Joe,
good to read this!
Regarding
the loading coil, I would agree with Stefan that a large multiturn air
coil is the best option. A laminated iron core would suffer from
excessive eddy current losses, and the effect of ferrites is limited by
saturation and hysteresis losses.
My
1.3 henry coil consumed 2.3 km of 0.4 mm enameled wire, using 7 buckets
with 480 turns on each:
df6nm.bplaced.net/VLF/VLF_110304-06/coil_legospacers.jpg.
The advantage is that due to magnetic coupling between layers, you will
need less wire for a given inductance. And the inductance is adjustable
across a wide range, using spacers. Disadvantages are the high electric
field between layers limiting voltage capability, and less effective
heat removal from the inner buckets. Stuffing the buckets too tightly
into one another is surely not a good idea:
df6nm.bplaced.net/VLF/pictures/arced_coil_140601.jpg
An
nonresonant earth antenna across high resistivity rock could also
radiate moderately well, avoiding coil making and high voltage issues
altogether. But to compete with your vertical in terms of radiation
resistance, it would need to be really long, on the order of a couple
of miles. It will have magnetic loop directional pattern which may be a
disadvantage.
For a
transatlantic detection eg. by Paul Nicholson, a Rubidium or GPS locked
signal source would be very beneficial. Using SpecLab with 1pps phase
lock to eliminate soundcard output glitches has worked well for DJ8WX,
PA1SDB, and myself.
Best
of luck,
Markus (DF6NM)
-----Ursprüngliche Mitteilung-----
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Di, 24 Jun 2014 12:48 am
Betreff: Re: LF: VLF in Canada
Hi Joe,
Fine to hear that you're give it a try. Please, don't ask Industry
Canada if the 10mW is RF power of ERP!
To get out a real signal on VLF, there is no alternative to a real large
coil without ferrites! Think about the high voltages... But 100m of
antenna wire is a good start. I remember 550 mH for my 100m kite
antenna. For me it was 2000m of 0.4mm diameter wire :-) Nice work is
that. Takes long but is a funny game :-)
73, GL, Stefan
Am 23.06.2014 21:33, schrieb [email protected]:
Dear Group,
I tried again to get an LOA for VLF. This time, the response from
Industry Canada was favourable: 10 mW 8.0-8.3 kHz. Yesterday, after a
few slight rf burns, and thanks to PA0RDT's miniwhip design and
DL4YHF's Spectrum Lab and advice, VLF sigs on 8.277 kHz were heard at
200m from the 100m wire aerial. This was a reception outside my back
yard! 10 watts from an 1970's keyboard amp (volume control set on 3)
were stepped up with an xfmr to a lossy 500 ohm tuning coil peaked
with a ferrite rod for maximum squeal at L=0.35 H.
Is it possible for someone who is not especially enthralled by winding
a mile of 0.7mm wire to use an iron core to make a VLF tuning coil?
73
Joe VO1NA
