Dennis,
I believe that the most likely mixing is occurring in the PA of the
146.970 repeater, where a second harmonic is mixing with the tertiary
146.700 signal. A dual isolator on the 146.970 PA would prevent the
146.700 (or any other signal) from getting into the PA. A bandpass cavity
filter set for 1.0 dB insertion loss and tuned to 146.970 MHz on the
output of the 146.970 PA may work- but it won't be nearly as effective as
an isolator. Since you have a bandpass cavity on hand, try it and see.
I always hedge a bit when trying to diagnose an IM problem from afar,
because there are often many mixes instead of just one, and I am only
addressing what I feel is the most obvious mix. Note that there is also a
third harmonic IM product of 146.700 MHz, resulting from 2 times 146.970
minus 147.240!
73, Eric Lemmon WB6FLY
Dennis Carpenter wrote:
> Eric;
> Tnx fer reply. U R correct there is no circulator on either the
> 146.700/R or 146.970/R. I have a bandpass cavity. Which rptr does it
> need to go on??? The 97/R has a Bp/Br wacom 641 duplexer. The 70/R
> runs dual antennas w/o any filtering on the TX.
> Jeff (w5ppb) owns the 147.240/R and is planning a freq change soon.
> This rptr is one we like to link to during WX conditions allowing us
> on the east side of MS to communicate with Jackson WX Service abt 90
> miles away. We are receiving a tornado warningas I type this. The 4th
> or 5th one today.
>
> TNX,
> Dennis ki5fw
>
> --- In Repeater-Builder@yahoogroups.com, Eric Lemmon <[EMAIL PROTECTED]>
> wrote:
> > Dennis,
> >
> > You have classic third-order intermodulation interference. 146.970
> times 2
> > = 293.940 MHz. Subtract the 146.700 signal and you have 293.940 -
> 146.700
> > = 147.240 MHz, the output of your linked repeater. Other mixing
> products
> > are possible. I suspect that neither the 146.970 repeater nor the
> 146.700
> > repeater has a circulator on the output. Bandpass cavities on the
> output
> > are another option.
> >
> > 73, Eric Lemmon WB6FLY
> >
> > ki5fw wrote:
> >
> > > Hey Guys;
> > > Why does my 146.970/Rptr when linked to a 147.240/Rptr get
> interference
> > > from a 146.700/Rptr. The 146.700/R is about 5-7 miles from my
> > > 146.970/R. When the link is up and someone uses the 146.700/R it
> > > creates terrible interference and you can actually understand
> what is
> > > being said on the 70/R.
> > > The 70/R will not be heard or cause a problem until the 97/R is
> > > accessed while linked to the 147.24/R. There is no problems when
> the
> > > link is down.
> > > Will a notch filter on the remote base T/cvr to notch out 146.700
> be
> > > the cure? The remote base is frequency agile and wonder if the
> notch
> > > filter is the way to go. Guess it depends on how wide and deep the
> > > notch is???
> > > I tried the intermod Calculator and I think I see what the
> problem is,
> > > but not sure if I'm looking at it correctly.
> > >
> > > TNX in Advance,
> > > Dennis ki5fw
> > >
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
>
>
> Yahoo! Groups Links
>
>
>
>
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