#48 UHF homebrew duplexer cavity build and testing

[@Kori114]

Now this the ham radio I got into the hobby for! Awesome project, thanks for sharing!

[@TheRadioShop]

Glad you like it!

[@brianshanahan3878]

I always wondered what was inside duplexer cans! Thank you sir!

[@TheRadioShop]

You are welcome.

[@acestudioscouk-Ace-G0ACE]

Fascinating! I'm going to check your other videos to see how the story ends.

[@VK6DXA]

I never thought this could be so simple to construct. Thank you for sharing.

[@TheRadioShop]

Simple, yep. But it is very doable, thanks for watching.

[@rollerbald]

Good information Buddy - thanks for posting. That's the first time I ever saw a real practical demonstration of how duplexers work - I love working on ham radio equipment. Got an Icom 45A I picked up cheap at a recent hamfest that I am trying to bring back to life! 73, Bill.

[@TheRadioShop]

+rollerbald Thank you Bill. Well glad I could share that bit of first time information to you. I also just uploaded part two of this video. Good luck on the 45A, I know you can do it.

[@RevGunn-jq3cq]

This is one of the best videos I have seen on the subject! Thanks

[@TheRadioShop]

Thank you

[@jeffbornes3986]

Simply Amazing. Thanks

[@TheRadioShop]

Thank you too!

[@ffp1974]

thanks for this video. You explained and showed how a repeater worked.

[@TheRadioShop]

Thank you very much. Glad it helped.

[@blpblp-tj7ux]

Excellent video..thank you.

[@TRXLab]

Great project Buddy. Like to see how it is working on the air... Thumps up. Take care 73

[@TheRadioShop]

+TRXBench Yes, will be interesting how this unit performs. Still doing a bit of testing here and drinking lots of coffee!. Thanks my friend 73

[@KK4CNM]

I'm in need of a duplexer for the 33cm band. They are few and far between and expensive! Any advice on building a DIY version?

[@TheRadioShop]

Building a efficient duplexer for 900 mhz would be next to impossible, They are so sensitive, However there are a lot of 800 mhz stuff on the market. I have several 800 mhz duplexers. I will experiment on one soon as I get a chance. Click on show more tab and shoot me an email, I will let you know.

[@MrCarlsonsLab]

LOL, Definitely heavily caffeinated. Great Job Buddy!

[@TheRadioShop]

+Mr Carlson's Lab Thanks Paul. I am also. Was up 24 hours working on this design. Drank plenty of coffee :)

[@AECRADIO1]

You can also 'roll' the tubing 'fingers' for more contact area without distorting the brass, and making an unstable contact.

[@TheRadioShop]

Good point

[@earlyadapter643]

I like the appropriate cans and actually it should read "Maxwell inside"

[@supyrow]

That is allot of work you put into that! definitely a fun project! 73!

[@TheRadioShop]

+su pyrow Thanks Bobby. Yes lots of hours already spent just for this little bit of video. many more to come lol.

[@m00nst0mp]

great video! thanks for sharing!

[@TheRadioShop]

Thanks for watching!

[@mikeredler4111]

This. Is. Amazing! Well done!

[@PowderMill]

Great video…. While it’s not going to be a real practical thing to construct for every repeater, it sure is cool! Thank you.

[@lylewatts6370]

Another great video Buddy, We have a problem with our 440 duplexer with the new DR-2X repeater. A couple attempts at tuning with crude tools has made it a little better. But it's a project that is not top priority as we have 4 repeaters and none have much usage.

[@TheRadioShop]

Thanks Lyle. I have done it with a handheld before but it is a bit touchy. Thanks for watching.

[@someguyinsantaclara]

You mentioned stability and silver coating. Are there any other materials you would recommend that would be slightly more stable?

[@TheRadioShop]

Only thing better would be gold.....

[@jaybats7865]

Such an interesting project I love it 👍

[@597388]

on a humorous note if you use a de caffinaited coffee can, will the signals be attenuated ? lol. btw great video thank you

[@PapasDino]

Great job Buddy! Homebrew duplexers are just cool. Look forward to the final system integration. 73 - Dino KL0S

[@TheRadioShop]

+Dino Papas Thanks Dino. Another whole day spent on this and a little redesign. But I did record the redesign. So maybe post it up tomorrow. Take care my friend and thanks for stopping in.

[@g1fsh]

Wow Buddy that is a great video full of useful information and it was very well presented. Really looking forward to more repeater building videos. Thanks mate

[@TheRadioShop]

+Gary g1fsh Thanks Gary. I will say this video was very fun to do. Tried to squeeze in as much information as I could but was getting way to long. Will cover more in the next segment. Glad you liked it my friend.

[@joekirklin]

I started watching thinking these are pass-band cavities, but finished thinking they must be notch filters. Can you explain?

