Small, sharp IF filter for use in dual-use WX rcvr/FM broadcast Rcvr
> I was curious if any have you have done this. I have the
>
midland wr-30 weather radio with fm on it. the reception is
> really good in pulling in very distant very weak signals.
> the problem is when it comes to cross over interference Ie
> 102.3 mixing with 102.5 it is really bad. I was curious has
> anybody tried to put modified if's (110khz filters) in their
> radios that have fm? or how you can do this
> thanks
> -OZ
>
Receiver/device discussed:
Midland WR-30 Wx and FM Broadcast radio
The filter in a receiver of this class is no doubt wider than
desirable in certain situations. The problem is going to be
size; do you have room for a larger filter in a device that
size. That is the question. There is also the question of
suitability - impedance matching and so forth.
The term you're looking for in lieu of "x mixing with y" is
X 'bleeding over' onto Y. I initially thought you had an intermod
problem with a couple of FM stations 'mixing' to affect your
weather radio on the weather radio frequencies!
Most likely, you have a narrow filter used in the Wx radio
portion of the receiver, and they switch in a wider IF filter
for use in the FM Broadcast receive mode, since the two modes
(Wx and FM Broadcast) have different over-the-air characteristics,
as shown here:
Wx band: 162.400 to 162. 550 MHz in 25 KHz steps
FM Deviation +-5 KHz
Highest modulating frequency: 4 KHz
Resulting IF Bandwidth: 20 KHz (approx.)
FM Broadcast: 88.1 to 107.9 MHz in 200 KHz steps
FM Deviation: +-75 KHz
Highest modulating frequency: 15 KHz
Resulting IF Bandwidth: 250 KHz (approx.)
