discriminator
 

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.

I am successfully monitoring pocsag and flex with none of this, but
obviously there is always room for improvement. So everybody's opinions
on this are hereby solicitied.

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

discriminator
 

it really depends on the build of the radio.
the only sure way to see if you do need a cap &/or resistor is to scope the
tapping point and look to see if you are 'loading' it too much or if you are
getting varying results on decode, to see if there is noise therewhich is
causing you the reliabilty problem.

i always do use a cap normally 1uf, but the value might need to be selected
to ensure you get the freqs you need.

the calc for capacitive reactance will give you the info you need.

mike


if you
"Peter Vollan" wrote in message
...

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.

I am successfully monitoring pocsag and flex with none of this, but
obviously there is always room for improvement. So everybody's opinions on
this are hereby solicitied.

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

discriminator
 

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!