[TenTec] Amp Hot Switching Prevention

[Dr. Gerald N. Johnson]

I can think of at least a couple solutions. One is to create a high 
external ALC voltage that decays 50 milliseconds after PTT arrives. It 
might be possible in some software to delay the tones, but I suspect the 
rig blaster can be creating PTT from the presence of the tone. It might 
need a different option to separate the sources of tone and PTT.

The box cure is to look up W1GHZ.com and his sequencer. This is a 
standard problem at VHF and microwaves with transverters and such. 
Typically a sequencer (and there have been several schematics published 
in QEX and proceedings of VHF conferences and Microwave Update 
Conferences over the past two decades), is started by the external PTT 
which then switches the antenna relay, then after a selected wait, keys 
the PA, then the transverter, then after all the relays have seated it 
applies PTT to the exciter. Does it in reverse to go back to receive so 
no relays get keyed hot, no exciter power hits a delicate tranverter or 
antenna mounted preamp.

Last I knew, WA3IAC sold kits for the W1GHZ sequencer kit. Direct or on 
epay. I bought one last year that I've not yet used, but I will probably 
need more in time.

Links:
http://www.w1ghz.org/small_proj/sequencer_V2.pdf

http://www.qsl.net/wa3iac/kits/

Or one can install auxiliary contacts (such as a microswitch) on the PA 
relays and wire them in series with the PTT signal from the rig blaster 
so the PA relays have to seat before connecting PTT to the exciter. 
Since the PA was built without provisions for those controlling 
contacts, the timed sequencer is what works.

73, Jerry, K0CQ


On 3/22/2010 6:36 PM, Gary Hoffman wrote:
> Hi All,
>
> I'm having a new (to me) problem with one of my rig/amp combinations.
>
> I've begun using my Corsair II with my SB-200 amp in some digital modes -
> mostly RTTY of course.
>
> These rigs were not meant for digital service nor computer control of
> course.
>
> What I have is a rigblaster, and I use a serial port from the computer to
> both send the digitaal data and the PTT signal to
> the Corsair through the Mic Jack - in the well known manner.
>
> The Corsair switches the amp into transmit through its key line.
>
> Unfortunately the rigblaster sends data and PTT to the corsair together, at
> the same instant.
>
> Thus when the amp relay is being switched - the corsair is already
> outputting RF.  Hot switching the amp in that fashion
> allows 1 kw of power to see momentarily an open circuit, as the amp relay
> has not yet reliably closed the contacts to the antenna.
> This does a LOT of damage !!!
>
> I'm sure others have run into this.
>
> What are people doing ?  Some other external control box I don't know about
> ?  Somehow delaying the production of tones in the
> rig control software ( I'm using N1MM) ?
>
> I'd appreciate any useful ideas.
>
> 73 de Gary, AA2IZ
>
>
>
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