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Old 12-05-2010, 7:06 PM
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Default Repeating a scanner using a CDM 1250 radio

I have been for the past week or so researching and experimenting with how to use my radio shack scanner and a CDM1250 as a single direction (or RICK) repeater. This is what i have come up with so far (Please let me know if you see any issues or have any other suggestions).

Take the audio out from the scanner and split it (one for the audio to be repeated and another to be used to create carrier). The one audio output to be connected to directly into a RICK repeater cable I had (RA-1M Repeater Adaptor Motorola GM300 CDM CDM1250 RICK - eBay (item 350272827387 end time Dec-25-10 13:38:03 PST))

The audio out from the scanner would be connected to that of what would be coming out of Pin 11 (if I was using a motorola mobile as the source).

The other audio out would be used to create the carrier, or to "key the radio." That output would first go into a voice operated relay switch (Super Sensitive Sound Voice Activated Relay Switch - Assembled). That would create a 3 amp carrier whenever the scanner produces audio (above a controllable level). However since motorola microphones do not work on carrier, they work on ground, the output from the voice operated relay would have to go into another relay.

From what I have researched motorola mics have a continuous 250ma current through them, when the mic is keyed it grounds thus "keying the mic." To recreate this i have a regulated 250ma transformer (a power supply for a small security camera), that will be connected to another standard relay. The voice operated relay will act a the switch however wired in a fashion to close the relay, thus creating a ground, keying the mic.

When the mic is keyed the audio input is from the scanner thus broadcasting the scanner audio. It is somewhat complex, but i am not aware of any other devices that will repeat audio from your 3.5 mm audio jack.

ALSO, it should be known the frequencies being repeater are all licensed by me (VHF and UHF) and is being repeated over another frequency licensed by me. So there is no legality issues.

Thanks
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Old 12-05-2010, 7:26 PM
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Quote:
Originally Posted by unioner101 View Post
I have been for the past week or so researching and experimenting with how to use my radio shack scanner and a CDM1250 as a single direction (or RICK) repeater. This is what i have come up with so far (Please let me know if you see any issues or have any other suggestions).

Take the audio out from the scanner and split it (one for the audio to be repeated and another to be used to create carrier). The one audio output to be connected to directly into a RICK repeater cable I had (RA-1M Repeater Adaptor Motorola GM300 CDM CDM1250 RICK - eBay (item 350272827387 end time Dec-25-10 13:38:03 PST))

The audio out from the scanner would be connected to that of what would be coming out of Pin 11 (if I was using a motorola mobile as the source).

The other audio out would be used to create the carrier, or to "key the radio." That output would first go into a voice operated relay switch (Super Sensitive Sound Voice Activated Relay Switch - Assembled). That would create a 3 amp carrier whenever the scanner produces audio (above a controllable level). However since motorola microphones do not work on carrier, they work on ground, the output from the voice operated relay would have to go into another relay.

From what I have researched motorola mics have a continuous 250ma current through them, when the mic is keyed it grounds thus "keying the mic." To recreate this i have a regulated 250ma transformer (a power supply for a small security camera), that will be connected to another standard relay. The voice operated relay will act a the switch however wired in a fashion to close the relay, thus creating a ground, keying the mic.

When the mic is keyed the audio input is from the scanner thus broadcasting the scanner audio. It is somewhat complex, but i am not aware of any other devices that will repeat audio from your 3.5 mm audio jack.

ALSO, it should be known the frequencies being repeater are all licensed by me (VHF and UHF) and is being repeated over another frequency licensed by me. So there is no legality issues.

Thanks

Can't tell from the information given, but you need to be aware of the DC bias voltage on the RX
filtered audio output on pin 11 of the CDM radio. Make sure when you connect up to this point that
the bias voltage is still present. Hopefully there is a coupling capacitor in the RIC circuit to block
the DC voltage.

The same thing will happen on the TX mic connection. There is a DC bias voltage on the mic high
connection that you don't want to short out. Again hopefully the RIC has provided a coupling
capacitor to block the DC bias from being shorted.

Happy playing with the RIC you found. If the RX audio from the scanner or RX source gets too
high, it will cause audio distortion on the transmitter. Again if the RIC is designed carefully, it
will have some sort of audio gain control to set the TX audio level.
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Old 12-05-2010, 10:30 PM
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Aside from the technical issues, yes the legalities do apply. Even if you are licensed for all the frequencies involved that in itself does not convey authority to operate a repeater without the applicable licenses to indicate repeater operation.
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Old 12-05-2010, 10:48 PM
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Originally Posted by rfradioconsult View Post
Aside from the technical issues, yes the legalities do apply. Even if you are licensed for all the frequencies involved that in itself does not convey authority to operate a repeater without the applicable licenses to indicate repeater operation.
Isn't it illegal to repeat audio from other communications onto separate frequencies, with the exception of radio patches and amatuer communications? One example- what I thought twice about doing in the car- plugging a scanner into an ipod fm transmitter and using it to have stereo audio in the car... I had that setup for about 10 minutes and then realized I should probably stop that.
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Old 12-05-2010, 11:18 PM
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Quote:
Originally Posted by Gezelle007 View Post
Isn't it illegal to repeat audio from other communications onto separate frequencies, with the exception of radio patches and amatuer communications? One example- what I thought twice about doing in the car- plugging a scanner into an ipod fm transmitter and using it to have stereo audio in the car... I had that setup for about 10 minutes and then realized I should probably stop that.
Using a licensed radio telephone interconnect or cell phone to retransmit scanner audio would be legal, right?
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Old 12-06-2010, 10:22 AM
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if he is licensed for repeaters on both bands, unless this is a fixed point that is above 6 meters i don't think it is completely illegal. if it was then PAC/RT and other cross band repeaters would not be allowed. there may be a certain designator required on the license, i dunno for sure as i have never licensed anything for cross band use.

we used to maintain a road construction company's radios and they had a low band/UHF cross band setup. all trucks had low band, and all base locations had a switch to choose which base to use on the remotes. any traffic on either freq was retransmitted on the other band so that local trucks heard the traffic on low band and distant trucks could hear/talk thru an identical setup at another tower. should a repeater be offline, the base could talk direct on low band but for the most part they talked UHF only to the repeaters which was then resent on both UHF and low band.
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Old 12-06-2010, 12:55 PM
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All legal issues aside, how will the setup prevent the scanner's receiver front end from being overloaded or "de-sensed" by the CDM mobile when it transmits? Is this setup going to use separate antennas or a single antenna?

The receivers in most scanners tend to be broad as a barn in terms of what the receiver's front end will pick up. The end result is they are much more susceptible to overload from strong nearby signals compared to 2-way commercial 2-way radio gear that has a tighter front end to it. A homebrewed repeater will work much better if it uses a commerical grade 2-way mobile for a receiver instead of a scanner.

Do you have another CDM1250 mobile or similar to use for the receiver?
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Old 12-06-2010, 1:17 PM
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Quote:
Originally Posted by davidgcet View Post
if he is licensed for repeaters on both bands, unless this is a fixed point that is above 6 meters i don't think it is completely illegal. if it was then PAC/RT and other cross band repeaters would not be allowed. there may be a certain designator required on the license, i dunno for sure as i have never licensed anything for cross band use.
PAC/RT and other vehicular repeaters are supposed to have MO3 as the station class.
As far as I know the 6.1 meter rule is only for control stations, not bases or repeaters.
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Old 12-06-2010, 3:31 PM
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The question is, what kind of traffic will you be re-broadcasting? If it is law enforcement or some other public safety, i is illegal to rebroadcast that.

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