Hi Mark,
All of the RF design is done...........I have built two
prototypes. On one of them, I use a ten turn pot to tune the VCO. The other
unit uses a PLL for tuning. I think we will have some time to develop the
tuning software, etc.
We were tied up with a big project for the last several months; this was the
Automark election machine that you may have heard about in the news. All
kinds of fun things, getting it through EMC certification.
Speaking of MW receivers, I did purchase the Boston Acoustics
Receptor clock radio. MW performance is not bad, but the selectivity is
pretty wide. It appears to be a single conversion affair that uses a 450kHz
I.F. It might be a double conversion unit, but when I peaked the Radio Shack
loop antenna on the image frequency, I was able to receive the image. It
could also be that the (2 X 2nd I.F.) rejection isn't too good, if this is
truly a double conversion unit. Is it worth the 150 dollars? Could be. I did
call up Boston Acoustics to see if I could get ahold of some service
information. The wouldn't make it available. When I asked them how to remove
the main circuit board from the unit so that I could change the 450kHz
filter, they explained that they couldn't give me that information, since I
if were electrocuted, they would be liable. When I explained that I was
going to quote them in my review, they said that it was ok. If anybody
figures out how to get this thing apart, feel free to contact me.
Oh, another thing............it could be off topic, but this is good for
you Drake '7 line folks. If you change the 1st mixer in your Drake R7/TR7 to
a Mini-Circuits SRA-3MH (Level 13) mixer, and you change the 1N4148s in the
2nd mixer to matched sets of 1N5711 hot carrier diodes, the receive
performance improves a bit. The original 1st mixer has an SSB conversion
loss of 6.5dB, while the Mini-Circuits mixer has a conversion loss of
4.75dB. As far as the 2nd mixer, it is good to get rid of those general
purpose switching diodes and replace them; the 1N5711 Hot Carrier diodes
have lower loss, better IM characteristics, and they are designed for RF
applications.
One thing about that Radio Shack cleaner. I have used some of it in the
past, and it has dissolved plastic switch wafers. I would stay away from
that. The Caig De-Oxit is in the same price range, and it doesn't destroy
components.
In the old days, we used to use Freon based solvents to clean circuit
boards. I would get ahold of the De-Oxit and play it safe. Caig is the same
company that marketed a product called Tweak.

Pete

"Mark S. Holden" wrote in message
...
pete ke90a wrote:
snip
If you brush the dust off the circuit boards, make sure that you don't
bump any of the trimmer capicators.

Pete KE9OA

Reminds me of when I was a kid - my best friend decided to soup up his
dad's radio and found the trimmer caps and the slugs in the IF
transformers were loose and needed tightening.

Any update on the enthusiast's MW radio you were working on?