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QRZ! Ham Radio 21
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QRZ Ham Radio Callsign Database - Volume 21.iso
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BC895-TA.TXT
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2002-12-30
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Subject: BC-895 Discriminator Tap
I've seen numerous complaints from those who have had trouble getting
applications working that need unfiltered base-band audio from the
BC895 discriminator.
Most people are tapping the discriminator at pin 9 of IC3 and this
seems to be the problem. IC3 P9 is NOT the right place to get at the
discriminator signal. The signal at that point is actually the 3rd IF
output with the base-band audio impressed on it (i.e. AM). What
you actually have is the desired signal, but translated to the 3rd IF
frequency (~450 KHz).
This is not going to work well with most applications that require the
discriminator output.
The actual base-band discriminator tap point is found on the bottom of
the circuit board and is MUCH easier to get at and solder to than IC3
P9 anyway.
The signal is ~1.5V P-P riding on a 2V DC bias.
To get at it, remove the bottom cover of the radio. Orient the radio
so that the rectangular silver shielded box is at the top of the radio
and the rotary VFO knob is at the lower right hand corner.
The tap point is a solder pad at the lower terminus of a vertical
trace about an inch long. The pad is located at a point 3.6" from the
top edge of the circuit board and 2.6" to the left of the right edge
of the circuit board.
I use this tap point with TrunkTrac and it works very well. Hope this
is useful. If you still have trouble locating the tap point I have
some jpegs I could upload if anyone has a place to put them.
Greg Knox
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