How to tune a Duplexer

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How to tune a Duplexer

Postby emsbuff3240 » Sun Oct 01, 2006 6:28 am

Anyone know how looking to buy one off ebay and i need to tune it so is there anyone out there that can help me out?
Thanks
-Jon
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Postby xmo » Sun Oct 01, 2006 6:51 am

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Postby 440roadrunner » Sun Oct 01, 2006 11:50 am

Since you don't know how to tune "one" you may not know what to look for, either. There are many many kinds of duplexers, some not suitable for the amateur 2 meter band, for example, with narrow frequency split. The typical notch duplexer, for example, only works at 5 mhz or so and wider split


Also, these cheaper "notch" duplexers do not offer any kind of rejection when used on a commercial site where there are several transmitters.

You might tell us more about your project. What freq is it going to be on, what is the offset, the power level, and where is it to be located?

A duplexer, and how it is tuned, is often THE most important part of a repeater installation.
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Postby emsbuff3240 » Sun Oct 01, 2006 1:32 pm

Ok, I need to put 2 m1225 mobiles on a 70' ground plane antenna, the antenna is going to be mounted to the side of my house, the repeater is going to be putting out 40 watts max. The repeater is going to be located in an upstairs room of my house with approximately 50 feet of cable from the duplexer to the antenna, the radios right next to the duplexer. This repeater is also going to be packed up and taken somewhere with a mobile antenna. So the duplexer would have to be a 50watt mobile one.
I found one on ebay I might buy, im not sure if he will tune it though. If anyone on here has one I have a WTB ad up.

The freq. pairs are GMRS 462/467

If someone on here could tune it and is on Long Island, shoot me a PM.
-Jon
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Postby wa2zdy » Wed Oct 04, 2006 11:31 am

Not to sound snippy, but if you have to ask here how to do it, you have niether the equipment nor experience to do it correctly.

Your call for help is the best action you could have taken.
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Postby Bruce1807 » Wed Oct 04, 2006 12:07 pm

Tend to agree as tuning can be a pain and if you dont have the required gear forget about it as all youll end up needing is new finals and/or a receiver front end.
Most good shops should be able to do it
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Postby kb0nly » Wed Oct 04, 2006 4:04 pm

Depends on the type, if its a pass band type only then its a cinch with basic gear. If its a passband / pass reject then it gets a bit trickier to get the reject notches correctly adjusted.

I've done the pass band four can duplexers, T1500 series, with nothing more than a HT with an adjustable power output and a wattmeter and dummy load.
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Postby Bruce1807 » Wed Oct 04, 2006 4:15 pm

I tend to prefer my HP 8720 but then thats me. I like them purrrrrrrrrrrfect
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Postby kb0nly » Thu Oct 05, 2006 6:54 am

If i could afford the test equipment i could do them perfect also, unfortunately i have to make do with the knowledge but no proper equipment.
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Postby N9LLO » Thu Oct 05, 2006 8:02 am

kb0nly wrote:If i could afford the test equipment i could do them perfect also, unfortunately i have to make do with the knowledge but no proper equipment.


I have done many duplexers over the years many ways. If you understand what you are doing you can get satisfactory results using even the most hokey setup. A few DB either way will make absolutly no difference in real world performance.

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Postby Bruce1807 » Thu Oct 05, 2006 9:56 am

N9LLO wrote: A few DB either way will make absolutly no difference in real world performance.

Chris
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Your not serious are you?
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Postby N9LLO » Thu Oct 05, 2006 11:19 am

Yes, quite serious. Tell me how you are going to tell a couple of DB difference in a repeater operation either on TX power or RX sensivity, It aint gonna happen without equipment to measure it. I am NOT talking about desense, just losses through the duplexer. I will only tolerate 1db or less of desense You CAN detect a couple DB desense with a very weak signal.

I work at a very large electronics manufacturing firm and have access to any type of test equipment imaginable. I have tuned duplexers every way you can think of. In the real world a couple of DB either way will have no noticable effect on repeater operation. We all know that a 3 DB (2X)increase in power will be barely noticable at the recieving end. That basic knowledge serves to validate my opinion.

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Postby emsbuff3240 » Thu Oct 05, 2006 11:25 am

Thanks everyone. I have found a duplexer that was tuned to the 462/467 pair I needed.
-Jon
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Postby Bruce1807 » Thu Oct 05, 2006 11:48 am

Except that 3dB gives about 20% more coverage.
In a PS application that can mean the difference between garbled and clear in a fringe area
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Postby n5tbu » Thu Oct 05, 2006 11:59 am

Well....you can't repeat what you can't hear,and ANY desence is not tolerated,on any system I maintain.
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Postby N9LLO » Thu Oct 05, 2006 2:00 pm

Bruce1807 wrote:Except that 3dB gives about 20% more coverage.
In a PS application that can mean the difference between garbled and clear in a fringe area


Pure salesman type bull. This cannot be validated by any engineering study or real world preformance. Sorry to raise the BS flag but I have
had a hand in at least 75-80 repeaters and "that aint happining in the real world" Atmosheric noise at VHF lo and even VHF hi can be an order of magnitude greater than any duplexer loss.

