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.01023245
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5-5
5.7 Heater Time Delay (HTD) State
Following the POST, if no fault was detected, the unit will automatically enter HTD.
The display shows these features: Local mode, time in 12-hour format, Heater Time Delay
countdown, Beam On (XMIT) selected upon conclusion of HTD, and default meters.
L O C A L 5 : 3 0 P
H T D 2 : 3 9 X M I T S E L E C T
H L X 0 . 0 0 K V
0 . 0 M A
A T T E N U A T O R 1 0 . 0 D B
In the tube during the Transmit state (Beam On), a beam of electrons is accelerated from an
electron cloud around the cathode, past the anode, through the helix structure, and finally
coming to rest in the collector structure. To create the cloud of free electrons, the cathode is
heated by the heater. Ideally, the cathode should be maintained at a specific temperature.
Cathode temperature is difficult to measure; however, there is a relationship between heater
time after prime power on and cathode temperature. HTD, therefore, is of variable length
(based on prime power off time) to provide optimum cathode temperature in minimum time
after power is applied to the CHPA.
HTD proportional time delay:
If time off
≤5
seconds, no HTD.
If 5 seconds <time off<1.5 minutes,
HTD 1.5 x time off + existing HTD
If time off
≥
1.5 minutes,
HTD = 3 minutes
During HTD, the user may press the TRANSMIT button to select Beam On when HTD has
elapsed; this action is displayed on the front panel as XMIT SELECT. The user may also press
the MENU button to scroll through available menu categories. See later in this chapter under
“Special CHPA Functions” for a description of the menu category hierarchy. See Appendix B
for a complete description of all menu categories.
5.8 Standby State
Once HTD has elapsed and Beam On has not been selected, the unit will be in the Standby state.
After one minute of Standby, the heater voltage is reduced by approximately 10% to extend
tube life. The display shows these features: Local mode, time in 12-hour format, Standby, and
default meters.
