DRAKE R8B Owner's Manual download pdf (Page 19)

17 Getting Started cont'd.

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 offset the IF passband without causing distor-

tion. If the 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

is set to within 1 kHz of 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.

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.

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.

Desired

Signal

PASSBAND OFFSET

CENTERED

Desired

Signal

Undesired

Signal

PASSBAND OFFSET

Undesired

Signal

PASSBAND OFFSET

FIGURE 9 PASSBAND OFFSET Operation

Desired

Signal

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. It 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,

to receive 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

at the 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.

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 42 43

Comments to this Manuals

No comments

DRAKE R8B Owner's Manual Page 19

Comments to this Manuals

Related products and manuals for Receiver DRAKE R8B