DRAKE R8A - FRONT PANEL LOCK (UNLOCK); PASSBAND OFFSET OPERATION; NOTCH OPERATION; AM SYNCHRONOUS DETECTOR OPERATION

17 Getting Started cont'd.
FRONT PANEL LOCK (UNLOCK)
First be sure the receiver is in the VFO mode, ( MEM or
SCAN not displayed). All button entries, display settings
and the large tuning knob can be locked if desired.
Press LOCK to lock front panel. All analog control
knob functions, except tuning, will still remain operable.
Press[_* | LOCK to unlock front panel if previously locked.
PASSBAND OFFSET OPERATION
When the PASSBAND OFFSET control is centered, the
receiver will properly position Its IF passband with mode
change. Occasionally, an interfering signal will appear
above or below the desired signal. Rotating the PASS-
BAND OFFSET “+” or “-" will reduce or eliminate this
interfering signal by electronically shifting the receiver’s IF
passband. Refer to FIGURE 9. This shifting of the IF
passband also alters the audio quality. For example, if you
are receiving a signal in USB and rotate the PASSBAND
OFFSET control “-", the audio will become low pitched.
Conversely if the control is rotated to the “+” position, the
audio will become high pitched. The results are reversed
in LSB; rotated “+” the audio becomes low pitched,
rotated “-” the audio becomes high pitched.
In AM, the PASSBAND OFFSET can enhance audio quality.
For example, with the PASSBAND OFFSET control at the
normal 12 o’clock position and the 6 kHz IF filter selected,
the maximum audio response will begin to roll off at 3 kHz.
If the PASSBAND OFFSET control is moved to one side or
the other, audio response exceeding 5 kHz is obtainable
thus enhancing fidelity. Try both offset directions to deter-
mine which side of the signal is least subject to any
possible adjacent signal interference. The PASSBAND
OFFSET control is also coupled to the synchronous detec-
tor (SYNCHRO) allowing the passband to be altered while
the detector is in use.
Desired
PASSBAND
OFFSET
Signal
CENTERED
Undesired Desired
PASSBAND
OFFSET
Signal
/
Signal
+
Desired Undesired
Signal
\
Signal
PASSBAND OFFSET
FIGURE 9 PASSBAND OFFSET Operation
NOTCH OPERATION
Audio notch will nullify signals from 500 Hz at the counter-
clockwise setting of the control to 5kHz at the clockwise
setting. Adjust control to nullify an undesired signal.
AM SYNCHRONOUS DETECTOR OPERATION
For general tuning and listening, the normal AM detector
is best. It allows normal AM reception while providing the
capability to offsetthe IF passband without causing distor-
tion. Ifthe received signal is experiencing severe fading as
is Common on many SW and BC bands, the synchronous
detector should be engaged. Make sure the main tuning
issetto within 1 kHzof the station’s transmitting frequency.
Adjust the PASSBAND OFFSET control and change band-
width as required to minimize any interference. Press AM/
SYNC to activate the synchronous detector. The word
SYNC is diplayed following AM to indicate the synchro-
nous detector is selected and locked. SYNC will flash to
indicate that the detector is acquiring lock. This detector
provides a very powerful aid in reducing the severe audio
distortion that can occur during the time period when the
carrier of the received AM signal is cancelled or reduced
by propagation effects.
When the synchronous detector has been activated,
moving the main tuning over £200 Hz will automatically
switch the receiver out of synchronous detection while
the synchronous detector re-aquires lock, The ‘SYNC’
annunciator will flash briefly until lock is achieved. Also,
moving the PASSBAND OFFSET control while the synchro-
nous detector is engaged, will cause the receiver to
momentarily switch out of synchronous detection while
the synchronous detector re-aquires lock. The ‘SYNC’
annunciator will flash briefly until lock is achieved.
RF FUNCTION (ATTENUATOR/PREAMP)
Occasionally, a received signal may be very strong such
as from a local broadcast station. When this happens,
distortion could degrade the signal’s quality. To help
combat this, the (attn) should be selected. If provides 10
dB of loss to the incoming signal, thereby allowing the
receiver to function normally. Also, when trying to listen to
a weak station in the presence of an undesired stronger
station, selecting the attenuator will lower the received
level of both. This action could make It possible, however,
toreceive the desired station. The attenuator is available
for use across the entire tuning range of the receiver,
except for the ranges covered by the optional VHF Con-
verter module.
Another RF function available is a preamplifier (pre)
which provides an additional 10 dB of gain to the re-
ceived signal. This can be useful on the higher shortwave
frequencies when trying to receive a weak signal perhaps
atthe noise level. Use caution when using the preamp as
it could amplify an adjacent signal causing distortion on
the desired signal. The preamplifier is not selected for
frequency ranges covered by the optional VHF Con-
verter module.
For general tuning, operate the receiver with both the
PREAMPLIFIER and ATTENUATOR off.
To enable or disable the PREAMPLIFIER or ATTENUATOR:
Press the function line button below the displayed PRE
ATTN annunciators. The selected function is indicated by
a displayed box| —_| around the function. Conversely,
no box indicates that the function Is not selected.