Message-ID: <22C8182174B34200BFF6AE3E3E90A40A@acer>
From: "henny van elst" <cpm@planet.nl>
To: <rsgb_lf_group@blacksheep.org>
References: <4EF3689B.1030902@iup.uni-heidelberg.de>
Date: Thu, 22 Dec 2011 20:38:53 +0100
MIME-Version: 1.0
Subject: LF: Re: Automatic Variometer adjustment at DK7FC
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Hello Stefan,nice job,
henny cpm
73's
----- Original Message ----- 
From: "Stefan Schäfer" <Stefan.Schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, December 22, 2011 6:27 PM
Subject: LF: Automatic Variometer adjustment at DK7FC


> LF,
>
> I'm totally thrilled.
> Yesterday in the night i designed a circuit to automatically resonate my 
> LF TX system by tuning the variometer. This allows to exactly hold the 
> phase and hold the antenna in resonance in changing sourrounding 
> conditions, like upcoming rain. But the most useful feature is: It 
> automatically adjusts the variometer if i do QSY (remote operation!),e.g. 
> if i go from 137.7 to 136.172 it re-adjusts the system in less than 5 
> seconds!
>
> A small drive engine is used to turn the small coil into the main LF 
> loading coil, see: 
> http://dl.dropbox.com/u/19882028/LF/LF_variometer_drive_engine_arrangement.jpg
> The drive engine works from 3...24V DC and takes 0.15A. It is steered 
> automatically by the circuit described below.
>
> The basic phase measurement circuit is taken from the M0BMU tuning meter 
> which one can find somewhere in the web and here: 
> http://dl.dropbox.com/u/19882028/LF/LFtunemeter.pdf BTW this tuning meter 
> is THE most useful device for antenna measurements at all, in my opinion. 
> The phase meter can directly drive an analog meter showing if there is a 
> positive or negative or no phase (=resonance) between voltage and current. 
> I took a very nostalgic and high quality analog meter to nicely display 
> the phase, see http://dl.dropbox.com/u/19882028/LF/phase_meter.jpg. The 
> circuit works very nice and accurate. Resonance showing and the maximum of 
> the antenna current  exactly coincides. The circuit need no external power 
> supply.
>
> The automatic motor drive circuit is here: 
> http://dl.dropbox.com/u/19882028/LF/DK7FC%20Automatic_variometer_tuner%20.jpg
> It uses a quad OP amp, TL084. The first stage low pass filters and 
> amplifies the input voltage (taken from the analog phase meter, i.e. 
> switched in parallel), which has a DC part and a 137 kHz ripple. Another 
> OP amp generates the ground level which is in the middle of the 12 supply 
> voltage (e.g. a battery or usual power supply). Then there are 2 
> comparators and a ICL7667 MOSFET driver. The 7667 works in a H bridge 
> configuration and inverse switches the outputs. The outputs can be 
> opposite in both directions, turning the engine CW or CCW or they can have 
> equal potential to stop the engine. 2  BAT42 shottky diodes are used to 
> generate a +- 0.3V threshold voltage to prevent self oscillation arround 
> the resonance point. The sensitivity of this circuit and the phase 
> threshold (hysterisis) can be aligned by adjusting the gain of the input 
> OP amp stage. The 7667 provides a low impedance output switching and easy 
> circuit design (no discrete push pull stages or so). A resistor is put in 
> series to the engine to reduce its speed a bit. Also a 0.1A poly switch 
> type fuse is put in series. This fuse is under-dimensioned for the engine 
> but will work for a few seconds before it interrupts. This a some fail 
> save protection in case the circuit may be damaged by what ever and wants 
> to turn the engine endless. Two anti parallel switched LEDs indicate a 
> running engine and its direction. They will be labeled with L+ and L- 
> later on the PA front panel.
>
> As a test i was transmitting a key down carrier at 137.7 kHz and activated 
> the circuit. A short impulse, indicated by one LED, set the variometer 
> EXACTLY to resonance. Then i QSYed to 137.0 kHz without interrupting the 
> TX. Since the frequency is lower, the L is to low. Thus the circuit acts 
> resistive-capacitive and the phase angle is negative. L must be increased. 
> The phase meter first jumped into the negative half of the meter but it 
> took about 2 seconds until it came quickly back to zero where it stopped 
> immediately.
> I took the SpecLab frequency generator for that test (have an IQ mixer 
> that adds 125 kHz to the soundcard output, so i have to generate 12 kHz to 
> come out at 137 kHz). Then i added the FM modulator within the signal 
> generator and choosed a frequency deviation of 300 Hz and a period time of 
> 20 seconds. This is how that transmission looks on the DF6NM grabber: 
> http://dl.dropbox.com/u/19882028/LF/137kHz_%2B_FM0.3kHz.jpg
> Without the automatic tuner beeing active the phase meter moves like a 
> windscreen wiper of course. When the circuit is active the needle of the 
> meter does very fine twitch but does not leave the resonance significantly 
> at all! :-)
> The experts know how the LED blinking pattern must look: Faster blinking 
> on one side, then slower, then the other LED starts to blink slow, then 
> faster, slower again and so on :-))
>
> There are still no mechanical switches in series to the engine supply, 
> which would be another fail save circuit, to be added later, hopefully ;-)
>
> This may be one way for other LF transmitting stations to increase the 
> comfort of running their TX system by automatically adjusting their system 
> to resonance, even when QSYing by > 1 kHz :-)
>
> 73, Stefan/DK7FC
>
> PS: A photo of the board is here: 
> http://dl.dropbox.com/u/19882028/LF/automatic_variometer_board.jpg
> PPS: Caution: This is not NEW and there are other circuits with similar 
> functionality existing!!!!!
>
>
>