The sequencer is not intended for real VOX operation. Normally you'd use
the PTT line output from your microphone, or a footswitch which would allow
either voice or CW mode operation. If VOX causes your transmitter to
generate RF, that's not a good thing for a sequenced operation intended to
protect a receiving preamplifier. -WB2WIK/6
"There is no reason anyone would want a computer in their home." - Ken
Olson, Chairman & Founder, Digital Equipment Corporation (1977)
> -----Original Message-----
> From: j4976@juno.com [SMTP:j4976@juno.com]
> Sent: Tuesday, October 05, 2004 10:42 AM
> To: Steve Katz
> Subject: Re: [BULK] - Re: [TowerTalk] ARR Preamp Failures
>
> Just a quick question about the sequencer: Do you need to key manually
> with one of these, or are they ok with a vox setup?
>
> - Thanks.
>
> On Tue, 5 Oct 2004 10:01:35 -0700 Steve Katz <stevek@jmr.com> writes:
> > What's commonly done with VHF masthead preamps and such, and I've
> > used these
> > for decades, is to simply install electronic sequencing in the shack
> > and use
> > control-line keying (not RF sensed keying). ARR used to sell a
> > sequencer
> > for this, maybe they still do; but the circuit's been in the
> > Handbook since
> > the 1970's, and of course designing one's own sequencer isn't
> > difficult. My
> > 4-stage sequencer uses sealed, small, mercury-wetted relays that
> > switch
> > quickly, have no contact bounce, and are good for millions of
> > operations;
> > they cost about $10 each. When I push the footswitch or mike PTT
> > bar, the
> > first thing to switch is the preamp, from RX to bypass; the second
> > thing to
> > key is the power amplifier T-R relay, from RX to TX; the next thing
> > is the
> > power amp's bias key line to switch it from cutoff to operate; the
> > last
> > thing is the exciter, to produce RF. Releasing the switch makes
> > them unkey
> > in reverse order. The sequence time needs to be more than the relay
> > contact
> > settling time; I use 30 mS. So, pressing the button causes four
> > relays to
> > key in sequence, taking up about a tenth of a second; releasing it
> > causes
> > them to unkey in reverse sequence, also taking up about a tenth of a
> > second.
> > I built my sequencers per plans from Chip, N6CA, that appeared in
> > the
> > Handbook maybe 20 years ago. Still work fine, and I use one on each
> > VHF
> > band. -WB2WIK/6
> >
> > "There is no reason anyone would want a computer in their home." -
> > Ken
> > Olson, Chairman & Founder, Digital Equipment Corporation (1977)
> >
> > > -----Original Message-----
> > > From: Tom Rauch [SMTP:w8ji@contesting.com]
> > > Sent: Tuesday, October 05, 2004 10:10 AM
> > > To: Jim Brown; Tower Talk List
> > > Subject: [BULK] - Re: [TowerTalk] ARR Preamp Failures
> > >
> > > > So the question is, is this a common problem? Am I doing
> > > anything wrong? Could I do
> > > > anything better?
> > >
> > > This is a common problem. The problem is the system
> > > configuration requires the radio output RF before the preamp
> > > switches out of line.
> > >
> > > This means the preamp has to handle nearly the full output
> > > power of the radio or any amplifier BEFORE the preamp relay
> > > drops and bypasses the preamp. If they did anything like add
> > > a diode across the relay or didn't do there homework in the
> > > switching system, it can be even worse!
> > >
> > > You need to switch the preamp out of line before
> > > transmitting and switch it back in line after a safe delay.
> > > RF detected circuits can't do this.
> > >
> > > In some designs, I had to add an intentional MMIC buffer and
> > > attenuator pad to allow RF switching the preamp out. The
> > > MMIC is rugged, and a pad of several dB limits the power
> > > applied to protection diodes and the GAsFET drain. It is a
> > > real PITA thing to design a preamp that won't fail from
> > > being banged with high power RF while waiting for the relay
> > > to transfer.
> > >
> > > 73 Tom
> > >
> > >
> > > _______________________________________________
> > >
> > > See: http://www.mscomputer.com for "Self Supporting Towers",
> > "Wireless
> > > Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041
> > with
> > > any questions and ask for Sherman, W2FLA.
> > >
> > > _______________________________________________
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> > > TowerTalk@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/towertalk
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers",
> > "Wireless Weather Stations", and lot's more. Call Toll Free,
> > 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
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> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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