[AReU] Elimination of desensing

[w4tas]

Sorry I didn't make it to the hamfest today Jim. I was just too pooped this
morning to face it. Pat and I went to a social function with some of our
friends and didn't get home until 11:30 PM. With a relatively hard week at
work and several nights of less that optimum sleep, I just found my limit
(so to speak).

I did make a contact on AO40 today. I could have made several but I was
trying out my new 3733 converter with the temperature controlled crystal
that I added to it. I also reconnected my preamp so as not to have a 6 inch
piece of coaxial cable between the helix connector and the input of the
preamp. Everything worked great! The signal to noise ratio was at least as
good as before and the converter frequency was much-much more stable after
about 15 minutes of warm up.

The only problem I encountered was desensing similar to the kind you were
getting at Orlando. I don't know what started it. It was probably the
mounting of the preamp in a different location without the short piece of
coaxial cable. The real sensitive equipment is pretty touchy when you
operate it in a strong RF field. I have never had a desense problem before
as serious as this one. The downlink was strong fortunately and I was able
to reduce power to 10 watts and find my downlink. If conditions had been
less favorable, I could not have made it. Once I found where I was there was
absolutely no problem. Signals were 5X5 both ways with a guy in Ottawa.

Now the even greater news.

I put a 5.8 inch open stub between the helix antenna jack and the converter
input. This eliminated the desense completely as far as I can tell. There
will be another pass in the morning and I will test it further. I removed
the stub and the desense re-appeared. This confirms that the 1/4 wave open
stub will probably clear up most of your desensing problems with AO40. I
will make you another stub in a few days. Right now I can't find another "N"
tee connector in my junk box. I could have sworn I had several of them but I
could only find one today.

I will order them along with some other odds and ends from Mouser this
weekend.

Hope you have lost your jet lag.

73

Tony