On Mon, 30 Jun 2008 17:50:50 -0400, ~db~®
<deepblack@[EMAIL PROTECTED]
> wrote:
>On Mon, 30 Jun 2008 08:08:28 -0700 (PDT), Connah
><connah@[EMAIL PROTECTED]
> 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~®
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