Adding squelch tone decoder to an old scanner?

peten1vak

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I have a Radio Shack Pro 2021 scanner that I keep in my house just to listen to fire department dispatch calls. I have a discone up about 40 feet and the problem is the scanner has no tone decoder on it so on one frequency I may hear three or possibly four fire departments from far away. Does anyone know a way that I can add a tone decoder to this radio so that I can program in only the tones I want to receive? I've heard there may be some software that may be able to do this but I'm just not aware of it. Any help would be appreciated.
 

gmclam

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The best tone decoding is done in a dedicated IC. If you're looking for a "project", a PCB could be designed ... but it's a lot of work. I've done this kind of thing in the past (added a CPU to a scanner than didn't have one). Realistically (no pun intended), you'd be better off to get a different scanner. Sounds like you don't need anything more complex than a PSR-400.
 

lebrunmn

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I haven't heard of a software solution, but I believe a hardware solution to add CTCSS or similar technology would involve adding a discriminator output to the scanner. That's a bit like old story of the King, the mice and the cheese... Probably easier to just purchase a basic unit with CTCSS capability onboard. I see that someone here is selling a BC780XLT for $60--that has what you need.

Of course, I could be mistaken about the need for a discriminator tap--I'm sure there are some others on the board who have more tech experience.

Good luck.
 

gary123

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Comspec and several others all made addon tone decoders. Installation is easy. 4 wires B+, Gnd, Discriminator in, Squelch out. If you know the IF IC ill give you the connections. There are a pile on Ebay too. for some of the modules you would need to figure out the connections on the module and wire harness.

NOTE: if you put the board into the scanner you will be dedicating it to that tone on ALL channels.
 

krokus

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Buying a model with the CTCSS built in is the better idea, as others have mentioned. An add-on will still pause scanning for any signal, then not allow the audio through. So you are likely to miss traffic you want, due to the traffic you do not.
 

bob550

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Since you're only using this scanner to listen to fire dispatch calls, and considering it's age (I owned one 34 years ago), I wouldn't put much effort into a solution. But, your use of a discone mounted 40 feet up is probably way more antenna than you need for local fire calls. Consider using either the original telescopic antenna, if available, connected to the top input, or another antenna connected to the rear input. As I recall, the rear antenna jack may have been a Motorola type, so you may require an adapter for that. In either case, reducing the signal level along with proper squelch adjustment should cancel the reception of most of what you don't want to hear. If you truly want to keep using the discone, consider connecting a variable attenuator to the antenna input of the scanner. Adjusted properly, that will also reduce the incoming signal to eliminate more distant stations.
 
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