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What repeater do YOU need, and can I DIY one.



Had a question ask on facebook by a member about this very thing.  Figured I would put it in here in detail for ALL to reference.


Three levels.

There are basically 3 levels of repeater system build out.  The "system" refers to the radio equipment, controller if external, antenna, line and the duplexer.  These are the building blocks to ALL repeaters.  Eliminate any of this and you no longer have a repeater.

So how do you decide what level you are building for?

Easiest way to answer that is your antenna and it's height.  If you are putting a an antenna under 50 feet then you are at level one.  Now of course if you are on a mountain, that's not gonna be the case, but if you are in a town or city and the house and not a tower is supporting your antenna, or it's a small tower under 50 feet, your coverage for the most part is gonna be fairly local and you are NOT gonna have a ton of people using your repeater. 

Second level is a GOOD antenna that is over 50 feet on a tower or other tall structure.

Third level is antenna's above 100 feet on a tower or other tall structure.

And of course, antenna height and quality will determine how far your repeater talks and can hear.  There are other factors, but height and gain are the two big determining factors.


Levels of repeaters...

First level is the little plastic box things that are two portables in a small box with a small duplexer in the box. 

These are the most basic entry level setups and are good for mobile and portable systems and small systems for your household to communicate with. 


Second is the DIY or "two radios in a box" repeater.  the GR1225, GR500, XPR8300/8400 and a host of other commercially available solutions fall into this category.  BUT YES you CAN build you're own repeater out of two radios and some sort of controller connecting the two together.  Add a duplexer and antenna and you are off to the races.  Which I make sound fairly easy,, and it actually is.  And cheap too.  You will need some sort of power supply as well to power the radios and controller but that's not hard to source.

What radios?

My choice for YEARS has been the CDM series radios from Motorola.  They are reliable, CHEAP now and available on eBay.  You will need to decypher the model number on what you are buying so you know that they will work on GMRS or HAM (for you ham guys) and the power output but those are the only considerations needed for selecting the right radio.  They have a common connector on the back that makes interfacing them to a controller very easy.  And in a pinch, they can be directly interfaced to each other with NO controller and will work as a repeater.    There are other radios out there that are equally simple to interface, but you need to verify they have the connector to do the interfacing with.  Kenwood for one had a number of radios that you had to buy an option cable to get the interfacing or open the radio and solder wires into it.  This is NOT in the scope of this post and if you KNOW how to do that, why are you reading this to begin with?  So, keep your life simple and buy a couple CDM750's and be done with the DIY radio part.

Then you have a duplexer.  This is an important part of a repeater system and cost range from 100 bucks or less for the small 'mobile' duplexers on the used market to thousands for a pass reject duplexer new in the box.  For the smaller level one and two setups the mobile duplexer is fine.  You can of course use a better duplexer but you aren't really going to see a performance gain from it until you get an antenna up in the air where it is going to start catching noise and co-channel RF that makes the expensive units shine.  But the mobile units should never be considered on a tall tower or in an area with a lot of other RF present. 


Lots of options here.  Starting with the Raspberry Pi and Arduino boards.  Either will make a fine repeater controller with minimal cost.  But you will need to learn some basic computer stuff to get them up and running.  When you start looking at the ham and GMRS off the shelf controllers, the prices goes up a lot and you will be quickly getting to the point of the cost of a used 'two radios in a box" solutions. 

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I did the DIY with a pair of Wouxun KG1000G units. Was not happy with performance as the RF is pretty sloppy on those.

The Bridgecom unit works way better.

also upgraded a cheap antenna to this https://theantennafarm.com/shop-by-manufacturers/results,1-24?keyword=DB408-B&x=0&y=0&limitstart=0&option=com_virtuemart&view=category&virtuemart_category_id=0

also made world of difference.


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On 4/13/2022 at 9:05 PM, wqpn591 said:

Or just buy one of these https://www.bridgecomsystems.com/collections/amateur-radio-repeaters/products/bcr-40du

and  decent antenna and away you go.


For only TWICE what a used MTR2000 currently costs that is a FAR better machine.

And I agree that the CCR's should be avoided for running back to back as a repeater.  Which is why I specified the CDM radios that are available on ebay for under $100 each.  Not sure you can even get new mobile CCR's for that money, and the CDM is a better radio than the CCR's. 

My point was you COULD build a decent DIY repeater for less that $500 all in from antenna to power supply if you were willing to figure a few things out.  Learn to program a couple radios and could solder (if you wanted to interface to the system as a Node). 



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I went Kenwood as they did what I needed out of the box and I work for an M shop. Could have a 5700 for cost but I would need an external controller to be able to do the same a K out of the box and ~800 bucks less.
As to antennas a medium gain professional antenna is the way to go (db 408/411 or comescope PD201)

Half inch Hard line for anything 50' -100' , 7/8 100'-200'

Duplexers IMO are a matter of site location, big noisy tower site nice professional filter, small stand alone roof/hill top w/not a thing for miles a small Celwave "mobile" one will do.

Height , it determines everything you are going to hear and how far you are going to talk. I you are going to put something on your roof in a pine grove don't expect much out of it. you will need to clear the tree tops at a minimum.
just my thoughts JE

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