SILTRONIX 1011B Betriebsanleitung PDF herunterladen (Seite 9)

GENERAL DISCUSSION

following manner. Carrier is generated by Q3 Carrier Oscil-

lator, which is a Pierce oscillator with the crystal operating

in parallel resonance. This stage operates in both the trans-

mit and receive modes. When transmitting, the RF output

of the oscillator is injected into the control grid of the

Balanced Modulator, VI3. This b'alanced modulator is a

beam deflection tube, and operates similar to a cathode ray

tube in that the electron beam from the cathode is deflected

to one output plate or the other by the charge appearing on

the deflection plates. The carrier signal fed to the control

grid of the balanced modulator appears on both plates of

the output. The two plates are connected to Transformer

T130I. The deflection plate DC voltages are adjusted by

means of the carrier balance control, RI30S, so that the RF

being fed to the output plates will cancel out, and the out-

put from Tl.301 will be zero. Audio signals from the Micro-

phone Amplifier, VI4, are applied as a modulating voltage

to one deflection plate, and the two sidebands resulting

from the sum and difference frequencies of the audio and

carrier signals appear in the output of transformer TI30I.

Carrier suppression is approximately 60 db down. The

Carrier Insertion control limits the amount of carrier that

~ be inserted in AM and thus protects the final amplifier

from being over driven.

The Siltronix 1011 B transceiver provides single sideband,

suppressed carrier transceive operation, and generates the

single sideband signal by means of a crystal lattice filter. To

permit a logical discussion of this mode of operation, cer-

tain definitions are necessary .

h1 a normal AM signal (double sideband with carrier), a

radio frequency signal is modulated with an audio frequency

signal. This is considered by many to be merely a case of

varying the amplitude of the carrier at an audio rate. hi

fact, however, there are actually sideoand frequencies gen-

erated, which are the results of mixing the RF and the A.F.

signals. These sidebands are the sum of, and the difference

between, the two heterodyned signals. In the detection ()f -

this conventional AM signal, the two sidebands are mixed

with the carrier to recover and reproduce the audio intelli-

gence. This is an inefficient means of transmission, because

only 25 percent of the transmitted power is used to trans-

mit intelligence. There are other attendant drawbacks also.

The bandwidth of AM voice transmission is approximately

6 KHz, while the actual demodulated audio is only approxi-

mately 3 KHz. The result is inefficient use of the fre-

quency band, and over haIf of the allotted band is unusable

due to heterodynes, interference, and congestion..

The double sideband, suppressed carrier signal is then cou-

pled from the secondary winding of Tl30l to the crystal

filter, which suppresses the lower sideband, and permits

only the upper sideband to be fed to the First IF Amplifier

V7. The carrier frequency is generated at approximately

5500.0 KHz, nonnal sideband. With the opposite sideband

crystal, the carrier crystal frequency will be 5504.6 KHz,

and this positions the double sideband signal on the other

side of the filter response curve, attenuating the tIpper side-

band by at least 50 db.

h1 the single sideband, suppressed carrier mode of trans-

mission, only one of the sideband signals is transmitted.

The other sideband and the carrier are suppressed to negli-

gible level. h1 addition to increasing the transmission effi-.

ciency by a factor of four, single sideband effectively

doubles the number of stations or channels which can be

used in a given band of frequencies.

It should be remembered that in the single sideband, sup-

pressed carrier mode of transmitting, the unwanted side-

band and carrier are only suppressed, not entirely elimin-

ated. Thus, with a transmitted signal from a transmitter

with 50 db sideband suppression, the other or unwanted

sideband will be present, and will be transmitted, but its

level will be 50 db below the wanted sideband. When this

signal is received at a level of 20 db over 59, the unwanted

sideband will be present at a level of approximately 55.

The same is true of carrier suppression. With carrier sup-

pression of 60 db, and a signal level of 20 db over 59, car-

rier will be present at a level of approximately S3 to S4.

Q1, the VFO 2N706 Oscillator, operates in the common

base configuration as a Colpitts oscillator. Q2, the buffer, is

used for isolation. The extremely good regulation achieved

through using the Zener diode regulator D1712 across the

bias supply voltage, also contributes to the stability.

The VFO in the ModellOllB exmbits extremely good sta-

bility after the initial wann-up period. Drift from a cold

start will be less than 2 KHz during the flIst hour. After

the initial wann-up period, drift will be negligible.

The single sideband, suppressed carrier signal from the First

I.F. Amplifier is fed to the Transmit Mixer, V2, where it is

heterodyned with the VFO signal. The resultant signal at

the desired transmit frequency is amplified by the Driver,

V3 ; and the Power Amplifier, V4. The signal from the VFO

Amplifier is initiated in the transistorized VFO/Buffer cir-

cuit QI and Q2. The signal from the VFO is routed to the

VFO Amplifier, and is mixed with the single sideband from

the IF amplifier, resulting in output in the 10 meter band.

When the transceiver is in the TRANSMIT mode, the gain

For the following discussion refer to the schematic dia.

gram, and to Figures 3, 4, and 5.

SIGNAL GENERATION

When the push-to-talk switch on the microphone is pressed,

the transmitter portion of the transceiver is activated, and it

generates a single sideband, suppressed carrier signal in the

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 31 32

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