CDM1550 Repeater Build

[SpringHill]

I'm looking to build a repeater out of a pair of cdm1550`s of which I have two ready to be put to use. I have purchased a repeater interface cable and I'm wondering if I need a repeater controller or if I can just use the interface cable. What are the pros and cons of both setups? I'm hoping to find a gr300 shell as I like that small compact metal case!

Thanks guys!

 

[mmckenna]

What radio service are you going to use them on?

Rules vary about ID'ing. On Part 90 you'll need to have the repeater ID.
On amateur, you should have the repeater ID, and you need to retain control over it, so if it's not located in your home, you'll need a way to disable the repeater.
On GMRS, ID'ing is optional, but you should still have a way to remotely disable the repeater.

Pretty much no matter how you look at it, you should have a proper controller. These CDM's are designed to be mobile radios and don't have the duty cycle of a true repeater. You'll need to take that into account. It's common to crank the RF output power down pretty far to reduce some of the heat issues. Even with that, you may need a fan to keep them cool if they get used more than occasionally.
A repeater controller, or setting up the radio with a time out timer set to nothing more than a minute, maybe less, would be a good idea. Add in the need to be able to remotely shut it down if the transmit gets stuck on, held open by noise, or is getting abused. And no matter the radio service, periodic ID'ing can be helpful.

 

[krazybob]

The advice that you've been given this pretty good so far. The CD M series radios although mobile radios do make good repeaters. 2 things to always do are to decrease the power output to 1/10 or even 1/5 no matter what. You may then put an actual repeater amplifier on it to get it back up to a reasonable level. No matter what you should put a fan on it because once the transistors heat up the fins like to pull up off the board. I have a te systems 200 watt amplifier that doesn't do nearly that because of the drive level. Not necessarily a cheap amplifier but definitely capable of continuous duty. You would be surprised though. A 10 watt repeater fed with hard-line and a good antenna from a high location will do quite well. People get fixated and high-power repeaters and I can tell you that 10 watt repeaters do just fine. When building it try to make sure to put RF chokes on power lines and if you want to do it the right way put bypass capacitors in on a grounded strip so that your audio lines go through the bypass capacitors before going into a remote controller. Motorola has made quite well out using the CDR repeaters that are basically CDM radios with a controller in between. So, the do work. I insist on putting a 4 inch fan underneath the transmitter by at least one inch blowing onto the sins. Experiment and see which works best either blowing onto the fins or pulling the heat off of.

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[SpringHill]

it will be used on GMRS as a portable repeater. It will mostly be traveling in my RV with me so the antenna i can easily put ontop of the bus with a 10 foot pole to make it easily 30-35 feet, and that makes grounding easy as well! its not going to be in CONSTANT duty, maybe a few days at a time and even then not much traffic. I just need to know if it will function without a controller and what ill lose not having one.

 

[mmckenna]

You're probably OK then. Under the GMRS rules, the repeater is not required to ID, so that can simplify things.
For the time out timer, you can set that in the radio.

Also, heed the advice above about turning down the RF power. Add an amp or a higher gain antenna to bring power levels back up.
If you are going to use a duplexer (and you should), make sure you get a decent one. The little Chinese $75 e-Bay specials are not a good choice if you want decent performance.

 

[krazybob]

Keep in mind that a higher gain antenna only gives you gain at the horizon. Gain is achieved by narrowing the aperture of the antennas focus. You can take for example a 6dB gain antenna and look at the lower lobes on it and see that the minor lobes drop below the horizon but not at the same level. Now make that a 9dB antenna and you'll see that you've got a rock-solid signal at the horizon 40 miles or more from the repeater depending on the repeater altitude but you can't hear anything below you. That's where a balance is needed on the antenna and if you can afford it one with down tilt. Usually the adage is antenna, antenna, antenna! But that's not always the case depending on the area that you need to cover. Or the frequency that you're using. There's a reason the National Forest Service uses unity-gain gain and generally no more than 3dB gain antennas on VHF. Living in the mountains where I deal with the Forest Service on a regular basis I can tell you that the 6dB gain antenna on my unit does worse than a quarter wave spike. All of our units use a 0dB gain broadband antennas so that we may cover 150 to 174MHz.

