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- Roger Dewhurst
August 14, 2009, 2:01 am
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Yes, but the radios would normally need to be fairly close and it will only
work on some frequencies.
IF is usually around 455kHz.
Get a radio and put it on a blank frequency near 1000 kHz. Tune the second
radio (held nearby) between about 1400 & 1500 kHz.
As local oscillator = tuned frequency + 455kHz you'll hear a swooshing noise
as you tune past.
If it's tuned to a weak station you'll hear a beat note which will change in
pitch when the second set is tuned.
Yes. Same principle except the IF is 10.7 MHz and local oscillator is 10.7
MHz above the dial frequency.
If you are in an area where TV channel 4 or 5 is used, you can blot out
either picture or sound with an FM radio because these TV channels are
near/in the FM broadcast band and the receiver's local oscillator frequency.
** Ch5 was taken off air way back in the early day of FM broadcasting in
** Err - the choice of using a local oscillator ( LO) above or below
an incoming carrier mostly relates to the "image response" frequencies. In
the case of FM broadcasting, the chance of interference to FM listeners from
images was worse if the LO was above the carrier.
For below, the image frequency range is between 66.1 and 86.6 MHz.
For above, the image frequency range is between 108.9 and 129.4 MHz.
The latter band is used for air traffic control and navigation beacons -
so it is possible for broadcast FM receivers situated near airports or under
flight paths etc to be swamped with interference if the LO was on the high
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