[Radio Wrangler]

Shanwick is SSB, so that would need a change to a linear IF plus product detector and CIO. The multiplier in the quadrature detector would make a product detector, but it's embedded with a limiting IF, I think.

I don't understand the 37.5375MHz bit.

A 26.8125 LO will mix 16.0875 RF into a 10.725MHz IF

37.5375MHz would be the image and wouldn't need a filter to pass it. A band stop might make more sense but if needed would be commercially disastrous. The receiver would need a different design of that filter for every different channel.

For NBFM, the difficulty arises of making a narrow enough discriminator. For NBFM in a 10.7ish IF either a crystal or ceramic resonator would be used for the quadrature detector, or a further conversion to a lower IF would be used. The latter is more popular because it allows better/cheaper selectivity on the lower IF.

HA12411 is just a limiting amp (3 stages) into a quadrature detector. It isn't one of the NBFM specific chips with an IF downconverter at its front.


Could those coils at 16MHz be an image trap and the 37MHz frequency be the wanted channel?


David