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

My name is Ron Kochanowicz. I have been in the repeater and land-mobile radio communications industry for over 20 years. I've built and sold thousands of repeaters that are in service all over the world. So I wrote this guide for you based on my experience.

There are many two-way radio repeaters on the market and it’s important to pick the right one for your application and budget.
I've written a brief guide of what I believe are five “MUST-HAVES”
you should consider as you make your repeater buying decision.
If you have any serious interest in repeaters, then you need this guide.
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In this guide, you will learn:

• What to look for in a good receiver -The repeater you purchase MUST have a good receiver
  

• How to fully optimize a repeater's transmit power - The goal is to get as much transmit power consistently out of the repeater as possible without destroying the repeater or reducing the repeater’s life
  

• Power supplies - Internal or External
  

• Controllers - Internal or External
  

• What kind of signals should be available on the repeater's accessory port
  

Click here to DOWNLOAD your FREE Repeater Guide:

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Hope you enjoy the "5 must-haves" guide.


All the best,

Ron Kochanowicz, KCØQVT

President and Chief Engineer - BridgeCom Systems.

 

You need someone to proof read the document, then correct the small grammatical errors.

I would dispute that a built in supply is needed, or even an advantage. Some sites have 12v power available that is already on float chargers. A built in supply is useless in these cases, and if your built in supply goes bad, it might be more of an ordeal to replace it than one that is external. Another thing to point out is that a repeater needs to be synthesized in today's world. The MastrII and Micors are good repeaters, but it is extremely difficult to get crystals to move them to new frequencies.

Another thing is to have a repeater with a good service manual and schematics, so anyone can troubleshoot and work on it.

 

K7JEM, AND leave that manual at the repeater so people can find it! Whoever removes it and doesn't return it, gets a good whipping.

Brian

http://www.trueladderline.com

 

As a retired Motorola guy of 25+ years I have an opinion on this.
I’ve installed a repeater or two....
First off the controller has nothing to do with the receiver/ transmit bandwidth, this is a function of the receiver and exciter.
In addition I strongly recommend a RF isolator on the transmitter. Even if intermod isn’t an issue, it protects the PA from a sudden antenna system failure, because the PA always sees a perfect 50 ohm impedance no matter How the antenna system is performing.
Duplexers should be BP/BR as in TX/RX Bird duplexers.
Just plain Band-pass isn’t really that good.
A quality surge/lightning protector on the antenna line like the Polyphasor brand.
Always try to use at least 7/8” heliax
RF jumpers should be RG-142 quad shield cable, jumpers to the polyphasor, duplexers. It should be kept short because it’s lossy but quad shielded. Getting the repeater antenna as high as possible and or the highest gain antenna isn’t always the best choice.
Antenna combiners and receiver multicouplers should be avoided if possible! This method is extremely inefficient, there is a tremendous amount of wasted RF power.
It is Only used in situations where antenna space/weight is extremely limited.
Using a accurate RF propagation plot as part of a system design tool is evermore important especially in areas where frequencies are congested. There are companies that Will do this for a reasonable price it is money well spent.
Motorola publishes a site standard for everything from ventilation to proper bonding. It is called “Motorola R56 standards” this is a must for site owners. It is a wealth of information!
There is so much more in repeater system configuration.
Once the system is installed an effective sensitivity test must be performed along with a repeat sensitivity test.
The effective sensitivity test is the only true test on how well a antenna system is working with the equipment connected.
It can Also be an indicator of other antenna system problems.
If you are unsure of what this test is or how it is done please feel free to IM me.

 

Duplexers need to be selected on a case by case basis. Some applications will use BP/BR, some may use pass only. Some may use a combination of both types. And others may need reject only duplexers. One size doesn't fit all.

RG-142 is double shielded, by definition. Not quad shielded.

This really isn't true. RX multicouplers can provide a much better RX signal to all in band RX's in the building, when designed correctly. And TX combiners don't have to be especially lossy. In today's tower environment, the fewer antennas on the tower the more cost effective it can be. You don't have to sacrifice performance when using an RX multicoupler or TX combiner. We use them a lot on several sites around here. At one point in the past, we had 18 UHF RX's multicoupled onto a single RX only antenna. Saves on duplexers, feedlines, and antennas.

 

I completely disagree.
The receiver multicoupler by itself is fine, antenna combiners are very lossy even when installed and designed correctly.
I’ve been to numerous Motorola schools and worked with large public safety systems. This practice is avoided when possible.
I’ve seen several LTR systems that used the combiner system where 100 watts out of 5he PA and 1-3 watts out of the combiner matrix.
I can show you documentation from Motorola on this practice.
It’s all about experience and training.
I expected at least one comment that would disagree with me.
That’s the nature of the forum. It is what it is.

M.A. Lacy

 

Correction, RG-142 is double shielded. I was discussing a quad band mobile with someone when typing, got distracted.
So, correct 142 isn’t quad shield

 

I don't disagree that there CAN be losses, I am saying that there are not ALWAYS excessive losses. Your comment about them being "extremely inefficient" is not always true. Sometimes it is, sometimes it is not. You have to look at each instance, and what it is trying to accomplish. You can't condemn an accepted practice, when there are many cases that make it the best way to go. A TX combiner could have less than a dB of insertion loss, if it is only combining 2 transmitters that are not close in frequency. Even a 4 TX combiner might only have slightly more than that, if the frequencies are far enough apart. The hybrid/ferrite type are quite lossy, but even they have applications.

