Просмотр сообщений

В этом разделе можно просмотреть все сообщения, сделанные этим пользователем.


Сообщения - rw3adb

Страницы: [1] 2 3 ... 304
1
A quartz piezoelectric crystal converts electrical energy to mechanical energy and vice versa.

It won't convert electrical energy into an electromagnetic wave by itself.

Magnetostrictive material such as Terfenol-D will convert mechanical vibrations into a fluctuating magnetic field.

This can generate an electromagnetic wave directly using the homopolar effect.

A piezoelectric transducer can be used to mechanically drive magnetostrictive material to produce an EM wave.

Efficiency is several orders of magnitude greater than a wire antenna enabling practical portable VLF transmitters.

73 de VA3VVV

2
Am 19.04.2019 um 17:28 schrieb Clemens Paul:

    РазвернутьРазвернуть

Hi Clemens and group,

here is the promised extension of my tests, for better comparability merged with the first results (my post on the reflector from 20190418):

Having no VLF quartz yet, I made some preliminary tests with a randomly available HC-6-U quartz, QRG 2434 kHz, wavelength 123 m.

    TX: Sythesizer Schomandl MG100M, 300 Hz ... 100 MHz, smallest step 0.1 Hz, Ri = 50 Ohms, P = 10 dBm, output tied to first leg of quartz, alternatively direct to the antenna wire
    RX: Perseus SDR with an active rod antenna on my garage, fed by a solar system, no external wire connections, air-line distance 100 m to my shack
    Antena wire: 2 m or 4 m, laid out in the shack, tied to second leg of quartz, alternatively direct to the TX output
    alternatively antenna wire only resonated by two roller plus one fixed inductors in series, fed directly from the TX output

Results with 2 m antenna wire:

    with quartz resonator: fres = 2,433,908.8 Hz, RX level at resonance = - 63,1 dBm, - 3dB-bandwidth = 48.3 Hz resulting in Q = 50391
    without quartz resonator: RX level = - 85,4 dBm resulting in a gain of 22.3 dB with quartz
    comparision: my 13 m T-Marconi with top load 4 x 33 m, tuned to 2434 kHz and fed by the synthesizer with 10 dBm results in a RX level of - 32.1 dBm ;-)
    with inductive tuning at 2,434,000 Hz: RX level = - 60.1 dBm resulting in a gain of 3dB compared with quartz. -3 dB-bandwidth = 249 kHz resulting in a loaded Q = 9.8

Results with 4 m antenna wire:

    with Quartz resonator: fres = 2,433,773.6 Hz, RX level at resonance = - 59 dBm. - 3 dB-bandwidth = 49.4 Hz resulting in Q = 49376
    without quartz resonator: RX level = - 75.4 dBm resulting in a gain of 16.4 dB with quartz
    with indctive tuning at 2,234,000 Hz: RX level = - 57.3 dBm resulting in a gain of 1.7 dB compared with quarz. - 3 dB-Bandwidth = 390 kHz resulting in a loaded Q = 6.2

With all tests there was no additional resistive matching at the TX output. The tests at resonance showed the usual unbalance between lower and upper - 3 dB-points. With L-tuning the upper is further away from the resonance frequency than the lower. With quartz-tuning this effect is contrawise and of course absolutely much lesser accented. At a first glance L-tuning offers advantages due to its comparable huge bandwidth and the higher fieldstength at the RX site but this could shrink if you really go down to VLF frequencies, very short antennas and short distances. According to the author´s claims the quarz resonated system is usable for short range communication only and there the Q of L-tuned antennas will also grow to high values as well as the losses in the tuning circuit.

As soon as my ordered XTALs will arrive I´ll make further tests in the 4 kHz-range. If the results happen to differ very much from the preceding tests at 2.4 MHz I´ll report about it.

73 es Happy Easter,

Tom, DK1IS

3
Продолжают активничать японцы:
JA1CGM QRSS120 137.7783
JH1OFX DFCW60 137.776
JH1OFX OP32 137.498

принимать то у нас могут тока Саша, Юра, Сергей...
но 120я - внушает. можно попытать. тем более у всех прием почти круглосуточный.

4
On Thursday, April 18, 2019 07:31:13 PM DK1IS wrote:

 

SNIP

 

> Anyway, the idea is fascinating. Having no VLF crystals up to now, I

> made some preliminary tests with a randomly available HC-6-U quartz, QRG

> 2434 kHz, wavelength 123 m. And yes, it works!

>

> * TX: Sythesizer Schomandl MG100M, 300 Hz ... 100 MHz, smallest step

> 0.1 Hz, Ri = 50 Ohms, P = 10 dBm, output tied to first leg of

> quartz, alternatively direct to the antenna wire

> * RX: Perseus SDR with an active rod antenna on my garage, fed by a

> solar system, no external wire connections, air-line distance 100 m

> to my shack

> * Antena wire: 2 m or 4 m, laid out in the shack, tied to second leg

> of quartz, alternatively direct to the TX output

>

> Results with 2 m antenna wire:

>

> * with quartz resonator: fres = 2,433,908.8 Hz, RX level at resonance

> = - 63,1 dBm, - 3dB-bandwidth = 48.3 Hz resulting in Q = 50391

> * without quartz resonator: RX level = - 85,4 dBm resulting in a gain

> of 22.3 dB with quartz

> * comparision: my 13 m T-Marconi with top load 4 x 33 m, tuned to 2434

> kHz and fed by the synthesizer with 10 dBm results in a RX level of

> - 32.1 dBm ;-)

 

 

63.1 dBm - 32.1 dBm = 31.0 dB : the quartz adapted antenna radiated power is 1/1000 respect the T-Marconi, so the efficiency is 0.1%

 

Good DX ;-)

 

Claudio, IK2PII

5
Радио любителей нет ни кого на диапазоне, так хоть на это полюбоваться  :)

не удалось определить что это?

