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Repeater Interface cable.

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darrelhillman

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Joined
Apr 3, 2012
Messages
23
Location
San Juan, PR
Hi friends and please bear with my ignorance. I am trying to make a repeater using 2 M120 Motorola Radius together. I already programmed the radios for receive and Tx. I have read as much as I can from the Batlabs page as well as Repeater Builders page. First of all both of my radios are 16 pin accessory connector, 2 channels, 40 watts. I bought a prefabricated cable on e-Bay with a delay integrated in as the interface cable. The connectors labeled Rx-D and Tx-D can go in either way, upside down or upside up. The cable only uses 3 wires to connect one radio to the other. Plugged it in, and it did not work at all. In fact during try-in, apparently I put it the wrong way and the 2 amps JU801 fuse.

My radio does not allow to program the 16 pins connector with the software, so I assume that the acc connector is factory programmed for repeater able. Can someone give me a diagram that shows which pins from the Rx radio should be connected to which pins on the Tx radio??? I am using 467.650 MHz as Rx and 462.650 for Tx in the Repeater. I will use PL codes 136.5 Hz for the Rx and 107.2 Hz for the Tx. The only information I could find for the interface is as follows Pin 3 with Pin 8, Pin 8 with pin 3, Pin 5 with Pin 11, and Pin 7 with Pin 7. Apparenttly both radios can work as Rx AND Tx. I would like a receive/Tx one direction repeater, (if this is the correct terminology).

Please reply if you have any information that can help me with this project.

Thank in advance, Darrel
 

WB0VHB

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Joined
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Messages
123
Location
Mt. Union, Iowa
Hi friends and please bear with my ignorance. I am trying to make a Rx and 462.650 for Tx in the Repeater. I will use PL codes 136.5 Hz for the Rx and 107.2 Hz for the Tx. The only information I could find for the interface is as follows Pin 3 with Pin 8, Pin 8 with pin 3, Pin 5 with Pin 11, and Pin 7 with Pin 7. Apparenttly both radios can work as Rx AND Tx. I would like a receive/Tx one direction repeater, (if this is the correct terminology).

Please reply if you have any information that can help me with this project.

Thank in advance, Darrel
The connector with Pin 3 will go to the TX radio since that is the PTT pin. The connector with Pin 8 will go to the RX radio since that is the PL detect pin. Pin 7 are common ground

Pins 5 and 11 are a little concerning especially since you are not using the same PL tone for receive and transmit. Pin 11 is discriminator audio and it should be filtered by default in the radio so no PL tone is leaking through. I don't remember the internal jumper to change between filtered and unfiltered receive audio but when using different PL tones, you certainly want filtered audio.

Pin 5 is flat TX audio which I'm not sure I would support. Pin 2 (microphone audio) is generally a better choice but you can leave it at Pin 5 for now. The downside of pin 5 over pin 2. IF there is any PL tone leaking through the filtered audio from Pin 11, it will be retransmitted using Pin 5. The only way would be to use a scope on Pin 11.

With all that said, replace the 2 amp Pico fuse that blew (or inject 12 volts DC on Pin 10 of that radio) and plug in the interface cable with the connectors positioned on the correct pins as described above. If it works like you want, case closed!
 

darrelhillman

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Messages
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Location
San Juan, PR
Thank you, very helpful. I can program both radios to have only 1 code such as 136.5 Hz. In such a case, pin 5 from Rx will go to pin 11 of the Tx radio? Thank you again, Darrel.
 

ramal121

Lots and lots of watts
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Sonoma, CA
I just recently had to throw an emergency repeater together (SM-50s no less). Made my own 3 wire cable.
Receive radio pin 11 (filtered RX audio) to transmit radio pin 2 (mic input) works and sounds just fine.
 

cmdrwill

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So Cali
I just recently had to throw an emergency repeater together (SM-50s no less). Made my own 3 wire cable.
Receive radio pin 11 (filtered RX audio) to transmit radio pin 2 (mic input) works and sounds just fine.
That will work on Gm300, M120 and SM radios. On Maxtrac or Radius radios you need a 2.2 K resistor and a 2 uF capacitor in series with pin 11 to isolate the opamp direct output from the Mic DC in the TX radio.

