Mathew,
I would think that you have a little more insertion loss on the TX side than
you think, or the cavity may need a little tuning. You may also need to try
different lengths of coax between the transmitter and duplexer.
I have had to change the coax length on one of my UHF repeater because the
coax was to short. After calculating the correct length for the coax I was
using for a full wavelength I was getting the proper RF out.
I believe someone else suggested doing this, and it is a very good idea. If
all else fails, and this is NOT recommended with 200 watts RF input, you can
make very small adjustments on the tuning rods. DO NOT tune the rods with
the transmitter on as you can ARC the cavity tuning slug and damage it. Try
1/8th turns at first and see if the output power goes up or down.
I have done this in the past, however it is NOT recommended. Great care must
be taken when tuning a cavity in this manor as the cavity can be damaged
easily at this power level. If you have 25 watts available you should be
able to tune it easier but still be careful.
Charles Miller
***************************************
>
> I agree, but at this point, I am only getting 100 watts out of the
duplexers instead of the 137 watts I would like to see. Now you mention
something that I might now be aware of, and that is the interaction between
the rx side and the tx side, could that have an effect on the power out,
however the rx side of them seems to be great, as I can hear much farther
than I can transmit. I'm up about 130' in the air with a DB224, the
repeater can be heard for about 30 to 35 miles, but can hear users in about
the 40 to 50 mile range.
>
> Mathew
>
***************************************
>
> Mathew,
>
> I think you will find that the RF at high power is probable correct. The
> difference you see between low power and high is about 17dB. Unless you
are
> measuring the low power down to 0.01 watts it will be difficult to find
the
> real loss. Provided all is working correctly the RF power levels you list
is
> about right. I would think a little minor tuning could get a little more
> out, but not much.
>
> The 2.2dB insertion loss is only one calculation. You have the connectors,
> coax, loops (very little here) and some going through to the other side
> (again, very little) has to be calculated.
>
> Taking this into account you probable have close to 2.5dB loss through the
> whole thing. If this is correct then 200 in and 137 out is about right.
>
> Just my thoughts.
>
> Charles Miller
>
>
> ----- Original Message -----
> From: "n9lv"
> To:
> Sent: Wednesday, November 30, 2005 8:29 PM
> Subject: [Repeater-Builder] Duplexer loss different with more power, Why?
>
>
> > 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
> >
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