Hi,
Am attempting to understand the timing of what goes
on between the instant of key "down" and the subsequent
flow, some 15 milliseconds later of RF from the Omni VI+.
This 15 mS is the "On" delay time per the ARRL Expanded
Test-Result Report, dtd. Nov. 1997 for the Om VI+.
The Ten Tec description of what goes on is given at the
explanation of the VI+ Control Board (81596), pg 4-16
of my manual copy. To quote a bit from that page:
"A request to key the transmitter is generated by grounding
either the rear panel or mic connector PTT lines, or the rear
panel CW KEY jack. Any of these inputs will turn on transistor
Q9 which sends a transmit request signal to the Logic board via
connector 66. The microprocessor calculates the transmit
frequency based on RIT, CW offset, etc. and reprograms the
phase lock loop. After a short delay [to do all the preceding
steps] of about 10 milliseconds the Logic board generates a
transmit acknowledge voltage at connector 63."
[Note that per the control board schematic, fig 4-18 this
"acknowledge voltage goes direct to the base of Q11 which
turns this transistor ON, and pulls the TX OUT terminal
jack signal to ground, or nearly so.] The Ten Tec manual
continues:
"This signal [from TX OUT] becomes the external keying loop
that is normally jumpered on the rear panel. If an external
amplifier is to be used, it can be included within the keying
loop so that the amplifier can control the timing of the keying
and prevent hot switching." end of the manual quotes.
Ok, so now we know from the manual and the ARRL test
report that about 5 mS go by from the time that TX OUT
drops to near ground potential before RF flows from the
Omni (10 mS after key down, TX OUT goes down, and
per the ARRL, 15 mS after key down, RF flows out).
Now, if you use a Ten Tec linear, the TX OUT signal is
wired to that amp and the signal is used to switch the
amplifier T/R relay to transmit; and when done, the amp
sends a ground signal back the Omni which enters
the TX EN jack to enable the RF from the Omni. With out
an external TT linear, TX OUT and TX EN are jumpered,
meaning the Omni is immediately enabled and some
5 mS later, out comes RF per ARRL. From the manual
description, you would believe that RF out from the Omni +
TT linear would be some milliseconds longer than when
the TO/TE jacks are jumpered together as the relay over
in the linear must activate and send a return signal to the Omni.
Now my question: when during this entire period does
transistor Q16 on the Control Board get turned ON, which
immediately closes the reed relay grounding, or nearly so,
the PTT relay signal to an external amp via the RELAY
jack on the rear panel? The turn on signal comes onto the
Control Board via connector 59, but where does it come
from and when? I have looked long and hard for the source
of the RELAY signal to Q16.
I do not have a TT linear, and am concerned about the timing
of the RF into my amp which is "notified" only by the ground
signal from the reed relay driven by Q16. Would there be any
advantage in tapping onto the jumpered connection between
TX OUT and TX EN: is that a faster drop to ground, at least
some 5 mS before the Omni generates RF.
How soon after the reed relay closes does RF
appear? The ARRL did not measure that time.
Thanks for any help, and 73, Jim KH7M
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