Uncover the Secret Behind Ham Radio Duplexers

Today I show what a duplexer does on a repeater, how they are tuned and how you can eliminate interference with other types of filters.
Learn more about repeaters 👉 • Ham Radio Repeaters
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⏱️Chapters⏱️
0:00 What is a duplexer/cavity filter
1:46 Vari-Notch filters
2:33 Bandpass filters
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[@HamRadioDX]

Learn more about repeaters 👉 kzbin.info/aero/PLSuX83ay4Oug4QxmLe8MLyXjEqFd1Qr8-

[@KD9VUK-]

Fascinating looking at other setups around the world, i work with these every day for work. It’s not all the time you get to see other peoples work. Thanks for the video!

[@HamRadioDX]

Thanks Aidan! I enjoy doing it (although I don't do it for work)

[@spikeywayent]

Love it when you post repeater information. I am fairly new to the hobby and my ultimate goal is to be be able to learn on how to work on repeaters. When you post these videos explaining this stuff just gets me so much more interested. My local club repeater trustee has been super exited to show me around as well, like to see other setups and maybe some day be the go to repeater guy because I just love them as well.

[@HamRadioDX]

That's awesome to hear! I gradually taught myself with help from mentors and others too. A great resource is also the repeater builder website - www.repeater-builder.com/rbtip/index.html

[@VK7DBX]

Excellent information

[@depluribusunum3128]

I used to tune duplexers. I have found you can tune the plunger a little after you have set the reject capacitor to get better rejection without sacrificing pass characteristics.

[@Ben_3113]

Great video, I learnt something here. Thanks

[@Capitaine.Albator]

Cool short video! Thanks 👍🏻✌🏻🇨🇦

[@captainwyattoutdoors1636]

very informative!

[@TheSmokinApe]

Very informative 👏

[@HamRadioDX]

Glad you liked it Ape

[@ingussilins6330]

Cavity resonator "power bank" :)

[@aussiedazvk4djh889]

It's lots of fun. 👍

[@yetiradiovk4yt]

Great video. I am fascinated with repeater systems. Am yet to have a lot to do with them as they’ve all been working well and No need to touch them.

[@HamRadioDX]

I wish mine always worked so I didn’t have to touch them 😂

[@DonzLockz]

Cool, I've always wondered how signals from other equipment gets sorted out in rf. :)

[@moozoowizard]

Are these set and forget or do they need regular adjustment? Given no changes to the local rf environment.

[@HamRadioDX]

Set and forget provided they don't get bumped or knocked about during transport. I usually set them up on the bench and then test again on site. I've had one set of older Motorola cavities that shifted over a bumpy 4WD track to the repeater site.

[@LeeMcc_KI5YPR]

Hayden, do you have a video with lightning protection devices?

[@HamRadioDX]

No I don't. We don't have a lot of lightning here. I do have some surge protectors in a box somewhere.

[@AECRADIO1]

Gas discharge 'tubes' can cause their own headaches, and I found in 40 years, they are more trouble than worth, if proper grounding and bonding is tightly adhered to. Folded dipoles are 'quieter' than colinear and corporate feed antennas by their design. Look at large commercial antennas, the metal cap is directly connected to the internal ground path, with the elements attached at the low impedance point, which allows lightning/electrical discharges to route directly to ground, and if ground straps are installed in the shield of the cables, along the length down a tower leg, that greatly increases the losses of the impulse to be shunted to ground, and not into the equipment. I work on sites that are at 5,000 + feet in elevation, often above 8,000 feet above average terrain, also with heavy snow loads, so you do your best to ensure you do NOT have to make your way back up and fight the cold and deep snow just to repair a minor failure.

[@LeeMcc_KI5YPR]

I was thinking specifically for a repeater, not at the shack. Shack bonding and grounding...there are MANY videos.

[@rohnkd4hct260]

Hey, project like that keeps you out of trouble 😝

[@HamRadioDX]

Always out of trouble.

[@vk6uu]

Repeaters are very difficult to get to work well. Many repeaters suffer from desensing that often is not recognised. Also split antenna repeaters in combination with notch and or pass cavity filters are much easier to get to work if there is the vertical antenna height available. Amateurs often want a high gain single antenna combined with a duplexer. If it works then this is the way to go but often a split antenna using just 2 dipoles will produce better results, simply because it is much easier to achieve zero desensing. BTW it is possible to measure desensing remote from the site provided the signal from the testing site to the repeater is fairly strong. Another way is when keying the repeater if the tail varies in length when you let the PTT go then the repeater is likely to have desensing. Will VK6UU

[@HamRadioDX]

Great tips Will!

[@chrisbjohannsen]

Those cans are so large, I don't know much about repeaters but I am intrigued.

[@HamRadioDX]

These are smallish ones for 2m… wait till you see 6m cavities. I’ve even seen photos of 10m cavities - over 7-8 feet tall!

[@KD9VUK-]

Wait till you see a P25 Combiner/Duplexer combo….. about the size of a large fridge

[@hfvhf987]

Glutton for punishment? haha

[@mhammer5]

I have duplexers for 220Mhz, 440Mhz and 900Mhz.

[@HamRadioDX]

Nice!

[@crazyham]

Awesome ⚡🙏⚡ Thanks for the interesting Video 👌👌👌

[@AECRADIO1]

BANDPASS, BAND REJECT, PASS, REJECT, NOTCH...DIFFERENT CAVITIES FOR DIFFERENT REQUIREMENTS. NOT UNUSUAL TO HAVE MORE THAN TWO CAVITIES FOR OTHER SERVICES TO BE PART OF THE MAIN REPEATER, TO NOTCH OUT SUM AND DIFFERENCE FREQUENCIES, AS WELL AS NEARBY HIGH LEVEL SIGNALS FAR OUTSIDE THE PASSBAND OF THE INTENDED INSTALLATION. NOTCH CAVITIES ARE GREAT FOR THIS PURPOSE.