7.5 Function Control/ALGTune
Refer to schematic Figures 9,10, and 11.
Basic amplifier function control is straightforward. Two logic inputs must agree before the amplifier
can be switched into the transmit mode.
1) The three minute time delay must be completed.
2) No RF may be present at the RF input detector; i.e. there is no incoming RF drive from the
transceiver.
When these conditions are satisfied the amplifier can be switched to transmit.
A T/R lockout will occur if the transceiver attempts to "hot switch" the amplifier. (Hot switching
occurs if drive RF is present before the T/R system is in transmit.) The amplifier requires the following
control sequence when switching from receive to transmit:
1) T/R relay closure signal (center pin of RELAY jack shorted to chassis ground).
2) RF drive follows approximately 5 milliseconds later.
When switching from transmit to receive:
1) RF drive level decays approximately lmW.
2) T/R relay "open" signal (center pin of RELAY jack open circuit to chassis ground).
If these conditions are violated so that the transceiver attempts to hot switch, a T/R "inhibit" occurs and
causes the bypass relay to drop out; the amplifier remains in STBY. Any RF applied to the RF IN jack will
bypass the amplifier and appear at the RF OUT jack. The T/R fault LED will illuminate. The fault can be
cleared by removing RF drive and then toggling the mode switch from OPR to STBY and back to OPR.
Provision is made for an alternative T/R control hookup with transceivers that may attempt to hot
switch. Basically, the amplifier itself is T/R keyed and it, in turn, keys the transceiver via reed-type keying
relay, K2. K2 closes under these conditions:
1) Time delay is complete.
2) The amplifier is in the OPR mode.
3) No RF is present at the amplifier RF IN jack.
4) The RELAY jack center pin is shorted to chassis.
If the amplifier is in off or in STBY, any keying or PTT control signal applied to the RELAY jack will be
passed via K1 to the KEY OUT jack. Relay K2 follows the input keying.
When the amplifier is properly (not hot-) switched, in transmit, and being driven, RF at the post T/R
detector is sampled and applied to the logic driven A logic "high" turns on Q6. When Q6 is turned on the
tube cathode bias is reduced from +36 VDC to +9 VDC. Plate current does not flow through Q6. Grid
current, however, does pass through this device and voltage drop across R24 is sampled and fed to the GRID
ALC circuit. The grid current sample also is routed to the display board via D22, R29, and R28.
A reflected power sample from the T/R board is monitored by the control logic. The reflected power
trip threshold is adjusted by variable resistor RP1 which sets the tum-on point of Q9. If Q9 turns on, the
output of USB changes state and T/R board input relay K1 drops out. This switches the amplifier back to
STBY and turns on the SWR fault LED. The fault can be cleared by removing RF drive and toggling the mode
switch from OPR to STBY and back to OPR.
The forward and reflected power samples from the T/R board are calibrated by variable resistors RP2
and RP3, then amplified by operational amplifiers USA and U5B and routed to the display board.
Power supplies providing ±15 volts are shown in Figure 9.
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