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Questions discussed in Part 4: (dates indicate last modification)
* What is single sideband? (11/92)
* Do I really get 120 channels on a radio with single sideband? (12/91)
* How can I reduce engine noise on my mobile CB? (3/92)
* What is GMRS? (9/93)
* What is the Family Radio Service (9/96)
* Where can I learn more about radio? (4/03)
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* What is single sideband?
To understand single-sideband (SSB), one must first have a picture of what's going on in a normal AM (amplitude modulation) transmission. For example, on Channel 21 (in North America, Australia, and Europe), a "carrier" is transmitted at 27.215 MHz. Your voice (or whatever you're transmitting) is used to change (modulate) the intensity (amplitude) of the signal so that it can be reconstructed as your voice on the receiving end.
Actually, the amplitude of the carrier does not change. The addition (modulation) of another signal, like your voice, onto the carrier will increase the amplitude at other frequencies adjacent to the the carrier. A 300 Hz tone, for example, would add signals 300 Hz above and below the carrier. Every frequency component of your voice has the same additive effect. These modulation effects are the upper and lower sidebands of the transmitted signal. Normal AM transmissions include the carrier signal, the upper sideband (USB) and lower sideband (LSB).
The difference in frequency from the bottom of the lower sideband to the top of the upper sideband is called the bandwidth of the signal; it will be twice as wide as the highest frequency modulated onto the carrier. (For poorly filtered radios, this can unintentionally interfere with adjacent channels if the bandwidth is too wide. Poor filtering becomes easily noticeable at higher power levels.)
There is enough information in either sideband to reconstruct the original signal. Therefore, radios which can use single sideband are able to filter out the carrier and the opposite sideband before transmitting them, leaving either the upper sideband or lower sideband, as selected by the CB operator. Obviously, for a conversation to take place, both the transmitting and receiving radios have to be on the same channel and sideband setting (i.e. Channel 25 LSB.) Some additional tuning will be necessary with a "clarifier" control.
Assuming proper filtering within the radios, it should be possible for separate conversations to occur on the upper and lower sidebands of a given channel without interfering with each other.
* Do I really get 120 channels on a radio with single sideband?
[This applies to the USA, Australia, Canada, and any other countries that use AM and SSB on the same 40-channel band.]
Yes and no. SSB does give you 120 different communications paths (40 AM, 40 USB, and 40 LSB) but they are not free of interference from each other. The upper and lower sidebands will interfere with the AM channel and vice versa. With some radios, even the opposite sidebands can interfere with each other.
For example, (and this works for any channel - just fill in a different number from 1 to 40) Channel 17 has an AM channel that every radio can use. Radios with SSB will also be able to use the upper and lower sidebands. However, within a few miles of each other, you can't effectively use the AM channel if people are talking on either sideband. Though not as strong, users of sideband will know if someone is using the AM channel but the higher efficiency on sideband gives them an advantage.
* How can I reduce engine noise on my mobile CB?
If you have problems with engine noise in a mobile installation, there are several things you can do to reduce or eliminate the problem.
- Make sure you've completely installed your CB and the antenna is
grounded properly. Check the amount of noise with and without the
antenna connected. If the noise is greater when the antenna is
connected, the source is probably the ignition system. If the noise
remains unchanged after disconnecting the antenna, the source is
probably in the CB's power supply.
- For ignition noise, there are several parts of the vehicle that can
act like RF noise transmitters if not properly grounded. Check (and
connect to ground on the chassis/frame, if necessary) the engine
block, hood, muffler, and exhaust pipe.
- Ignition noise can be further reduced by installing "magnetic
suppression" spark plug cables. (These are significantly more
expensive than normal spark plug cables.)
- For power supply noise, check if you have a capacitor attached to
your ignition coil, alternator, electric fuel pump (especially on late model
Fords) and distributor. These can act as filters right at the source of the noise.
- Ensure that your antenna feedline and power lines are as far as
possible from any of the noise sources mentioned above, especially the
engine block.
- A shielded power cable can help as well. Make sure it is of
sufficient gauge to handle your radio's power consumption and that the
shielding has a good, strong connection to ground on the vehicle
chassis or frame.
- Electronics stores such as Radio Shack sell low-cost power filters for
noise-reduction purposes. But remember, you get what you pay for. Most
comments on this newsgroup are that they are not as effective as the
other measures above.
