Changing the length of the coax won't change the SWR seen by the transmitter
by much.  A given SWR can be caused by a whole range of resistance and
reactance values (these values are shown on a circle on a Smith chart and
can be calculated using some trig functions).  But this could explain why
some 5:1 SWR conditions can be tolerated by your transmitter's internal
tuner while other combinations of resistance and reactance that result in a
5:1 SWR make the tuner unhappy.

I just read your message about the AM station, and suspect that it is
messing up your readings, especially for 160.  So SWR readings taken at,
say, 50 watts, will be more accurate than readings taken at 5 watts, because
the AM station will appear to cause some reflected and forward power on your
transmission line whether you are transmitting or not.

Lloyd Rasmussen, Kensington, Maryland
Home:  http://lras.home.sprynet.com
Work:  http://www.loc.gov/nls
 

> -----Original Message-----
> From: For blind ham radio operators [mailto:[log in to unmask]]
> On Behalf Of Tom Behler
> Sent: Friday, November 11, 2011 10:00 PM
> To: [log in to unmask]
> Subject: Re: Need helping making sense out of contradictory SWR readings
> 
>     Mike:
> 
> You have a very interesting point here about local broadcast signals.
> 
> I happen to live about a half mile from the tower for the only commercial
> A
> M radio station in our little Michigan town. ... It broadcasts on 1460 AM,
> with a night-time power of, I believe, 1000 watts.
> 
> Are you saying that this is what's messing the analyzer  up?
> 
> Again, just to be sure I'm understanding you, are you saying ignore the
> analyzer, and just go with what my TW1 and TS590 meters are saying?
> 
> Obviously, my 160 meter antenna is still too long electrically, so that
> will
> need to be shortened.
> 
> But, here's another question:  When we put up the 160 meter sloper, I only
> had a 100-foot piece of RG8X coax to connect between the antenna and the
> rig, which gives me about 40 feet of excess coax. ... Should I cut that
> coax
> to only what I need?  Would that change anything?
> 
> Again, you are giving me some very interesting observations here.
> 
> 73 from Tom Behler:  KB8TYJ, Big Rapids, MI
> 
> 
> ----- Original Message -----
> From: "Mike Cozzolino" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, November 11, 2011 9:30 PM
> Subject: Re: Need helping making sense out of contradictory SWR readings
> 
> 
> > hello tom, the analyzer is almost useless on 160 and 80m
> > antennas.  the reason is because you have so much broadcast signals
> > coming down the feed line that the analyzer is all messed up.  in
> > areas where folks don't have the broadcast crap the analyzer does the
> > fine job.  so go by the swr bridge and ignore the analyzer.  even a
> > swr bridge is influenced by the length of the feed line, you could
> > have a 1:1 some where along the coax where the swr is really much
> > higher.  the only way to use an swr bridge is through a electrical
> > half wave to the antenna or with the swr bridge at the feed
> > point.  you can also use multiple electridal half waves between the
> > swr bridge and the ant.  take care, c u 73 mike
> >
> >
> >
> > At 05:28 PM 11/11/2011, you wrote:
> >>Hi, folks.
> >>
> >>Well, I have managed to get hold of an MFJ 259B antenna analyzer to help
> >>try
> >>to figure out what is going on with my 80 meter and 160 meter sloper
> >>antennas that we put up a few weeks ago.
> >>
> >>However, when taking some preliminary readings with the analyzer
> tonight,
> >>and comparing them against what my TW1 watt meter and the SWR meter on
> the
> >>TS590 say, I am getting very confusing results.
> >>
> >>Let me give a few examples:
> >>
> >>On 80 meters, my sloper has an SWR of about 5 to 1 on the top and bottom
> >>of
> >>80 meters, with a dip of 1.0 to 1 around 3.887 mhz.  But, when we put
> the
> >>analyzer on the antenna, it shows the lowest SWR to be about 1.3 to 1 at
> >>3.887 MHZ, but the SWR's skyrockets quickly on either side of that null
> to
> >>infinity on the lowest part of the band, and to over 8.1 to 1 on the top
> >>of
> >>the band.
> >>
> >>With my 160 meter sloper, my lowest SWR is about 5 to 1 at the very
> bottom
> >>of the band, according both to my TW1 and the TS590 SWR meter, but the
> >>needle on the analyzer doesn't even budge when tuning through the entire
> >>band, and stays up at some ungodly figure of an SWR of about 20 to 1.
> >>
> >>I just checked for a short  on my coax feed lines, and there does not
> >>appear
> >>to be any problem there.
> >>
> >>We are using fresh batteries in the analyzer which were just bought
> >>tonight.
> >>
> >>Are we perhaps not adjusting the analyzer correctly?
> >>
> >>I am sure that, to some, all of this seems very elementary, so please
> bare
> >>with me while I do some learning here.
> >>
> >>73 from Tom Behler:  KB8TYJ
> >