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One thing is being overlooked.
Assuming that this is actually a dual-feed antenna,
the pigtail for the top antenna will be longer than that of the bottom antenna.
This will present an unequal feed to the two halves when using a power divider
and needs to be taken into consideration. One could add feedline to the shorter
cable so that it's the same length as the longer one, then use a power divider.
The other solution is to simply replace the entire harness with the right
one.
Chuck
WB2EDV
----- Original Message -----
Sent: Tuesday, May 30, 2006 1:24 PM
Subject: RE: [Repeater-Builder] Re:
Double the gain or double the power?
Jeff I was going to say the same thing. Sounds like he is
mounting two, lets say for conversation sake, say DB-222's on top of each
other to make a DB-224. Sounds like he is still using the 222 harness' with a
T inline. That being said we have an impedance mismatch. The only way to do
that correctly other than using a 224 harness is to use a 50 ohm power
divider... Antenna model #'s would be a great help
here..
Shane
'Jeff DePolo' <[EMAIL PROTECTED]>
wrote:
>
Yes, I was using the Top Half of a 4-element antenna. I have
> now
added the 3-Way connector and now have the entire antenna
>
connected.
> I have noticed it has cleaned up the receive on week
stations
> but, it seems to have dropped a little in the
signal.
>
> System was just re-tuned, duplexers and radios.
It's a
> Motorola MSR-2000 Canadian 40 Watt version. When I add the
> duplexers and the top half of the antenna I get 25 Watts out.
> When I add the second half I get 10 Watts out. Measuring
>
the wattage just after the duplexers.
This doesn't make sense. The
transmitter output shouldn't be changing.
It sounds to me like when the
second set of bays was connected it wasn't
done with a proper
matching/phasing harness, but rather just by "teeing"
the two halfs
together. This would throw the match off (a 2:1 VSWR
mismatch best-case),
which results in a detuning effect at the duplexer
which makes its
insertion loss go up, which is why you're seeing less
TPO. Have you
measured the reflected power at the antenna both before
and after adding
the second set of bays (or if you can't measure at the
antenna, measure
at the output of the duplexer and tell us what kind/how
long your
feedline is and we can back-calculate from that).
Sneak preview the all-new
Yahoo.com. It's not radically different. Just radically better.
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