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Re: [Amps] Best source for Gigavac GH-1 ?

To: <amps@contesting.com>
Subject: Re: [Amps] Best source for Gigavac GH-1 ?
From: "Paul Christensen" <w9ac@arrl.net>
Date: Mon, 11 Nov 2013 07:12:31 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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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