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OK
Andy,
it was
just an old idea,never tried it out.for lf I am using an old fasioned class c
tube PA,500W from 100 to 700KHz without switching.
73
Victor
To prolong an already long thread :-)
A differential line receiver of the 26xx32 and 26xx33 type gives you a
good performance. It has guaranteed switching thresholds;
bias both input at half way and AC couple to one of them. But also
has a small amount of symmetrical hysteresis - . The '32
devices has 200mV, the '33 has 500mV,
You'll find hysteresis very advisable when you actually start
radiating a signal using the interface. A normal comparator has so
much gain that if you were to remove the RF source, there is more than likely
to be enough pick up from the antenna to feed back round and cause all sorts
of spurious oscillations. (In my case 700 watts of 137kHz at a frequency
set by the resonance of the loding coil / antenna). Having the
hysteresis means a minimum signal has to arrive before there can be any square
wave generated.
Precede the comparator input with a two stage bandpass filter , Ql = 10
or so, , and you should be able to feed it with any waveform in the knowledge
a nice 50% square wave out will result.
Andy
On 2 August 2011 15:55, <[email protected]> wrote:
Hi
Stefan,Rik,
i didn't want to make the story too long,but i agree with
you.
73 gl
Victor
-----Oorspronkelijk
bericht-----
Van: [email protected]
[mailto:[email protected]]Namens
Stefan Schäfer
Verzonden: maandag 1 augustus 2011 19:04
Aan: [email protected]
Onderwerp:
Re: LF: RE: frequency doubler and divider
Hi Victor,
Yes,
that should work too. But as Rik says, there must be a 50% duty
cycle.
And if it's a sine wave, using CMOS gates is not a good idea i
think,
because there is a wide range where the gate can switch from L to
H or H
to L. So a comparator must be choosen. And so the sine wave
should look
clear (no modulation).
Anyway thanks, these are all useful ideas that
makes us a bit more
creative :-)
73, Stefan/DK7FC
PS:
Hmmmm, indeed, not bad that idea! My PA driver has a rectangular
output.
I will feed that to the optocoupler stage (6N136) to prevent EMC
problems
in the shack (already works sufficient). Amplified by a BC548
and a
transformer between + and collector to a core that comes in
saturation,
one could form a curve at 2x f input that has a sharp rising
slope and a
lower falling slope. This 2x f signal should be suitable to
drive the
SG3525. Ah, i'll try all that tomorrow. Hope the PA will be
active next
weekend :-)
Am 01.08.2011 16:40, schrieb [email protected]:
> Hi
Stefan,
>
> wat about a bridge rectifier with a divider? Also
broadbanded?
>
> 73
>
> Victor
>
>
-----Oorspronkelijk bericht-----
> Van: [email protected]
>
[mailto:[email protected]]Namens
Stefan Schäfer
> Verzonden: zondag 31 juli 2011 15:06
> Aan: [email protected]
>
Onderwerp: LF: frequency doubler and divider
>
>
> LF,
VLF,
>
> I just re-invented the wheel ;-) Just by thinking i
found one possible
> way how to double and divide a rectangular
signal, to achieve an
> accurate 50 % duty cycle :-)
>
>
One could take a simple XOR gatter like a CD4070 and a RC circuit.
The
> time constant has to be about the half of the period of the
wanted
> frequency, e.g. 3.6 us for 137 kHz. The output of the RC
circuit
> (voltage across C) and the original signal is fed to one
single input of
> the gatter. Then the output frequency will be 2x f
input.
>
> All this can be found in the internet as well, of
course. But if you
> don't know about that possibility you don't know
what to seach in the
> web too. At least i haven't found that method
by searching and it also
> wasn't discussed here in the recent time.
Furthermore i never saw it on
> a PA design by amateurs i found in the
web.
>
> The output signal of the 4070 is then fed to the well
known frequency
> divider consisting out of e.g. a CD4013. Then output
frequency will be
> the same as on the input but the duty cycle will
be accurate 50%!
>
> This is one method to (re-) obtain a
suitable drive signal for a H
> bridge PA or class D PA after passing
the driver signal through an
> optocoupler or so. I'm sure i will use
that method now in several
> circuits, like in the new LF PA that
still causes some problems,
> excactly on that matter!
>
>
Later i found on the German wiki site:
> http://de.wikipedia.org/wiki/XOR-Gatter#Frequenzverdopplung
>
>
73,
Stefan/DK7FC
>
>
>
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