Author Topic: Homebrew repeater  (Read 7883 times)

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bkt

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Homebrew repeater
« on: June 01, 2016, 02:42:38 PM »
I'd like to experiment with building a low power (5W) repeater using two Baofeng UV-5R radios. If I plug a cable from the speaker-out jack of the receiving radio into the mic-in jack of the transmitting radio and enable vox on the transmitting radio, I should be good to go. Obviously, I'd set my offsets: receive on one frequency and transmit on another. I'm familiar with repeaters in my area and would be sure not to use frequencies that are in use.

How far apart should the radios be to avoid desensing on the receiving radio? Do the radios themselves have to be some distance apart or is it enough that just the antennas are separated? Again, the transmitter puts out 5W max. This would be on VHF if that matters.

Thanks!

Tevin

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Re: Homebrew repeater
« Reply #1 on: June 01, 2016, 08:08:32 PM »
I can't answer your exact question; a lot of this will depend on the antennas.

I suggest start with the radio antennas 10-12 feet apart and let trial and error guide you.

This article gives a good overview of what you are trying to do:

https://survivalcomms.wordpress.com/2016/05/22/setting-up-2-radios-as-a-repeater/

Flight-ER-Doc

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Re: Homebrew repeater
« Reply #2 on: June 01, 2016, 09:22:21 PM »
Single band will be a lot more difficult than cross band.  The more separation between the radios, the better...and vertical separation works better on the antennas than horizontal separation.

bkt

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Re: Homebrew repeater
« Reply #3 on: June 02, 2016, 07:15:05 AM »
Thanks for the links. I think I have the cable already set and working right and it's about 8' long. That might be OK for brief testing...and an extension can be purchased to make sure desensing isn't an issue. This test repeater will be located indoors and each radio can be in separate rooms with the transmit antenna several feet above and several more feet away horizontally from the receive.

For a portable repeater setup, something like this inexpensive cross-band duplexer would be ideal: only one antenna and no risk of frying the receive radio. I prefer the idea of sticking with VHF but cross-band might work out fine for my purposes.

BTPost

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Re: Homebrew repeater
« Reply #4 on: June 03, 2016, 01:47:57 PM »
Also understand that the FrontEnds of these Cheap Chinese HTs are NOT very selective, and very subject to Overloading from local Transmitters.... which is an inherent Issue with Repeater Operations.... Crossband would be a LOT easier to accomplish. A good Mobile UHF 6 Cavity Duplexer can make a UHF 5Mhz Split Repeater, not to hard to accomplish, especially at the 5-8 Watt Tx Level.... Lots of Portable Repeaters have been built using these type of Duplexers, and made in Pelican Cases, for Emergency Deployments....  One question you will need to get worked out is finding the COS Signal, (Carrier Operated Squelch) in the Receiver HT, and bringing it out to be used to trigger the PTT of the Transmitting HT... I don't think that the COS Line is available in these HTs, externally...  Using the VOX function will be problematic, as it may also trigger on local Noise, coming in from the local Mic... COS is a much better, and more Positive Control....
« Last Edit: June 03, 2016, 01:51:07 PM by BTPost »
Bruce in alaska AL7AQ

AD

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Re: Homebrew repeater
« Reply #5 on: June 03, 2016, 06:16:15 PM »
I think Greekman posted his HT repeater set up here just a few weeks ago.  I am running for a Glock Shooting match tonight and if you havent found it after I get back I will search for it.
The only dumb question is the one that did not get asked!!

AD

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Re: Homebrew repeater
« Reply #6 on: June 03, 2016, 10:07:08 PM »
I cant find it here but i PM him to see if he will repost.
The only dumb question is the one that did not get asked!!

AD

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The only dumb question is the one that did not get asked!!

GreekMan

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Re: Homebrew repeater
« Reply #8 on: June 04, 2016, 01:24:59 AM »
yep! and here is my original post here

http://www.preparedham.com/forums/index.php?topic=1299.msg10625#msg10625

also

https://www.facebook.com/photo.php?fbid=1000361340072059&set=pcb.1000361590072034&type=3&theater
https://www.facebook.com/photo.php?fbid=1000361310072062&set=pcb.1000361590072034&type=3&theater

I went for vertical seperation too. Unfortunately we had not a 4 radio with us, but I set the B channel of the testing radio at the "repeater" out frequency, and i would get the PTT press back with a delay.

For me this was a project just to document the idea.
A wouxon -6 costs as much as 2 baofengs and cross-band repeats by itself. And you only need a single antenna, power source etc.
« Last Edit: June 04, 2016, 01:26:57 AM by GreekMan »

bkt

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Re: Homebrew repeater
« Reply #9 on: June 04, 2016, 08:20:24 AM »
Thanks for the tips, folks. BTPost - your point about VOX became obvious once you pointed it out: ambient noise could end up getting transmitted. That'd be bad. I gotta learn about and look into COS.

GreekMan and AD - thanks for the links.

Initially, I'm going to set it up cross-band using an MFJ-916B VHF/UHF duplexer. This will make portability a lot easier.

AD

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Re: Homebrew repeater
« Reply #10 on: June 04, 2016, 08:41:33 AM »
GM

I used my search function and could not find that post. 

Thanks for coming back and reposting sir.
The only dumb question is the one that did not get asked!!

GreekMan

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Re: Homebrew repeater
« Reply #11 on: June 04, 2016, 11:42:49 AM »
it is the least that i could do.
this forum has been very helpful to me.

Tempstar

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Re: Homebrew repeater
« Reply #12 on: June 05, 2016, 10:12:22 AM »
Here's mine, if it helps. Two UV-5R with extended batteries, Duplexer for 440, repeater controller, in a "scratch and dent" $7 Harbor Freight "Pelican" case. Everything is mounted with industrial Velcro. We can easily get 12 miles (24 between radios) with it on the 200' hotel I have access to. Oh yeah, it's waterproof as well. Not shown id the NMO connector on top for the antenna. I'm adding another on the front so I can pull it up in a tree and have the antenna still be vertical.
"Preparedness is a lot more than just buying stuff"

AD

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Re: Homebrew repeater
« Reply #13 on: June 05, 2016, 01:39:23 PM »
Temp

Do you have a parts list and pricing?
The only dumb question is the one that did not get asked!!

Tempstar

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Re: Homebrew repeater
« Reply #14 on: June 05, 2016, 06:59:40 PM »
Let me try to get close off the top of my head. I built it a year ago
2 UV-5R radios with extended batteries $70
Sure-Com repeater controller from Ebay $60
Case $7
The duplexer I had, probably $100 to buy
Figure $20 for cabling, though I pulled from my parts bin


Looks I get when someone realizes that is what they were talking on, priceless
"Preparedness is a lot more than just buying stuff"