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
Got it and thanks. Nice the way the download is packaged as a single
ZIP file. The docs are in Chinese. I haven't tried Google translate
on it yet. The new schematic is very difficult to read the text. I'm
also having problems decoding the "forum description". It's readable
imported into MS Word as Unicode-8. The photos of the PCB seem to be
the old design, which lack the extra divider chips. This is going to
be a challenge.
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.
Yes, except it's meant to be (and mine are) and MB506.
It also says MB506 on both the old and new schematics.
http://www.qsl.net/n9zia/900/mb506.pdf
That's odd because it's a divide by 128 or 256 that goes up to 1.6GHz.
At 2400MHz, divide by 128 yields 18.75MHz. I originally thought that
it would need to use all of the 60MHz counter frequency range, but now
I'm not certain. The PIC used is apparently slow, and won't go that
fast. 18.75MHz seems about right for the PIC16F628a where the data
sheet says it quits at 20MHz.
http://ww1.microchip.com/downloads/en/devicedoc/40044f.pdf
The ForumDescription.txt file says that it's divide by 64 on the first
page, but then claims that the low channel goes to 75MHz, and later
claims that the prescaler is an MB501. Kinda looks like the
ForumDescription.txt file is a mixture of the old and new designs.
Looking at the new schematic, I see that one bipolar front end
transistor was replaced by a dual gate mosfet. However, it doesn't
look like the gates were tied together on the schematic. The original
schematic is tiny, but after enlargement, I don't see a dot where the
wires cross.
Also, if you follow the signal path through the prescaler chip on both
the old and new schematics, the higher frequency range input goes
through the prescaler, into the DG MOSFET, and then to the PIC
counter. If there is a sensitivity problem, it would only be on the
lower frequency range input, which goes to the DG MOSFET directly.
Earlier schematics show two 4-bit counters before the PIC,
which by itself does not have a 60MHz counter.
Probably correct, but I can't tell what those are. Also, I think you
have it backwards. The older schematic shows no dividers, while the
new schematic shows what I guess are dividers.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558