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mods to AIDC 3733 to get rid of image noise and the notch at 2...



NN0V,

Your measurements are accurate, they match mine and others who have made 
these measurements and posted them.  The two preamp filters are designed to 
pass about 2.1 to 2.7 GHZ and the IF amp works from around 50 to almost 500 
MHZ.  The notch can be at 2400 MHZ or nearby.  Others have made quite a few 
comments on this BB on changing the frequency of the LO.

My long range plans are to change the LO to 2.00 GHZ on a downconverter.  
With this, the 2.05 to 2.50 GHZ input signal would come out at 50 to 500 MHZ 
on my receiver.  This takes care of the image problem and gives me the 
extended range on my RX.

If you want the notch at 2150 MHZ, then the small rigid coaxial cable that 
makes the stub needs to be replaced with a slightly longer stub.  You can 
then cut it until the notch is were you want it.  If you want the notch 
higher in frequency, then the stub needs to be shortened.  I have measured 
the stub, the cut end is not a short, it is an open circuit at the cut end.  
Obviously you need some good test equipment to change the stub's frequency.

The two bandpass filters have tuned elements that are "fingers" that are 
various lengths, to provide the bandpass characteristics.  The longer ones 
could be cut at the ends to shorten them a little and to bring the lower 
frequency bandpass limit up a bit.  The elements could also be replaced with 
new ones, cut out of thin copper, with all the elements cut to around 2.3 
-2.45 GHZ.  Even a small single sided circuit board could be made to 
duplicate these elements and be designed for passing 2.3 to 2.45 GHZ.  These 
changes would take a lot of time and effort and some good test equipment to 
implement.  Most people will find it works OK as is.

TNX & 73,


Bob Seydler
K5GNA
k5gna@aol.com
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