Icom IC-251A Instruction Manual page 7

For DC operation:
If you would like to use your car battery or any other DC power supply, be sure that its output
voltage is 12 ~15 Volts and the current capacity is at least 3 Amps. The maximum power con-
sumption of the set during transmission runs from 2.5~3 Amps, so keep that in mind if the unit is
installed in your automobile. Attention should also be paid to the condition of the battery and
electrical system.
The connection of the DC power cord supplied with the I1C-251A/E is done in the following way:
First make sure that the power switch of the unit is in the OFF position and the T/R switch is in
the receive position. Connect the cord to the DC power supply with the RED lead to the positive
terminal and the BLACK lead to the negative terminal. (Reverse connection will cause the pro-
tection circuit to operate and blow the fuse.) Connect the DC plug to the socket on the rear panel
of the IC-251A/E. Refer to the drawing below.
For AC operation
FO? ee?
| a
HAUUAOGIGNOUOQUGOONINON ©
WALLOHHUTTATHMTTTH @
0)
For DC operation
a) 099 O@
- 30
mn
UIIIHETINLTHEN)
&> re tk
ANTENNA
The most important single item that will influence the performance of any communication system
is the antenna. For that reason, a good, high-quality, gain antenna of 50 ohms impedance is recom-
mended, fixed or mobile. In VHF as well as the low bands, every watt of ERP makes some dif-
ference. Therefore, 10 watts average output plus 3dB of gain antenna equals 20 watts ERP,
presuming low VSWR of course. The few more dollars invested in a gain type antenna is well
worth it. When adjusting your antenna, whether mobile or fixed, by all means follow the
manufacturer's instructions. There are some pitfalls to be aware of. For example, do not attempt
to adjust an antenna for lowest VSWR when using a diode VSWR meter not engineered for VHF
applications. Such readings will invariably have an error of 40% or more. Instead, use an in-line
watt meter similar to the Drake WV-4, Bird Model 43 or Sierra Model 164B with VHF cartridge.
Further, when adjusting a mobile antenna, do so with the motor running preferably above normal
idling speed. This will insure proper voltage level to the transceiver.
The RF coaxial connector on the rear chassis mates with a standard PL-259 connector. Some
models may have metric threads. In any event, the RF connector will mate with almost any,
PL-259 connector if care is taken to seat them properly.
EXTERNAL SPEAKER
The 1C-251A/E contains an internal speaker, and is also designed so that it can drive an external
speaker from the external (EXT) speaker jack on the rear panel. Be sure the impedance of the
external speaker is 8 ohms, and remember that with the external speaker connected, the internal
speaker is disabled.