The $100 Lunchbox Repeater

This is what YouTube was actually made for. I remember the long long ago. Thanks for Keeping that spirit alive and encouraging others by publishing a video such as this.

I would love a video where you take everything out and show how everything is wired together. Please let us know at a later date how well its working. Thanks, I was happy to sub!!

Loved this video & the idea execution was super sweet. I think having a typed & laminated card instead of a handwritten one would really enhance how official this looked in the field as well

Lots of good feedback here for you regarding desense (the rx won’t do weak signals since the tx antenna is inches away from the rx antenna). You can reduce some of that desense by putting one antenna on top of the box and the other on the bottom. This gives them vertical separation AND also gets them farther away from one another. Another even better separation would be to hang one antenna a few feet below the box (let the antenna swing freely on its coax). Have fun experimenting. I did almost exactly the same thing 25 yrs ago and had a blast doing it!

Looks like a fun project. I think I will steal your idea for myself and build one.

Awesome experimentation and learning. You will find you need more (and unfortunately big, expensive ,and heavy) parts in the system to get this to be reasonably functional. For a repeater to work, it needs to be able to receive a very weak signal while transmitting a relatively large signal. To be able to do that on relatively close frequencies, you need some very powerful filtering in the form of a duplexer. Without that, this device may be able to function ok as a cross-band repeater using 2m and 70cm, but desensitization may still be a problem with a Baofeng as the receiver. Keep tinkering, have fun, and please be sure to share your progress as you develop this further.

This is a fantastic video and very inspiring. Now i have some ideas that i may also want to try.

LOOOOVE me a lunchbox, particularly for a simplex repeater. These things are basically perfect for non-permissive environments where you need to extend range or get around obstacles in an emergency.

Great video, thank you. You inspired me to put one of these together.

An idea to make things even more apparent would be an ID tag stamped out of aluminum that has your callsign, phone number, and "radio repeater".

Learnings... are good. This is amateur radio....and the fun is in your journey! Technical inspiration: Words provide context. But the answers are always in the numbers! And for a repeater, it is all about isolation between TX and RX, etc. With those antenna's so close, yes you have "some" isolation, but I'm thinking only 20dB. So you are transmitting at say 5W (+37 dBm) - 20 dB = +17 dBm at your receiver. The Third Order intercept of a cheap radio is likely -50 dBm and you are 67dB stronger into it! Your transmitter noise has been reported by many as only -45dBc, so +37 dBm - 45 dB = -8dBm noise. You have two issues affecting your "open" receiver... being mixer overload making it deaf, as well as TX noise which covers up weak signals. A weak signal into your receiver without any TX or noise affecting it could be -120dBm for 12dB SINAD. Now look at the numbers.... -120dBm operating floor but with the TX noise producing -8 dBm! These are extreme numbers... reality may be a bit different... this setup will not work for anything but nearby radios. You can tell you are experiencing desense, when you can trip your repeater, but it goes deaf the instant the TX comes up... you get that roger beep, but nothing more. Add a mobile duplexer... they are compact enough, but generally require 3MHz or more separation between TX and RX. And mobile duplexers at these freq's are notch type devices, never bandpass. If you go cross-band repeat (146.520/446.000), now you have 300 MHz to work with. A simple High Pass / Low Pass filter like a mobile antenna duplexer will do the trick and you will have your lunchbox repeater on one dual band mobile whip antenna. This is another reason some use a "simplex" repeater module instead where it records your message and then keys up and repeats it after you are done. No duplexing or desense issues. Good luck in this most excellent hobby!

Good stuff Great Build

Thank you for this great video, really helpful. Cheers from Sweden!

Nice build!

Thats absolutely pretty cool, thanks for the great video!

Im a noob to ham and love watching vids like this.

Awesome build.. Great explanation video. Needs a trail cam added.

cool project !!

Awesome video. I’ve been wanting to try making a cheap repeater using Boefangs with a duplexer.

Neat Project! Would be nice if you had a diagram of the goal with the device (max range communication) as well as the maximum number of repeater hops you can have in the mix for clandestine long range communications in case of an EMP pulse. Would love to set something like this up on a mountain so I would be able to communicate with family 100 miles a way to check in with them. Would like to also give family some sort raspberry pi communicator in a an aluminum faraday briefcase so that they can foldable solar panel power it and type a message on their unit and my unit could log it for reading when I am in front of it. Do drills with it every week to make sure system is operational. Solar powered repeater high in the hills.