I am wanting to place a 45MHz, 2-pole crystal filter between the first mixer output and 2nd IF input. (Mixer output is a SA602 and IF input is SA605).
The mixer output is around 1500 Ohms and the IF input is around 4500 Ohms with 2.5pF capacitance parallel.
The required source and termination for the filter is 800 Ohms par with
3pF. The insertion loss of the filter is 2dB max.Would the impedances be close enough to use resitive pad between mixer and filter (680R in series with 1k2) and a small cap to ground across the filter input. Then a 980R resistor to ground at filter output and no capacitance (use SA605 2.5pF and stray to make up the 3pF).
This would give total loss around 4.7dB.
Or would I be better to use say a tapped capacitor or L match from Mixer to filter with added C on filter input.
Apparently the SA605 has a "swet spot" for noise at around 800R so maybe the Res to ground on the input would be ideal ???
Thanks for any help, I have not used crystal filters before and unsure of implications of the approach.
Regards
David Huisman