Solid State Fremodyne Receiver

This article was originally published in Electronics Australia, in May 1970. It follows on from a valve design presented earlier in the same magazine, which was based on the Hazeltine circuit. If you have not already come from there, I suggest you see my Fremodyne page to learn the background of the Fremodyne receiver. Note that the article presented here has nothing to do with the Hazeltine Corporation. The original valve Hazeltine Fremodyne receiver was obsolete well before solid state devices became available. Here, the term "Fremodyne" was used by EA to mean a VHF superhet receiver with a 27Mc/s super regenerative IF channel.
My presentation of the material here is to satisfy the curiosity for those who have asked about it, or are curious about the Fremodyne in Australia. I am not presenting this as a constructional article. I have not built this receiver, and I am not going to scan the seven pages of the original article.
However, anyone who is familiar with VHF construction will not have a problem building this receiver with the following information.


Circuit of complete receiver. 30 to 190Mc/s coverage was possible using plug in coils. 10K preset sets operating point of the 27Mc/s super regenerative detector. Adjust it to point just past where oscillation commences for greatest sensitivity. The 560R is required for stability and might not always be required.


Layout of tagboard for the frequency converter, super regen IF stage, and audio preamp. Note spacing between the two coils operating at 27Mc/s.
 


Layout of tagboard for the local oscillator.


How the boards are laid out on the chassis. To the left is the audio power amp, centre is the local oscillator, and at the right is the converter and IF stage.

Coil Data:
Aerial: 30-70Mc/s:  8 turns 3/8" diam, 1/2" long. Tap at  2 turns. 18 gauge.
             70-130Mc/s: 4 turns 1/4" diam, 3/8" long. Tap at 1 turn. 18 gauge.
             120-190Mc/s: 2 turns 1/4" diam, 5/15" long. Tahp at 1/4 turn. 18 gauge.

Oscillator: Low frequency: 7 turns 22 gauge, 1/4" diam, 3/8" long.
                 High frequency: 2 turns 18 gauge, 1/4" diam. 3/8" long.

These coils were mounted in four pin speaker plugs.

L3 & L4: 12 turns 24 gauge, wound directly on 7mm slug, 1/4" long, grade 900 Neosid. Tune both to 27Mc/s.

Note that there are only two local oscillator coils. The design relies on local oscillator operation below and above the received frequencies for complete band coverage.
I have constructed the 27Mc/s super regenerative part to use on its own, as a CB receiver, and modified for the VHF FM band, so know something of its performance.
 

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