I use sequencers on VHF/UHF to prevent fragile GaAs Fet preamps up on the
tower from being fried with up to 1500W. Sequencers are very common on those
bands and circuits have been in QEX and various VHF/UHF conference books
which I believe are all available thru the ARRL. These are a lot more than a
few resistors, cap, and diode as we are not talking PTT here as on AM. The
best follow right along with the digital modes. I use VOX CW and SSB.
In the 60's many were using regular relays with identical coil specs but
feeding with slightly different voltages to control delays. Worked good with
PTT and foot switches and the usual clunky external coax relays.
Carl
KM1H
----- Original Message -----
From: "John Lyles" <jtml@losalamos.com>
To: <amps@contesting.com>
Sent: Monday, April 05, 2010 6:34 PM
Subject: [Amps] contact bounce
> Don, k4kyv, wrote a good description of how he tackled sequencing, for old
> buzzard AM stations, in the following:
> http://amfone.net/Amforum/index.php?topic=6211.0
>
> Maybe something there that can be learned for amplifier switching.
> John
> K5PRO
>
>
>
>> Date: Mon, 05 Apr 2010 12:16:45 -0700
>> From: "Bill, W6WRT" <dezrat1242@yahoo.com>
>> Subject: Re: [Amps] contact bounce
>> To: <amps@contesting.com>
>> Message-ID: <e7ckr5pdvdikmehm9v5lskvbk53nqbsuib@4ax.com>
>> Content-Type: text/plain; charset=us-ascii
>>
>> Maybe I'm swimming against the tide here, but all this discussion
>> about speeding up or slowing down relays is missing the real
>> underlying point: Avoiding hot switching the amp relays on both going
>> to TX and returning to RX. The schemes I have seen so far only address
>> the turn-on issue, not the turn-off one.
>>
>> This is not a problem of speed, it is a problem of proper sequencing.
>>
>> What should take place is this.
>>
>> When going to TX:
>>
>> 1. Key the amp relays, both of them (if separate relays are used for
>> input and output)
>>
>> 2.A few milliseconds later, key the transceiver.
>>
>> When returning to RX:
>>
>> 1. Unkey the transceiver.
>>
>> 2. A few milliseconds later, unkey the amp relays.
>>
>> Done correctly, you don't have to worry about relay speed because the
>> amp will never "see" any RF except when its relays are closed, thus no
>> hot switching. Likewise the transceiver will never see an open load
>> when transmitting. The relays could be as slow as molasses and the amp
>> and transceiver would still be protected
>>
>> Easier said than done, however. I am trying to come up with a circuit
>> using only relays (no solid state logic), possibly using the relay's
>> own contacts to switch in or out a capacitor across the relay coil,
>> but I'm stymied so far. Some clever person out there will no doubt
>> find a way. Please let us know when you do.
>>
>> 73, Bill W6WRT
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|