Hi All:
Our Website is NOT intended to offer a complete treatise on station and
amplifier design. There are lots of places (like this one, for sure!) to
go to get all kinds of different information on how to do, or not do,
things. We build a product that is loved by most, and hated by a few
(pretty much like a lot of products). Yes, we have VSWR protection, and it
is indeed driven by firmware in a PIC. It takes about 400-600 milliseconds
for it to respond (on purpose, see below.) So, for instantaneous problems,
it isn't going to do much. But it will prevent long term (e.g. 20 minute
keydown) problems, and will always let you know when you've forgotten to
select the right antenna, icing, etc.
In terms of how you interrupt an amplifier: many amps do not have
sequenced relays. We have had feedback from many users that they prefer to
use the ALC approach. Most use the PTT-block approach. Most responses
from users tell us they both work fine (within the limitations mentioned
above).
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.
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
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).
We design our meters to offer the most performance for a reasonable amount
of money. You can't buy a Bird and a full set of slugs for $249, and even
if you do pay all the extra money for a 43, peak kit and a full set of
slugs, you won't get VSWR computation and an alarm.
To those who do not like our new sensor: you can still buy the old one to
use with the VFD. It has mounting ears and is in a cast aluminum box.
Contact us if you would rather do that. It just costs more (and works the
same). And to those that object to the "project box": how much extra
would you pay for a metal one?
Thanks for reading & 73,
Bruce R. Knox W8GN
RF Applications, Inc.
PS: Yes, I know there's a mod for the AL-1200 relay. Just need the time
to do that!!!!!!!!!!
-----Original Message-----
From: Chuck Counselman [SMTP:ccc@space.mit.edu]
Sent: Monday, October 30, 2000 10:44
To: amps@contesting.com
Cc: W8JI@contesting.com; bknox@rfapps.com
Subject: Re: [AMPS] High-SWR protection
Tom Rauch <w8ji@contesting.com> wrote:
>If the relays in the amp are properly sequenced, dropping the relay
>line won't hurt a thing.
That sounds right. Thanks. Sorry -- I was guilty of mindlessly parroting
the advice on RFApplications' website. Perhaps someone from RFApplications
will chime in to enlighten us?
>I'd be reluctant to use application of ALC voltage as the sole means
>of shutting off the exciter, because ALC lines can be a bit slow and
>you also must depend on an external negative supply. Anything
>gets unplugged or shorted and you have no protection.
>
>If I used ALC, I'd be darned sure I also dropped the antenna relays
>during a fault.
Sensible advice. Thanks again.
73 de Chuck W1HIS
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--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
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