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tuning a duplexer

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

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johnny1225
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tuning a duplexer

Postby johnny1225 » Wed Nov 10, 2004 8:09 am

I have a GR1225 UHF Repeater with a sinclair duplexer that needs retuning. I have a R2600 Motorola Analyzer here at the shop and would like to know:

1) how to hook up the duplxer to my r2600

2) what screen do I use i.e tracking generator or sweep gen or what

3)exactly how i tune the duplexer to frequcy. TX460.9250 RX 465.9250

can someone step by step tell me how to tune this duplexer.

It is just one of the small sinclair duplexers that you but inside a GR1225..


thanks

john

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kcbooboo
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Postby kcbooboo » Thu Nov 11, 2004 4:32 am

I'm not familiar with the repeater or the type of duplexer, but I can give you some generic instructions. Sit back, this is gonna be long !

The purpose of the duplexer is to allow the transmitter's signal to go out to the antenna and prevent it from affecting the signal coming in to the receiver. There are two common types of duplexers: notch-only, and pass/reject. (Various companies may have trade names for their particular design, but as this is a general discussion, I'll limit it to these two styles.) The notch-only style usually has one adjustment per section, and it serves to reduce or eliminate the signal that it's tuned on. Most mobile duplexers are this type. The pass/reject style usually has two adjustments per section, one that notches one frequency, and one that passes the other frequency. There are usually two or three sections per side: transmitter to antenna, and receiver to antenna. When I speak of the "transmit" side, I'm referring to the sections that are in the half that attaches to the transmitter. Most duplexers are symmetrical, i.e. they have the same number of sections per side, and the antenna port is in the center.

With a notch-only style, the sections on the receive side are tuned to eliminate the transmit frequency, and those on the transmit side are tuned to eliminate the receive frequency. For example, if your repeater is transmitting on 460.0 and receiving on 465.0, the transmit side would be tuned to notch out 465.0, and the receive side would be tuned to notch out 460.0.

The pass/reject style has notch tuning which works just like the notch-only style, but it also has additional components that attempt to only pass the desired frequency to/from the antenna. Using the same frequencies as above, the transmit side would be tuned to pass 460.0 and reject (or notch) 465.0, and the receive side would be tuned to pass 465.0 and reject (or notch) 460.0. Pass/reject duplexers usually offer better performance but also cost more and are larger. You'd usually find these in larger base station repeaters.

On either type, the notch should be 30-40 dB per section. The more notch, the better. There will also be some loss between the transmit port and the antenna port, and between the antenna port and the receive port. Typically this loss is in the 1-2 dB range. The less loss, the better.

As for tuning, you can do it with a tracking generator and spectrum analyzer, or the equivalent functions in a service monitor. Normally, you use the tracking generator as a signal source, and the spectrum analyzer as a receiver or detector. You will also need a low power dummy load, preferably one that's exactly 50 ohms.

You can do either side first, but I'll start with the transmit side. Disconnect the three cables (transmit, antenna, receive) that go to the repeater, and hook the tracking generator output to the duplexer's transmit port, the spectrum analyzer to the duplexer's antenna port, and the dummy load to the duplexer's receive port. Using the same frequencies as above, set the equipment to 460.0 MHz and adjust the pass tuning on the transmit side for maximum signal level through the duplexer. Then set the equipment to 465.0 and adjust the notch tuning on the transmit side for minimum signal level through the duplexer. These may interact, so go back and adjust them again. You're looking for 1-2 dB loss on 460.0 and at least 60 dB on 465.0 MHz.

Now swap the connections so the tracking generator feeds the receive port and move the dummy load to the transmit port. Set the equipment to 465.0 MHz and adjust the pass tuning on the receive side for maximum signal level through the duplexer. Then set the equipment to 460.0 and adjust the notch tuning on the receive side for minimum signal level through the duplexer. These may interact, so go back and adjust them again. You're looking for 1-2 dB loss on 465.0 and at least 60 dB on 460.0 MHz.

If you have more sophisticated (or additional) equipment available, you can fine-tune the adjustments and often get better performance. You can also sometimes do a fair job with just a transmitter and receiver, or a signal generator and a receiver. While I explained the tuning for a pass/reject duplexer, you can skip the "pass" tuning if you have a notch-only duplexer, as the notch/reject tuning is the same procedure in either case.

Hope this helps. There might be some info on Sinclair's web site. There's also a web site called repeaterbuilder (or something like that) that has additional information on duplexer tuning, or you can ask more questions here.

Bob M.

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Postby CTAMontrose » Thu Nov 11, 2004 6:28 am

excellent writeup bob!

thanks!

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Postby RESCUE161 » Thu Nov 11, 2004 7:15 am

Does it matter which section of each side is done first? Say you have a 6 section duplexer with 3 RX cans and 3 TX. Should you start with the ones closest to the antenna port or the TX/RX ports?

