32
HF-250 User Manual
HF250 User Manual
33
should ever need to transport the receiver it will survive the
journey much better in the correct carton.
General notes.
If there is a momentary power failure, or if you plug in the
power connector whilst the receiver is switched on, you may
find that the receiver does not receive, or fails to respond to
its controls. The problem is caused by the microprocessor
controller having crashed. The fault can be rectified by
disconnecting the power plug, waiting a few seconds, and
then put it back in again - all should be well, but occasionally
the frequency information in the memories may be garbled.
In the same way that high volume levels from the internal
loudspeaker may cause microphonic effects, external shock
or vibration can cause frequency fluctuations.
Of course it is not normal to bang the receiver
around....Strange effects can also occur if the receiver is
placed in a strong altemating magnetic field, for example in
close proximity to a large mains transformer in another piece
of equipment. When tuning the HF-250 you will notice that
the output will be muted for about half a second as you tune
through the local oscillator range switching frequencies at
5.000, 11.000 and 19.000 MHz.
This is quite normal and should not be taken as a fault. Also
one other effect that you may notice when tuning the
receiver in some parts of the band is a whining noise as the
tuning control is rotated. It is caused by the data transfers
inside the receiver being picked-up by the input circuitry and
it is normally not audible above the noise and signals coming
from the aerial connected to the receiver.
As in any receiver there are a few spurious signals
generated internally, mostly at or slightly above the
background noise level of the receiver. Again these signals
are usually masked by aerial noise and rarely cause any
degradation to reception of radio signals.
Optional Units.
RC-250 Remote Keypad.
The External keypad provides direct frequency entry and
memory selection for the HF-250 receiver. All Normal
functions of the radio are accessible with your RC250 with
the exception of setting the clock and on and off times of the
timers, or tone and volume. The acknowledge beep can be
activated for the RC250 by holding the Mhz up button (11)
and turning the radio on, hold the button untill a repeated
beep can be heard, repeat the same process to turn it off.
DU-250 Detector Unit.
The detector unit in fact combines two separate detectors in
one unit, and provides narrow-band FM reception and
synchronous AM detection for the HF-250. Synchronous
(DSB LSB USB) detection can offer improved audio quality
compared with the normal envelope detection, especially
under band conditions where selective frequency fading
occurs. The FM detector will allow monitoring of FM
communication channels, but it is for narrow band signals
only and will not work with FM broadcast signals. The
detector unit is installed inside the HF-250, and dealer fitting
is recommended.
