2 watts reflected into the isolator does not sound good. It should
have better return loss than that unless it is tuned wrong.. I would double
check tuning and try capping it with a dummy load on the output side (
where the tx duplexer port goes) and see if it is different. An isolator
can exhibit non-linear operation if the loads are not all 50 ohm on all
ports... It could be a duplexer tuning issue or a bad acable too for that
matter....
I would also check the power/swr going to the duplexer and see if
the duplexer is an issue..
A dual isolator should be 50db down on reflected with a dead short
on the output, while looking at the power input port ( tx port) 100w - 50
db is a lot less than 2w.. it should hardly wiggle a low power slug if tune
correctly....( swr I am referrring to )
Doug
KB8GVQ
At 08:19 PM 10/02/2004, you wrote:
>I'm trying to install a repeater and have encountered a puzzlement.
>
>I re-tuned a Telewave dual-isolator down from 452.xxx to 443.55 MHz for
>installation on a new GE M-II 100W UHF repeater. At the site, I
>connected the xmtr's coax cable to the the isolator's input (yes, it was
>the Input port). I connected the isolator's output to the duplexer's
>xmtr-side port. I used only RG-214 coax cable. I put a 10-watt load
>resistor. on the LOAD port nearest the transmitter and a 100W load on the
>LOAD position next/nearest to the isolator's output.
>
>Then I inserted a BIRD wattmeter between the Xmtr output coax and the
>isolator's INPUT port and keyed the transmitter, I read 110W fwd and 2W
>rev. OK! But after 45 seconds of continuous transmission, the reflected
>power had risen to 7.5 watts and was rising. I unkeyed the xmtr.
>
>I am puzzled. I expected the isolator to behave constantly: X watts fwd;
>and Y watts refl. This variability I'm seeing makes me think that I have
>a changing impedance inside the isolator . The 100 watt load was
>beginning to warm up in the 45 seconds duration of my test. I swept the
>duplexer with my IFR to see if the rcv/xmt ports were labeled
>wrong. Nothing unusual here . I put the GE's transmitter direct to the
>antenna through the wattmeter and got 110W fwd and 1.5 watts reflected
>
>What is going on with this isolator? Should I be concerned? and what do
>I do about it?.
>
>I would like to have some suggestions
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