I think this should be a "sticky".
Scott
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Postby CTAMontrose » Thu Nov 11, 2004 7:20 am

RESCUE161 wrote:I think this should be a "sticky".


agreed

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Tuning Duplexers

Postby Dan562 » Thu Nov 11, 2004 2:37 pm

Hello Bob and Johnny,

That was an excellent description for Tuning Duplexers! The only thing I can add to the subject is use high grade double shielded 50 Ohm coaxial cables such as RG-400/U (stranded center conductor), RG-141/U (solid center conductor) or equivalent. The RG-400/U and the RG-141/U are identical uses Teflon dielectric except for the center conductors. The outside cable diameter is identical to RG-58/U but provide much better signal characteristics for isolation while using them to tune RF duplexers or bandpass filters.

I would suggest that you make up a set of 2 cables 3 Feet in identical length with Male BNC connectors on one end and Male N Type connectors on the opposite end. You should also have pairs of RF adaptors that provide the ability to go from Female BNC to Male N, Female BNC to Male UHF (PL259), Female BNC to Male Mini-UHF and Female N to Male BNC, Female N to Male UHF (PL259) since you never know what application you will be required to use these test cables in.

As far as the MOTOROLA Service Monitor R-2600, I believe you can call Parts I.D., get an Owners Manual number and order it from Elgin AAD Parts Dept. 1-800-422-4210 if you're allowed to access that 800 number from Toronto, Canada. Be sitting down when AAD quotes the price on the owner's manual, I expect it to be expensive in typical /\/\ style.

Dan

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Postby kcbooboo » Thu Nov 11, 2004 4:38 pm

It should NOT matter which half of the duplexer you do first. But there could be a "high" half and a "low" half. This relates to the two frequencies being used. Many commercial installations have a transmit freq that's lower than the receive freq. Amateur repeaters can go either way, so it's important to connect the higher frequency (transmitter or receiver) to the port marked "high". Not all duplexers make this distinction however.

On the Celwave base station units, which use coax jumpers between sections, I have found it easier to disconnect them all (keeping track of which jumpers go where - they ARE different lengths) and tune each section by itself. Then I reconnect them and the job is finished.

The Celwave jumpers are made from RG-214 double-braid coax. Apparently you do not need solid shielded coax, even though some leakage could get through the two layers of braid. I have made jumper cables to go from my repeater to one of these duplexers using two feet of RG-214 with crimped-on male N connectors and am getting zero desense with 80 watts out of the transmitter and 55 watts feeding the antenna.

Glad so many people enjoyed reading my small dissertation.

Bob M.

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Tuning Duplexers

Postby Dan562 » Thu Nov 11, 2004 8:56 pm

Bob,

My opinion of making up a pair 3 Foot RG-400/U or RG-142/U double shielded coaxial cables were more for test / tuning purposes than using them between the duplexers and the repeater. I know for a fact that /\/\ has used the RG-400/U for forty years even on their Motrac & Micor Series 1/4 KW stations. It was widely used every where in their RF Product Lines. GE (M/A-com) and RCA (bought out by GE) smartened up and switched to RG-214 25 years ago.

About 3-1/2 years ago I asked one of the Material's engineer why /\/\ was still using the RG-400/U instead of Heliax and it came down to one thing ... material cost .... the RG-400/U was "cheap" to purchase in large quantities. You just knew one day the RG-400/U would have to fall at the wayside and some other OEM would step in and take over for supplying a newer bio-degradable coaxial cable. The material characteristics on the newer cable uses a solid center conductor, foam dielectric, braid, foil wrap and a black PVC outer jacket with a blue stripe on the lenght of the entire coaxial cable. It's 50 Ohm and is suppose to be equivalent to RG-142/U. Of course it's less expensive than RG-400/U and it's not manufactured in the U.S.A.

The /\/\ Part # 3013943A for the RF coaxial cable but don't try to order any cable under that generic number because /\/\ SCOG has a series of cable assemblies set up in their e-inventory, based on connectors and cable lenghts, and they're not all active in their database. /\/\ owns the Patent rights on this cable. Some one discovered this new cable wasn't quite as good as the engineers had specified for handling 100 RF Watts at VHF and UHF frequencies so the Materials personnel went back to using RG-214 for XMTRs.

Here's an actual /\/\ Part # 3013943P26 BNC M - Mini-UHF M 36" Long.

I myself preferr using Super Flex Heliax and regular Heliax because it has so much better Loss and RF Power handling characteristics and last a very long time if sealed correctly from moisture on the connector ends.

Dan

rad21
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Re: tuning a duplexer

Postby rad21 » Wed Dec 22, 2010 8:26 pm

Are there any pictorals out lining step-by-step procedures using Motorolas r2670 on tuning duplexers, notch, pass/reject, window filters etc.

