Posted-By: auto-faq script Archive-name: cb-radio-faq/part4 Rec.radio.cb Frequently Asked Questions (Part 4: Technical Trivia) ------------------------------------------------------------------ [last modified 4/15/92] Questions discussed in Part 4: (dates indicate last modification) * What is single sideband? (1/92) * Do I really get 120 channels on a radio with single sideband? (12/91) * What are "linear amplifiers" and can I use them with a CB? (4/92) * Who is "Skip" and why can I hear him all the way across the continent? (3/92) * How can I reduce engine noise on my mobile CB? (3/92) * Where can I learn more about radio? (3/92) --Rec.radio.cb Frequently-asked Questions-----------------------------Part 4-- * What is single sideband? -------------------------- To understand single-sideband (SSB), one must first have a picture of what's going on in a normal AM transmission. For example, on Channel 21 (in the U.S. and Australia), a "carrier" is transmitted at 27.215 MHz. Your voice (or whatever you're transmitting) is used to change (modulate) the height (amp- litude) of the signal so that it can be reconstructed as your voice on the receiving end. A side effect of this modulation process is present on some of the closest frequencies adjacent to the carrier, above and below it. These are called sidebands. Normal AM transmissions include the modulated carrier and the upper and lower sidebands. However, 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 (USB) or lower sideband (LSB), 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 sep- arate 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 U.S., Australia, and any other countries that use AM and SSB.] 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 legal power settings on sideband give them an advantage. * What are "linear amplifiers" and can I use them with a CB? ------------------------------------------------------------ In the US, UK, Australia, Japan, France, and Germany, it is ILLEGAL to use a linear amplifier on Citizen's Band radio. (Sorry, we don't yet have info on Canada or other countries.) In the US and Australia, the maximum amount of power that is rated for CB is 4 watts on AM and 12 watts PEP (peak envelope power) on sideband. In Japan, the Citizen's Radio band is limited to 1/2 watt on AM and the Personal Radio band is limited to 5 watts on FM. In France and Germany, CBs can transmit up to 1 watt on AM and 4 watts on FM. For other countries, if there is a power limit on CB transmissions, any amplifier that boosts a radio's power beyond that point is obviously in violation. Linear amplifiers allow a radio to transmit using much greater power than is legal. They may range from 30 watts to above 500 watts. The problem is that, in reality, you can't communicate with anyone you can't hear. But you can easily interfere with people you can't hear if you use more than legal power. So a good antenna is the best solution for getting better range out of your CB. The reaction to questions about linear amplifiers on this newsgroup will vary with the country you are from. In countries where they are illegal, you will probably find yourself severely flamed... In other countries, to avoid a negative response, you may want to limit the distribution of the article to your country or continent, as appropriate. Besides, most black-market linears are low quality and will distort your signal and interfere with consumer electronics or other radio services. (Stray signals from a linear outside of the CB frequencies can bring a swift response from whoever it interferes with.) It is far better to run a clean radio with a clean signal into a high-quality coaxial feedline and antenna tuned for low SWR. Most radios are deliberately undertuned from the factory (to make sure that\ they are well within type-acceptance limits). Take it down to a 2-way radio shop and get it a "full-legal maxout" to 4 Watts AM, 12 Watts SSB at 100% modulation. * Who is "Skip" and why can I hear him all the way across the continent? ------------------------------------------------------------------------ If you've heard the term "skip" before, it refers to a condition where a radio signal bounces (actually, refracts, but that's getting technical) off the Iono- sphere, a higher layer in the Earth's atmosphere. For all practical purposes, this only happens during daytime hours because it's the Sun's radiation that charges up the Ionosphere and allows the signals to be bounced back to the surface. (Some residual "charge" remains in the upper atmosphere during the night but it is normally not as noticeable.) It's called "skip" because, in terms of where a given signal can be heard, it skips over a long distance before reaching the surface again. The distances vary but they can easily be over 1000 miles (1600km). For example, in Califor- nia, under skip conditions it's possible to hear signals from Alabama or other eastern states. However, skip is not a reliable means of communication. Besides, it may also be illegal to intentionally use skip for communications. For example, in the US you may not use CB for communications beyond 150 miles. (150mi = 240km) CB is intended for local communications. Skip signals are normally weak, though enough of them from different places can add up to a lot of noise. If you hear a strong signal, the person is prob- ably using a linear amplifier which, as discussed above, is illegal in at least the US, UK, Japan, France, and Germany and frowned-upon almost everywhere. Though there are some conditions when a legally-powered station with a special antenna can create a strong signal via skip, these are rare. Most CB users' experiences with skip is to turn their squelch higher to cut out the heavy background noise during the daytime. This means that anyone you talk to (locally) will have to be close by to send a strong enough signal to overcome the background noise and your squelch setting. There's really no way around this so get used to it. * 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 "magenetic 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, 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 guage 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 cheap power filters for noise- reduction purposes. You get what you pay for, though - 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. * 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 atmos- pheric 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. In what may become a trend in other countries, the US has authorized a new amateur radio "no-code" technician license which requires only a written test (no morse code). However, the test is challenging enough to necessitate several weeks of study so don't go unprepared. More information can be found in other newsgroups such as rec.radio.amateur.misc. Even if you don't want the license, books intended for amateur radio operators make available a wealth of information on understanding transmitters, recei- vers, antennas, modulation, signal propagation, electronics, and many other topics which also apply to CB.