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

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!