Thanks for all input.

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Re: tuning a duplexer

Postby Jim202 » Thu Dec 23, 2010 5:53 am

One thing that I would add that most people forget about or ignore is that the match to the duplexer needs to be kept constant all the time. What this means is that each port of the duplexer should be terminated into a 50 Ohm load. What I tell everyone is to use at least a 6 db inline termination pad. A 10 db is even better.

The down side to doing this is that you need 3 of the pads and it will require a high output from your signal generator. Leave the pads in place while your doing the tuning. Just move the cables around as needed to do the tuning.

I generally use a portable radio that can receive on the notch frequencies. This way you can use your ear when tuning the cavity notches. Works much better than straining a spectrum analyzer straining to see a real low level signal.

Jim

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Bill_G
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Re: tuning a duplexer

Postby Bill_G » Thu Dec 23, 2010 6:10 am

Jim202 wrote:I generally use a portable radio that can receive on the notch frequencies. This way you can use your ear when tuning the cavity notches. Works much better than straining a spectrum analyzer straining to see a real low level signal.


The earball is the best tool for getting rid of fried eggs if your sweep gen can't get low enough.

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Re: tuning a duplexer

Postby drepre » Thu Dec 23, 2010 6:42 am


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FMROB
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Re: tuning a duplexer

Postby FMROB » Fri Dec 24, 2010 7:01 am

Stupid question here.

Regarding a 450-470 RFS 526 duplexer. I have tuned them up into the 477/480 area without noticing any "loss" in the spec an, via ear, and live testing.

So I ask, the cables on the duplexer are factory cut for 450-470, what difference does the cable actual make when tuning these things up into the high T-Band and not changing the cables out for the "proper" factory length. We see that our 526's running in the t-band are pretty hot and work well.

- Rob

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Bill_G
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Re: tuning a duplexer

Postby Bill_G » Fri Dec 24, 2010 8:12 am

If it ain't broke, don't fix it. (grin)

The cables you're talking about are between the cavity stages in the duplexer I assume. They are meant for impedance matching, and do affect the bottom of the rejection curve to a degree. But, if they work, don't try to improve on them.

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Re: tuning a duplexer

Postby FMROB » Sat Dec 25, 2010 9:49 am

Bill,

Thats what I kinda thought. We ordered a brand new, factory tuned 470-490 MHz 526 duplexer. We hooked it up to our service monitor and noted all of our test settings. We then took hi res pictures of each screen, each cavity, and cumulative.

We then took one of our abundant 450-470 526 and tuned it up to spec, using the same settings that we shot the original facotry duplexer at. We again took hi-res picutres.

After doing side by side comparisons of the pictures we noted nothing different, at all. And you are correct, I was reffering to the cavity interconnects (rg-142) cables.

Am I missing something, or is there a possibilty that we are getting false positives. Everyone talks about the critical nature of those cables, but we didn't see it??

Merry X Mas all, any thoughts on this.

sdranaweera
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Re: tuning a duplexer

Postby sdranaweera » Tue Feb 08, 2011 10:56 pm

Dear friends,
I have try to tune my duplexer CELWAVE HFD8190A.. When I tune my Tx with Max out put it only half of out put.. but I can increase it by adjusting Rx cavity . but by the time RX sensitivity goes very low(more than 0.9uv..) then to improve I have to adjust any side TX or Rx which problem to the other side ... so can any one explain me..this and way to improve
Thanks
Rana

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Re: tuning a duplexer

Postby emtprt » Wed Feb 09, 2011 6:24 am

I am far from a radio tech. but your output will be reduced when using a duplexer. I have 3 40 watt r1225 repeaters and the transmit power set at 40 watts with swr less then 1 they put out 25-28 watts using a dulpexer. The duplexers are rated at 50 watts and you can often increase the power on your transmitter beyond the documented power rating of 40 watts. I did increase the power on the transmitter and had the r1225 (pre-duplexer) set to an output of 50watts. The power incrrease left me with 35 watts out post duplexer and the receiver clipping out. I returned the power to 40 watts out pre duplexer.

You will never get the actual power rating of the transmitter post duplexer.
I have learned many things through the members on this site and one simple thing to remeber is- if you are concerned about coverage a good antenna system is key.

1 of the 3 sites, the repeater is putting out 25 watts, 100+ cable run (hardline andrew 5/8") and the current antenna I have an ERP of 60 watts,
Another site, which is in need of an antenna upgrade, has an identical radio and cable run but a low gain antenna has an ERP of 22 watts.

sdranaweera
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Re: tuning a duplexer

Postby sdranaweera » Thu Feb 10, 2011 10:56 pm

Thanks
Yes same experience even I have .... But once we can improve by tunning ..we must learn the real procedure to tune it thats why i am asking help from you all thanks your help .. we can learn many things from this web
please give others view..


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