Hi Jeff,
Your next test would be to swap in a bandpass
cavity into the receiver side of the duplexer
output. If the problem goes away, you should
consider leaving the bandpass cavity in line.
The problem is probably not a traditional
ground loop as suggested by others. But you
can't know the exact cause "yet".
Another possible solution would be a shorted
1/4 wave stub inserted into the receiver -
duplexer side.
Depending on where the cavity or stub is placed
in the coax line, some of the external (to the
duplexer internal cable harness) cable lenghts
might become critical.
The duplexer tuning migh change slightly unless
you are really good with pads, test gear and
time.
I lean toward the additional series band pass
cavity in the receiver path/leg. If it solves
your problem, leaving it in line is a proper
long term solution. Simply set the insertion
loss near or less than 1/2 dB.
If you don't have an extra bp cavity, the shorted
stub is a low cost alternative, but can be
touchy to set up and properly install.
There's another test using your old notch pass
duplexer with your new duplexer, but it takes 5
minutes to type out how it's done... and is
only a test to confirm what you've already
tested.
Cheers,
skipp
skipp025 at yahoo.com
www.radiowrench.com
[Also, if the AM Station is playing Talk-Radio
with Rush, your tuning adjustments probably pull
hard to the right and are out of normal alignment.]
: Hi Skipp,
: Yep, as soon as I put the old Notch Duplexer
: back inline the problem goes away.
: Some feedback from others have suggested
: grounding as a possible resolution.
: I am leaning towards thinking I have a
: ground loop.
: I am going to fool around with the grounding
: this weekend.
: I appreciate your information.
: Jeff
> "skipp025" <[EMAIL PROTECTED]> wrote:
>
> Hi Jeff,
>
> Swap the old duplexer back in and see
> (hear actually) if the AM Station problem
> goes away.
>
> If the problem goes away with a duplexer
> change, the physical construction of the
> duplexer probe might be an issue. Some
> bpbr duplexer probes are not DC grounded.
>
> One thought would be to follow the receiver
> output with a single band-pass cavity,
> which has grounded (for dc) loops (probes).
>
> cheers,
> skipp
> www.radiowrench.com/sonic
>
>
> > "W2JRT - Jeff" <[EMAIL PROTECTED]> wrote:
> >
> > I have a 70cm repeater that is located about
> > .75 mile from a commercial radio station.
> >
> > I was using a Cellwave Notch type mobile duplexer
> > and experienced no problems what so ever. Recently
> > I purchased a new Sinclair Bp/Br Q318GR, 4
> > cavity duplexer and replaced the Cellwave. This
> > morning I have noticed that the nearby radio station
> > is now coming through on the repeaters transmitted
> > signal.
> >
> > Anyone have an idea what causes this and how
> > to get rid of it?
> >
> > Thanks,
> > Jeff
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