 

A built in power supply might be a good thing, it should be done on a case by case basis. One size doesn’t fit all.
My Yaesu DR-1X repeaters work great on the internal power supplies with the B/U DS back-up battery
Moving on........

 

To each his own!

 

Good post. Don't let the responses drag ya down. Opinions are like assholes. Thanks for the info. You'd think all these responders would publish books on how to set up repeaters. Eh, maybe some have. Anytime somebody post anything on these pages trying to help people out everybody know a better way to go about it. The experts that know better come out of the woodwork. Tnx again for the info.

 

My pieces here on what more to consider.
1. Use a good and reliable antenna that can withstand bad weather for years to come.
2. Better to have a high gain antenna than more power in the repeater since the high gain antennas also improves reception. *
3. Best possible cables that are economically feasible.
4. Keep the cable length as short as possible for RF - cable losses can be significant even with the best cables and those losses eats into the sensitivity of the incoming signals.
5. Make sure the antenna is tuned to the frequencies you use.
6. Select the site and antenna height for the intended coverage area. Notice that towers can mask a considerable coverage sector (which can be used for your benefit as well)

* However a high gain antenna like a 4-stack antenna mounted on a tower on a hill may cause you to "overshoot" the intended coverage area. In some areas the terrain is wrinkly like a raisin and you may have to take that into consideration. Even leaning the antenna could be the answer - even though it then would look to the casual observer as it's on it's way down.

Most repeaters that you buy today are one "complete" unit with transmitter, receiver and logic that you just have to add external filters to and program so even though the guide is good it's more for those that plans to build their own repeater. Right now my preference is the Hytera DMR repeaters, which are decent and relatively easy to work with even though the software documentation is a bit quirky (Chinese to English auto-translation). But there are other "off the shelf" repeaters as well that you can use.

The real fun comes when you want to do cross-band and multisite repeating.

 

It is refreshing that you included the ability to convert to digital via an accessory port. While a dedicated port is not required, it can make things easier for someone to convert their analog repeater to digital, for instance using a MultiMode Digital Voice Model (MMDVM.) Glad to see you mention this capability.

 

Antenna choice is paramount, style, type and service life must be considered above all others.
Feedline comes next. Again, type, loss and service location are important factors here.
System core design: Receiver sensitivity, selectivity, frequency range. Also, how good is the dynamic range?
How does the recovered audio sound while being re-transmitted?
Preamp selection (if used)...does it overload your receiver's front end? Do you need to pad the output to reduce or eliminate IMD products?
DUplexers: Or lack of them...port to port isolation, selectivity, power handling capability over time.
Do you have to return and constantly adjust the depth of rejection/notch often, or can you perform a final tune, and leave it for 6 months?
I put a system together that has NO duplexer, it does use a comb filter I designed, along with a single notch cavity for the main RX antenna, and a Yagi feeding two 1/8 wave notch cavities, that feed a HPF and GaAs FET preamp.
Both vertical antenna and Yagi, have high pass filters on their respective ports.
I included a drawing that illustrates the actual system that is in operation.
The receiver is a CM300 tuned to the RX frequency, and a lot of time was taken to tweak its performance, so much so, that I can hear a signal at -128 dBm without a preamp attached. This required days of fine tuning the front end filters, VCO and squelch level, to say the least.

In-service coverage is 35 miles, but due to actual terrain, there are losses due to rocky outcroppings, but my southern view gets me out near 50 miles.
I use 1/2" Heliax for cables, and 1/4" superflex for interconnects between equipment in the rack.
TX has a simple setup, but it is effective. A single cavity notch filter, dual isolator, LPF, and harmonic filter, feeding a 6 dB gain collinear.

Yes, this is actually a THREE antenna system, but it does work far better than I imagined...careful selection of components, finicky adjustments for the receiver, and proper filtering of the transmitter, have made this a real low cost winner.

Total cost estimate: $840.00

Why talk about mulicouplers, combiners and so on, when 99% of amateur repeaters will never require such elaborate systems to begin with?
If one was installing an LTR 4540 repeater, fine, but highly doubtful.

I want solid, repeatable PERFORMANCE for my money, not gadgets that do nothing.
Anybody can set up a rabbit repeater, but they will soon lose users...if you can not hear who you are talking to, transmit power is of little use.

The illustrated system is running at 40 Watts...more than enough power to balance coverage.

I will be adding a pair of 4-Element Yagis in the near future though, but I will redesign the secondary receiver system to reflect the additions.
Controllers are nice, but not necessary. Simple control is all that is required,
Power supplies are a personal choice, stand-alone, to built-in. I prefer stand alone. For me, this makes servicing a lot easier, and I can swap out supplies faster, with little down time.

I had a budget I had to work with, a strict budget...I think I came through.
Users are happy, the repeater provides more than enough coverage for their needs, and it runs 24/7.
Only one hiccup was found, and that was a defective 'N' connector.

Proper design and construction, tuning and final adjustments, alignment of the entire system as a whole, and individual alignments for best performance for the cost.

I prefer a rabbit over a alligator.

Thank you for your time!

Sincerely
Ernest...KA9UCE
aecradio1@gmail.com

 

The main thing is that the repeater fits your budget, performs as you want it to, and that it fits the site constraints. These parameters all can and do change, depending on where the repeater is, and what it is expected to do. A CM300 may not perform well on a highly congested site, but may be the perfect thing for your application. The biggest thing to remember that "one size doesn't fit all", so hard and fast rules don't necessarily apply to repeaters any more than they apply to an individual's HF installation, antenna choices, or radio selection.