Duplexer question.....

Larry · Post by **Larry** » Fri Dec 10, 2004 5:12 am

How do you tell which connection goes to the TX and RX??

Dan562 · Post by **Dan562** » Fri Dec 10, 2004 9:54 am

Hello Larry,

Normally the duplexers are marked with Pass / Reject Frequencies on the filter cans. Rx Input should be marked as the High Pass and Tx Input should be marked as the Low Pass.

Example: 463.925 MHz Low Pass and 468.925 MHz High Pass

Dan

Larry · Post by **Larry** » Fri Dec 10, 2004 10:52 am

There are labels on the cans but they are blank.... it appears as if when the duplexer was tuned there is a place to write the frequency on the label, but the labels are all blank and there are not indications on which connection is for "IN" "OUT" or "TX" "RX".... didn't know if there was an industry practice of having one side (left or right) designated for the tx or rx.....

Dan562 · Post by **Dan562** » Fri Dec 10, 2004 11:59 am

Hello Larry,

There are several manufactures of duplexers .... Cellwave (RFS), Sinclair, Tx/Rx Systems, TeleWave, WACO and even /\/\ (but /\/\ has gotten out of manufacturing their own duplexers and now use OEM). Not knowing which brand you have nor a model or kit number makes your question a little more difficult to answer. I'm not even sure if you have small mobile type or conventional base station duplexers? I don't suppose you a JPEG picture of the duplexers that you could post or could provide some kind of model or part number. How cavities (filter cans) per side 2 or 3?

Dan

Larry · Post by **Larry** » Fri Dec 10, 2004 12:15 pm

This is not a mobile type duplexer. This is a 4 can (2 per side) duplexer mounted in a 19" rack pannel. I do have photos of it... There are absolutely no manufacturer tags or model numbers... Each can has it's own label with fill in the blank decal.... the fill in's are all blank...

Dan562 · Post by **Dan562** » Fri Dec 10, 2004 3:47 pm

Hello Larry,

I hate doing this but I'll ASSuME that these duplexers you've got are brand new. They're definitely rack mountable Base Station Repeater version Duplexers without any markings. Since there's no picture provided, the next best idea and/or suggestion I can make would be to connect a 50 watt Resistive Dummy Load to the repeater's XMTR output port.

Then take a RF Signal Generator and/or a Service Monitor and set it up on the repeater's receiver frequency in the generate mode. Connect the RF coaxial cable between the signal source and the station's receiver input to measure either 12 dB SINAD or 20 dB Quieting, your choice. Once you've established the RF reference level then disconnect the coaxial cable from the receiver's input port. Move the RF cable to the common antenna port on the duplexers and take an additional RF coaxial cable connecting it to the station's receiver input port. Now you will be required to choose either side's antenna port for the signal heard on the repeater's receiver.

You could have roughly .5 to 1 dB insertion loss through the duplexer path with the least amount of receive attentuation. Obviously the other port would connect to the XMTR. The mark the individual filter cavities with the information for Tx and Rx connections.

Dan

doi · Post by **doi** » Sun Dec 12, 2004 1:16 am

at what frequency should he do that? because as far as I can see there is no way to tell the frequency they might be tuned to other than some general cosiderations such as vhf/uhf or similar

I think the best way to tell what freq the duplexer is on would be with with a network analyzer. there might be a huge probability you don't have one so you might try a very time consuming approach that involves manualy sweeping the band you think the duplexer might be tuned to with a signal generator or even a transmitter. yet again this is very time consuming and I recommend you find someone with at least a spectrum analyzer and a sweeping generator if not the network analyzer above.

there is still a better chance that someone on this forum could tell you more about your duplexer if they saw some pictures

Dan562 · Post by **Dan562** » Sun Dec 12, 2004 5:59 pm

Hello Larry & doi,

Larry, Do you have access to a Network Analyzer or Spectrun Analyzer with a Tracking Generator or a Service Monitor with a Tracking Generator option that will cover up to 1 GHz (1000 MHz)?

For doi's benefit, Why didn't you provide the Tx/Rx Frequencies when you inquired about this duplexer's unmarked antenna ports?

Since I'm inquiring again about your UHF duplexers, Are the Filter Cans painted Biege and/or a very light Brown in color?

Are each of the individual Filter Cans 4" X 4" X 8.25" Rectangular not Round in for the dimensions?

Do the Tuneable mounting shafts have a large Mounting nut for the 19" rack panel, a smaller Locking nut so the tuning can't be adjusted after tightened and a large 2" Diameter X .75" Black Tuning Knob for adjusting each Filter Can?

If you measure the overall lenght of each Filter Can including the shaft and tuning knob, Is it roughly 11-3/8" long?

Are you using these UHF Duplexers with the following equipment?

(1) GR1225 UHF Repeater
(1) External 50 Watt RF Continuos Duty Amplifier
On GRMS Frequencies ... Assuming you know which frequency pair you plan to license the equipment on for use.

doi,

When you read through the thread, you might have noticed I asked several questions and recommended some ideas about his duplexers. I don't believe there are many field technical service personnel or amateur radio operators that own Network Analyzers. I happen to own one, an older HP3577A but mine only covers 20 kHz to 200 MHz which falls way short of the UHF Business Band ... otherwise I would have offered to sweep his duplexers and marked the I/Os.

Dan

Jim202 · Post by **Jim202** » Sun Dec 12, 2004 6:32 pm

[quote="Larry"]How do you tell which connection goes to the TX and RX??[/quote]

You might try looking at the coax jumper cables going from one can to another. They should be some sort of quarter wave length plus the fudge factor of the velocity of the coax cable. The low pass should be just a slightly longer length cable than the highpass.

If I had my old TX / RX catalog here I could maybe make a guess. It had the cable lengths in it for a number of both VHF and UHF frequencies. The newer books don't have it. The catalog would have to be from back in the late 80's or so. They didn't publish that info after that.

Jim

Microwave Mike · Post by **Microwave Mike** » Mon Dec 13, 2004 8:52 am

Is the duplexer Grey in color? If so it is a EMR duplexer. If there is a single coax connection on each can then it is a Pass/Notch type. If there are two connections, then you have a band-Pass type of duplexer.
The band-pass type will tune for RX or TX on either ports. The Pass/Notch
may only be high side, low side. IE one port will go 455, high and the other 450, low side. Both type of duplexers will do a 5 Mhz split between Rx and Tx.
A network analyzer should be used for tune up. It will show how good the port match is to 50 ohms as well as loss through the system, a spectrum analyzer will only show system loss.

Good luck

mm

bernie · Post by **bernie** » Tue Dec 14, 2004 8:37 am

My two bits worth:
If this is a "Pass only" it makes no difference which one is high/low.
This is of importance only for the "reject", and "Pass-Reject" duplexers.

If you had a network analyzer, you would likely have the experience so you wouldn't have to ask this question.

Perhaps if you posted a picture one of us could identify the unit for you.

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