Seems to me the three most-likely causes of your problem are:
1. Antenna itself is bad/noisy. Substituting antennas may help rule this
out.
2. Not enough isolation between radiating antenna and equipment. The 100'
of horizontal separation may not be enough to keep the strong RF out of your
equipment, effectively bypassing/negating the isolation your finely-tuned
duplexer is attempting to provide.
3. Mis-match due to out-of-band antenna is causing other problems, possibly
even transmitter going spurious. While I generally don't recommend using
isolators or Z-matchers as band-aids to cure antenna ills, using one to help
rule this out as possible cause might be helpful as a short-term experiment.
4. You mention "metal building", which conjures many bad memories of
rooftop installations where all kinds of noise problems related to HVAC
units, duct work, corrugated metal panels, metal screens/grills, ventilation
stacks, cooling towers, etc. resulted in countless hours of time spent
trying to reduce noise and passive intermod mixes. You're on your own on
that one...
--- Jeff WN3A
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301
> Sent: Tuesday, September 01, 2009 4:03 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: [Repeater-Builder] Re: Antenna SWR = Desense?
>
>
>
> Hi Joe,
>
> The repeater/duplexer is in my workshop (a large metal building).
>
> The heliax goes out the window to a smaller portable building
> about 100' away (horizontally spaced). The antenna is on
> that building about 10' off the ground.
>
> Don - took the dummyload & analyzer to the end of the hard line,
> fed it into the iso-tee there. No desense is noted. Something's
> not right when the antenna gets hooked up. Maybe I should put
> up the ringo for a test..... at least it's probably a bit better
> of a match.
>
> --- In Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com> , Joe
> <k1ike_m...@...> wrote:
> >
> > You state "DB-224 100' horizontally & 10' vertically separated". I
> > don't understand what you mean by that.
> >
> > Joe
> >
> >
> > tahrens301 wrote:
> > > However, putting the system on the antenna (a 150-160 mhz
> > > DB-224 100' horizontally & 10' vertically separated)
> > > through a metal building fed with 7/8 heliax, there
> > > seems to be no end to the desense!
> > >
> > >
> >
>
>
>
>
>
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>
