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Homemade Repeater Issue

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Old 08-14-2010, 01:17 PM
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Question Homemade Repeater Issue


I wanted to try a project that until now I figured would be pretty simple. I have heard many people talking about making a radio use VOX when the radio doesn't have VOX originally built in - by making a "squelch-controlled VOX" system. I have a Midland Regatta I VHF marine mobile radio with a squelch knob on it. I wanted to do a little work on this radio to try to make it use VOX so it could be connected to a scanner (receiver) and basically used as a repeater. I have no idea where to begin with this project. Anything helps! Thanks in advance!

-Dave.


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Old 08-14-2010, 02:40 PM
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You want to turn a VHF marine radio and scanner into a repeater?

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Old 08-14-2010, 03:30 PM
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You would need to use your volt meter to find a place within the squelch circuit where the voltage changes as the squelch opens. Then use something between a 10K to 100K ohm resistor to prevent loading of the squelch circuit to feed this voltage into the base of an NPN transistor (2N2222A). Ground the emitter. Connect the coil of a 12 volt relay to the collector and the other side of the coil to 12 volts. Depending on if the squelch control voltage goes high or low when it opens will determine if the relay closes or opens. Just use the appropropriate contacts to control the transmitter.

That's the easy part. The real issue will be interference of the broadband receiver in the scanner when the VHF transmitter is keyed. Realistically your only hope here is if the input frequency on the scanner is set to low band or UHF. It probably will have no chance of working if both frequencies are in VHF high band. That would require a much more selective receiver with complex cavity filters. An easy to build half duplex repeater as described uses a CB and a VHF radio. I used one planted on a water tower for many years.

The squelch control voltage used should be from a place in the circuit where it changes between some positive value and close to zero as it opens and closes. Low values not close to zero are more complex to trigger from. The resistor used should be high enough in value that it does not load down the control voltage when it swings high. In some cases the impedance of the circuit could require a Darlington transistor to prevent loading. The relay coil should also have a diode across it to prevent inductive kickback that could burn out the 2N2222A transistor.

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Old 08-14-2010, 03:44 PM
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Not to mention the fact that it would be extremely ILLEGAL!
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Old 08-14-2010, 03:51 PM
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There is that but it was overlooked at 18.

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Old 08-16-2010, 10:52 PM
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Thanks for the help. It was way over my head but I might be able to figure it out. And actually, depending on the frequencies and the wattage of the transmitter, it's not illegal at all. Especially when you are a volunteer firefighter and are using it for a secondary fireground communications channel. When it's a low-wattage channel used for emergency communications, it's not even close to illegal lol. Thank you for your concern though. Again, thanks for the help everyone.

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Old 08-17-2010, 03:14 AM
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Quote:
Originally Posted by dspurg7310 View Post
When it's a low-wattage channel used for emergency communications, it's not even close to illegal lol. Thank you for your concern though. Again, thanks for the help everyone.
Unless you are licensed to use that frequency it is illegal regardless of the power output used. The emergency aspect only comes into play when there are NO other means of communications available to summon help. Configuring a marine radio to broadcast a scanner feed does not fall into the "emergency" aspect of things.
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Old 08-17-2010, 11:49 AM
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For example when my wife and 2 of my kids studied for there Tech they ey went in and took a Saturday and Sunday course to give them the extra knowledge and a better understanding of the things I had help them study and help by better explaining things to them just in more detail.

There first day they were told a story from the 4 instructors about a man I believe it was California that had came upon an accident and used his 2 meter rig to summon help mind you this was a licensed operator he was later contacted about his meathod he used to get help. Well unfortunately the poor fella was actually taken into court and was fined and found himself in hot water!!

I being a licensed operator myself was puzzled and found this story kind of hitting a nerve. This was until (my kids) gave me the explanation. The man was sited and issued a fine because he had modified the radio prior to this incident like it was looked at as a premeditated thing I guess. Ok I get that part but what got me was what the hell they expect?/ A guy to open a radio and modify that radio to then beable to get help?? Well then he might aswell dispatch the county coroner!!

I noticed that one of my Yaesu FT-2800M takes a internal mod to expand frequency TX and my newest one only takes shutting off the radio then holding 2 buttons in while powering it on and one turn of a dial and the push opf a button its done!! And the open TX mod can also be reversed the exact same way unlike theo older model although they look and operate the exact same way!!! Kind of funyy but made light of the kids story after thinking about these to FT-2800M

All in All it doesnt matter who you are what license you posess there are thin lines to what you can and cannot do and it depends on what the big boys decide there going to do when or if you get caught doing whatever it is your doing. This story will always stick in my head because it just bothered me that a man helping got in trouble over his radio. Theres thin lines and red tape in all of this radio stuff and I know one thing Ill never be the Guinea Pig or Lab Rat to test these waters!!
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