Tom:
Are there two relays in the AL-1200? I guess that was my real question.
It acts like there is one relay (DPDT format) and I get my alarm when it
is between connecting the input and output together (STDBY) and when I
transmit (PTT grounded).
With regard to the protection system, I was more referring to the "spike
ignoring" than the "instant VSWR alarm". I agree that a properly adjusted
system shouldn't have the VSWR alarm problem. As I know you know, you have
to adjust products like this for a very broad audience of users or you'll
get eaten up on the telephone!
I guess I need a schematic for the 1200!
73
Bruce R. Knox W8GN
RF Applications, Inc.
-----Original Message-----
From: Tom Rauch [SMTP:w8ji@contesting.com]
Sent: Monday, October 30, 2000 17:50
To: amps@contesting.com; Bruce R. Knox
Subject: RE: [AMPS] High-SWR protection
> 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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