David wrote:

Andy,

The input to the mixer on G1 is the second stage of a DTC. The DTC was
designed to provide the appropriate RP for a 6MHz bandwidth. I then
assumed that G1 will be extremely high impedance compared to the DTC
and therefore would not load it down.

The gain was measured by first measuring the power output of the mixer
and then measuring the power output at the end of the filter.

The manufacturer data for the filter specifies maximum loss of 3dB (they
supply 2 matches filters that connect to form a 4-pole).

The output of the filter was stepped down to 50 Ohms with a C-Tap
impedance transform on the tuned circuit.

The input was matched from 2800 Ohms (Rp of the coil in the mixer tank)
to 800 R using a C-Tap transform also.

-- snip --

This could be your problem right here -- at 45MHz it's probably not
realistic to expect no loss in the mixer drain circuit. I'd find the Q
of the mixer tank without the filter, and use that to calculate the
effective parallel resistance, as well as the attenuation of the filter.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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