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AIDC 3733 Murata Filter boards



>From K5GNA:

I have had some printed circuit boards made for mounting the Murata filters.  
These will allow you to replace the second filter in the AIDC 3733 type 
downconverters with the Murata filter very easily.  This filter, combined 
with the broader filter in the front end will give you a very sharp passband 
from a little less than 2400 MHZ to about 2480 MHZ and eliminate the image 
and the LO frequency.  These will provide a true SSB noise figure of less 
than 1.4 dB and eliminate most kinds of interference.

For those of you (like me) who used the original copper filters for a ground 
plane for the Murata filter, the network analyzer display was a real shocker. 
I have a few of the preamps only out of the AIDC 3733's disconnected and 
connectorized for testing.  The filters got here Friday and I soldered the 
Murata filter to the original fingers of the old filter (dead bug style) and 
used only the grounding provided at the bottom of the filter. Big mistake.  
There was a notch and other spurious responses in the passband. They went 
away when I pushed the top of the filters to ground.  I abandoned this method 
and designed the PCB for it.

The PCB provides an easy way to mount the tiny SMD Murata filter even for 
those not used to SMD work.  The second filter is the filter that needs to be 
replaced, replacing the original first filter with the Murata filter will 
only increase the noise figure.  The measured board losses from the PCB are 
lost in the Murata filter's insertion loss and passband ripple.  The measured 
loss in converter gain is negligible with the second filter replaced by the 
Murata filter and board.  

The filters will arrive next Wednesday and I will have pictures from the 
network analyzer to post.  The plots from my Xacto knife made version look 
good, with a little better tolerances and plated through hole grounding on 
the PCB version, they should look very good.  I will post the pictures next 
week, when I have a plot from the commercially made board.

The boards are $5.00 each, post paid.

Bob Seydler
8522 Rebawood
Humble, Texas 77346-1789

TNX & 73,

Bob Seydler
K5GNA
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