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Date: Mon, 16 May 2016 17:17:34 +0200
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: LF: A transductor instead of a traditional variometer on VLF/LF/MF?
 Done!
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Status: O

Hi all,

The Q of such a coil will of course depend on the signal amplitude 
because it is can become nonlinear. For example, you can use it in a RX 
loop, a tank circuit, L and C in series, then you can steer the 
resonance frequency in a wide range. It will not be overloaded. It may 
be even a better choice than a varicap diode. I thought about many 
fields where it can be used on LF/MF/VLF and also on the higher frequencies.

OK, i've made a Q test at signal amplitudes of about 1V. This 
transductor was designed for VLF, so i will stay at the low frequencies. 
You may try the same on LF, using just 2 cores instead of 4 and less 
turns, for higher currents and less L!

9.72 kHz | I = 0 | Q = 157
16.42 kHz | I = 0.1A | Q = 137
26.34 kHz | I = 0.25A | Q = 167
43.67 kHz | I = 0.5A | Q = 218
72,44 kHz | I = 1A | Q = 131
Not really consistent, hm? BTW i increased the number of the DC turns to 
40 yesterday, so about 2x the value.

During the measurements i saw the remanence, so it is not so easy to 
measure the Q accurately with the simple method i used. So the results 
are just a rough idea. The transductor has some drawbacks like remanence 
and temperature dependency. But if used in an automatic variometer, this 
has no negative effect i think.

In a first test putting the transductor into the VLF antenna system 
yesterday (Tom is right, the latest version is outside the stacked coil) 
it was possible to move the resonance arround 6470 Hz to +- 20 Hz, which 
is already quite helpful but may still be a bit to low. I will make 
further measurements.

73, Stefan


Am 16.05.2016 12:02, schrieb DK1IS:
> Am 16.05.2016 um 11:20 schrieb Wolfgang Büscher:
>> Or, depending on how the ring core is oriented in the "mostly air 
>> core" coil, the AC flux lines would run perpendicular to the DC flux, 
>> which also eliminate the need for a large AC-blocking coil for the DC 
>> exciation.
> That´s right, Wolf, but I think Stefans latest approach is to use the 
> transductor as an external inductivity in series with the main coil 
> and no longer as a ferrite core with controllable permeability inside 
> the main coil (what should be possible too). Nice idea anyway but as 
> Roeloff alredy asked: what about the Q of the variable unit? Its 
> influence on the whole system shouldn´t be so large because of the 
> only small variable part of the inductivity but one should take care 
> for a possible heating of the transductor cores at full antenna 
> current. Already tested, Stefan?
>
> 73,
> Tom, DK1IS
>
>
>
>