6
Hi group,

a little bit OT, but the public interest seems to rise ;-)! At April 15, Roman, RW3ADB, pointed out here a similar article leading to a more detailled link:

https://www.nature.com/articles/s41467-019-09680-2.

The paper describes a kind of matching a low source impedance to a very high load impedance by using a piezoelectric resonator. Thus it is possible to feed an extremely short antenna with a very high voltage in resonance without using lossy L-C-circuits, resulting in a relatively "high" antenna current. Of course such a system has a very small bandwidth and is frequency-wise very sensitive to stray capacitances at the high-impedance side. The authors turn this to an advantage with regard to a fast capacitve re-tuning when using it in DAM systems (Direct Antenna Modulation). A second problem is that the crystal has to stand voltages in the 100 kV range which is impossible for commercially available quartz resonators. Therefore the authors use a special lithium niobat crystal at about 35 kHz with 94 mm length which is mounted in a chamber filled with hexafluoroethane gas - not so easy for a normal ham ...

Anyway, the idea is fascinating. Having no VLF crystals up to now, I made some preliminary tests with a randomly available HC-6-U quartz, QRG 2434 kHz, wavelength 123 m. And yes, it works!

    TX: Sythesizer Schomandl MG100M, 300 Hz ... 100 MHz, smallest step 0.1 Hz, Ri = 50 Ohms, P = 10 dBm, output tied to first leg of quartz, alternatively direct to the antenna wire
    RX: Perseus SDR with an active rod antenna on my garage, fed by a solar system, no external wire connections, air-line distance 100 m to my shack
    Antena wire: 2 m or 4 m, laid out in the shack, tied to second leg of quartz, alternatively direct to the TX output

Results with 2 m antenna wire:

    with quartz resonator: fres = 2,433,908.8 Hz, RX level at resonance = - 63,1 dBm, - 3dB-bandwidth = 48.3 Hz resulting in Q = 50391
    without quartz resonator: RX level = - 85,4 dBm resulting in a gain of 22.3 dB with quartz
    comparision: my 13 m T-Marconi with top load 4 x 33 m, tuned to 2434 kHz and fed by the synthesizer with 10 dBm results in a RX level of - 32.1 dBm ;-)

Results with 4 m antenna wire:

    with Quartz resonator: fres = 2,433,773.6 Hz, RX level at resonance = - 59 dBm. - 3 dB-bandwidth = 49.4 Hz resulting in Q = 49376
    without quartz resonator: RX level = - 75.4 dBm resulting in a gain of 16.4 dB with quartz

So it seems the best effects can really be achieved with very short antenna wires. The long range performance is in no way comparable with more fullsized antennas but for special applicatios the features could be interesting. For instance realising some capacitive feedback from the vicinity of the antenna rod could result in a small low power beacon with integrated matching - it even could be used as a presence detector with direkt frequency read out ...

- But yes, Rik, I`ll certainly will keep my Marconi - making QSOs on VLF costs enough efforts even when using a big antenna. But I´ve alredy orderd some VLF crystals on the bay ...

73 es Happy Easter!

Tom, DK1IS

8
 Rick - good signals from JA1CGM and JH1OFX last night on 137 QRSS/DFCW

Here is an example - OFX continued into the night, CGM shut down close to his normal time.  WH2XND was the only wspr decode no JA's last night. I have a repeating blip of a carrier 137.7776  which is local I believe

http://kl7l.com/CGM041119.jpg

73

Laurence KL1X BP51IP Alaska
L400b up a tree

Dear Laurence,

 In addition to JA1CGM(EIRP=1W), a part of JH1OFX(EIRP=0.5W) is recognized by myself at 137776Hz (Say TMO M).

 I was watching both side signals during their transmission last night.

73  7L1RLL Rick

 


Sent: Thursday, April 11, 2019 12:27 AM
To: rsgb_lf_group@blacksheep.org
Subject: LF: overnight conditions

 

Au or post Au making a mess up here and very little on 475kHz by ways of Dx beyond sea paths. JA1CGM continues on QRSS on 137 on a noise variable night. Notice no sign of DCF39 now over the pole - just too light

 

http://kl7l.com/CGM041019.jpg

 

73 Laurence and GL KL7L

10
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

11
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)

12
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

13
Прием на длинных волнах / Re: SWL 600m
« : 02 Апрель 2019, 19:10:29 »
0146 -23 -0.6 0.475687 0 EI0CF IO65 23 2397

окак. много лет не было видно. думал уж помер Финбар...

14
Технический раздел / Re: GPS-module
« : 02 Апрель 2019, 19:09:19 »
Применение модуля Ublox в Ultimate3S

http://www.ra3apw.ru/wspr-u3s-gpsdo/

15
Подозрительная трасса 137778.5!
Там работает JA1CGM - сравнил с японскими грабберами. Что-то подозрительно совпадает по частоте!
Жаль, не успел посмотреть сразу же. Теперь не ясно, работал ли он в тот момент, как идет трасса у меня.

пиши ему самому. спроси работал он ровно в это время или нет?

Страницы: [1] 2 3 ... 304