[AMPS] Hot Switching

[Ian White, G3SEK]

Rich Measures wrote:
>>Someone asked me a question about hot switching today. I thought I
>>understood this subject, but while I was thinking it through, I realized
>>that I'm not entirely sure. The context was the unfortunate design flaw in
>>the Yaesu FT-990 that causes it to apply RF a mere 3ms after keying the amp
>>(it actually delays the RF envelope until 10ms after key closure, but
>>inexplicably waits 7ms after key closure before keying the amp.) 
>
>A potentially disastrous delay could be caused by the relay in the radio 
>that keys the RL control line.  To avoid hotswitching this relay is 
>removed and replaced with transistor switch.  

That's a good point, Dick - did you measure the 7ms delay in the FT-990
using the transistor remote switching option, or the relay option?

Another possibility for the 990 might be to route the key closure
directly from the key jack to the rear ACC socket. A couple of steering
diodes should ensure that the amp gets the PTT signal in real time,
while the 990 can still hold the PTT line down for a few extra ms on un-
key.

(Sorry, I'm without a workshop  at the moment, or else I'd try these
things myself.)

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

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