OOPS! I meant _on_ the back of an envelope.
John
On 22 Dec 2011, at 21:20CET, John Rabson wrote:
> 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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