Mal,
Are you totally unable to say ANYTHING good, supportive or kind to anyone?
Stefan does not need, or deserve, your sarcasm or ill will and neither do the
rest of us. Please, have the good grace to acknowledge a piece of good work or
say nothing at all.
Stefan,
Excellent work - well done.
73s
Roger G3XBM
-- Via my iPod Touch 4g --
On 22 Dec 2011, at 18:08, "mal hamilton" <[email protected]> wrote:
> 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!!!!!
>>
>>
>>
>
>
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