[@TheRadioShop]

You are actually correct on both. A repeter systems use different frequencies for transmit and receive, the duplzer allows you to use on antenna. Each radio will have a pass and notch filter then it couples to one antenna for both transmit and recieve.

[@dennisqwertyuiop]

Great project, instead of tin foil , I have the aluminum tape used for hvac ducks its heaver and very sticky just run a few strips on lid,, Cant wait to see more Thank you

[@TheRadioShop]

+DENNIS N Thanks Dennis. yes the aluminum tape would work also. But I do see a problem using any type of aluminum foil or tape. Over time the seal is going to corrode since aluminum and steel will interact and cause corrosion to form. Not sure how long this will take but should be ok for a while. Probably the best method is to solder a thin steel sheet to the bottom once the unit is perfected. Just random thinking. Guess we do not see that so much since the trunk system under most houses are galvanized? Anyway glad you liked the video my friend. More to come....

[@dennisqwertyuiop]

yes just save the bottom you cut out with can opener and solder it back,, good idea

[@TheRadioShop]

+DENNIS N Now that's a thought! The big vegetable cans from a café would come that way. About the right size too.

[@Sm0keDr]

You can use double sided PC board and solder them to the can in place of the lids or as the other chap indicated save the cut out and solder it back.

[@pierrelataillade7564]

Excellent video buddy...... Thank you.

[@TheRadioShop]

Thank you

[@PelDaddy]

I thought the brass pieces were shell casings to begin with! Thanks for sharing.

[@TheRadioShop]

lol, someone else thought that. Now if you can find some large shell casing, makes for nice cavities.

[@mackwood2164]

Thank you for this knowledge.

[@TheRadioShop]

Thank you for watching.

[@PaulBaur]

Thanks for sharing this, I really enjoyed it! Great information. 73's de KC9O

[@TheRadioShop]

Thanks for watching

[@k7ilo_Las_Vegas]

Years later but question. What is the best way to solder the brass to the aluminum. You did not show what your process was... Thanks

[@kiloinvegas]

Anybody????

[@mikesradiorepair]

Looking good Buddy. Still need another can? Sounds like somebody needs to get busy drinking some coffee. :) Wish I had known last week you would be needing the BNC T. Could have dropped a handfull in the mail for you. If you do get a SA with tracking generator you'll wonder how you ever lived without one. I opted for the option and love it. Great for things like this, tuning low pass filters and checking crystal and ceramic filters. Mike

[@TheRadioShop]

+MikesRadioRepair Yeah, drinking a pot full this morning. Keeps me going lol. Getting ready to cancel the order I made on the tee's. They are out of stock so have to search elsewhere. As far as SA I really like to get the Rigol DSA815-TG, but 1400 bucks will be a while. Also like the get a Rigol DSG815 signal generator so I would have more modern equipment. Well maybe one day. Would be a nice addition to the shop. Guess I can search a used piece but even that is sort of high. Surly not making a killing here in the shop lol. Thanks for the comment Mike, always look forward to them.

[@mikesradiorepair]

+The Radio Shop How many T's do you need? I have a bunch of them. They are the good silver plated ones. Not the cheap junk ones from China. Mike

[@TheRadioShop]

+MikesRadioRepair Hi Mike. I am in need of 5. They all need to be of the same type/make so they do not cause problems at UHF.

[@mikesradiorepair]

+The Radio Shop Hmm, don't have 5 exactly the same in silver plated. Do have exact match in normal plated versions made by MXT if that works for you.

[@TheRadioShop]

+MikesRadioRepair Cool, anything works. can be 2 of one kind, 2 of another kind, then a single. Other words the 2 on receiver side needs to match, the 2 of transmit side need to match, then the antenna tee can be either. This way there is no impedance bump.

[@IamDerick]

Pretty cool project. I really enjoy this one. :)

[@TheRadioShop]

Very simple to do. All it takes is a little will. Thanks

[@jaybats7865]

So to adjust the transmit frequency you slide the rod and to adjust the receive frequency you turn the nut. Is that correct?

[@kinggreene]

you can use the swivel type pipe cutter to swage the brass pipe down to size just go slow

[@ryan_niemi]

The filter isolation and insertion loss would be much better if the resonator rod were the right diameter. The resonator outside diameter should be 3.6x smaller than the inside diameter of the cavity for a 50 ohm impedance. A cavity filter is, effectively, a 1/4 wave coax stub with one end shorted and the other end open-circuit. If the resonator is not the right diameter in relation to the cavity to match the system's impedance, insertion loss increases and isolation worsens and the cavity filter performs poorly. Also, about paint cans being too long, it doesn't matter if the cavity is longer than necessary. The cavity can be any length as long as it isn't so short it touches the end of the resonator rod. Only the length of the resonator rod (and to a much smaller degree, capacitance from the cavity to the resonator rod) matters.

