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CB Radio - Antenna Basics: Choosing an Antenna

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Old 01-07-2010, 05:24 PM
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http://www.worldwidedx.com/cb-antenn...-part-2-a.html

Choosing an Antenna
To start this off right, I am not going to tell you to buy any one particular 'brand x' antenna. I am going to help make a choice that will work for you. More than that - I will attempt to give reason as to why one antenna may work for you over another. This will include your location, weather, resources, and then cost. I will make some recommendations down the line as well. I will discuss base station setups first; mobile antennas will be considered at the end.

One must keep in mind, that the antenna is the true heart of any radio operator's station. That bears repeating; so read it again. It doesn't matter if you are a seasoned Ham (who know this wheeze well!) - or a newbie who first used someone else's radio before deciding to get your own setup. Because it is what radiates everything that your station has going on. Linears are great - if used properly; but the antenna is what people hear at the receiving end. A better mic might give you some added character or flavor, but the antenna is at the root that goes between point A to point B. You can still do well on a budget, but I would be lying to you if I didn't tell you that the bettter antenna is the best place to spend your hard-earned cash - first! Don't worry; you will need to spend as much as it takes to do the job right. Sounds fair enough - right?

Let's say that you live in the country - like rural CO, VA, LA, AZ, or even ND or MA. Didn't mean to exclude you if your state wasn't mentioned. Let's say NW Kansas for a start. Relatively flat land, the Earth has decent grounding properties, but the weather can be a real issue. Severe winds, tornadoes (seen them in KS myself!), ELECTRICAL STORMS, and hail/ice/snow. Most rural areas in the US east of the Rocky MTS can be afflicted and influenced much like Kansas is.

You will need to get the antenna up about 30-35 ft in the air with masting/guy wires - or a concrete-base tower. This is the height you will need before any antenna is attached. Towers are expensive; masting is much cheaper. Of all the environmental threats, lightning and wind will be your biggest considerations. When installing a base antenna, it would be highly advisable to have a friend or two help you. It will make it happen much faster, and be less dangerous that way.

You will need to spend some money on your grounding system. This cannot be avoided at all. It is ESSENTIAL that your station be well- grounded. Three 8 ft rods in the ground tied together 20 ft apart in a line with wire bonding between them buried 1 ft below the surface is a practical setup - about $50-60 with a tailwind. You might have scrap metal that you can work with if you are on a farm, rural home, or a ranch. This will save additional $$$. But this would be the way to ensure an optimal and safer radio station.
http://www.worldwidedx.com/tech-repa...and-radio.html

The cost of masting will be dependent if you cannot find used 1 1/2 inch pipe thirty feet long. It need to be stiff enough over its 30-35 ft length to support itself w/o guy wires when upright; so with guy wire support you should be good to go. Two sets of guy wires with four legs each ninety degrees apart - placed at the center of the mast and at the top - should be ideal. Cost is about $30 if you cannot find a suitable substitute for the guying materials. Be sure that it is firm under wind load - and that if it were to fall over in a severe wind that it will NOT hit a power wire! When anchored securely, this should be able to withstand winds up to 70mph - provided the antenna isn't so massive that it requires more support. If you have to buy masting, it might cost as much as $20 for every ten feet section.

The most common, inexpensive, practical antenna is the 1/2 wave or 5/8 vertical ground plane antenna. They are often made of aluminum and will be 19 to 22 ft tall by themselves - respectively. The FCC states that a free-standing antenna can be 60 ft from ground to tip; so use this guideline to the maximum - I would. If the 1/2 wave antenna you chose is 18 ft; then you can have masting as high as 42 ft - provided it is properly supported with guy wires. If you have a 5/8 wave at 22 ft long; then 38 ft of masting would be best. If you go over a foot or two - I wouldn't worry about it. The FCC isn't going to shinny up your antenna and measure the height. Just stay close to tolerance.

Verticals are called 'omni-directional antennas'; they receive/transmit poorly in all directions. I believe that the 5/8 wave vertical antenna is probably the best choice for an antenna. They propagate radio energy better than the 1/2 wave, works extremely well for local communications, and works long distance 'skip talking' with better efficiency. But if you have a 1/2 wave antenna - don't fret. The extra height that you can put it up will help make up a little of the difference.

