Ramsey Electronics FR6 Manuel d'utilisateur télécharger pdf (Page 22)

FR6 • 22

SOME NOTES FOR ADVANCED USERS

Unlike Ramsey HF receivers and transmitters, the FR-series of VHF receivers

do not offer much PC board space or real need for customization or other

modifications. These receivers do what they are intended to do at the lowest

price that we are aware of for a tuneable VHF FM receiver with squelch, AFC

and generous audio output. Therefore, while we are certainly interested in

hearing about significant performance improvements, we do not recommend

casual modification attempts.

However, there is one practical customization which could be undertaken by

experienced VHF experimenters who wish to take advantage of the SA602's

ability to accept a crystal resonator instead of the existing L-C tank circuit. The

goal would be a one channel repeater monitor or dedicated packet receiver.

Inductor L3 and associated capacitors would be replaced by the appropriate

crystal tank components. Remember that the crystal oscillator should be

planned to operate 10.7 MHz. above the desired receiving frequency. Please

do not attempt such a project unless you have a clear knowledge of oscillator

design and have reviewed and understood the terms of your Ramsey Kit

Warranty. We regret that the factory cannot offer any assistance in performing

this or any other modification, so... you're on your own; but that's what

experimenting is all about!

A helpful article on the Signetics NE602 IC, including a discussion of crystal-

controlled oscillator configurations, was written by Michael A. Covington with

acknowledged assistance from Signetics personnel, published with good

circuit illustrations in Radio-Electronics magazine for April 1990 (Vol 61, No

4). This will help you understand your SA602 IC.

A less complex approach to the same general goal, eliminating the expense of

a crystal and the logistics of adding it to the PC board, is to "undo" the

excellent tuning range we designed into your receiver! This would require

selecting appropriate values for C9,C10 and C12 and reducing the effect of

the varactor tuning to perhaps a 100 KHz swing for fine tuning purposes only.

Try reducing C12 to 1 or 2 pF for starters.

Finally, the only pin of the MC3359 not used in our circuit is pin 15, for scan

control. Perhaps you will come up with some fascinating idea for it!

Again, please be sure that you understand your warranty, and that you

understand your receiver and how to keep it working, before attempting any

modifications.

If you've enjoyed this kit, be sure to check out the entire Ramsey kit line. Call

or write for our catalog.

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Ramsey Electronics FR6 Manuel d'utilisateur Page 22