiments.

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Spurred on by a friend who has been experimenting with these new low frequency bands we now have access too, I stated to experimenting my self. I decided to build a series of modules connected together by BNC jumper cables. As my only LF/VLF receiver, an Icom IC-R71E, seemed to have quite poor performance at these frequencies I decided to use a converter and use the receiver at 4.00 to 4.50 MHz. Looking on the web I found several designs and some kits. The first kit I bought was just too simple to be on any use and this was not helped by having an NDB on 377 KHz almost in my front yard. I built a very sharp low pass filter with a cut-off frequency of 500 KHz to keep the broadcast stations out that were also causing problems. At Christmas a couple of years ago I found a much more sophisticated converter from Spectrum Communications in Practical Wireless magazine and as it was not yet listed on their web site I emailed them and soon had a kit on my bench. Rod, VK5ZRK, had built a simple tuned amplifier and he loaned it to me and I started to look for signals on the 630M band without much success at first. One afternoon, while experimenting with my growing collection of LF/VLF modules, Rod and I had success hearing a beacon from one of our fellow VK5 hams, VK5CV. The antenna I was using is a simple 8.5 Metre vertical mounted on the back verandah. Rod and I experimented with this, putting a matching network on the base of the antenna and managed to hear a time signal or two on VLF using a bunch of ferrite rods inside a BIG coil and the signals from VK5CV using a permeability tuning unit from an old Philips Car Radio.

This spurred me on again in my quest to experiment some more. I built my version of the tuned LF amplifier in another small die-cast box and was surprised how sharp the tuning was. Knowing that most of the signals will be CW and WSPR and knowing my CW skills are sadly lacking these days, I tried the various software decoders available but eventually settled on buying a K2 CW Keyboard kit from Hamcrafters. As I had not worked with WSPR for two years I reinstalled it and connected a fancy Creative Labs sound interface on the shack computer, a Creative X-Fi, model SB1090.

Enthusiasm for the project then lapsed for several months as other projects took over my time and a nine week over seas holiday. When I arrived home from nine weeks holidaying in Europe, Rod greeted me with great news, the NDB had been turned off. That will make my quest to hear LF and VLF signals much easier, I do not have to make that very sharp 377 KHz filter I had designed using an on-line calculator.

Recently I put the LF tuning inductor in a Jiffy box and mounted that, the 500KHz LP filter and the LF tuned RF amp on a wood board attached to the frame of the veranda next to the Vertical Antenna and the SGC tuner that looks after it, when I wish to use it on HF. The matching inductor and the tuned RF Amp tune quite sharply to 475.7 KHz, the WSPR frequency that seem to be used on 630 Metre now. There is sometimes a 4 S point hum/buzz in that area of the spectrum at night. I have been round the house turning things off but it must be coming from outside my property. I suspect there may be a Plasma Television near by. Luckily they seem to go to bed quite early and from about 9.30 PM my noise level on the 630M band is quite acceptable.

Here are the details of the LF amplifier and if you would like my original Sprint PCB art work send me an email to VK5SRP@WIA.ORG.AU.

Here are two screen dumps of my first successful decodes on the 23rd and the 24th of October 2016. The decodes from VK5ABN came in for a lot longer than this image shows. Berndt is located in the Adelaide Hills and my QTH is in the North East suburbs of Adelaide.

Details of the Spectrum Communications VLF converter kit

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Written by and Copyright, Phil. Storr © Last updated 26th October 2016