I'm building a 2 metre Rx with an IF of 10.7 MHz. It will be used for FM. I
have three crystal filters with the following bandwidths: 15 KHz; +/- 6 KHz
and +/- 3.75 KHz. Which one should I use?
Thanks. Howard.

On Sat, 12 Mar 2011 18:48:14 +0000, Howard James wrote:

I'm building a 2 metre Rx with an IF of 10.7 MHz. It will be used for
FM. I have three crystal filters with the following bandwidths: 15 KHz;
+/- 6 KHz and +/- 3.75 KHz. Which one should I use? Thanks. Howard.

You mean 15kHz, 12kHz and 7.5kHz. You probably want 12kHz, unless your
channel spacing is really narrow.

FM bandwidth is calculated as 2 * (signal bandwidth + deviation), but for
the life of me I don't know what the deviation is supposed to be for
amateur narrow band FM!

--
http://www.wescottdesign.com

I would think the 15 KHz filter. The amateur deviation is normally 5 KHz.
for VHF and above. There is a push for going to 2.5 and closer spacing for
repeaters.


"Tim Wescott" wrote in message
...
On Sat, 12 Mar 2011 18:48:14 +0000, Howard James wrote:

I'm building a 2 metre Rx with an IF of 10.7 MHz. It will be used for
FM. I have three crystal filters with the following bandwidths: 15 KHz;
+/- 6 KHz and +/- 3.75 KHz. Which one should I use? Thanks. Howard.

You mean 15kHz, 12kHz and 7.5kHz. You probably want 12kHz, unless your
channel spacing is really narrow.

FM bandwidth is calculated as 2 * (signal bandwidth + deviation), but for
the life of me I don't know what the deviation is supposed to be for
amateur narrow band FM!

--
http://www.wescottdesign.com

On Mar 12, 1:48*pm, "Howard James"
wrote:
I'm building a 2 metre Rx with an IF of 10.7 MHz. It will be used for FM. I
have three crystal filters with the following bandwidths: 15 KHz; +/- 6 KHz
and +/- 3.75 KHz. Which one should I use?
Thanks. Howard.

Hey OT:
In ITU region 1 you use +/- 3.75Khz. If you are across the pond then
use +/- 6Khz.
Since they spell metre that way across the pond I think you are going
to be using +/- 6Khz

73 OT
de n8zu

Most 2 meter rigs start clipping around 5 KC.




On Sat, 12 Mar 2011 13:36:47 -0600, Tim Wescott
wrote:

On Sat, 12 Mar 2011 18:48:14 +0000, Howard James wrote:

I'm building a 2 metre Rx with an IF of 10.7 MHz. It will be used for
FM. I have three crystal filters with the following bandwidths: 15 KHz;
+/- 6 KHz and +/- 3.75 KHz. Which one should I use? Thanks. Howard.

You mean 15kHz, 12kHz and 7.5kHz. You probably want 12kHz, unless your
channel spacing is really narrow.

FM bandwidth is calculated as 2 * (signal bandwidth + deviation), but for
the life of me I don't know what the deviation is supposed to be for
amateur narrow band FM!

..... Since they spell metre that way across the pond I think you are going
to be using +/- 6Khz...

It depends on what kind of metre!

5kHz is the norm.

JOHN

On Mar 20, 12:31*pm, "John W"
wrote:
.... Since they spell metre that way across the pond I think you are going
to be using +/- 6Khz...

It depends on what kind of metre!

5kHz is the norm.

JOHN

Hey OM:
That may be so, maybe you should looky at a Kenwood TM261EJ, designed
for the European market, it has a 20Khz channel spacing on 2 metres, I
wonder why? Since 5Khz is the norm BW?

73 OT
de n8zu