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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