This is a terrific achievement and you are so excited, if you need one. In
my case I DO NOT
G3KEV

----- Original Message -----
From: "Stefan Schäfer" <[email protected]>
To: <[email protected]>
Sent: Thursday, December 22, 2011 5:27 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.j
pg
> 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.jp
g
> 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!!!!!
>
>
>