Using headphone jack for discriminator tap ?

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Gilligan

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I was just looking at a discriminator tap on a Pro-97 and thought about how difficult it was to find a place to mount an output jack. I was wondering how difficult it would be to use the headphone jack and just put a tiny switch to determine speaker/discriminator output for the jack. Any ideas or concerns?
 

Mattsenft

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Well........... I don't own a pro-97, but I do own several other Radio Shack handheld scanners. If the scanner is built similar to most that I have seen the jack is mounted directly to the PCB. Based on that assumption, to use the jack for a discriminator output you would first have to remove the existing jack from the PCB and the case. Then you would have to install a new jack in the existing hole in the case (space permitting). Then you would have to install a switch in your desired location in the case. Finally you would have to run wires from the PCB at the existing headphone jack points and discriminator output points to the switch and new jack. This is all based on the assumption that the jack is mounted directly on the PCB. While all possible (except for possible space constraints)
it sounds like a lot of work to me. I think I would check in to all other possible options before pursuing it if it were me.
 

car2back

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the scanner audio is mono right? could you pipe the audio through the left channel and the discriminator output through the right side of the headphone jack?
 

Mattsenft

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The scanner audio probably is mono. The jack would be mono as well and still need to be replaced with a stereo jack at the very minimum.
 

car2back

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Mattsenft said:
The scanner audio probably is mono. The jack would be mono as well and still need to be replaced with a stereo jack at the very minimum.
I see. just a brain storm :D
 

wyldman

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They make some pretty small 2.5mm jacks,like the little ones used for cell phone headsets.

You can also just run the wires out of the case,and use a regular covered jack on the end.This is what I do for units that are quite small inside.It does hurt portability somewhat though,as you have an extra cord hanging off it.

One last resort is to hide the jack inside the battery compartment.Most scanners have enough room in this area to mount it somewhere.It will be a little tough to plug in,but it will work.When your using the tap,you will most likely be plugged into the A\C adapter anyways.
 

rescue161

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I tried to do that very thing with a Pro-92. After cutting all of the traces and routing wires from the disc tap to the headphone jack, I lost all audio... Seems that GRE ran ALL audio through the headphone jack, so I had to replace all of the traces and solder back in a few components. I then put a seperate jack on the side. The PCB ain't pretty anymore, but at least I got it to work again.

My 2 cents, just install a seperate jack and be done with it.
 

slicerwizard

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rescue161 said:
After cutting all of the traces and routing wires from the disc tap to the headphone jack, I lost all audio... Seems that GRE ran ALL audio through the headphone jack
Well, that's how they all do it. Ever notice how the speaker shuts up when you plug in headphones? :)
 

rescue161

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slicerwizard said:
Well, that's how they all do it. Ever notice how the speaker shuts up when you plug in headphones? :)
No, lol, I mean I bypassed that and hooked the speaker up, but it still didn't work. I've taken Uniden scanners before and did what I did and they all worked, but the GRE was different.

Granted, these were old Unidens that didn't have that "protect you hearing" circuit in them.
 

rescue161

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What I'm getting is that if the scanner has some sort of protection set up so that you don't blow your ears out when the headphones are plugged in, i.e. the volume isn't as loud even on an external speaker, then it would be best to steer clear from using the headphone jack as it is way more complicating than just hooking the main speaker direct.

Good luck.
 

slicerwizard

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Mattsenft said:
The scanner audio probably is mono. The jack would be mono as well and still need to be replaced with a stereo jack at the very minimum.
It's not uncommon for scanners to have stereo jacks, since that makes it easy to plug in typical stereo headphones.

If the ground leg of the jack (sleeve) runs to ground, either directly or through a small resistor or through an electrolytic, one channel can easily be wired up as a slicer output. 396T's are wired this way.

If the jack is driven by a bridged output, the sleeve connects to one side of the audio amp and there is no way to piggyback a discriminator output. 246T's are wired in this fashion.
 

slicerwizard

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rescue161 said:
What I'm getting is that if the scanner has some sort of protection set up so that you don't blow your ears out when the headphones are plugged in, i.e. the volume isn't as loud even on an external speaker, then it would be best to steer clear from using the headphone jack as it is way more complicating than just hooking the main speaker direct.
No it isn't. The protection mechanism used a few years back was nothing more than a small resistor running from the sleeve to ground, which was why shorting the sleeve to the BNC connector would restore full external audio levels. Running a discriminator signal through that return path would have no effect on decoding whatsoever.

It's only with circuits like this...

http://home.ica.net/~phoenix/wap/BC246T/Audio.gif

...where you have to spend a bit more time:

- remove 18 ohm resistor and connect sleeve to ground

- remove 10 ohm resistor and connect ring to discriminator

- wire discriminator plug to use ring and sleeve

- if external speaker/headphone functionality is desired, wire its plug to use tip and sleeve and install a DC blocking capacitor (100-200 uF) in series with external speaker/headphone

- if jack will not be used for external speaker or headphones, VO2 can be connected directly to internal speaker
 

rescue161

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slicerwizard said:
No it isn't. The protection mechanism used a few years back was nothing more than a small resistor running from the sleeve to ground, which was why shorting the sleeve to the BNC connector would restore full external audio levels. Running a discriminator signal through that return path would have no effect on decoding whatsoever.

It's only with circuits like this...

http://home.ica.net/~phoenix/wap/BC246T/Audio.gif

...where you have to spend a bit more time:

- remove 18 ohm resistor and connect sleeve to ground

- remove 10 ohm resistor and connect ring to discriminator

- wire discriminator plug to use ring and sleeve

- if external speaker/headphone functionality is desired, wire its plug to use tip and sleeve and install a DC blocking capacitor (100-200 uF) in series with external speaker/headphone

- if jack will not be used for external speaker or headphones, VO2 can be connected directly to internal speaker
I stand corrected. Either way, I've done it with older scanners that didn't get that complicating, so when I tried it this way, I ran into problems.

TYhanks for clearing that up.
 

Gilligan

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Slicer, I know this is off topic (I started this post, so I'm allowed :) ), but would there be an easy way to increase the speaker volume for the 246T? Would it be as simple as shorting a resister? This could even be at the expense of the headphone level limiter. Thanks.
 

AZScanner

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Paging Paul Opitz...

Yet another thread showing the value of having a discriminator tap straight from the factory. Come on Uniden and GRE... how about it? I'd pay an extra $5 or $10 for this convenience built in.

Until then though, my advice is to get your hands on an old 780 or 895 to tinker with and add taps for this or that. Much easier to work on then a handheld and far less heartbreaking if you muff up and fry it.

-AZ
 

SCPD

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AZScanner said:
Yet another thread showing the value of having a discriminator tap straight from the factory. Come on Uniden and GRE... how about it? I'd pay an extra $5 or $10 for this convenience built in.
Thanks AZ.

Not meaning to give UPman a hard time but I'll go the disc. tap one better. Anyone with a PRO-96 or PRO-2096 that wants to monitor a P25 system can do so out-of-the-box without tapping the radio. The PC/IF provides raw packet data.

The sad thing is only P25 packets are supported - not LTR, EDACS or Motorola. I see an opportunity for GRE to expand on this and/or a chance for Uniden to one-up (isn't that what "UPman" stands for?) the competition.

-rick
 
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