On Tue, 22 Nov 2005 21:25:47 GMT, Peter Vollan
wrote:

I have a question about discriminator tapping, and please don't tell me
to read up on in because I belive I have read all the web pages, the
problem is that they are not consistent.

Bill Cheeks seems to recomment a capacitor in line with the
discriminator tap, but even he seems unclear on the recommended value.
It seems to vary from 0.1 to 10 uF depending on who you talk to, other's
say you don't need it at all. A more recent post recommends a 10 K
resistor instead. Also a small 0.001 uF cap is recommended by some folks
connecting the tap and ground.

Any value between 0.1 and 10 uF will probably do the job. It's not
critical.

The main reasons I use a 10 k resistor are twofold:

- Connecting or disconnecting an interface to the discriminator
output might cause a short-circuit. The 10 k resistor prevents
the discriminator IC from being loaded or damaged.

- With some discriminator ICs, especially the MC3361, some IF
signal 'leaks' into the discriminator output. The 10 k resistor
with an additional 2.2 nF capacitor to ground forms a simple
filter that attenuates the 455 kHz IF signal, while leaving the
digital baseband signal intact.

Also, it looks like I should build a data slicer; at this time I am
using my sound card.

You can find the schematics of a slicer optimised for paging at
http://www.discriminator.nl/hamcomm/index-en.html

Regards,
Rene
Webmaster www.discriminator.nl/english/


--
Brace for impact. Brace! Brace! Brace!