I will finish with this. As an amateur radio operator living at 6300 ft I did an experiment with local hams. I started using a disc own antenna and just about everyone could hear me including those 100 miles away. I have a fantastic location! Then I switched to a 6dB gain base antenna and I started beginning to lose some of the listeners. Finally I switch to a 9dB gain antenna and I was talking to a station in Mammoth Lakes up near Nevada and the California border near Reno. The local people were asking who the hell I was talking to. My 9 DB gain antenna had a narrow aperture with no down tilt and was talking over their heads. Antenna gain is not always the answer. If you are a low-level site with no more than 500 ft - 1000 ft above average terrain a 9dB gain antenna may be the absolute best choice you could make. A 6dB gain Station Master type antenna is a vertical beam width of 70 degrees. The average 9dB gain antenna has a vertical beam width of approximately 20 degrees. If you are repeater sits thousands of feet above your coverage area you need to consider the vertical beam width of the antenna.

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[SpringHill]

Thanks for all the info guys! I got my cable today but unfortunately, it didnt come with information on how its pinned out.

repeater Interface cable for Motorola radio CDM750 CDM1250 M1225 Maxtrac GM300 | eBay

this is what i bought. what do you guys think? im trying to get this programmed to test out camping tomorrow

 

[mmckenna]

There's an e-Bay seller with the name MRE1032 that makes similar Motorola cables. If I'd know, I would have recommended you buy from him. Not only does he make a great product, he's got a great record on e-Bay. He usually send that sort of info along with the cable.

None the less, should be pretty easy to figure out. Batwing Laboratories might be a good source of info. There's also a website called "repeaterbuilder" that has a lot of useful stuff. Searching on those will probably get you the information you need.

 

[mmckenna]

Also,
You'll either need duplexer cans or the transmit and receive antennas spread VERY far apart to make this work.
Since the repeater transmit signal will desensitize the repeater receiver, it may not work the way you are expecting.
The way this is done on the professional side is to use a duplexer setup to allow the TX and RX to use the same antenna and provide enough separation between them.
You -might- be able to get away with separate antennas, but you will need a LOT of antenna separation. I'd start with 2 runs of good coax, 50 feet long. Put the two antennas in opposite directions from the repeater. You can use vertical separation, but you'll need a tall mast.

And you may already know this, but I'll say it anyway: Do not connect the TX and RX radios together with a "T" coupler. That will push the transmitter RF into the RX radio and destroy the front end.

Good luck.

 

[N4GIX]

Why do you need the pinout diagram? That harness is quite literally plug-and-play.

I do not recommend "trying it out" until you have settled on either a duplexer (tuned of course) or separate, widely separated antennas!

 

[mmckenna]

Probably not the pinout he needs, probably needs to know if any of the programmable pins need to be changed. Since these may be previously owned radios, they could have had their settings adjusted at some point.

 

[SpringHill]

I have a duplexer i will be using for this and will be attempting to test a few antennas this weekend. like i said it will be super low use. And yes i basically am asking for an educated guess as to how i need to pinout within CPS on each radio.

Thanks!!

 

[SpringHill]

I was able to track down the diagram on this cable from the creator.


TX:

pin7-ground
pin3-PTT
pin2-Tx audio

RX:

pin7-ground
pin8-COR out
pin11-Rx audio


My issue is: I have a dropdown with many Accessory package options.. and with those i only have access to certain pins. This will be my first time setting one of these up so i dont know what pin is what on those pins that arent listed.

 

[SteveC0625]

I was able to track down the diagram on this cable from the creator.


TX:

pin7-ground
pin3-PTT
pin2-Tx audio

RX:

pin7-ground
pin8-COR out
pin11-Rx audio


My issue is: I have a dropdown with many Accessory package options.. and with those i only have access to certain pins. This will be my first time setting one of these up so i dont know what pin is what on those pins that arent listed.

