I know all of this Paul. I was asking Jim, W8ZR what his compelling
reason was for relay sequencing was.
Thanks
73
Jim W7RY
On 11/11/2013 4:12 AM, Paul Christensen wrote:
Can you tell me why sequencing is a requirement? I have found that
the RF never flows (6 ms after the tranciever control circuts
energise)until way after the relays and cathode bias has switched
which as you have pointed out is 3-4 ms.
Sequencing is mostly a non-issue when using recently manufactured
transceivers. Almost all of them will delay RF by at least 8 ms.
after the transceiver's PTT line goes low. They will also allow
enough time for RF to decay before reversing the sequence. Apart from
any changes in delay by mode, the time from PTT activation to RF
shouldn't change. As both of you point out, there's generally ample
time for bias de/activation and for the waveform to ramp up/down in CW
mode.
I think sequencing is more of an important issue with some older
transceivers - like a KWM-380 I once owned, or where classic separates
are used into an amp. In addition to sequencing, I think it's a good
idea to include RF sensing at the amplifier input. In the presence of
any input RF, the amplifier's T/R should be inhibited from R=>T or
back from T=>R until the RF envelope decays to near zero. Even
without sequencing, that one feature alone will prevent relay
hot-switching accidents.
Consider a case where a multi-transceiver station controller is used
and a transmitter is keyed at 100W while maybe adjusting a tuner.
Then, you accidentally go to the transceiver controller while the rig
is still in transmit and select the hot transceiver into the amp and
the amp immediately keys with RF. Since the transceiver is already
generating RF and the rig's key line is low, the amp will hot-switch
when the PTT line is quickly routed to the amp from the controller
accessory. RF input sensing at the amp would prevent this accidental
form of hot-switching and save the amp's relays.
Paul, W9AC
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