Hal wrote:
"dickw1ksz at gmail.com
<http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com> said:
>/provide frequencies at 72.5, 725 and 7,975 MHz that are /
What's interesting about 72.5, 725, or 7975 MHz?"
Nothing, unless you're using those frequencies. But, if you want to
multiply up to expand the resolution of a counter, anything you can use
that will work well enough at 10 MHz reference, in conjunction with a
little math, can help a lot.
Perry, I'd suggest that you can use a number of old PLO "brick" type
oscillators that are commonly available - if they can operate well (or
be easily modified) with 10 MHz reference. Most were intended for 100
MHz-ish inputs, but will also be just fine at lower frequencies - but
consider the extra phase noise. The actual output frequency can be
almost anything as long as it's big enough for sufficient
multiplication. Simple calculations to get the desired scaling and info.
I have a bunch of 5 GHz PLOs that work fine with 10 MHz in, planned for
a two-stage multiplier. I just happen to have been working on this
differential frequency counter project over the last few days, and have
the design worked out for the high frequency range stage 1000x (delta
+/- 2 kHz gives +/- 2 MHz). It takes in two 10 MHz signals, and provides
an output IF of 10 MHz plus 1000x the frequency difference between the
inputs. One input is taken as the reference, converted to 5040 MHz and
90 MHz LOs. The other input is converted to 5000 MHz (500x), and mixed
down to 40 MHz IF. This is then doubled to 80 MHz (2x), then mixed with
the 90 MHz down to 10 MHz, netting 1000x the difference. This can be
viewed on a suitable counter (1 Hz resolution at 1 second gate) at
modest frequency. The display is 10 MHz plus 1000x the difference, or
say 8-12 MHz range, representing 9,998-10.002 MHz. Essentially, it takes
the middle three zeros (or nines) out of the 10 MHz shown on the
counter, while expanding so the 1 Hz digit represents 1 mHz, and so on.
The other (similar but specially modified) 1000x multiplier will be
cascaded in front of or behind this one, depending on how things work
out. The first 1000x is easy, but the second is of course, a whole
'nother story - the two cascaded would be similar in noise to
multiplying up to 10 THz. The plan so far is for the +/-2 Hz range to
provide E6 multiplication, so 1 uHz resolution at 1 second gate - or
maybe 10 seconds, or more, depending on how things work out. My
experiments indicate that I can go pretty far with it, once things are
clean enough. Right now I'm fighting line noise mostly, which dwarfs the
random close-in phase noise. I can't even even get a second stage to
lock with my experimental setup, but expect much better results once I
build a very clean power supply for it, and fix the numerous ground loops.
So anyway, a good old-school PLO can help with pretty good
multiplication factors, so may be worth considering, especially for
one-time use, or to avoid having to commit a piece of regular test gear
to the application. Also note that nobody in their right mind would use
the approach I've outline above - except for me, since I have lots of
the right kinds of microwave pieces, and it's a lot of fun.
Good luck.
Ed
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