[@BitsBlitzPH]

Could you please for the sake of two meter fans make a vid of the 2 meter duplexer. Great video and Thank you very much

[@TheRadioShop]

I would really like to do that. However, I do not have a 2 meter duplexer or the materials needed to build one. Would be fun to do one.

[@BitsBlitzPH]

:( i really wanna build one but couldn't find any steps as clearly as what you have showed here. having a hard time to follow your source's instructions.

[@chrisdowland]

rex pogi larger can longer rods

[@kb5zcs]

Would these duplexers work for a D-star UHF repeater,BTW great video.......

[@TheRadioShop]

No reason why they should not.

[@AECRADIO1]

Tubing pieces should be matched better for a tighter joint, otherwise the tuning can change easily by simply touching them.

[@TheRadioShop]

That is correct. Hard to find tubing here. The way you do this one is when you get it tuned you are to solder the tubing on the inside.

[@neogeo8267]

Silver solder or just flux core lead?

[@MrCorynick]

I'm hoping to apply the same theory to a 900mhz filter using maybe quart or pint paint cans. Wish me luck

[@DoRC]

a 1/2 gallon paint can is just under 6" tall so that might be an option.

[@TheRadioShop]

That would work

[@jonka1]

Not knowing anything about these devices I wonder if the use of foil and a plastic end cap might be physically non-rigid enough to allow for slight de-tuning with time and temperature.

[@vk2amv]

Can you tell me the diameter and length of your cans? We don't have coffee sold in cans like there here in Australia, but I should be able to find something similar if I know what size can I am looking for. Thanks

[@TheRadioShop]

No problem. These are 30.6 ounce cans (0.000904.95 ml). They are 5 7/8 inches tall (150 mm). And 6 inches in diameter (155 mm) Hope that helps.

[@vk2amv]

That helps very much. I think I can use a large beetroot can to do the job. Thank you

[@Dazzwidd]

the Nescafe 500G tins are the same dimensions I think. Fairly easy to get, many workplaces have them in the lunch room for staff to get their caffeine fix. If you drink it, wait until it's on special and buy some when they're $16 each. Then either donate the coffee to a good cause or wait until you finish drinking it all if you're patient enough. You could talk to some tradieswho restore wood floors and ask them for empty stain and varnish cans also :)

[@Etherionix]

Excellent.

[@TheRadioShop]

Thanks Don

[@محمدالسعوديه-ج9ل]

👍👍👍👍👍👍👍👍

[@rakotondramananasamuel3970]

is it possible to create lte band with cavity duplexer like this

[@TheRadioShop]

I do not think it would work that good at high frequency.

[@arduinou5944]

It seems you abandoned this project, it was very interesting

[@TheRadioShop]

Not really, was waiting to pick up a used repeater at a decent price.

[@kg4hlz]

Relay good video! 73s.

[@TheRadioShop]

Thank you very much

[@nutlock2857]

Hi Buddy -thank you for another great video! Can I ask you, did you manage to find any new info about the CB Sig- gen ? I have looked myself with no joy 73 from the UK

[@phantomsurvivor6169]

Better than a cheap $100 Chinese flatpack duplexer?

[@kj4ilk]

Can you send me a link to the can duplexers on how to build them

[@TheRadioShop]

www.arrg.us/pages/WB3AYW/UHF-duplexer.htm

[@kj4ilk]

Thanks

[@TheRadioShop]

You are welcome

[@LavaKimo]

Your link to N4GUS doesn't work. The "p" in pages needs to be a capital "P" and then it will work.

[@Subgunman]

How many watts will it handle?

[@TheRadioShop]

The claim is 100

[@sdrrds2119]

please give the dimensions and drawing of the filters. Thanks

[@dennispeake1877]

g'day mate don't know what the name is but what a excellent job. Thanks for sharing your project. 73 de Dennis vk4oc.

[@TheRadioShop]

+Dennis Peake Thanks Dennis. Name is Buddy. Glad you found the video entertaining. So much detail was left out though but to keep the video short had to edit out an hour.

[@FaZeWIDOW]

thats funny the only radioshack near me is also thomson tv

[@TheRadioShop]

The one I know of is in Washington NC. You near by?

[@Assburgersaretasty]

AFR 1200, classic ;)

[@TheRadioShop]

Agreed!

[@AECRADIO1]

CHange your frequency error...it's too wide for an accurate reading.

[@w8fg]

I still want to do this project, cant find anyone who drinks coffee from a can! Anybody want to save me some coffee cans ?

[@TheRadioShop]

Buy the cheap CFG brand, give the coffee to the homeless. :)