Difference between FM and WFM

[James]

I programmed a local freq (in Cambridge 453.1) into my scanner twice
by accident. One on FM and the other on WFM. When its active I
switched between the 2 and the FM drops off somtimes -- is the
difference just signal strength? or is there more to it than that?

Thanks

[tony sayer]

In article <970e3cf3.05041...@posting.google.com>, James
<jamesba...@hotmail.com> writes

Wide FM will do just that, you widen out the bandwidth your receiver
will accept especially for FM broadcast. Narrow FM is used for narrow
channels such as FM PMR channels. Having it set wide will pickup more
that what you really want for PMR radio....
--
Tony Sayer

[Brian]

"James" <jamesba...@hotmail.com> wrote in message
news:970e3cf3.05041...@posting.google.com...

Hello,

all to do with channel spacing and deviation levels. Narrow is for radio
comms, wide is for radio stations. So you might have 3KHz deviation for PMR
and 75KHz for FM stereo. So more narrow channels would fit into the same
space as a wide one!
If you see what I mean. If you switch to narrow on a FM stereo broadcast it
will sound like listening down a phone - similar to digital radio.
Most services you can hear on a scanner are switching to digital networks.

[Jeff]

The receiver has to have the correct bandwidth top suit the signal being
received.
WFM is generally only used for broadcast FM stations. NFM for 2 way radio
etc.

The practical difference is if you use NFM to receive Broadcast stations it
will be very distorted. This is because the deviation is greater than the
bandwidth of the receiver, this means that the signal moves out of the range
that the filter will accept.

The other case, the one that you have observed, is receiving NFM with WFM
bandwidth. In this case the deviation is much smaller than the rx bandwidth.
The result of this is, firstly, the one that you noted; the audio will be
quiet. Secondly the wide bandwidth will let in more white noise, this,
coupled with the lower deviation will result in much poorer sensitivity.
(signal to noise ratio). Thirdly the wide bandwidth will allow signals on
adjacent channels to appear along with the wanted one.

Hope this helps.

Regards
Jeff