[INRAD] FT 920 filter blowby.

[George Cutsogeorge]

The Inrad 920 Switchboard has been very popular and we have sold a bunch of 
them.  Imagine my surprise when I received an email from a customer telling 
me that the filter blowby after he installed our Switchboard was worse than 
before it was installed.  When I was developing the board, several isolation 
tests were run and the new board had some 30 dB better isolation than the 
radio with it's OEM filter.  After some discussion and some work on the 
customers part, he discovered that soldering the case tabs to ground cured 
the problem.  I had suggested in the installation instructions that this is 
not necessary.  Then the light dawned!  The Inrad filters have two ground 
pins, one for in and one for out.  They are connected directly to the case 
internally, so grounding the case has no effect.  However, the OEM filters 
for the FT 920 are completely isolated from the shield case.  This customer 
was using an OEM on the switchboard.

So, if you have an Inrad Switchboard in your 920 which has a Yaesu filter on 
it, you have some work to do.

Credit for this information goes to Alan, N7BF.  Thank you Alan.  A suitable 
note is being added to the installation instructions.

George