Mal,
The basic equations of rocketry can be put in the back of an envelope. The
engineering aspects are much more challenging.
John F5VLF
On 22 Dec 2011, at 19:47CET, mal hamilton wrote:
> Maybe you need one, you seem to have gone off Resonance!!!!!!!!!!!!!!!
> again. A variometer is hardly rocket science.
>
>
>
>
> ----- Original Message -----
> From: "Roger Lapthorn" <[email protected]>
> To: <[email protected]>
> Sent: Thursday, December 22, 2011 6:22 PM
> Subject: Re: LF: Re: Automatic Variometer adjustment at DK7FC
>
>
> 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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