BTDTDW......
 

darrelhillman

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Apr 3, 2012
Messages
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Location
San Juan, PR
Thank you all

Case is closed. I soldered a new 2A pico fuse to the board, assembled everything together and noticed that the pre-fabricated cable from ebay had a broken wire at the pin 2. Re-soldered that white wire and is working ok although I haven't test the audio sound.

Tomorrow I will replace my DRC-200 with the M-120, and test it during the day. I then can compare the range of this repeater with the DRC-200 using the same antenna. Again this unit is for a boat, but I would like the same range as my DRC-200 which is about 6 miles in the city.

Thank you everyone, I did learn several concepts, not just a cook recipe.

Darrel
 

brin831

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Jun 15, 2009
Messages
64
Location
concord nc
i have two radius radios that use a similar cable ... works fine and is pinned properly ... it usually has a little pot to attenuate the rx audio just leave it all the way up/down (you don't want to use to attenuate) you should be able to adjust the mic gain will give you a cleaner sound.

when plugging in you are correct they connectors don't have that tab that keeps you from plugging them in upside down so be sure you follow the pinout and you should be fine ... the connectors usually have a 2/16 or 1/15 printed real small on them to designate which side is which and you can orientate with the accessory connector on the radio.

Last thing i would say is the cable used isn't shielded very well not terrible but you could use to get a short segment of good shielded mic cable from most any music supply store and soldier that in place I did and it cleaned up the audio noticeably.

glad you got it going !
 

darrelhillman

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Apr 3, 2012
Messages
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Location
San Juan, PR
F/U on the assembled repeater, I did tried and compared the range with the DRC-200. Results were very low reception for the M120 repeater. I sent it to a certified technician who checked the entire unit. He only found an open center female connector in the duplexer that was not having good contact with the UHF antenna connector. He also adjusted the duplexer to improve power transmission to 38Watts instead of 24 watts before tunning. Tested it today, but results are more or less the same. Reception does not compare with the DRC-200. I can hit the DRC-200 repeater with my EX500 in many places that I cannot hit with the M120 using the same Tram 1486 tuned antenna.
I am suspecting in a poor tunned duplexer at the high pass filter side. How can I improve the receiver sensitivity? Where can I send the mobile duplexer to have it tunned? Can I get around the sophisticated needed equipment to tune the duplexer?, such as having a far transmitter received by the repeater while adjusting the high pass filter cavity.

I am quite ignorant in this topic, please forgive if I offend anyone.

Darrel
 

WA0CBW

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Dec 8, 2011
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1,453
Location
Shawnee Kansas (Kansas City)
Now you know why people who work on repeaters have no hair "oooooo".

A good technician might be able to get it to work without good test equipment. A poor technician might be able to get it to work with good test equipment. But a poor technician without good test equipment will just loose his hair!

A good technician would go through the receiver and compare his measurements with published specifications. He would do the same thing with the transmitter and duplexer. Using test equipment he would correct any deviations from the manufacturers published specifications. He would then test for "in cabinet" desense with a dummy load and make corrections as necessary. He would then go to the site and measure the noise floor using the existing antenna. Again he would check for any desense and make sure the equipment is still performing according to the manufacturers specifications.

If you made it this far and it still doesn't seem to work properly start pulling your hair out. At this point you will require the help of those of us who have "been there and done that"! There are numerous things at this point that can prevent it from working correctly. Now comes the part of analyzing exactly what is happening and trying, substituting, and swearing at the equipment. Your search starts from the tip of the antenna to the AC power plug in the wall to surrounding repeaters, base stations, and broadcast stations.

Good Luck!

BB
 

darrelhillman

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Joined
Apr 3, 2012
Messages
23
Location
San Juan, PR
Thank you BB

I have an Erickson Repeater model DRC-200 that I placed at home using a Tram 1486 antenna with 60 feet of LMR400 solid core 2ble shield low loss cable with PL259 at the antenna end and Type N connector at the repeater end. This unit works great. I am assuming that the antenna and cable are adequate. I think this unit have a problem receiving and Tx. I am activating the Rx from my office using a Vertex mobile and a Yagi antenna (about 5 miles away), but still I cannot hear myself at the handheld, which I always do with the Erickson. I thought that if Tx was ok, I should hear the Tx at the handheld, The antenna at my office is on top of the 5 story building almost at line of sight. I was going to try Rx only as a base station with the RX radio attached to the antenna to hear how it receive from far away. I thought that the TX was ok with the 30 watts of power, the DRC-200 is only 15 watts. I also tried the DRC-200 at the boat and results were awesome.

