Mathew,
Actually, if the duplexer insertion loss is really 2.2 dB, you should get
120.5 watts out for 200 watts in. Once you consider the small additional
loss in jumpers, connectors, adapters, etc., you're not too far off the
mark. The tolerance and linearity of your power measuring instrument may
contribute a small error.
The major difference between your two conditions is that in one, the PA is
feeding a resistive load, and in the other, it is feeding a highly
reactive load- the duplexer. If you experiment with the length of the
jumper connecting the PA to the duplexer, you will probably see a
significant change in output power- which may be better or worse. You can
also try an impedance matcher ("Z-Matcher") at the output of the PA, to
see if you can optimize the match between the PA and the duplexer.
Bear in mind that when a duplexer leaves the factory with precisely-set
tuning and insertion loss, it may suffer considerable vibration during
shipment. That's why I always check duplexers and bandpass cavities on a
network analyzer before installing them. It's rare that such devices
arrive in perfect adjustment.
73, Eric Lemmon WB6FLY
n9lv wrote:
> Ok, running the TX-RX duplexer, with a 2.2 dB insertion loss, I tuned
> the duplexers on the monitor. All three of them looked identical,
> with rejection on the rx side of -80 dBm on each single cavity. Once
> I tied them all together, the rx rejection was better then -10 dBm,
> all went well there. I input 4 watts into them all tied together,
> connected to a dummy load, and got three watts out. Then I tied the
> duplexers back into the repeater, with 200 watts input, I am getting
> 100 watts output, into the same dummy load. Refelcted power was less
> than 1/10 of a watt. What am I missing here. If I am thinking right,
> I should be getting about 137 watts back out of the duplexer, or close
> to there. Any ideas? Could there be a mismatch bewteen the duplexers
> and the amp? Cables are all ingood shape.
>
> Mathew
>
>
> Yahoo! Groups Links
>
>
>
>
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