Amateur Radio Pages
updated November 2014
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8th December 2010 - 9kHz Receive Pre-Amp Upgrade .
I have now constructed and fitted the 7.8 to 10.5kHz filter to the pre-amp. I have tested it initially using a shielded ferrite loop indoors & all seems to be OK. At first it appeared that the pre-amp lost gain compared to when the filter is switched off but it may be that having the filter in use removes a lot of noise which is apparent when in wide-band position, possibly generated due to the MSK transmitters higher up the band and the high noise levels from lower down the band. The proof will be seen when I install the pre-amp at the main loop again. Upper right is the filter board and center right shown fitted in the pre-amp box.
26th December 2010 - 9kHz Transmit Antenna .
As you have seen earlier I have carried out tests to match the VLF transmitter from 8 ohms into 50 ohms and constructed a matching transformer.

Whilst waiting for my NoV to arrive from Ofcom and some spare time during the Christmas break I have been working on a coupling transformer to use with a suitable antenna. Not wishing to make changes to my LF/MF vertical system my initial idea is to use a loop.  As my only experience has been with VHF quads and receive type small loops  I feel this is going to be a steep learning curve.  I do not have the garden space to follow  the lead of other experimenter’s with ground loops and probes so it will be a suspended type using the 12 metre mast in some way.
13th January 2011 - 9kHz Special Research Permit (NoV).
Today I received my SRP from Ofcom to carry out research and experiments on the 9kHz band. The NoV is effective immediately and expires on 10th January 2012. The allocated frequency, power and additional conditions are the same as for other UK 9kHz operators, ie. 8.700kHz to 9.100 kHz with a maximum of 100mW (-10dBW) e.i.r.p.
Sub 9kHz - 5
My starting point is an adjustable matching transformer wound on a PC monitor scan coil toroid of 7cm diameter average. It has 13 turns interleaved with a 21 turn winding using 2.5mm insulated wire, depending on results either winding could be primary or secondary. There are tapping points very 2 turns except the first three are at each turn on both windings for fine adjustment. These ferrite's are normally used at 15,625kHz (line scan frequency) so should be OK for 9kHz.  The smaller matching transformer is wound on a PC monitor line output transformer ferrite core.
Matching and coupling transformers
M0BMU VLF
pre-amp & filter
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