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INTRODUCTION
There's not a lot to say about using the FR-10 receiver once its been
correctly built and aligned. If 10 meters is "dead" you'll hear little or
nothing. If Ten is "open" there will be an amazing variety of crystal-
clear signals from many thousands of miles away.
In the first serious test of this receiver, booming signals from the US
Northeast and Midwest as well as Scotland and Ireland were logged
from a site in Florida! The strength and clarity of GM4DLU in Scotland
was simply astounding! Another listening session logged a station in
Washington, DC conversing with one in Wisconsin via a repeater in
Dallas!
This receiver is a good project for amateurs wishing to become more
familiar with 10 meter FM before choosing a transceiver, or for those
active on 10 who want an inexpensive receiver to take on trips, keep
in a briefcase or to watch for band openings.
Most Ramsey Electronics can be classified as "Skill Level 1" if we use
the old Heathkit guidelines for ease of assembly. That means that our
kits are intended to be successful for first-time kit builders. This FR-10
FM Receiver is best regarded as a "Skill Level 2" project, and should
not be taken lightly, even by experienced, licensed radio amateurs.
Still, this step-by-step manual is written with the beginner in mind,
because we are well aware of the fascination that Ten Meters and its
maze of repeaters holds for newcomers, which means this could be
your very first kit project. The same holds true for those who just want
to peek in on LOW VHF public service communications without the
cost of a scanner. To be honest, we'd like to see first-time builders
start out with an easier kit such as the Ramsey HR-40 Forty Meter
receiver before assembling the FR-10, but we are confident that you
can construct the FR-10 successfully if you follow this manual
carefully and patiently.
Before beginning the project or even studying the circuit description, it
is worthwhile to develop some prior respect for how much receiver is
packed onto the circuit board. The nine semiconductor devices
(diodes, transistors and IC chips) give the equivalent of about 30 or
more transistors and diodes. And, in addition to four inductors, a
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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 tunable
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 NE602'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).
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.
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