On Mon, 30 Jun 2008 17:50:50 -0400, ~db~®
wrote:

On Mon, 30 Jun 2008 08:08:28 -0700 (PDT), Connah
wrote:

Perhaps the image of the first IF and the
tx/rx
split is the same?

Hi, Brad! Thanks for your input. I must admit, I
am ignorant of the
subject of images though I have heard of this
topic repeatedly. Would
you mind explaining your thoughts in layman's
terms or pointing me to
a site where I could educate myself on this? I'm
very interested in
learning about. Thanks again, Brad! Have a good
one.

Matthew


Every modern radio receiver uses intermediate
frequencies in the demodulation process. This
results in better quality signals being fed to
the
audio anplifier; thus, better quality sound from
the loudspeaker. Usually the IF is given in the
specs of the scanner, and by convention, 10.7 MHz
is used in consumer radio sets. To get the
image
frequency of any given channel, double the IF and
add and/or subtract the result to/from the given
frequency.

For example, my local NOAA frequency is 162.4
MHz.
Image frequencies for it will be at 162.4 MHz. ±
21.4 MHz., or at 183.8 MHz. and 141.0 MHz. (2 X
10.7 MHz. = 21.4 MHz.)

Tune your scanner to a given station's image
frequency, and you may hear a signal strong
enough
to make you think that the station is operating
on
that channel; or stations operating on an image
frequency may effectively jam reception of a
desired frequency. Which as Brad points out, may
be the case with your base/handset channel pair.
Receivers which employ multiple intermediate
frequencies aren't as susceptible to this issue.


~db~®


To add a little bit of hopefully useful
information to the above, high end receivers will
say in their specs that they employ "dual
conversion" (two IF's) or "triple conversion"
(three IF's). A good explanation of how radio
signals are demodulated can be found in Robert W.
Shrader's "Electronic Communication," published by
McGraw-Hill. The most recent edition retails for
over $100 US; one might try to pick up a used copy
somewhere, or borrow one from the public library.


~db~®