AMX TXC16 Plus Specifications download pdf (Page 21)

SG-2000 MANUAL 14

The SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA

Once amplified to a standard level, the audio is sent to a jack on the back of the SG-2000

which allows for connection to a control head. In the control heads, the audio signal is

further amplified and processed.

A syllabic squelch circuit (which was pioneered by SGC in 1976) is used to turn off the

noise coming out of the speaker in the event that a signal is not being received.

The next step is a digital gate which controls the volume of the receiver by very rapidly

sampling the signal and passing only a certain number of samples — a number which

varies by the setting of the volume control on the front panel of the radio. Naturally,

this happens at speeds which you can not hear, so your ear hears smooth control of the

volume function.

4.2 Transmitter Signal Path

Pressing the push to talk button grounds the push-to-talk line, placing the SG-2000 in

the transmit mode. At the same time, the sound of your voice is shaped by an audio

amplifier in the control head. This is brought up to a standard level to be sent out the

transmit audio bus.

This line leaves the control head via the 10-conductor control head cable and returns to

the SG-2000 RF unit via the rear panel connector where the head plugs into the rear

panel of the radio.

Inside the radio, the audio signal is shaped and amplified. It is turned into an AM

signal which is then processed to remove the desired amount of carrier. This is

accomplished by a balanced modulator. In the single sideband mode, all of the carrier

is removed. If required, the carrier is reinserted for other modes.

In the AME (AM Equivalent) mode, 40-50 W of the carrier is reinserted. And if you are

operating in the A3A mode which is used for certain kinds of commercial radio work,

then you put back about 1/8th of the carrier, leaving just enough of the signal to act as

a "pilot carrier" for specialized receivers.

Next, the signal is amplified and passed through a crystal filter, where one sideband is

removed. This is done by offsetting the transmit frequency slightly. On one side of the

filter slope, the upper sideband is removed, while offsetting on the other side of the 10.7

MHz filter will remove the lower sideband.

When you are in the single sideband mode, you have now developed either the desired

upper or lower sideband filter at this point. From here on, the amplifiers which will be

processing the signal are called "linear amplifiers" because if they are not linear, they

will distort the signal, just like a non-linear audio amplifier would distort a signal on

your home stereo.

The 10.7 MHz single sideband signal is then converted up to 82-88 MHz, where

harmonics are eliminated by the helical filter. The output of the 82-88 MHz filter is

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AMX TXC16 Plus Specifications Page 21