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Re: [Amps] Optoisolator for Keying Collins 30L-1 to Modern Rigs

To: "Tom W8JI" <w8ji@w8ji.com>, <amps@contesting.com>
Subject: Re: [Amps] Optoisolator for Keying Collins 30L-1 to Modern Rigs
From: "JOS Earthlink" <jsternmd@earthlink.net>
Date: Sat, 9 Dec 2006 10:14:39 -0500
List-post: <mailto:amps@contesting.com>
Dear Tom,

Thanks for the clear and detailed answer. I impulsively bought the Ampkeyer
recently which really is a great value and beautifully constructed.  But the
Ampkeyer manual says not to use the MOSFET circuit for amps like the 30L-1
as they were not designed to handle the 30L-1 antenna relay voltage/current.
So I used the Ampkeyer's mechanical relay option and it was at that point I
realized that I could have put something identical together much more easily
and cheaper from my junkbox (though the Ampkeyer is pretty inexpensive).  I
guess the bottom line is how well can the finals in my TS-950SD handle the
transient high SWR's until the 30L-1 relay kicks in - probably not a problem
in the short-term but the noise you pointed out makes much more sense as an
issue to avoid.

The Ampkeyer doesn't show its schematic but the MOSFET is a IRF644B which
has a rating of 250v and 14a but I guess it cannot handle the negative 170
voltage of the Collins antenna relay??  Are there any solid state solutions
that would work with the neg voltage?

73 Jerry
K1JOS


-----Original Message-----
From: Tom W8JI [mailto:w8ji@w8ji.com]
Sent: Saturday, December 09, 2006 6:13 AM
To: JOS Earthlink; amps@contesting.com
Subject: Re: [Amps] Optoisolator for Keying Collins 30L-1 to Modern Rigs


> Question is for routine SSB (and some occasional CW) does
> one really need an
> optoisolator circuit controlling a relay rather than just
> a lowvoltage power
> source plus a well rated (250vdc 2a) low voltage relay?

The problem with a relay keying another relay is activation
times are added. Whatever small relay's time you add in, it
makes an already poor situation worse.
Say you have 13mS on the large amplifier relay and 5mS on
the small relay. Pull in would now require 18mS.

Virtually all rigs actually output RF before the antenna
relays can transfer in an external PA. This can cause
amplifier bandswitch or tank component arcing or damage,
annoying pops or clicks up and down the band, and chopping
of the first part of transmission at every VOX or key
closure if you are not using push to talk or manual transmit
switching.

With a solid state buffer circuit you don't add the time of
another relay.

It does not take a special expensive circuit to do this or a
high speed relay. All it takes is one or two transistors, a
resistor or two, and a diode. You can also use a very fast
external relay, like a HV reed relay, but you have to watch
voltage and current transients.

It might be less time and worry to buy one. Ameritron also
offers a relay buffer. But they are easy to build.

73 Tom



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