Duplexer tune

Tuning a Motorola T1500 Duplexer with an IFR FM/AM 1200S Service Monitor
Note: Subsequent to publishing this video, I discovered the cabling is wrong, and the Antenna "T" connector is installed incorrectly. The process of aligning the duplexer remains the same, but please don't use the cabling on this T1500 as a model for your own configuration. It was wrong.

[@zapityzapzap]

I’ve often found it makes things a lot easier to separate the cavities for the initial tuning when possible.

[@BryanTorok]

I was wondering about that. I was thinking that it might make it easier to get the broad double peaks together on one frequency.

[@bigpimp347]

@@BryanTorok That's what you're meant to do, do each filter first get them peaked then put together and fine tune again.

[@BryanTorok]

@@bigpimp347 Thanks.

[@TheRadioShop]

Michael that was a great explanation. Very well presented. Thanks for taking the time to do this. I believe I can use this to test mine out. Got to see if I can round up a uhf duplexer to try it on. Yes I have the homemade set but a commercial set will confirm I am doing it right. Thanks again my friend. 73. I am sure I will have more questions later So may shoot you an email. Buddy.

[@kd2eat]

Thanks, Buddy. I'm glad I could give something back for you to look at. I've spent hours and hours learning from your videos. You da man! ;-) Please note, I'm no expert on duplexers. This is my first rodeo tuning one. I just noticed that the curves looked MUCH different from your home made duplexer test, so I wanted you to see what a commercial one looks like on the IFR. Enjoy and keep those great videos coming! Thanks & 73 - Mike

[@TheRadioShop]

Thank you Michael. I now have the idea on how to start it. For the past hour I have been playing with my homemade duplexer. I do not have enough "Q" to notch the frequencies. So I need to trim my pick up inside the duplexer.. I can get a good define notch on each side but the isolation is terrible. I know what I have to do to make them better now. Thanks to your video got me on the right track. Going to see if I can locate a uhf duplexer commercial built to play with. Buddy

[@tonyf1253]

Michael, I have struggled with cable lengths when tuning duplexers. After tuning a duplexer, if I change the two cables with different lengths, the IFR shows the tuning at different frequencies than first tuned. What is the correct cable lengths used to tune a cavity/duplexer. 300/f x VF x 1/2 wave length?

[@lesliehill8229]

Who was your favorite chipmunk?

[@ralphmowery2898]

Nice video, There are a couple of things you should do to tune it better. Set the tracking generator to HIGH when checking the notch frequency. At that it will put out about - 3 db instead of -40 you are using . The duplexer will have over 80 db,more like 100 db of notch. You will not see that unless you go to the high output. You may only be getting 70 db of notch instead of 100 or more. Always use double shielded cables or better at those levels of signal. To tune the pass frequencies using a return loss bridge would be best, but if you do not have one you are fine with that part of the video.

[@ralphpercy4846]

You near Seattle? I need help with mine

[@9783moerox]

Thanks Michael. I learned a lot until the part where you "diddled the knobs" then I spent 10 minutes rolling on the floor laughing and lost track of what we were doing. Otherwise very informative!

[@kd2eat]

I do my best to provide information in an entertaining way. ;-p

[@lesliehill8229]

I swear i think a guy named Alvin had a part in this video

[@jbx907]

the Motorola duplexer is not the best, its producing effects on the opposite set of filters lol

[@kd5ozy]

practice

[@bigpimp347]

you shouldn't have two peaks, you should be able to get both cavity peaks to become one, when they become one you have an even better peak. maybe try the coax lengths in between cavities and something was still wrong.