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Postby emsbuff3240 » Thu Oct 05, 2006 2:41 pm

Ok now I have a duplexer on 462.700/467.700. If I transmit on 462.550 and RX on 467.550, will there be alot of signal/power losss? Or will the difference not be noticeable?
-Jon
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Postby Bruce1807 » Thu Oct 05, 2006 5:11 pm

N9LLO wrote:
Pure salesman type bull. This cannot be validated by any engineering study or real world preformance. Sorry to raise the BS flag but I have
had a hand in at least 75-80 repeaters and "that aint happining in the real world" Atmosheric noise at VHF lo and even VHF hi can be an order of magnitude greater than any duplexer loss.

Chris
N9LLO


Damm I must of wasted my money buying 6dB antennas, Thanks for the advice next time I'll buy 3dB as coverage will be just the same. I can save our Public Safety System a fortune every three years when I replace 30 odd antennas.
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Postby wa2zdy » Fri Oct 06, 2006 4:34 am

emsbuff3240 wrote:Ok now I have a duplexer on 462.700/467.700. If I transmit on 462.550 and RX on 467.550, will there be alot of signal/power losss? Or will the difference not be noticeable?


Get it tuned for your frequency pair or you're gonna have a very poor repeater, then no receiver when the front end gets fried, then no finals in the transmitter when they go.

The finals will be the last thing to fail as they're tougher than the RF amp in the receiver. I'd expect THAT to last a few milliseconds.
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Postby mastr » Fri Oct 06, 2006 10:59 am

Bruce1807 wrote ..."I must of wasted my money buying 6dB antennas, Thanks for the advice next time I'll buy 3dB as coverage will be just the same. I can save our Public Safety System a fortune every three years when I replace 30 odd antennas."


Depending on the terrain, your coverage may improve with 3 db antennas. (I'm guessing you are referring to mobiles as a good station antenna should last much longer than 3 years) "My" system has about 1200 mobiles, we deploy both 3 and 6 db antennas, and find the 3 db model performs better in areas where elevation varies widely.

If you have a public safety system that cannot stand an additional 3 db of path loss, you don't have nearly enough infrastructure.
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Postby emsbuff3240 » Fri Oct 06, 2006 1:07 pm

[quote="wa2zdy"]Get it tuned for your frequency pair or you're gonna have a very poor repeater, then no receiver when the front end gets fried, then no finals in the transmitter when they go.

The finals will be the last thing to fail as they're tougher than the RF amp in the receiver. I'd expect THAT to last a few milliseconds.[/quote

So if I use the radios on a frequency that is 1mhz different, it will fry the radios?

ugh anyone on here that can tune a duplexer?
-Jon
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Postby N9LLO » Fri Oct 06, 2006 1:52 pm

emsbuff3240 wrote:Ok now I have a duplexer on 462.700/467.700. If I transmit on 462.550 and RX on 467.550, will there be alot of signal/power losss? Or will the difference not be noticeable?


You need to get it tuned. If you cant do it I'm sure there is someone on the list that can, probably closer to you than I am in Indiana. I will do it if you dont get any better offers, what do do you have for connecting cables? You may well need to take the whole thing to someone who can get it hooked up and tuned to operate with negligible desense and loss.


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Postby n5tbu » Fri Oct 06, 2006 1:58 pm

"So if I use the radios on a frequency that is 1mhz different, it will fry the radios? "

Yes! A duplexer is tuned to keep the transmitters power from reaching the reciever,it is a very narrow window at the tuned freqs.and 1 Mhz away is too far.
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Postby wa2zdy » Fri Oct 06, 2006 5:12 pm

emsbuff3240 wrote:So if I use the radios on a frequency that is 1mhz different, it will fry the radios?


As N5TBU said, the duplexer is much narrower than that.

In a non duplexer situation, just a base or mobile radio and antenna, 1 MHz would not matter. But with a duplexer, the 150 KHz difference you describe is too much.
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Postby 440roadrunner » Sat Oct 07, 2006 10:03 am

With respect, sounds to me like you need to do some more (a lot more) research and self education before you attempt this project.

http://www.repeater-builder.com/


http://www.k7pp.com/articlesbyk7pp.html


http://www.ak2o.org/srg/index.html (select the "technical page")


http://eagle-1st.com/notes/duplex/body.htm


There used to be some excellant articles by some outfit called "seits" or "siets" but I can no longer find it


This appears to be part of the site in pdf:


http://www.utm.edu/staff/leeb/duplexer. ... uplexer%22


Here's the thing. There's a lot more to repeaters than buying a couple of junk mobiles, haywiring them together, and throwing up an antenna.

There is interferance to other services, TX spectral purity, overdeviation, poor audio quality, CTCSS or other tone protection from interferance from others, proper ID'er operation, shutdown protection from jamming or other interferance.

You need a good antenna, and good quality feedline. The feedline alone can add to desense and other problems, because if it is radiating power right from the (poorly shielded) coax, that right there can cause desense and other RF feedback problems.

