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Registered Member #43294
Joined: Mon Feb 24 2014, 06:40PM
Location: Near Walsall in the UK
Posts: 11
Paul Nicholson wrote ... There are no amateur radio allocations below 9kHz but in some countries you are allowed to transmit. In the UK you need a 'Notice of Variation' to your licence.
I enquired as to the standing of this area of experimentation in the UK with OFCOM. The response was as you said, you need an NOV.
Also I was told that no portable operation was allowed. The NOV I was informed might not be issued at all even if OFCOM was supplied with the fullest info that they requested. If the NOV was granted it would be for an initial period of 6 months and then would be reviewed, but they would offer no guarantee of renewal.
The main 'user' in the UK I was informed was the Met Office. They apparently monitor lightening down there.
OFCOM were concerned that my small battery powered audio oscillator fed into two metal tent pegs in our back lawn would interfere with reception of 10+ megawatt lightening discharges...
Registered Member #47220
Joined: Fri May 30 2014, 12:20AM
Location:
Posts: 4
Does polarisation matter?
Yes, only vertical polarisation will propagate more than 100km or so. The other polarisation is strongly attenuated.
Surely what's good for the transmitter is also good for the receiver? Or is it the case that environmental noise exceeds practical device noise, so antenna/LNA matching is moot?
Natural radio noise comfortably exceeds the typical device noise floor, although to ensure this, you need to make sure that the front end device is chosen appropriately for best noise match with the antenna impedance. That's down to having the right ratio between device voltage noise and current noise. op-amps work well, eg AD823 for high impedance E-field probe and LT1028 for low impedance magnetic loop.
I can't imagine the vertical that would not create lots of corona with 240 kVrms at 9 kHz
Would be quite difficult to cope with on a wire antenna. Amateurs are using up to about 30kV on the wire and tend not to use corona rings, etc. Higher voltages ought to be possible, especially by the HV and Tesla experts on this forum.
The NOV I was informed might not be issued at all even if OFCOM was supplied with the fullest info that they requested. If the NOV was granted it would be for an initial period of 6 months and then would be reviewed, but they would offer no guarantee of renewal.
That about sums up the NoV situation. Only about three UK amateurs have followed that process. It is much easier in Europe and there are several active stations. Yes the Met Office are the main VLF user in the UK and there are a few university VLF receivers used for research. OFCOM are obviously concerned to protect those operations. In Germany, VLF is also used for weather tracking, in the band 8.3 to 9kHz and amateurs operate below 8.3 kHz because of this.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
What about folks who set up electric fences? Would these not be a significant noise source, as most of these use fairly high loss (eg wood) poles to support the HV ropes and no doubt a significant amount of power leaks into the ground in this way.
Registered Member #43294
Joined: Mon Feb 24 2014, 06:40PM
Location: Near Walsall in the UK
Posts: 11
Conundrum wrote ...
What about folks who set up electric fences? Would these not be a significant noise source, as most of these use fairly high loss (eg wood) poles to support the HV ropes and no doubt a significant amount of power leaks into the ground in this way.
If the radiation is incidental, or accidental, very often a blind eye is turned towards it (unless major interference were to result).
Most of the VLF/ULF systems I have seen over the years have antennas that are so inefficient you would be lucky to get anything from them at all.
It would be quite easy for the 'powers that be' in the UK to allocate a spot frequency for Hams to experiment sub-9khz, and that way all of the lightening monitors would know what to ignore (how difficult is it to set up a DSP notch filter in this day and age?)
By the way, a very good source for ideas and designs for low frequency reception can be found at www.vlf.it
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High voltage amateur radio - VLF
