Hi Gary
Yes I see Jim 'tunes' his loop after the coax feed or is it HF
filtering.
My Loop is 800mm sq 50 turns and 3.6mH according to rjeloop.
I am using SpecLab and PC
73 Eddie
.
On 05/03/2011 18:52, Gary - G4WGT wrote:
Hi Eddie,
Firstly, I have not detected any signals on any of the three
VLF antennas during the test period.
I haven't tried my loops without a pre-amp or resonated
them but I note that Jim's (M0BMU) loop is smaller than mine
at 800mm x 800mm & only 30 turns (2.85mH) were mine is
1100mm x 1100mm, 46 turns & about 4mH. Jim,s pre-amp also
has a tuning capacitor (fixed value) which I removed. The
strange thing is that most successful loop systems seem to be
800x800 but all use a pre-amp.
Well, the results of the tests show that the noise level
varies quite a lot. Using a sound card & SpecLab the noise
levels are as follows, the ferrite loopstick is -140 dB, the
Mini-Whip is -150 dB & the large loop is -120 dB. This
surprised me as I believed the loops would be quieter. The
best visibility & strength of the Alpha's was using the
Mini-Whip. The Mini-Whip may be the best choice for me being
omni-directional & I have never seen all four of the Alpha
pulses on one RSDN before using this modified Mini-Whip. At
the moment (1840utc) RSDN 1 & 2 I am seeing 3 signals
& RSDN3 seeing 4 signals.
So, a worth while test result for me but disappointed not
to receive any amateur signals.
BTW, are you using SpecLab on a PC or receiving on a real
receiver ??
73, Gary - G4WGT.
On 5 March 2011 16:48, [email protected]
<[email protected]>
wrote:
Hi Gary
Thanks for the reply, first thing, for "10dB hump at
8.9kHz" read 20dB. Direct coupling of coax to the feed
was killing the Q, I have added a 4 turn coupling loop.
The flatness was only really noted once it was outside.
I can see the need for an amplifier on a broad band loop
as with the E-Probe which is non resonant and at a few
inches long hasn't got a lot going for it but not for a
resonant loop which untuned produces 10dB of noise and
resonant 30dB I am dubious still.
Maybe M0BMU will have a comment :-) please.
73 Eddie G3ZJO
On 05/03/2011 15:21, Gary - G4WGT wrote:
Hi Eddie,
Yes, you will need a pre-amp, don' forget that
the E-Probe has a pre-amp. I advise you to build the
M0BMU VLF pre-amp with 7 to 10 kHz band-pass filter,
circuit attached.
73, Gary - G4WGT.
On 5 March 2011 14:22, [email protected]
<[email protected]>
wrote:
Hi Gary
I am testing a very similar loop to your 1.1m
square, mine is 800mm sq. and uses Litz wire.
Results at the same hight as my E-Probe are
disappointing as yet.
I have no pre amp on it, and am wondering
whether it would be advantageous as when tuned
to 8.9kHz the noise level rises by 10dB. I
suppose I shall end up building an amp to try
but I would welcome any thoughts from the group.
73 Eddie G3ZJO
On 05/03/2011 12:35, Gary - G4WGT wrote:
Hi All,
Whilst monitoring 9090kHz & 8970kHz
using SpecLab at 423uHz, I am testing 3
different VLF Rx antenna types :-
1 - An 84mH shielded ferrite loopstick
(10mm x 200mm), 1 metre above ground
2 - A modified PA0RDT Mini-Whip, 8 metres
above ground
3 - A 1.1 metre square loop with 46 turns
of 1mm insulated wire, 1 metre above
ground
Both of the loops using M0BMU VLF pre-amp.
I have had No. 1 connected since 2000utc
last night until 1030utc this morning, no
signals detected on the SpecLab display. I
have connected No. 2 at 1030utc &
notice a fall in noise level of about 10dB
& a greater visibility of the Alpha
signals. Later today I will connect the
large loop & report my findings.
73,
Gary - G4WGT - IO83qo.
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