Of course, the best performance can be obtained from a more expensive radio with better noise suppression circuits. These measures, however, will improve the engine noise levels for nearly any mobile radio.
* What is GMRS?
[This applies only to the USA.]
The General Mobile Radio Service is another personal radio band. Its
frequency allocation is in the ultra-high frequency (UHF) spectrum,
co-located with some other radio services in the range from 460-470
MHz. It requires a license but there is no examination. Though GMRS is
not CB, it is listed here because it is intended for use by
individuals. A single GMRS license also covers the members of the
licensee's household. The license fee is US$35 for 5 years.
Frequencies (MHz) and modulation description:
460 - 470 FM General Mobile Radio Service (GMRS)
Regular channels: (simplex or repeater outputs, repeater inputs are 5MHz higher)
462.550 462.575 462.600 462.625 462.650 462.675 462.700 462.725
Simplex low-power channels:
462.5625 462.5875 462.6125 462.6375 462.6625 462.6875 462.7125
31.0-31.3 GHz any mode microwave band now open for individuals to use, requires GMRS license
GMRS is used for mobile-to-mobile or base-to-mobile communications but base-to-base communications are prohibited. One useful aspect of GMRS is that repeaters are allowed so that a mobile GMRS station can extend its range well beyond the limits of an ordinary 5-watt mobile transmitter.
Only individuals may obtain GMRS licenses. Some businesses still have licenses from before the rules were changed in 1989 but no new licenses are being issued to "non-individuals."
Recent changes in regulations have given GMRS licensees access to the microwave band at 31.0-31.3 GHz for both fixed and mobile use. The licensee must notify the FCC of each transmitter with a standard FCC form.
A source of information is the Personal Radio Steering Group. A reader said they have lots of good information and are enthusiastic about GMRS.
Personal Radio Steering Group
PO Box 2851
Ann Arbor MI 48016
Phone: (313) MOBILE 3
BBS: (313) 995-2100
Compuserve: 73016.163
* What is the Family Radio Service?
[This applies to the U.S.A only]
Recently, in the US, the FCC authorized a new service for use by the
general public. The Family Radio Service is a new service for use by
individuals. Tandy Corporation has pressed the FCC for this new
service.
The FRS is a very short range UHF Radio service. This service consists of 14 channels in the UHF band. Equipment is restricted to a handheld radio with non-detachable antenna, and 500 mW Effective Radiated Power on output. CTCSS tones are permitted, and will be used on some equipment. Range has been said to be "a few city blocks."
Repeater operation is not permitted, nor is data communications. Only type-accepted FRS equipment is permitted for use on this service.
* Where can I learn more about radio?
If you like what you see here and want to learn more about the technical aspects of radio, you may be interested in getting an amateur ("ham") radio license. These licenses are available in almost every country in the world, including all of the countries that have CB.
Amateur radio is very different from CB. This is neither good nor bad - they have different purposes. With the training that a licensed amateur radio operator is expected to have, much more powerful transmitters are allowed - but the operator should know when that power is not necessary and refrain from it. Amateurs have no limits on the range of their communications (at least by law or treaty) so it is possible to make distant "DX" contacts using atmospheric skip, satellites, or even bouncing signals off the Moon. Again, training and the willingness to cooperate (to avoid interference with others) are necessary for obtaining and using these privileges.
Japan, Sweden the USA and many other countries have authorized a new amateur radio "no-code" license which requires only a written test (no morse code). However, the test is challenging enough to necessitate several weeks of study (or a few days if you already have some familiarity with the subject) so don't go unprepared. For more information, see the FAQ articles in the rec.radio.amateur.misc newsgroup or contact the American Radio Relay League at: http://www.arrl.org/
Even if you don't want the license, books intended for amateur radio operators make available a wealth of information on understanding transmitters, receivers, antennas, modulation, signal propagation, electronics, and many other topics which also apply to CB.
Here's an update on German CB magazines by Henning Gajek.
Printed magazines on CB-Radio:
"CB-funk" was closed down in March 2003.
"funk" reports on CB, Amateur, Shortwave and other Radio topics.
source http://www.vth.de in German language.
"CB-Kurier" privately run CB-magazine
source http://www.cb-kurier.de (in german)
###END### rec.radio.cb FAQ