Автор Тема: VLF: New DK7FC experiments on 17.47 kHz - Антенна из дорожного отбойника  (Прочитано 2101 раз)

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 ;D

катаюсь!

Hi VLF,

You probably know:

IOTA - Islands On The Air

SOTA - Summits On The Air

but did you know

GOTA - Guide-rails On The Air ??!!

The year 2019 should be the year of GOTA! Try it out. You can do it! No
excuses like problems with the large coils, the high voltages, the XYL
occupying the garden. Just go out, take a walk, and see what you can do
with some wire and a transmitter and some other equipment! :-)

73, Stefan
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Hi VLF,

Last weekend i improved my ground loop antenna by increasing its length
from 900m to 1130m, i.e. +25 % of length, which should give about 2 dB
more signal from the same antenna current. This is, when assuming that
the shape of the virtual ground loop is rectangular.
Now when having two antenna segemnts it allows to do more research:
1. The resistance of each earth electrode can be calculated.
2. the shape of the virtual loop can be estimated: The resonance
capacity (to series-resonate the R-L network at the feed point) can be
compared for the 900m segment and the new 1130m segment. For a
rectangular loop shape we would expect that the L rises with the square
of the length.

The old loop was in an angle of 54 deg to my tree. This angle changed to
45 deg now.
I expected a theoretical gain of
G = 20 * (lg(1130/900) + lg(cos45/cos54)) = 3.58 dB.

A carrier transmission was done at 8270.1 Hz, using an antenna current
of 2 A on both antennas.
900m Ant: T2019-03-31_13:58,+10m : E-field 26.8 dB, H-field: 33.7 dB
1130m Ant: T2019-03-31_14:12,+10m: E-field 31.2 dB, H-field: 37.1 dB

Looks like an improvement of 4.4 dB in the E field and 3.4 dB in the H
field.

Attached is a spectrogram (11 mHz FFT bin width) showing the
improvement. The first dash is a tunng procedure, second is the 900m
ant, and the 3rd is the 1130m ant. Top is E field, bottom is H field.

I wonder how the level difference looks at other locations? Did someone
else track the data and can tell me the difference? :-)

73, Stefan
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At DL0AO, we produced spectrograms and plots during the 5.17 kHz test last weekend. During the first session with the shorter guiderail antenna, signficant fading and a dip occured, most pronounced on the H-field receive antenna. Another deep dip happened immediately after Stefan switched to the long antenna, however that period may perhaps have been affected by a short retuning interruption at 12:58. Considering around 17 dB SNR in 1.5 x 3.8 mHz, the 6 dB variations seems to be too large to be explained by random noise alone. Thus we have been speculating about ionospheric variations or scintillations on a ten-minute timescale. Note that no solar x-ray or SID event had happened at the time.

Therefore I asked Stefan to repeat the test, which he did today, this time starting on the long antenna (10:39 - 11:15) and then going to the short one (11:19 - 12:10). This time the SNR was even better, and only small variations occured, perfectly within the range of noise statistics.

Best 73,
Markus (DF6NM)
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Hi Paul,

Thanks for your measurements.
Good idea to calculate B relative to I.
Would be interesting to see how this varies with frequency.

BTW i did now actually order one of those:
https://www.dhgate.com/product/60-v-60ah-lifepo4-60-v-60ah-lifepo4-de-litio/445395613.html#s2-21-1b;searl|3512104843
Wonder how long it takes to arrive here, and even more, if it actually
has 60 Ah at 60V, i.e. 3.6 kWh!! If so, i will order 3 more of them!...

Considering the 13 dB advantage of night/day in recent transmissions
with that ground loop antenna, at least on 8270 Hz, I'd like to try a
night transmission tonite, at 2970 Hz, trying a 7 character EbNaut
message. So far we have no message decode at ULF between DL and UK. I'd
like to reach that mile stone and think the ERP should be fine now, but
hopefully the QRN stays low enough.

Everyone else is invited to try as well!!!

73, Stefan




Am 05.04.2019 19:06, schrieb Paul Nicholson:
>
> Stefan wrote:
>
> > These were the transmissions today (+ some more parameters):
>
> Received at 5170.1 Hz,
>
>  2019-04-05_10:39,+35m: 1130m, I=2,39 A, 0.63 fT S/N -5.07 dB/1Hz
>  2019-04-05_11:19,+51m: 900m, I=2,92 A, 0.63 fT S/N -4.92 dB/1Hz
>
> Yes, the same fT in both tests.  Then we have
>
> 900m
> ----
>  2.74 A -> 0.50 fT,  0.182 fT/A
>  2.92 A -> 0.63 fT,  0.216 fT/A
>
> 1130m
> -----
>  2.12 A -> 0.50 fT,  0.236 fT/A
>  2.39 A -> 0.63 fT,  0.264 fT/A
>
>
> Nothing received at 970.1 Hz.
>
> --
> Paul Nicholson
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