[AMPS] High-SWR protection

[Tom Rauch]

> So, Chuck, your "mindless parroting" wasn't so far off base.  I haven't
> looked to be sure, but my AL-1200 acts like it does not have sequenced
> relays (there seems to be just one T/R relay that is just marginally fast
> enough), so the ALC approach (and the PTT approach) might make sense for
> that application.  When I put a VFD or WinWatt between my 756PRO and the
> AL-1200, I get a momentary VSWR alarm as the AL-1200 T/R relay pulls in. 

Pull in time is about 10 mS. This is typical of amps that don't use 
vacuum relays....like the TL-922, Heathkits, Drakes, Dentrons, etc.

The relay is sequenced, if it wasn't the 756PRO would eat 
bandswitches in the PA since it hot switches the PA.  

Some radios delay transmit RF several mS while waiting for an 
amp to energize, some don't. Some very stupidly wait several mS 
to send out RF, but also for some reason wait the same time to 
energize the PA!

>  Because of situations like this, we have built in an intentional delay
> that occurs after we have sensed a problem and when we drop out the alarm
> relay.  Much like our "spike filter" that ignores the sometimes GIANT
> initial spikes that come out of a lot of modern rigs.  Those giant spikes
> cause the peak detectors to read sometimes hundreds of extra watts coming
> out of a 100 or 200 watt transceiver for some number of milliseconds. 
>  Indeed, there are quite a few competing wattmeters out there that exhibit

PA relay delay will not trigger a fault detection system. The fault 
detector should be located after the PA. If the fault detector is 
properly located in the system, and it trips on transmit closure, the 
relays are out of sequence and the output relay is switching hot. 
That's the ONLY way you can have an output high SWR pulse from 
slow relays. 

If you do get that fault, the PA relay timing should be corrected.
  
> this flaw.  These are typical features of our design that focus our meters
> on OPERATING, not lab testing.  Sure, an "instant" VSWR alarm and display
> of a transient excessive initial peak would be great in a lab, but I can't
> see how you'd want to have those functions or indications while you're
> trying to run some rate (or check in to the Maritime Mobile Net for that
> matter).

I have a system like that and have used it for years. It works with 
any PA I connect, unless the PA has the output relay hot-
switching.

 
73, Tom W8JI
w8ji@contesting.com

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