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BCT15 discriminator tap “how too”!

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#1
Ok…so I finally got around to gathering enough info to do the tap on my BCT15.
It took me a while to sort through various postings on how to tap your BCT996T to do so.

As there was nothing specifically pertaining to the BCT15, I thought I would post it in a short and concise manner for others looking to do the mod.

Items needed:

BCT15 ;)
10uF tantalum capacitor
5k to 10k resistor
3.5mm mono jack (female)……keep in mind that I’m using a 3.5mm male to 3.5mm male patch cord to run to the “mic in” on my laptop running Universal Trunker. Others have used an RCA jack instead of the 3.5mm jack.

Photo of the tap point can be found here http://www.radioreference.com/forums/showpost.php?p=297579&postcount=7

Solder the positive “+” side of the 10uf Cap directly to the spot marked “DISC”…then solder the resistor in series off the cap (the orientation of the “resistor” is not important). Run your ground wire from the ground on your “jack” to one of the mounting screws on your board…and your wire coming off the “resistor” to the mono jack.

How and ware you mount is your call...and thats it.

Good luck!
 

ka3jjz

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#2
It only makes sense that it would be in the same place as the 996, since the 2 are brothers to one another. I'll add a comment in the wiki somewhere so we keep a file of it.

Thanks es 73s Mike
 

letarotor

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#3
PYR8,

Why use both the resistor and tantalumn capacitor? I've seen one or the other used but this is the first I've seen both being used. Just curious is all. Thanks

Mark
 
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#5
ka3jjz said:
It only makes sense that it would be in the same place as the 996, since the 2 are brothers to one another. I'll add a comment in the wiki somewhere so we keep a file of it.

Thanks es 73s Mike
Great idea...thanks!

P.S. i noticed you edited the message a tad?!
 

letarotor

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#10
Slicerwizard wrote:
"The resistor provides isolation and the cap eliminates any DC bias." I've got a general idea what you mean, but could you please elaborate a little further? In techno challenged BillyFred language, please!!! Thanks
 
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#11
Without the resistor, you're exposing the discriminator circuit to the capacitance of the cable that you run to your slicer or sound card input. You're also directly exposing it to any signals that the cable picks up. Also, if you're using a sound card and you run the cable to line in, rather than mic in, you're likely connecting to a 600 ohm load, which is probably way too low for the discriminator chip.

The capacitor provides an audio signal that is centered around zero volts (no DC bias), which is what a data slicer wants to see. It also provides some protection for the scanner if the data slicer is miswired; data slicers run on (up to) +/-12V leeched from a serial port. If those voltages were directly connected to the scanner's innards, damage might occur.
 

andrewccm

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#15
My BCT15 should be here tomorrow. I plan on making this modification. Is there any general rules for soldering that I should know about. I know how to solder, but not on circuit boards.

I appreciate your help.
 
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#16
andrewccm said:
My BCT15 should be here tomorrow. I plan on making this modification. Is there any general rules for soldering that I should know about. I know how to solder, but not on circuit boards.

I appreciate your help.
My only advice is to make sure you are soldering the right spot...and make sure you don't overheat anything.
 

mancow

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#17
BTW, the interor of the 15 and 996 appear to be the exact same radio except for the memory devices. It looks as if they added a bit more memory to the 996 and loaded the appropriate software for IMBE decoding. Even the DSP chips are the same.
 
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