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Harris XG75 1-Way Crossband Repeat to CDM1250

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

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emtb3839
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Posts: 3
Joined: Thu Oct 11, 2007 7:13 pm

Harris XG75 1-Way Crossband Repeat to CDM1250

Postby emtb3839 » Wed Nov 11, 2015 3:42 pm

So Im messing around with a project at my local volunteer station. We have been approved for a new vhf frequency. We need to take the Audio and COR from Harris XG75P and link it to a VHF CDM1250 Radio. Basically we are trying to build a 1-way crossband repeater from 700MHZ Trunked TAC1 to our Licensed VHF Frequency to broadcast to our members multi-channel voice pagers.

The XG75P Has (Fig 1 Below)
► +5V COR when voice traffic is received, 0 - 0.2 volts dc when no voice is present.
► Amp Speaker out that also has an External Ear Bud Connection (.03 watts of audio out of the ear bud jack)
► Ground

CDM1250
► Carrier Receive TX Input (COR)
► MIC Audio In
► Ground.

Both items are plugged in to the same power supply, same ground. XG75 +5VDC COR is plugged in to Carrier RX on CDM1250 when this is set to Carrier (-) Debunce on
the CDM1250 Transmits continuously when the COR out of the XG75 is connected to the CDM1250. I changed the Carrier detect to (+) but this just causes the radio to beep beep beep until I turn it off or reprogram the radio back to (-) Carrier. (Fig 2 Below)

What am I doing wrong (Other then using a Harris Radio)? I am using what we have available to keep down on cost.

Once I figure all this out I want to have a cable professionally made to use.

XG75P Pinout (Fig 1)
Image

Schematic (Fig 2)
Image

Thanks for your input guys and gals.

Brian

Wiregeek
Posts: 61
Joined: Thu Nov 06, 2014 9:53 am

Re: Harris XG75 1-Way Crossband Repeat to CDM1250

Postby Wiregeek » Thu Nov 12, 2015 1:00 pm

John Higham gives us some useful information here at http://jhigham.blogspot.com/2012/07/mot ... -tm-1.html , and your statement of ► Carrier Receive TX Input (COR) gives us some more.

What I _think_ is happening is that you have the COR/Carrier Detect from the XG75 (pin that goes hot when the radio is unsquelched and receiving) connected to the same pin on the CDM1250! Instead, you need to connect that to a PTT input configured for active-high. suggest Pin #3, that's normally PTT already (to maintain compatibility with the GM300 radios, IIRC).

To look at it a different way, you don't want Carrier Recieve - that's not an input, that's an output. Make it PTT, Active High. Debounce is maybe, maybe not.

Karl NVW
Posts: 85
Joined: Wed Sep 03, 2003 7:13 am

Re: Harris XG75 1-Way Crossband Repeat to CDM1250

Postby Karl NVW » Tue Apr 24, 2018 12:01 pm

You and your dept chief both do understand that ANY SIGNAL appearing on your 700 MHz TAC1 will be transmitted on the HB channel, even if there is an emergency conversation already in progress? I doubt that operation will pass muster with your state SCIP; I know it would be rejected by the APCO committees in most Regions.
Karl - WA8NVW AFA5VB
SHARES + NCS

ve3nsv
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Joined: Sat May 27, 2006 8:43 am

Re: Harris XG75 1-Way Crossband Repeat to CDM1250

Postby ve3nsv » Tue Apr 24, 2018 12:12 pm

I would take the +5 and input that into an npn transistor with a 1k resistor. That will give you an active low signal that you can feed into the CDM.

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tuckerm
Posts: 545
Joined: Thu Jun 10, 2010 12:21 pm

Re: Harris XG75 1-Way Crossband Repeat to CDM1250

Postby tuckerm » Wed Apr 25, 2018 5:27 pm

Karl NVW wrote:You and your dept chief both do understand that ANY SIGNAL appearing on your 700 MHz TAC1 will be transmitted on the HB channel, even if there is an emergency conversation already in progress? I doubt that operation will pass muster with your state SCIP; I know it would be rejected by the APCO committees in most Regions.


OP didn't ask about SCIPs or APCO committees. Sounds like they're patching their 700mhz trunk system to a newly licensed VHF channel. Since most MInitor pagers can handle two freqs, sounds like CH1 is their paging channel and CH2 is the patch so they can monitor the trunk channel without having to all carry portables. Regardless of what OP is doing, this isn't RadioReference and the rules and regs don't need to be quoted here.

/rant
Schrodinger's Radio: It is simultaneously too loud and too quiet, but you will never know which until someone transmits.

Karl NVW
Posts: 85
Joined: Wed Sep 03, 2003 7:13 am

Re: Harris XG75 1-Way Crossband Repeat to CDM1250

Postby Karl NVW » Sat Apr 28, 2018 5:41 pm

Sorry for stomping on toes, it won't happen again. I didn't realize that content of the FCC rules was board-dependent.
Karl - WA8NVW AFA5VB
SHARES + NCS

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tuckerm
Posts: 545
Joined: Thu Jun 10, 2010 12:21 pm

Re: Harris XG75 1-Way Crossband Repeat to CDM1250

Postby tuckerm » Mon Apr 30, 2018 4:54 pm

Karl NVW wrote:Sorry for stomping on toes, it won't happen again. I didn't realize that content of the FCC rules was board-dependent.


I didn't even realize this, but there is NO NEED to bump a three year old thread with that info.
Schrodinger's Radio: It is simultaneously too loud and too quiet, but you will never know which until someone transmits.


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