On Sun, 28 May 2017 16:13:52 +1000, Clifford Heath
wrote:
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 couldn't find any such project. I suspect that it might have gone
the same way as the various M328 component test meters being sold
online. The original project was open source. It was then
commercialized by various vendors with wildly varying pricing. Much
of the stuff I've found was early versions of the board and firmware.
Meanwhile, the project has done on to add features and improve the
firmware, but the online stuff seems stuck with early revisions. This
link includes some history:
http://www.instructables.com/id/AVR-Transistor-Tester/
I can't seem to find the original development site, which was in
Germany.
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.
If the amplifier is used to simply produce a square wave out of
whatever it fed into the input, low gain might be a big problem. So
will noise around 0v which is why a "threshold" adjustment is usually
supplied. Getting such a simple amplifier to work from 0.1MHz to
2.4GHz is unlikely, which might explain the lack of sensitivity.
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.
May I suggest that you remove the input amp and setup something that
give the prescaler a 50 ohm input. Then, design a broadband RF
amplifier that has a chance of working over the frequency range.
Something similar to a CATV or OTA TV/FM amplifier might be suitable.
However, don't worry about getting a flat frequency response. Just
take whatever you can get that produces enough drive to make the
MB501L prescaler happy. A collection of communications freq range
bandpass filters would be nice to prevent triggering on out of band
junk.
The main counter is a PIC.
I'm not PICky.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558