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'question on increasing pic internal clock speed'
1998\06\20@211735 by Dominic Gualtieri

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First of all I would like to thank everybody who replied to my question.
Your advice has been greatly appreciated. Secondly, I have decided to
use an oscillator running at  1 ( 1ns per foot) gigahertz with a counter
and have a PIC do the conversions. While I am in the process of finding
info on constructing a frequency stable 1 gig oscillator I am curious to
know if anybody on the list has any knowledge or suggestions on building
an oscillator for my PIC based application. Hope this question is not
off-topic.

Thanx again!!

Dominic

1998\06\21@070040 by tjaart

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Dominic Gualtieri wrote:

> First of all I would like to thank everybody who replied to my question.
> Your advice has been greatly appreciated. Secondly, I have decided to
> use an oscillator running at  1 ( 1ns per foot) gigahertz with a counter
> and have a PIC do the conversions. While I am in the process of finding
> info on constructing a frequency stable 1 gig oscillator I am curious to
> know if anybody on the list has any knowledge or suggestions on building
> an oscillator for my PIC based application. Hope this question is not
> off-topic.

I have a feeling finding 1GHz counters won't be easy. You could probably
use an array of /2 prescalers and try to gate the signal, but it won't be easy.

Someone suggested mixing the reflected signal with the transmitted one,
and sweeping the transmitted signal. This not only sounds like the most
logical solution, but also the easiest to implement. There is a s***load
of mixer-amplifier solutions from various manufacturers you can choose
from.

You will have to have some frequency synth anaway, so why not take one
with serial access, then you can even sweep the frequency with the PIC.

--
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Tjaart van der Walt
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1998\06\22@000701 by Regulus Berdin

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> From: Tjaart van der Walt <tjaartspamKILLspamwasp.co.za>
SNIP
> I have a feeling finding 1GHz counters won't be easy. You could probably
> use an array of /2 prescalers and try to gate the signal, but it won't be
easy.
SNIP

I think it is not difficult to make.  I made once before using a 1.1 GHz
%64
prescaler (Motorola MECL MC12022A) as the frontend.  The final frequency
will be
about 15Mhz (a PIC can read up to 50MHz), which is easy for the pic to
read.
On my case, the value inside the prescaler was not needed.

But using the already known technique to read the value of the prescaler,
by
self clocking, should not be too hard to implement.


Reggie

1998\06\22@012917 by Mike Keitz

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On Mon, 22 Jun 1998 12:14:17 +0800 Regulus Berdin <.....rberdinKILLspamspam.....SKYINET.NET>
writes:
>> From: Tjaart van der Walt <EraseMEtjaartspam_OUTspamTakeThisOuTwasp.co.za>
>SNIP
>> I have a feeling finding 1GHz counters won't be easy. You could
>probably
>> use an array of /2 prescalers and try to gate the signal, but it
>won't be
>easy.
>
>On my case, the value inside the prescaler was not needed.

Single-stage (divide by 2) prescalers are made.  You could connect a few
in series as a ripple counter and have a way to read out the count.
After the first few stages the frequency would be low enough for ordinary
digital counters, including possibly the PIC's timer.  The count-reading
circuit can be slow since it would only be used while the count is
stopped.  It also isn't necessary to reset the counter, just subtract the
previous reading from the next one.

Probably the gate could be implemented by just throwing the DC bias of
the first stage off so it doesn't count, or clamping the 1 GHz clock to
ground with a diode.  A 1 GHz oscillator can be built with a bipolar
transistor.  The frequency could be stabilized by any conventional PLL
chip used for radio and TV tuning.   If a really stable frequency is
needed, use a low frequency crystal and multiply up.

It is generally folly to attempt to measure distances along the ground by
radar.  Radio signals reflect off of everything, including the ground
itself.  Even with the ideal conditions of perfectly flat terrain, there
will still be two paths to the target, one direct and one having taken a
bounce off the ground at the halfway point.  These path distances and
signal strengths can be very close to the same and hard to resolve.
Usually such measurements are taken by light, using laser beams and/or
telescope optics to produce a single path to a specific target.  The
range-determining methods are the same as used in radar; pulses, chirps,
multiple CW frequencies, etc.  For light of course the ranging signal is
applied as AM to the light.


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