Motorola Jedi (MTX8000 Probably) - Tapping a 'COR' line?

[Mrbmw99]

Hello! I am interested in finding a COR (aka: 'COS') line in a MTX8000 radio, or a Jedi series radio in general. What I need is some sort of a line that comes from the radio into my repeater controller. There needs to be about 5 volts. It can either be active high or active low, either way. 1st off, I dont know where there are ANY taps in this radio as I have not opened it yet to attempt to look. BUT: Here's the catch! (Yes, I know) The radio will be on a trunked system! NOT A CONVENTIONAL! So, the line has to become active only when there is a transmission being received. The reason I'd like to be able to do this is because we have several 482MHz radios set up on a repeater, as well as several 800MHz radios set up on a Type II Smartnet system. We will be moving (slooowly) to the Smartnet, but until that is completed, we need cross-communication. If there are any devices out there that accomplish this, let me know. I do not need a moblie repeater setup, as both are already on a repeater and we wont always be near the cars. If you have any idea's or suggestions, please let me know! -Bret W, Mrbmw99@aol.com

 

[SCPD]

Bret,

Have you tried the batlabs site or posting your question on the repeater builder list (on yahoo groups) ?

How are you planning to tie the two systems together? Will there be a talkgroup assigned that gets repeated on the 482 Mhz channel and vice-versa?

-rick

 

[pmoore4321]

There are some technical issues involved in crossbanding to a trunked system. One thing to keep in mind is that if the channel is busy on the trunked system, then the user on the conventional radio will not get the "busy" tone. It becomes important because the conventional user will think his/her message got through when it actually didn't.

 

[Mrbmw99]

rfmobile: Yes, there will be a certain talkgroup on the system that will be linked to 482. So if a conv. user keys up, it repeats both on the 482 repeater as well as the 800 talkgroup, and vice versa. As far as the second post goes, there is no "busy" tone... it will just key up over the other user. It's set up to be PTT-ID style. I need to find a COR line in the Jedi though to tell the controller when it is receiving a signal. I havent seen it on BatLabs, but I'll go look a second time. MAYBE there is a way to use a VOX solution to get a COR, but I'm not too familiar with this style of system. Thanks a bunch! -BW

 

[SCPD]

there is no "busy" tone... it will just key up over the other user.

Pre-emptive keying! I like it. This gives the conventional users a slight advantage at the getting the last word in on a conversation - a minor training issue. *shrug*

Are you using a console feature on the trunking side to do this or is this directly supported by the trunking controller? Is it an MTC3600 or something newer/older?

-rick

 

[Mrbmw99]

Are you using a console feature on the trunking side to do this or is this directly supported by the trunking controller? Is it an MTC3600 or something newer/older?

Thanks for the reply, Rick... I too prefer the "PTT-ID" style so it keys up no matter what -vs- the other style (message-trunking i think). Anyways, on the truking side..... I'l copy you on this *shrug*.. We are users on the system, and we have talkgroups alocated to our use. We dont have a console nor are we in any way tieing into the conrollers. Help! :? Thanks!

 

[SCPD]

We are users on the system, and we have talkgroups alocated to our use. We dont have a console nor are we in any way tieing into the conrollers. Help! :? Thanks!

Hi Bret;

In that case, as pmoore was pointing out, the conventional UHF users won't get the busy tone - training issue for the UHF users to avoid getting the first syllable of every key-up cut off. Sounds like the MTX radio will appear as just another mobile on the trunked side.

The big decision could be in how to handle a trunking failure. The simple, straight-forward solution is two audio paths A & B.

A - audio from UHF repeater input is passed to MTX's microphone input.
B - audio from MTX's speaker output is passed to UHF repeater's transmitter.

This gives the trunking dispatchers decent flexibilty (ie. dealing with a stuck UHF mike or patching the UHF system into another talkgroup).

However, if the trunking system fails, it takes the UHF repeater out of commission too. A fix for that is let the UHF repeater controller (path "B") get audio from two sources - the UHF repeater input and the MTX trunked radio. The controller should give priority to any audio coming from the MTX. (You do NOT want to mix the two - the controller needs to switch - select one or the other but not both). Should the MTX go silent (ie. trunking system failure), the UHF repeater system will continue to operate.

