David wrote:
Andy,

Thanks for the information. So my matching circuit may look like....

Mixer Out(1k5) - Series coupling cap(1n) - Var L to ground - C-Tap
across L - Crystal Filter - C-Tap - var L across C-Tap - Coupling
C(1n) - SA605 Input (4500//3.5 pF)

C-Tap caps to ground are also tuneable.

I suppose the Q of the match would not need to be particularly high as
the selectivity is provided by the Crystal filter.

Regards

David


Andy writes:

There is a formula for the required Q to perform the match.

Qreq'd = Square Root of ( (Rhigh/Rlow ) - 1 )


1500
or Sqrt of ( ------------ - 1 )
800

It's been a while so, if I got this wrong, I am sure some of the
local RF engineers will correct me...

Anyway,,, this is the minimum Q required in the tank to allow the
match
to be accomplished....

This comes from the equvalency formulae for series to parallel
comversion:


2 2
2
Rp = Rs ( Q + 1 ) Xp = Xs ( Q + 1) / Q

for coverting parallel resistance or reactance into equivalent
series resistance or reactance.....

Sure you can use Z and Y, but the above are much much easier.....


I can't follow your diagram very well, but I think you have it....
.... I am assuming SINGLE ENDED OUTPUT. For balanced
output, it is different...

Andy W4OAH