[TowerTalk] [Towertalk] Preamp sequencer PTT to RF delay

[Ian White, G3SEK]

Chet Pierson wrote:
>
>Not a problem, but some people use a sequencer to make sure the relays
>have settled before
>TX occurs. 

Very advisable - otherwise you risk burning out the preamp and/or the
coax relay contacts. 

HF amplifier builders are well on top of this problem, because it
affects QSK performance, but a surprising number of VHFers still use
"simultaneous" switching... and then wonder why they have reliability
problems. 

>I made a sequencer using the PTT line, and it works fine, but
>on CW, the rig is
>semi break in, so it "keys itself". If I use the rear aux port keying
>line, to trigger the sequencer,
>RF may already be headed "up the pipe". Does any one know, or can you
>point me to
>information on the amount of delay, that is the time after PTT before a
>typical radio will
>begin to produce RF. If I can't find out, I guess I can use a 2 ch
>storage scope and see
>the time peoid from PTT to RF out.

You can easily measure the delay without a storage scope. With timebase
set to single-shot and the brilliance turned up high, persistence of
vision makes it easy to see what happened.

>My current rig is a Kenwood TS790A.

I don't know the details of that particular rig, but in general more
modern rigs handle this problem better.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.com/g3sek

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