On 28/05/17 14:25, Jeff Liebermann wrote:
On Sun, 28 May 2017 08:09:04 +1000, Clifford Heath
wrote:
On 28/05/17 04:35, Jeff Liebermann wrote:
On Sat, 27 May 2017 12:55:02 -0400, wrote:
Look for something that has a built in prescaler. Something like
this:
http://www.ebay.com/itm/Blue-RF-Signal-Frequency-Counter-Cymometer-Tester-0-1-60MHz-20MHz-2400MHZ/172396798620
I have two of those. I bought the second because I thought I'd
broken the first, it performed so badly. They're as bad as each
other.
Thanks. I was thinking of buying some of those. I should have known
as much of the low cost "modules" that I've purchased seem to have
deficiencies as a result of crude design or cost cutting exercises.

It was developed by a good hobbyist who posted everything online.

I think that full schematics of slightly earlier versions are
available online. He uses a dual-gate MOSFET before the prescaler
and before the main counter, with the inputs paralleled. I think
that affects the sensitivity (though I don't have measurements)
so for my 2nd module, I cut a track to separate the input paths.
I might wind up adding an independent input amplifier with AGC,
or even a pot to adjust the 2nd gate bias on the MOSFETs for a
manual gain control. A little difficult though, as parts of the
circuit are underneath the LED displays, so I'd need to remove
those.

The main counter is a PIC.