ALC

The sensible way to control the output power of the VX-1700 is to apply a negative voltage to the ALC pin on the 'accessory' socket.

This will normally require an isolated DC/DC converter to generate the negative voltage line.

Test setup

I used the following equipment:

• VX-1700 - set to 100W on 14Mhz
• RF power meter (reads 99-100 with no ALC bias)
• Dry dummy load
• Bench power supply, set to apply negative voltage to the ALC line

To generate the RF signal, I grounded the "TX REQ" pin on the ACC port.

Test results

High power (100w)

0v 98w

-1.59v 50w

-1.77v 25w

-2.02v 10w

-2.90v 5w

-5.88v 2.5w

Medium power (50w)

0v 52w

-1.30 50w

-1.61 25w

-1.81 10w

-2.01 5w

-2.52 2.5w

Low power (10w)

0v 9.8w

-1.61 5w

-1.76 2.5w

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Control Signals

TX REQ

Normally pulled high (+5v) by the radio. When grounded (or below 1.7) the radio emits a CW signal.W hen disconnected (or above 2.6 volts) the radio stops emitting CW.