Duplexer Questions

[Vercomm]

I'm heading out to site this Thursday and will be re-tuning a Sinclair Q2220E duplexer. My question is how can I tell or check to see if the duplexer is in fact 50ohms. I'm having some suspicion that perhaps it is not. The reason leading me to believe this is that when I make the jumper from the antenna port of the duplexer to the lightning arrestor shorter is creates a high VSWR alarm on the MTR2000. When I use a longer jumper between the antenna port of the duplexer and the lightning arrestor the VSWR alarm goes away on the MTR.

The antenna is a Sinclair SRL210C4, the feed line is Andrew LDF5, and the lightning arrestor is a Polyphaser. I have swept the line with an Anritsu Site master and everything upstairs looks ok.

So I'm wondering what to check with the duplexer. I will be re-tuning the duplexer and check Insertion loss and Isolation when I'm onsite. Any other things that I should be checking for?

Thanks!!

[Edgar]

hi, this is Edgar, if the notch pass frec ok, check for humidity or loss conectors on your feed line , also feed junper within rptr an duplexer, you can trust sinclair duplexer, never runs out off tunning, check first all feed lines and connectors on duplexer, and antenna, should be dry an tight.

[Wowbagger]

First, are you sure that it is not the lightning arrester that is not 50 ohms? If it failed short, as some arresters are designed to do, then you would be putting a short on the end of a cable - in other words a tuned stub.

IF you have a spectrum analyzer and a reflectance bridge, you could sweep the duplexer with the other ends terminated to 50 ohms and see if you see a high reflectance - that would tell you if you were getting a match or not.

[Vercomm]

Hi Wowbagger,

I do not have a reflectance bridge, and other ways? I will take another lightning arrestor with me and check the one that is on site.

[Einstein]

I would also check the jumpers. Further you need to get hold of a bridge, Eagle or Wiltron are excell. If you use one of those, I have tuned cavities where the transmitter was 300 watts and I used a Bird wattmeter with a 1 watt element to check the reflected power and the needle barely moved. You can use just a spectrum analyzer with tracking generator but are not going to get the accuracy and it will show reflected power.

[xmo]

The Anritsu Site master has a built in bridge.

That unit should be able to find your problem.

[Vercomm]

Hey xmo,

I'm very, very, very new to this type of investigation on duplexers. Anybody have a MOP (method of procedure) of how to setup test equipment and some basic steps to follow. Again, I've never attempted this before and a basic plan would be great to have onsite. If I can get something before thursday I'll try it in the shop to see what happens!!

The anritsu I'm using is a SiteMaster S332D.

Thanks Again!!

Jamie

[xmo]

Your Sitemaster should show you if there is a problem with the Polyphaser.

To verify the alignment of the duplexer you will need other equipment such as a spectrum analyzer with tracking generator or a service monitor with that capability, for example, the Aeroflex 2975, or an HP8920. The General Dynamics 2600 series can also do this but you have to work a few tricks since these instruments have only a 60dB display dynamic range.

The instruction manuals that come with the service monitors show how to align duplexers.

Using a spectrum analyzer / tracking generator is covered in many manufacturer's application notes such as this one from Agilent:

http://cp.literature.agilent.com/litweb ... -1650E.pdf

Wowbagger may have links to similar app notes at Aeroflex. You can also find a lot of info on duplexers and their alignment at repeater-builder.com

[Wowbagger]

Using a spectrum analyzer / tracking generator is covered in many manufacturer's application notes such as this one from Agilent:

http://cp.literature.agilent.com/litweb ... -1650E.pdf

Wowbagger may have links to similar app notes at Aeroflex. You can also find a lot of info on duplexers and their alignment at repeater-builder.com

Last I'd checked, while Aeroflex has a couple of really useful application guides for using a service monitor for various tests, including duplexer alignment, the Marketing/Communications guys haven't put PDFs up on the site for easy download: they want you to give them your contact info for the (IIRC) free printed versions. I've told them that many people feel that giving contact information will result in being "marketed at" (as opposed to marketed to) and that they would do better to lure people to our web site with free downloads and thus get our site in people's bookmarks (and in Google's ranking system). Some of the marketing people are receptive, some are, shall we say, not.

I just design the gear: I don't price it, sell it, or advertise it.

I'll double-check when I get into work and see if this has changed.

[Vercomm]

Problem solved!! When I got onsite I checked the duplexer and found the Rx side was out of tune. Found the nuts around the tuning rods loose!!!!! The I.L. was around 12dB. So I re-tuned the duplexer and got the Rx I.L. to 1.27dB and the isolation to be greater than 95dB and things are working great.

Thanks for all the help.