Steve,
Swr is a very good indicator for antennea matching, but nobody was talking
about the measuring point. Even with a duplex filter in line. When not sure
one should add a (Lamba/4 x v f ) in the coax line, and watch the
diffirence.
Had a customer working for years with no antenna at all connected, just the
coax served as a antenna. We only find out when the tower came
down.......... coax cables dont like shot guns......
Jos on4kj
----- Original Message -----
From: "Steve Katz" <stevek@jmr.com>
To: "'steve sala'" <stetrekve@yahoo.com>; <Towertalk@contesting.com>
Sent: Thursday, November 21, 2002 9:30 PM
Subject: RE: [Towertalk] high SWR at receiver inputs
> Yep, in a simplex system, I agree with you.
>
> It is certainly unusual that an antenna mismatch creates RX problems that
> are found sooner, or are more severe, than TX problems. Of course "SWR
> problem" could mean a lot of things....
>
> I'm not used to having "SWR problems" in systems I install! I've had
> repeaters (VHF-UHF) up an on the air for 15+ years at a time with no
change
> in SWR, period -- in high-wind and lightning prone environments. I guess
it
> depends on the components used and how they're installed!
>
> 73,
>
> Steve WB2WIK/6
>
> "If everything seems under control, you're just not going fast enough." -
> Mario Andretti
>
> > -----Original Message-----
> > From: steve sala [SMTP:stetrekve@yahoo.com]
> > Sent: Thursday, November 21, 2002 1:10 PM
> > To: Steve Katz; Towertalk@contesting.com
> > Subject: RE: [Towertalk] high SWR at receiver inputs
> >
> > Let me clarify. This is a simplex system. 4 watts of
> > rf between 136 and 174 MHz for a detector system. The
> > field troubleshooters sometimes find that the problem
> > is high SWR so either antenna or coax is remedied.
> > The initial call is for a communications failure in
> > one direction, but many times it is the receiver with
> > the high SWR antenna system that is not receiving the
> > correct signal, and not the transmitter problem
> > connected to the same antenna system. My gut feeling
> > is that the high SWR would not affect the receiver as
> > much as the transmitter unless the antenna fell down,
> > etc. If anything degraded, would not you see the
> > rffect at the other receiver end where the high SWR
> > would cause most of the transmitters energy to be
> > lost?
> > 73
> > Steve K7AWB
> >
> > --- Steve Katz <stevek@jmr.com> wrote:
> > > That explanation doesn't make much sense to me.
> > >
> > > Are you sure this discussion is not relating to VHF
> > > "repeater" systems,
> > > which are transmitting and receiving simultaneously
> > > at each site?
> > >
> > > Then, the RX impact can be disastrous if the antenna
> > > match degrades, due to
> > > the immediate desense that occurs when a duplexer is
> > > terminated in a
> > > mismatch. That would be perfectly normal. But for
> > > a "simplex" system,
> > > where each station is only transmitting, then
> > > receiving, my observation is
> > > that the TX is usually more affected than the RX.
> > >
> > > WB2WIK/6
> > >
> > > "If everything seems under control, you're just not
> > > going fast enough." -
> > > Mario Andretti
> > >
> > > > -----Original Message-----
> > > > From: steve sala [SMTP:stetrekve@yahoo.com]
> > > > Sent: Thursday, November 21, 2002 11:43 AM
> > > > To: Towertalk@contesting.com
> > > > Subject: [Towertalk] high SWR at receiver inputs
> > > >
> > > > A coworker asked me this question since I was a
> > > ham.
> > > >
> > > > He has noticed this with several radio system
> > > > installations. There have two identical radio
> > > systems
> > > > communicating with each other, same two
> > > transmitters,
> > > > receivers, coax and antennas. And it is on vhf so
> > > > there is no skip, maybe a few miles apart - Normal
> > > > good communications, transmitting data either by
> > > dtmf
> > > > or by fsk.
> > > >
> > > > He says that if the swr goes high on one antenna
> > > > system (maybe due to an coax/antenna malfunction),
> > > the
> > > > system behavior could be as follows: The radio
> > > signal
> > > > from the system with the high SWR antenna system
> > > will
> > > > still be received at the other station fine, but
> > > the
> > > > receiver (at the high SWR antenna system) could
> > > have
> > > > receive problems due to the effect of high SWR at
> > > the
> > > > receiver input.
> > > > The other radio system, with no SWR problems, will
> > > > still receive fine from the transmitter with the
> > > high
> > > > SWR and transmit as usual due to its low SWR.
> > > >
> > > > In other words, he notices problems at the receive
> > > end
> > > > of the system with the high SWR problem first.
> > > >
> > > > My justification for this happening is that you
> > > can
> > > > normally lose a lot of transmitter power and still
> > > be
> > > > received, yet the receive portion is more
> > > critical.
> > > > There is less room between good reception and bad
> > > > reception (the noise floor) since you are playing
> > > with
> > > > microvolts.
> > > >
> > > > Could I get a few comments on this from any of you
> > > > whether we are on track or not.
> > > >
> > > > Steve K7AWB
> > > >
> > > >
> > > > __________________________________________________
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