DRAKE R-4C Especificaciones descargar pdf (Pagina 14)

audio voltage applied to the audio amplifier stages.

The outer control which is adjusted with the lever

is the RF Gain control. This control increases the

AGC threshold or bias level on the RF and IF stages

which prevents signals below a certain level from

being received. Normally this control should remain

in the full clockwise position.

3-11.

AGC.

This switch selects the release time constant of the

automatic gain control circuit or turns off the AGC.

In the OFF position, the receiver gain may be con-

trolled manually with the RF gain control. In the

(fast

release). M (medium release), or S (slow re-

lease) positions, the AGC is operative. The release

time constant

approximately 1 second in the S

position, 350 milliseconds in the M position, and

50 milliseconds in the F position. Attack time is 1

millisecond in F, M, S modes.

3-12.

NOTCH.

The NOTCH control can be used effectively in all

modes of reception for attenuation of heterodyne

interference from a carrier near the desired carrier.

A permeability-tuned T-notch filter in the 50 kHz

IF is used for this purpose. The filter produces a

deep notch which can be tuned across the IF by

rotation of the NOTCH control knob. On any mode

of operation, an unwanted carrier is attenuated by

tuning the notch across the receiver passband until

the unwanted carrier is removed by the notch filter.

Since the notch filter will remove the wanted car-

rier just as readily as an unwanted carrier, the

NOTCH control must be

adjusted carefully for

maximum effectiveness. In the SSB, CW 1.5, CW

-5,

or CW

.25

modes, the PASSBAND TUNING will al-

so affect the NOTCH frequency. Therefore, the

PASSBAND

TUNING control should be set before

the NOTCH control is adjusted. However, after ob-

taining a notch, the PASSBAND TUNING may be

moved slightly to fine tune the notch for maxi-

mum null. When a notch is not needed, the NOTCH

control should be returned to the detent in the

OFF position.

3-13. S METER.

The S Meter indicates relative signal strength, and is

a convenient indicator for peaking the tuning of

the receiver. The lower (left hand) portion is cali-

brated in S units from S-l through S-9. Above S-9

the scale is calibrated in decibels. Each S unit is

equal to approximately 5

dB.

S-9

signal is ap-

proximately 30 microvolts input to the antenna

Jack.

3-14. PHONE JACK.

The phone jack is used when private listening is

desired. Connection of the headphones automa-

tically mutes the speaker output. While headphone

impedance is not critical, a good quality set of 600

Ohm phones will work well. If 8 Ohm headphones

are used, a pad should be connected between the

phone jack and the phones to reduce the audio

power to a reasonable level for the phones. Normal-

ly connecting a 100 Ohm resistor in series with the

8 Ohm headphones will provide adequate attenua-

tion.

3-15. S METER ZERO.

NOTE

The antenna should be disconnected from

the R---4C while making this adjustment.

The S meter zero control is on the rear panel of the

R-4C.

It may be used to set the S meter needle to

S-l under no-signal conditions.

3-16. BASIC CONTROL SETTINGS.

For operation in any mode, preset the following

controls as indicated:

a. SetFUNCTION switch to ON.

b. Set

BAND switch to Desired Amateur Band.

c. Set

XTALS switch to NORM.

d. SetNOTCH control to OFF.

e. SetRF GAIN lever fully clockwise.

3-5

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DRAKE R-4C Especificaciones Pagina 14

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