Ok, it is official. I have a set of sinclair Q202 duplexers that didn't come as
a set. At least two of the cans have different serial numbers and different
factory tuned frequncies. DRAT! Ok, so here is the problem. With my trusty
Aeroflex 2945 (I think that is the model) I can easily get a -35db notch on
each of the hi pass cans at 147.825 pass and 147.225 notch. No problem with
that side. Ok, the problem is on the low pass pair (mix-mached I am sure). I
can barely get a -30db notch on each can even if I spin the loops. So, just out
of (morbid) curiocity, I pulled the loop out of one just to show a fellow ham
what was in there. Lo and behold there was a 12pf cap soldered accoss the notch
tune cap. Hmmmm... What would happen if I took this cap off there since to get
the -30db notch the tuning cap is almost screwed all the way out (min
capacitance). So I got out the soldering iron and removed it. It worked, sort
of. I was able to get a -35db notch on my lo pass (147.225 pass 147.825 notch)
side, but at the expense of some pass loss higher than the high pass side. What
happend is it seemed to make the low pass can into a high pass can. The notch
went to the other side of the pass. I spun the loop to get the best result and
tuned the notch cap near its max capacitance to get the notch wher it should
be. It worked barely and with a bit more loss in the pass. I am thinkin I may
need to go back and put a 6pf cap accross the notch tune to get it where I want
it, but I am not sure. On the second can of the lo pass high notch side I tried
to remove the cap, but it didn't turn out the same. The loop inside it was not
silver plated like the previous can, it was just plain copper and appeared to
be a bit longer. When I removed the cap on this can, the notch went to the low
side of the pass and I couldn't get it to come back around. I will definitly
have to try a 6pf cap accross the notch tune cap on this one.
Now, I just replaced the harness with RG-214/U jumpers the length needed to get
14" between centers of the "Tee's". The old ones were RG-142/U and were also
apparently the correct lenght as well. Changing the jumpers didn't seem to
affect the tuning ability of the cans. It was a waisted effort really, but oh
well, they have a really nice new harness on them, makes em look 10 years newer.
Any suggestions guys. It lookes like I may have a modified pair of cans that
are actually high pass instead of low pass. Should I play with the lenght of
the loop? What about changing the 12pf caps accross the notch tune caps
(parralell) to 6pf or so? Right now, they are working, but the high pass pair
look really good and the low pass pair look so-so to kinda oK. The repeater is
working very well, but I feel if I get the cans right it will be even better.
Anu suggestions?
Call me if you like 251-234-0295.
73 de N5NPO
Norm
