Advertisement
PRO-28 30 Channel Programmable Scanner 200-0508 Guide to Scanning
866.0125 - 868.9875: ................................................. PSB
Common Carrier
869.010 - 894.000: ................................................... CCA
Private Trunked
935.0125 - 939.9875: ................................................. PTR
General Trunked
940.0125 - 940.9875: ................................................. GTR
Frequency Conversion
The tuning of a station can be expressed in frequency (kHz or MHz) or in
wavelength (meters). The following information can help you make the
necessary conversions.
1 MHz (million)=1,000 kHz (thousand)
To convert MHz to kHz, multiply by 1,000:
9.62 MHz x 1000 = 9620 kHz
To convert from kHz to MHz, divide by 1,000
2780 kHz / 1000 = 2.780 MHz
To convert MHz to meters, divide 300 by the number of megahertz
300 / 7.1 MHz = 42.25 meters
A Note on Image Reception
Radios work by simple mathematics.
by mixing that frequency with another (local oscillator) frequency which
is slightly different. This mixing process primarily gives us the two
original frequencies, their sum, and their difference.
Intermediate Frequency (I.F.) filter normally passes either the sum or
difference frequency, and this is then processed into the sound we hear.
Because nothing is perfect, certain "harmonics" will also get through if
they are strong enough. For example, if a radio's I.F. is 10.7 MHz, we
might be able to tune to a frequency 21.4 MHz (2 x I.F.) above (or below,
depending on the radio's design) a strong signal and hear it! This is more
evident in a double-conversion radio than a triple-conversion radio,
because the triple-conversion radio's 1st intermediate frequency is quite
high.
This causes the image to be so far off frequency that it is easy to
effectively filter it out.
So remember that just because a radio doesn't receive something which
another does is not necessarily an indication of a problem.
may simply not be "tricked" into picking up an image!
undesired signals is one reason that a triple-conversion receiver costs
more than a similar dual-conversion model.
You might be interested in finding more out about radio.
location to start looking is your local public library. You might also
wish to contact the A.R.R.L., as they are an excellent source of
informative texts on the subject.
Contact:
Amateur Radio Relay League
225 Main St.,
Newington, CT 06111-1494
USA
(CD EB 2/22/00)
9 of 10
http://support.radioshack.com/support_electronics/doc17/17653.htm
For example, most tune to a frequency
This rejection of
Well, the radio's
The one radio
One good
7/29/2007 11:46 AM
Advertisement