On the TX radio, Radio Configuration --> Accessory Pins tab:
Use the dropdown and set Accessory Pins to Default.
Pin 3 should now be External Mic PTT (input) with Active Level Low and Debounce checked.
All other programmable pins should be Null.

Then go to the Accessory Configuration tab and set External PTT Audio Source to Ext. Mic Audio.

On the RX radio, program Pin 8 as PL & CSQ Detect/Talkgroup Detect (Output), Active Level Low and Debounce unchecked.

Then on the Accessory Configuration tab, set Receive Audio Type to Filtered Audio.

You will notice that the RX and TX settings don't overlap each other. That means you can program both radios to operate as either RX or TX. You will have to add some extra personalities for that, but it's worth it. You will be able to swap radios in the repeater in a flash.

That should do it.

For others who may read this thread, these instructions will work equally well with CDM750 and CDM1250 models.

FWIW, I am in full support of mckenna's reference to mre1032's repeater interface for these radios. I have one sitting on my desk ready to build up a similar repeater. It came with 9 pages of instructions and information. It was more than well worth the extra cost. I hghly recommend mre1032's products.

 

[SteveC0625]

My issue is: I have a dropdown with many Accessory package options.. and with those i only have access to certain pins. This will be my first time setting one of these up so i dont know what pin is what on those pins that arent listed.

The pinouts for the CDM series is easily found in any number of internet locations with a simple search. batlabs.com has it as a .jpg.

But, here's the complete list:

CDM Series Mobile Radio Accessory Connector Predetermined Functionality
Pin Description Direction Comments
1 Speaker (-) ................Not Programmable
2 External Mic Audio Partially Programmable
3 Digital In #1 Input Only Fully Programmable, 12 Active Low Only
4 Digital In #2 Output Only Fully Programmable
5 Flat TX Audio Input Partially Programmable
6 Digital In/Out #3 Input Only Fully Programmable
7 Ground ................Not Programmable
8 Digital In/Out #4 Selectable I/O Fully Programmable
9 Digital In #5 Special Input Tri-state Emergency Switch
10 Ignition Sense Special Input Not Programmable, Active High, 12vdc(+)
11 Flat RX Audio .........Partially Programmable
12 Digital In/Out #7 Selectable I/O Fully Programmable
13 Switched Battery (+) Not Programmable, 12vdc(+), max. 1 amp.
14 Digital In/Out #8 Selectable I/O Fully Programmable
15 RSSI (Radio Signal Strength Input) Not Programmable
16 Speaker (+) Not Programmable
17 BUS (+)* ........Not Programmable (Programming & Flashing)
18 Boot Control* Not Programmable
19 Reserved
20 Reserved

One more thing: All of this info is in the Motorola section of repeaterbuilder.com

 

[krazybob]

Pin 8 is usually turned off and may need to be turned on. That is your COR. I also agree that MRE1032 is an excellent seller on eBay. I have bought many items from him in the past and if you have an issue you can always text him and he'll reply as soon as he can.

If you are doing this on gmrs you do not need an identifier. If you are doing it for ham radio you're going to want to pick up an inexpensive controller that has a built-in idea. They are more involved in the simple crossover cable that you have. They run about $80 but have additional features that are quite beneficial including the ability to take the repeater down remotely with a DTMF command.

I don't recall where you indicated what frequency you will be using but if you don't have a duplexer you are going to want to run half inch Hardline which runs about $2 a foot unless you get it on eBay at a discount. NEVER use LMR400 outdoors. You may use it for interconnecting cables inside but never outside because it will corrode and cause intermod. There has been much discussion on this topic. for a two two separate antennas. If you use UHF you're going to want about 20 ft of vertical separation to 40 ft of separation with your receive antenna higher on the tower.

Bob - AF6D
Owner/Trustee
K6ECS Linked Repeater System

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