Re: BitX17 IF Frequency

Ashhar Farhan <farhan@...>
 

it is best to use as high an IF as is possible. At higher frequencies, the
pass-band appears to be narrower, hence the phase delay is better and the
skirt is better. I would imagine that the PC's standard 14.318 MHz crystals
are ideal. going higher in IF would compromise your Image rejection (for
instance, with 16MHz IF, the 18 MHz will have an image at 14 Mhz).

- farhan

On Feb 16, 2008 1:14 AM, Greg Derda <gderda@...> wrote:

Thanks to all who have replied so far!

Arv,

Thank you, this is what just I needed to help visualize the whole
process! Now i can stare at the schematics and figure out what is
going on. I actually have a "spare" stabilizer from my build of a WN5Y
ELR kit (long story - I ended up with two stabilizers). Picture is
here...

http://jezebel.ucns.uga.edu/~derda/elr/P6200001.JPG<http://jezebel.ucns.uga.edu/%7Ederda/elr/P6200001.JPG>

I thought about using it (once I figured out "how") with my BitX20a,
but I am very happy with the stability of that radio. Of course, I am
telling myself that I might build my third Bitx (I ordered the version
3 boards from Sunil) for PSK31, so I might want to use it there ;-).

Anyway, thanks again, I think I have enough information to keep my
noodle turning for a while.....

Greg
ki4mmm

On Feb 15, 2008, at 2:16 PM, Arv Evans wrote:

Greg

My latest BITX20A H&P stabilizer taps the VFO output at the junction
of
R-27 and Q-6 collector (top of R-27 on the kit circuit board). I fed
the common point between H&P integrator caps to a 150K resistor that
connects to the junction of R-38 and D-9.

At present I am using the G8SEQ idea

<http://downloads.hanssummers.com/sprat122b.pdf>

of an intact watch unit providing 32 Hz reference with half a 74HC74
as
the latch. The other half of the 74HC74 is used as a buffer to square
up
the VFO output.

The Ron Brink PA2RF circuit is probably a more elegant solution, but
this simpler method seems to work well enough for my needs.

Arv
_._

Greg Derda wrote:

Martien,

Thank you for the reply and info. I have considered a stabilizer,
and
I have tried to learn more about them, but what is not clear to me
is
where to tap the VFO for the output to, and input from, the
stabilizer.
For example, if a person wanted to add one to the Farhan-circuit
VFO,
where would you tap it?

Greg
ki4mmm

On Feb 15, 2008, at 10:25 AM, Martien wrote:

--- In BITX20@... <BITX20%40yahoogroups.com> <mailto:
BITX20%40yahoogroups.com>,
Greg Derda <gderda@...> wrote:
Hello Greg,

You could use the 10MHz standard with an 8Mhz VFO. This VFO can be
easily stabilised using a "Huff and Puff" circuit. There are many
examples on the web. I used this simple one (fig.1 schematic)):
http://home.hetnet.nl/~brink120/huf2.htm<http://home.hetnet.nl/%7Ebrink120/huf2.htm>
<http://home.hetnet.nl/%7Ebrink120/huf2.htm>
VFO is rock solid, PSK 31 is no problem.

Text is in Dutch but the schematics are quite clear.

Martien PE1BWI




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