-rick

 

[Mrbmw99]

Hi Rick,

Yes, the MTX IS just another mobile on the system. As far as the trunking system going down, I REALLY doubt it... What I mean is, it hasnt before. There are no consoles on this talkgroup. A stuck key on the UHF side doesnt really matter (technically speaking). A stuck mic on the UHF should act like a stuck mic on the 800 side. Now, you were suggesting I have the UHF controller pick out of the 2 audio sources. I can't do that, I dont have access to it. I am trying to do this all remotely. Maybe explaining my use will help you see what situation I am in better... We are a group of Police Explorers. We currently have a few UHF radios on the old Police UHF repeater that we use on events and the like. The Police Dept. is now on the trunked system. We would like more radios, but I suggested buying 800's and linking them (and we already have some 800's). This also allows us to be able to change channels to the PD main on the 800 radios. We will slooowly transition into all 800's (probably). So, for now I am trying to find out how to link them. BUT: I do not have access to either the 800 system equipment or the UHF repeater equipment. I am just a user on both. I understand that the audio out from the UHF mobile goes into the MTX mic, and the MTX speaker goes into the UHF mic, but I need to somehow tell one radio that it needs to key up because there's traffic. So, I need a COR/COS line from the MTX radio. Ideas? Better solutions? Thanks! -Brett W

 

[SCPD]

BUT: I do not have access to either the 800 system equipment or the UHF repeater equipment. I am just a user on both.

Ohhhhh ... Bret you really need to talk to the system administrators - either the UHF admin or the trunked admin (preferably both). Are you sure they'll be okay with this?

-rick

 

[Mrbmw99]

I dont really see a big problem with this because of the fact that the UHF repeater is basically ours to use for whatever we need. We are the ONLY ones that use it, so... It's just the Police Dept's property, so we can't really mess with it at all. No, I havent talk to either system administrator yet, nor do I even know who they are. -Brett W

 

[Mrbmw99]

So, does anyone know how to get a signal out of the MTX8000 that will tell me when there is a signal being received? Thanks! -Brett W

 

[wavetar]

Just about anything is possible, just varying degrees of it. This will require someone with a fair bit of know-how & good soldering skills. I haven't looked at doing this on an MTX8000 myself, but the best place to start is the side accessory connector. You can find the pin-out here:

http://www.batlabs.com/images/mtsxacc.gif

As you can see, there isn't anything labeled as COS/COR, but many Motorola speaker circuits are balanced, which means there may be a DC voltage on either speaker lead when the audio PA activates. I know it's that way with many mobiles, such as GM300, LCS, MCS & Spectra/Astro Spectra. If you're lucky you'll find a useable DC voltage there. Just use it with a simple transistor switching circuit for a reliable COS/COR.

If this doesn't pan out for you, then the next spot to look at is the interconnect pins between the RF & controller boards. You may find one of them changing state when the audio circuit unmutes.

Last resort is to look at the schematics & board layouts & see if there's an accessible point to source a change of state, such as a 'mute' line or similar. The problem with that is it may only appear on the underside of an OMPAC IC or something.

I assume you want to use the MTX8000 because it's an existing radio you have & wouldn't have to purchase a new one. This would be far easier (and more reliable, IMO) using mobiles as opposed to portables.

There is a small interconnect box available from Motorola that plugs directly into the speaker/mic connector in a trunked portable such as a GTX or LTS2000, and has connections to wire into the conventional radio of your choice on the other end. I have used this box on several Telario systems to provide interconnect to trunked systems. I can look up the part# if you wish. Good luck,

Todd

 

[Mrbmw99]

Yes! If you could look up that number i would really appriciate it! Also, I will look into those suggestons tonight. The reason I wanted to use the Jedis were because of portablity as well as programming. I do not know how to program any of the mobiles to a Smartnet system. Nor am I sure on what models will do it, so. Thanks Todd!

 

[Mrbmw99]

MAYBE!!???!!?!?

Hi! I *THINK* I have found something that will work! I'm hoping so! What I did is: I put my digital multimeter on DC, and placed the ground lead to the common ground (Pin 8) on the acc. connector, and the positive lead to the speaker output line (Pin 2). I get -135mV when there is no audio, and a positive voltage when there is audio. The thing is, the positive voltage is sometimes around +.5v (once) and +2.5v (several times). Can you suggest a transistor that would work ok with these specific voltages? Also, I would like to be able to run down to RadioShack and grab a transistor to test this out before I spend too much time on this method or special order unnecesary parts. Can you sugest anything in particular from RS? Your help is appriciated! -BMW

EDITED: I have attempted to wire a microcontroller (by itself) to sense the voltages. It works, but not always. When it DOES sense the higher voltage, it's ok and drops when it should. But, there are a lot of times when it wont sense it at all. Can somebody confirm that this is because this is only 2.5v, not 5v? Thanks!

 

[Mrbmw99]

YES!!!! I HAVE IT! I found a source to get a COR from! I was probing around inside the radio with a voltmeter when I came across the Speaker's common lead. This lead compared to the Ground DOES CHANGE like I need! It's at 1.5 volts when not receiving, and around 5.5 volts when receiving! Works great!

Todd: If you could give me that model number, it would be great! The device was also suggested to me by somebody else. I appriciate it!

 

[jconner]

Have you looked into the ACU-1000 from JPS? It will do what you need and more but it's expensive (25K) Motorola mobiles put 5 volts on the speaker line that you can use as a COR

www.jps.com

 

[MattRiley]

you could also always enable vox....

 

[Grog]

you could also always enable vox....

#1 enable VOX on what?

#2 This thread is four years old