There are plenty of homebrew frequency meters on the market, basically
amp, PIC and display. Problem is I haven't seen one yet that works
above about 50Mhz. Does anyone know of a circuit diagram for something
capable of about 3Ghz? Something like a homebrewed version of the
Optoelectonics offerings.....

Thanks,

Tim

Generally frequencies that high are done using prescalers. It's also
possible to do it with a mixer, and there are some other specialized
techniques. Several companies make prescalers. They tend to be
expensive and not very easy to find. An alternative way to do the
prescaling is to use a PLL chip. Many of them (like the National
PLLatinum series and the Analog Devices parts) have one output pin that
can be programmed to monitor the divide-by-n chain output, and you can
program the divide-by-n to give you some useful fairly large division,
to get down to a frequency that's easy to count at that output pin.
The PLL chips like that tend to be inexpensive and more readily
available than the prescalers. So what if you're not using about 75%
of what's in the chip? You may want to use an MMIC gain block between
the signal input and the PLL or other prescaler to get the sensitivity
up a bit.

Cheers,
Tom

On Thu, 21 Jul 2005 14:51:43 -0700, Timothy wrote:

There are plenty of homebrew frequency meters on the market, basically
amp, PIC and display. Problem is I haven't seen one yet that works
above about 50Mhz. Does anyone know of a circuit diagram for something
capable of about 3Ghz? Something like a homebrewed version of the
Optoelectonics offerings.....

Thanks,

Tim

I built one last year. I used a PIC16F628 and LCD display.
The HF input uses a 74F74 as a 1:4 prescaler and works up to
about 150MHz. The UHF input uses a Fujitsu 1:128 prescaler,
IIRC it is an MB510. The prescaler is rated for 2.7GHz. I have
used mine up to 1300MHz. The timebase is a very high quality
9MHz TCXO from Ericsson mobile phone equipment. It never
wanders more than 1Hz away from my 10MHz oven controlled
oscillator.

At HF, gate times are 400mS and 4S for 10Hz and 1Hz
resolution. At UHF the gate times are 1.28S and 12.8S
giving a resolution of 100Hz and 10Hz.

I don't have a schematic of the counter. Most of the
hardware design is stolen from my old display/stabiliser
circuit: http://www.eircom.net/~ei9gq/stab.html (from memory?).

The PIC and lower frequency circuitry is on Veroboard. The
VHF/UHF is built dead bug style on copper clad board.

73 Ed. EI9GQ.


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On Thu, 21 Jul 2005 16:23:23 -0700, K7ITM wrote:


Several companies make prescalers. They tend to be
expensive and not very easy to find.

Dead sat-tv receivers and some UHF tv tuners are a good
source of prescalers. I have never paid money for one.

73, Ed. EI9GQ.


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