While very important, the duplexer is actually just one part of the overall problem, but it alone can account for gigantic headaces, including poor SWR, erratic performance because of internal corrosion, poor isolation and so on. It obviously can lead to the destruction of receiver front end components.

Not too many years ago, before Al Gore invented the internet, repeaters were pretty much left to full time professionals, and for good reason.
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Postby Bruce1807 » Sat Oct 07, 2006 10:46 am

mastr wrote:Depending on the terrain, your coverage may improve with 3 db antennas. (I'm guessing you are referring to mobiles as a good station antenna should last much longer than 3 years) "My" system has about 1200 mobiles, we deploy both 3 and 6 db antennas, and find the 3 db model performs better in areas where elevation varies widely.

If you have a public safety system that cannot stand an additional 3 db of path loss, you don't have nearly enough infrastructure.


I live in a flat enviroment (20ft difference in terrain from one cornert o the next) so gain is great, Actually I use 9dB TX/RX antennas, used to use penertrators but nodes were a bit brutal.
High salt enviroment, High Sun enviroment, High Wind enviroment and High lightning strikes (I have strike counters to prove it on every tower).

Tower painting every two years, Inspection and touch up every six months, Antenna replacement every three years, Cable replacement every 6 years. Just replaced every single nut and bolt in a 300 ft tower that was 10 years old.

With our infrastructure any site can fail and we will still have coverage. as every site overlaps and those at the edges have coverage from the next site.
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Postby mastr » Mon Oct 09, 2006 4:03 pm

Sounds like you have a good case for high gain antennas. What kind of shape are those antennas in after 3 years? I took down a DB420 last year that was easily 20 years old, it looked as if it was put up last year except for sun fading on the label- we are 400 miles from the nearest salt water.
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Postby Bruce1807 » Thu Oct 12, 2006 6:38 am

TX/RX antennas are normally dark green, after 3 years they are a very pale green, If we have had a heavy season of winds there are sometimes stress fractures in the fiberglass.
In some cases the salt and sand in the wind has worn the gelcote off the antenna and the actual glass matting is exposed although this really only occurs with some cheaper antennas like the local ham club 2m antenna which is a stationmaster II. We also use a variaty of DB VHF antennas and these also get a beating from the enviroment.
We also have a lot of lightning which can be seen on the ground spikes at the top of the antennas as well as the black connectors when you pull off the waterproofing.
Every 3 to 6 months (depending on what conditions have been) I put a Bird site analyser on all antennas to check them against the original graphs for degridation.
It is easy to lose an element and a standard what meter wont pick it up.
The first thing we hear is poor coverage at one side of the tower.
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Postby kj7xe » Thu Oct 12, 2006 12:31 pm

Bruce1807 wrote:In some cases the salt and sand in the wind has worn the gelcote off the antenna and the actual glass matting is exposed although this really only occurs with some cheaper antennas like the local ham club 2m antenna which is a stationmaster II. We also use a variaty of DB VHF antennas and these also get a beating from the enviroment.
We also have a lot of lightning which can be seen on the ground spikes at the top of the antennas as well as the black connectors when you pull off the waterproofing.


Speaking of stationmaster - the pic below is one of our higher altitude sites (about 8300ft) during the winter, notice the solar panels and antenna on a monopole, and the panels covered with snow/ice. The antenna is a PD220 super stationmaster that has lasted up there for about 10 years.

Image

It has since been replaced, so instead of continuing the high risk of a lightning strike or antenna-breaking ice & winds, we're going to give the Bluewave Summit antenna a try. Better lightning protection by using an exposed dipole configuration with lightning rod on the top, quite a bit more support for ice loading, and no more problems that come with fiberglass antennas. Also far beefier material and physical support than any of the Sinclair or RFS antenna I've seen. The only antenna i've seen that compares is the Comprod Avalanche series, which I think is the strongest you can get.

http://www.bluewaveantenna.com/products/pdf/BSE139FQ0.pdf

http://www.comprodcom.com/english/products/base/index.php
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Postby emsbuff3240 » Thu Oct 12, 2006 2:16 pm

Could this be anymore off topic? You guys went to my question about a duplexer, to a topic about antenna gain.
-Jon
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Postby n5tbu » Thu Oct 12, 2006 4:01 pm

Casey,keep in mind ,some of us are real technicical by nature,and any chance to talk about something we believe in,is gonna sway a little.
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Postby mastr » Thu Oct 12, 2006 4:06 pm

We had the duplexer issue pretty well covered anyway.
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Postby Bruce1807 » Thu Oct 12, 2006 5:06 pm

emsbuff3240 wrote:Could this be anymore off topic? You guys went to my question about a duplexer, to a topic about antenna gain.


Is that what the question was?

By now you should know its not just about the duplexer but the entire system and that enviromental conditions have a big influence on system design and maintenance.
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Postby 440roadrunner » Thu Oct 12, 2006 7:25 pm

Well for starters, I don't see where you ever did post the model of the duplexer you bought........
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