Icom IC-21 Instructions Manual page 5

When adjusting your antenna, whether fixed or mobile, by all means follow the
manufacturer 's instructions.
There are some pitfalls to be aware of. If a SWR meter is
used remotely that is a diodé-VSWR meter, and not engineered for VHF applications,
readings will invariably have errors of 40% or more. Rather than this, use an in-line Watt
Meter similiar to the Drake WV-4, or Bird Model 23, with VHF cartridge. Further, when
adjusting a mobile antenna, do so with the motor running, preferably above normal idlirig
speed. This will insure proper voltage level to the transceiver.
Do not become alarmed if your transceiver fails to transmit at times during the antenna
tune-up procedure. Remember, your transceiver has a built-in Automatic Protection -
Circuit (APC) that will disable the transmitter if VSWR, a shorted coaxial line or
connector, or other antenna deficiency is present. A quick check on a good 50 ohm
dummy load will show the transceiver to be working. The difficulty will lie with the
antenna, or its transmission line. The RF coaxial connector on the rear chassis mates
with a standard PL-259 connector. Some models may have metric thread, if this is the
case, a matching metric PL-259 is provided. In any event, the RF connector will mate
with almost any PL-259 connector, if care is taken to seat them properly.
Microphone:
A high-quality dynamic microphone is supplied with your transceiver. Merely plug it into
the proper receptacle on the front panel. Should you wish to use a different microphone,
make certain it is of the high impedance type; at least 10K, or better. Particular care should
be exercised in wiring, also, as the internal electronic switching system is dependent on it.
See the schematic for the proper hook-up. Under no circumstances use a "gain pre-amp"
type microphone. The audio system in your transceiver is more than adequate and
additional pre-amplification is unnecessary. To use this class microphone 15 to invite
distortion and possible damage to the transceiver.
Crystals:
Your transceiver has twenty-four channels, both transmit and receive, or a total of
forty-eight crystal positions. The channel selector switch selects in each position one trans-
mit and one receive channel of its twenty-four positions. It also has a plug-in, external VFO
accessory socket. Merely plug in the remote VFO to the remote VFO accessory plug (see
Fig. 3), then plug in the interior plug, located at the top of the crystal board (see Fig.
' 3). To order additional crystals from a manufacturer, the following correlation data is
_ provided. Remember to specify high activity as a prerequisite to your acceptance:
Crystal Data
Holder type: HC—25/u
Calibration Tolerance: 0.0025%
Load Capacitance: 20 pf
Effective Resistance: 15 ohms, or less
Transmit Crystals: Crystal Frequency
Desired Operation Frequency
8
Receive Crystals: Crystal Frequency
Desired Operating Frequency — 10.7 MHz
9
Trimmers have been placed on the crystal board to assist you in "tweaking" new crystals
on frequency. Consult the trimmer location chart (see Fig. 1) for their positions.