Re: VLF Loop Antenna Amplifier

Chris Moulding

I've included a screenshot of SDRUno running a SDRPlay RSPDx receiver from 0 kHz to 500 kHz.

The antenna is using a VLF Loop Antenna Amplifier with a 1m diameter coax loop at 4.5 m above ground with the plane of the loop aimed north/south.

The location is Bolton in north west England.

This was recorded at 13.37 local in the early afternoon at probably the worst time of the day for VLF signals. It's taken with everything powered up in the workshop. If I was to take it out into the countryside the noise floor would be reduced in level.

First thing to point out the pulsing noise from 350 to 500 kHz is a local switch mode charger. I could use a portable version of the loop to seek it out (and destroy it).

The big signals are BBC Radio 4 at 198 kHz from Droitwich, England with the carrier 70 dB above the noise floor and RTE Radio 1 from Ireland with the carrier 50 dB above the noise floor.

E-Loran can be seen around 100 kHz, Royal Navy from Anthorn on 19.6 kHz, 22.1 kHz and 81 kHz.

One I don't usually see during the day is TFK/NRK US Navy from Grindavik on 37.5 kHz.

There are also many NDB beacons sending CW from 300 to 350 kHz.

Any one wanting to identify more signals in the picture may find the VLF broadcast list useful:

If you can't see the image then here is another link to it:



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