AOR AR8000 Operating Manual page 11

(frequencies such as 1.215 MHz = 1215 kHz). If signal strength appears weak,
try rotating the receiver as the bar aerial is directional.
The internal ferrite bar aerial should provide adequate results in city and
high population areas or when visiting airshows which operate a
commentary service on medium wave. Better results may be achieved
by using an external aerial.
It is not possible to further increase sensitivity on medium wave firstly due to
the up-conversion receive circuit employed (which is required for high quality
VHF-UHF reception) and secondly due to the potential noise from the
microprocessor and LCD driver which are located close to the ferrite aerial
(being a compact hand-held design).
Aerial attenuator
An aerial attenuator system allows selection of 0dB or 10dB. This is especially
useful in reducing the potential for breakthrough when using external aerial
systems and for achieving optimum audio quality for SSB and short wave
operation.
Do remember, if considering the use of an external aerial, there will be a
greater chance of signal overload and breakthrough. While this will not
damage the receiver in average use, it may degrade the receive performance
due to the effects of "signal mixing".
VHF - UHF discone aerials
Ideally, separate aerials should be employed for each frequency or band of
interest. Of course, except for government listening stations this is totally
impractical. For this reason most people choose an externally mounted
discone aerial such as the AOR DA3000 aerial. The DA3000 has a usable
coverage of 25 to 2000 MHz.
Shortwave long wire aerials
For the shortwave bands a different type of aerial will be required. The most
common form is the random long wire, please see sections 22 & 23 on aerials
and propagation for further information.
Aerial Tuning Units (ATU)
An ATU can improve the selectivity of any shortwave receiver when connected
to long wire aerials. This valuable extra selectivity is achieved by the ATU
rejecting out of band signals enabling the receiver to "single out" one band of
frequencies while rejecting potentially strong unwanted transmissions.
An ATU is usually constructed in a small box with about two or three controls
on the front panel. One disadvantage however is the need to constantly retune