[Wendymott]

Hi peeps.
At present I am trying to develop a dual band 2 m / 6 m receiver that will be eventually a RX/TX.
I decided to use the AD831 mixer as it claims to have no insertion loss and a low L / O level requirement.
I attach the circuit of the Mixer, 2 X crystal filter from a FT290 then a BF998 amp into the SSB Filter, again ex FT290. The measuring point is the output of X3. The input is as on the schematic.
The query is this, The output level at the filter for an RF input of -73dbuv is 73 db at 145 Mhz. Ok so far. However the RF output of the I.F with the RF input at 51 Mhz is 6 db down. "Same input level"... I found I was 6 db down, I increased the RF input by 6 db to get the same amplitude out. Looking at the data sheet of the AD831, it is very flat to well above what I want. I tried adjusting the input coupling cap to 1 nF and 100 nF with no appreciable difference. I had noted that 6 M was less sensitive with the previous version of the mixer / IF, but I didnt realise it was the mixer / IF causing the error. Your comments would be greatly appreciated, but dont include any maths.... not my subject.
The L/O is from the Anritsu MG3642 and the RF source is the Marconi 2023.