Batboard

I have a small Celwave duplexer out of a gR300 repeater. How tough is it to retune to a new freq and is there any website that would help instruct me on such a task?...Can it be done with one service monitor and a receiver? Thats what I have to work with.....

Hi,

The website in the earlier post is great....

The easy way is to use your comm monitor and power meter and
a couple of 50 ohm resistors placed in connectors as loads.


Place your meter on the antenna port. Place a load on the RX
port. Inject your TX sig into the TX port. Adjust for max at the meter.
Place a load on the TX port. Inject your RX sig into the RX port.
Adjust for max at the meter. ----- and your done.

"...Adjust for max at the meter. ----- and your done...."
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No, that would be a procedure for a bandpass duplexer. The original post said: "I have a small Celwave duplexer out of a gR300 repeater..."

That would be a notch only duplexer - tune that for max and you will be in big trouble.

There are 3 types of duplexers, bandpass only, notch only, and bandpass+bandreject [BpBr].

When tuning a duplexer, be sure you understand which type you have and use the appropriate procedure.

The way I do them is with an HP spectrum analyzer, my service monitor as a generator, and a dummy load (usually one built into an N connector).

Generate the RX freq into the antenna port, put the dummy load on the RX port, analyzer on the TX port, adjust TX side of duplexer for lowest signal, swap the dummy load and analyzer, switch generator to TX freq, and adjust the RX side same way.

You should have a good sensitive analyzer, or you won't be able to determine the exact nulls.. I've had to redo ones other people tuned with just their service monitor as an analyzer.

I have used 2 receivers only to tune band reject duplexers of that type, it basically is a mobile duplexer. NEVER use power at all, you could cause an arc internally in the duplexer, rendering it useless. Also if possible use the actual cables that are going to be used on the repeater. Sometimes I have found that the cable length will change the tuning.

How far in frequency are you moving? Those notch only type duplexers have a fairly broad response. If you are sure of the tuning now for a specific frequency pair, you should (read this: in my experience in the field using the proper equipment to verify..) be able to move about 200 Khz in either direction on both TX and RX frequency. Say your freq now was 461.200 TX 466.200 RX. You get a new frequency of 461.2875/466.2875. This is 87.5 KHz higher, within the 200 Khz +- guideline and I would have no problem reprogramming and going with it.

Of course, the absolute best thing is have an experienced tech do it for you if you don't feel comfortable. It'll save you in the long run..

Dave