With your help here at the Forum, and testing the individual parts, I might be able to fix it. The gold standard for me at this point is the Erickson DRC-200. I thank you for your comment.

Darrel
 

cmdrwill

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So Cali
The 60 feet of LMR400 solid core can cause desence in your receiver.
You will need to do the ISOT measurements with and without the TX and a separate load on the TX.

LMR cables generate low level RF noise due to dis similar metals in the two shields.
 

darrelhillman

Member
Joined
Apr 3, 2012
Messages
23
Location
San Juan, PR
Thank you

Thank you for the information. Don't understand why the same cable does work adequate, not saying it can be improved, with the Erickson desktop repeater. Is there a difference in having a factory assembled repeater and the M120 home brewed repeater? I call my Tech. and he told me to evaluate the power source and any interference with other transmitter or receiver in the area. I do have an Icom Ham radio that is on 24/7, but again does not interfere at all with the Erickson.

I noticed that whenever the repeater is activated, the auxilliary fan lowers RPM. Measured voltage and it did dropped from 11.9 VDC to 9.7 VDC. I changed the power supply to a Pyramid variable voltage 25 amps., and started at 13.0 VDC and when activated it drops only 0.1 VDC (12.9). Thought that was the problem, but still reception is limited, or not near the performance of the Erickson unit. Tech will schedule a visit to see the site where is located and have some tests there.

Any thoughts or comments are welcome. Thank you.

Darrel
 

darrelhillman

Member
Joined
Apr 3, 2012
Messages
23
Location
San Juan, PR
Duplexer tunning

I keep thinking my problem is in the duplexer. Another tech I consulted told me that one symptom of having a poorly tuned duplexer is that it works ok when you are near the repeater and starts having interruption when you are getting away from the repeater, because frequencies are mixing up. This is the same sign I have. The range is very poor for Rx and Tx. He also told me that in PR there is no one that tune the duplexer due to lack of equipment.

I am calling GMRS Outlet to see if they can check the duplexer tunning. The other test I was considering is to place the duplexer of the Erickson into the M120 radios and test for range.

If yo have any thoughts or test I should do, please let me know.

Thanks!!!

Darrel
 

darrelhillman

Member
Joined
Apr 3, 2012
Messages
23
Location
San Juan, PR
Well tuned duplexer

Well, after a couple of weeks waiting for a used, professionally tuned Celwave duplexer, installed in the same M120 system and a 90% improvement is seen. The range is almost the same as the DRC200, although the audio is slightly distorted, and I dont have the delay after actvating the repeater that I have with the DRC so is difficult to test the quality of audio at the position you are activating the repeater.
I just want to leave this information in case some rookie like me have this kind of problem, to think on the duplexer which is a vulnerable part of a repeater that need specialize and expensive equipment to be tuned. In PR, I am not sure that someone have a good spectrum analyzer to do this job.

I am going to try to increase the Squelch at the potentiometer of the Rx radio to see if I can improve the range to the same of the DRC200. In the DRC the manually adjustable squelch, does change the Rx sensititvity and hence the range.

My next project is to place an SM50 inside a watertight case with a UPS battery to make it portable and water resistant to take it along when fishing in the Dinghy.

That is for now, thanks for reading

Darrel
 

jim202

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Mar 7, 2002
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New Orleans region
Well, after a couple of weeks waiting for a used, professionally tuned Celwave duplexer, installed in the same M120 system and a 90% improvement is seen. The range is almost the same as the DRC200, although the audio is slightly distorted, and I dont have the delay after actvating the repeater that I have with the DRC so is difficult to test the quality of audio at the position you are activating the repeater.

Darrel
My guess is that you have the audio levels set up too high and it's being clipped or put into distortion by the compression it causes.
 
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