On 29/05/17 14:51, Jeff Liebermann wrote:
On Sun, 28 May 2017 21:22:33 -0700, Jeff Liebermann
wrote:
On Mon, 29 May 2017 08:45:50 +1000, Clifford Heath
wrote:
I downloaded, see he
https://www.dropbox.com/sh/z91pqvcpg470tuy/AAAIRnVfRDqrbrJwA3yBVQVPa?dl=0

I missed the translated user manual (in English). It shows a
sensitivity graph for the high frequency range with the following
comment from Pg 12:
It is noted that the UHF channel allows measurements up to about
450 MHz. This path comprises a divide by 64 stage claimed to be
able to operate to 2.4GHz according to the published specifications.
It is therefore surprising that the sensitivity fell as quickly
as it did.
Looking at the schematic and layout, my never humble opinion is that
the designer didn't know anything about RF design and layout.

That was my conclusion also, and that (plus the earlier published
versions) is why I said "advanced hobbyist". Not even very advanced,
certainly not RF-experienced

I don't know what frequency the PIC counter input is capable of,
but I know that the AVR counter is clocked; so you can only count
at half the CPU clock frequency. Bah, humbug.

The schematic shown on Pg 13 is quite different from either the old or
new versions of the design that I previously mentioned. Instead of
the extra divide by 4 packages, it has a 2nd DG MOSFET in front of the
PIC counter. It also lists the prescaler as an MB506 which is divide
by 128/256, not 64.

Both my units have MB506.

It also shows that the gates of the DG MOSFET are
NOT tied together.

The units I have have both pairs of protection diodes, and the inputs
are joined only at the connector. I cut the trace and soldered a bit
of co-ax onto the prescaler input capacitor.

I don't have a good RF source (yet - currently building, see
https://github.com/cjheath/AD9851LCD) so I can't evaluate the
sensitivity.

Clifford Heath.