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BC895 Discriminator Tap Information

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, here is an image.  Click on the image for a much larger (199KB) view.


Greg Knox

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