Five “MUST-HAVES” To Consider When Buying A Two-Way Radio Repeater

Certainly, one size does not fit all.
The CM300 I used, does perform quite well with high levels of RF, as this is how I test receivers before placing them into service.
I was restricted by budget, not choice. Proper filtering on all I/O ports, as well as D.C and control lines is always a requirrement for me.
Site requirements are different from location to location, unless you are the owner, and can set the rules.
Our peaks here, are not overly congested, but can provide serious IMD regardless.
My little system was built for ease of service, and its location is on the property of the owner, so they have exclusive control over it, which is perfect for their needs at the time.
If they need a site on a peak, then this will need to be changed, as there are too many cables and ancillary equipment that will need to be changed, and thinned out.

For now, the customer is pleased, it works better than they expected, and serves their needs...plus their budget was not exceeded, saving them $$ for other things.

 

These short interconnect feeds today are normally RG-400 coaxial cable.
Receiver multi-coupler systems work quite well today. I am quite familiar with them as I've designed both 700 MHz trunked P25 systems for Motorola and managed the upgrades concerning my current 800 MHz Harris trunked system. Successful multi-coupling usually requires some amount of filtering between the multi-coupling panel and antenna. Or, the tower-top amplifier incorporates the proper (needed) filtering before amplification takes place, sending sigs down the hardline to the multi-coupler.

At 700/800 MHz, normally I see per channel combiner losses between 2 and 5 dB -- and that's okay in almost every case. I see this with cellular-like trunked systems on 700/800 MHz, with purposefully designed down-tilt and null-fill antennas that limit and provide excellent shorter range coverage and purposeful soft hand-offs. Many systems in this freq range don't require massive ERP levels... and should be balanced (typically lower TX power levels) with the receivers on the matching multi-coupler. Modern tower-top amplifiers are typical and are the "cat's meow" these days. I contend that modern systems don't require fantastic coupler efficiencies. Like you said... it depends on the system design.

Long-range or macro coverage sites reside in the amateur radio realm anymore. Hams have different goals with typically much wider coverage areas sought.

 

I'm looking to buy a DR-2X in the near future, but I was wondering what the separation would be for the two antennas on max power (without using cans...)?

 

What frequency band is it on, and what is the output power of the transmitter? Typically you want at least 80dB of antenna isolation, or more. There are charts that show the vertical or horizontal separation needed to get to that point. But vertical separation takes a lot less. On 2M, you need around 80+ feet of vertical separation, but 25' would work on 440, usually. Horizontal separation would be around 1500' on 2M and around 500' on 440, but it might work at more or less than those numbers depending on other specific factors such as output power, RX sensitivity and front end selectivity, and other objects in the near field.

 

The discussion is very educational - thank you!

 

Thanks for the reply. I was planning on running 20w on 2M. I was curious to see if my calculations were right. They seem to right around where you said. 80/1500 feet. I was going to play with it experimentally. I've seen some pretty good deals on cans lately and was contemplating on making a "canless" repeater just for fun. First I need to get myself the repeater.

Though I am looking to scrap the DR-2X idea and get two FTM-3200DR and use an arduino to link them and make a repeater interface with the remote shutdown, callsign annunciator, etc.

Maybe a winter project.

 

How about "Don't build it out of two mobiles that aren't truly rated for 100% duty cycle". So much of that kind of thing flying around today. The OP should know alllllllll about what I'm talking about here.

I'll gladly pay for a used Motorola station over any new "mystery boxes" that have a pair of mobile radios in them.

While I appreciate and enjoy digital operation as much as anyone else, it should be remembered that a certain degree of interoperability is always desirable, especially in instances of emergency communications. Analog isn't dead.

Getting back to two mobiles in a box. Just because you CAN doesn't mean you SHOULD. This is definitely a case of caveat emptor.

 

Two things I did not agree with here. First RF output power is not the most important thing by a long shot. First, if you can't hear it you can't repeat it, thus don't put out more power than your receiver is capable of hearing, maybe a little more power, but just putting out max power an having bad ears is just senseless. Next, a good circulator is important, at least a single stage should be required and any commercial site probably will require a dual stage. This will protect your PA AND all of the other repeaters at the site. Of course any commercial site will also require good duplexers, not just band pass, but band reject. So I guess that is 3 things I disagree with. Propagation maps are great, but then go out and test, if your site puts out 50 watts and can be heard well within the area of coverage planned, but can't hear, then add a pre-amp and test again, no sense and the next county being able to hear your repeater but not be able to use it.