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Am 19.04.2019 um 17:28 schrieb Clemens
Paul:
Do you think it is possible for a more
true comparison to compare the quartz resonated wire antenna
against he same wire resonated conventionally by an inductor
regarding field strength and 3dB BW?
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
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