You might find that if you have more money to spend on your first setup, that you might want a beam antenna. They are the most efficient of all antennas. But there are caveats. They cost more, you will need to install a rotor to change its direction, and you will have to make the masting stiffer. Rotors can be had used/refurbished with the control box from $85 up to $300; a simple $85 one with a single element beam should be more than enough. Beams will have more wind load; which means it will be affected more by the wind than a vertical antenna would be. The BEST part of having a beam antenna, is that the energy from your radio is FOCUSED in one direction. This will help you immensely in transmitting. The cost twice as much as most vertical antennas do - but they are hard to beat. Beam antennas can also get very large and expensive - but even a simple beams works tremendously well.
The Ultimate Guide to 11 Meter CB Antennas

Let's say that you live in New York City. Good Luck. You probably live in a multiple dwelling, in which case Landlords have strict rules against such activities. Your best bet is to have a mobile radio and antenna. A magnetic mount antenna can be taken down and put inside the vehicle so that it doesn't get vandalized or stolen. So -you too- have a means to talk on the radio. Some of the better mag mount antennas can talk great distances as well. You can also run a decent sized linear w/o having to put in an extra battery or larger alternator. I know some radio operators that I talk to in San Francisco (50 miles N of my home) who do just that - and transmit very well too. So, you do have some options! This method will work for those who cannot set up a station any ither way.

Many live in the 'burbs' - the suburbs. I do. I have a 5/8 wave antenna that is properly mounted and grounded. As described above - quality mast with guy wires and a decent ground system. A beam antenna may well be my next antenna, because they work better focusing more radio power in a given direction. It may not a new one - but I want to get more usefulness out using just one antenna. But the suburbs can get you into trouble IF you are considering running a linear. I don't use a linear amp; I let the quality of my antenna and its proper installation to make it possible to talk to Quebec, N Canada, Alaska, Hawaii, Mexico, Texas, S Carolina, Virginia, and New York - and everything in between. Goes to prove THAT THE ANTENNA MAKES ALL OF THE DIFFERENCE!

This was written and meant for the beginner.
Tomorrow will be the last part in this series...
http://www.worldwidedx.com/cb-antenn...nna-final.html

First picture: For reference - to the right is what a tower looks like, and to the left is what a mast looks like. Both the mast and the tower have vertical antennas mounted on them.

Second picture: This is the difference of the radiation pattern of a 1/2 wave and 5/8 wave antenna. Notice that the 5/8 wave moves out far more horizontally across the ground than the (dotted line) 1/2 wave antenna does. Important difference!
Attached Images
File Type: jpg tower.jpg (155.7 KB, 12 views)
File Type: jpg gain.jpg (20.8 KB, 11 views)
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Old 01-07-2010, 06:10 PM
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Thanks Rob, I am going to move from the "Burbs" with HOA to the country without. I hope to start on a base (my first) next summer. This info will help alot.

What would be a good coax for a total run of around 70ft. 5/8 wave w/gp, with no more than a 1x4 in line? Im thinking mini 8, but not sure.

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Old 01-07-2010, 06:34 PM
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Decent Question!

With length; inefficiency in the coax becomes a major player - IMO. I use Belden 9913Flex for just a 55 ft run. I get practically all of my power out of my radio to the antenna this way. One must also consider, that receiving these miniscule 'microvoltages' into our antenna and down into the radio can be resisted, capacitanced (if there is such a word -lol!), and choked right out your receiver by poor coax.

Another brand of really decent coax is the Davis RG-8 213U. Which is highly resistant to weather of all kinds - including UV attack. It can even be buried; often referred to as 'BuryFlex' by the mfr. Another coax similar in quality to the Belden 9913 Flex is the Times-Microwave 'LMR-400 Flex'. Pricey; but not as expensive as the 'best' coax on the market - which is the Andrew/Heliax brand - which is astronomical in price with virtually no loss whatsoever. But the Belden 9913, 213 Bury Flex, or LMR-400 are also top performers at a fair cost - IMO. These RG-8 coax's are all almost twice as expensive as the RG-58/mini 8.

I think this next link is a very useful tool to calculating power loss. It uses a number of simple variables for you to fill in. Such as the frequency to be used, SWR, cable length you intend to use, radio power output , the cable type/brand you have - and then it will display a precise answer. Try it!
Remember: that even small percentages of loss can vastly change the amount of output power actually seen by the antenna.
Choose your coax carefully!
Coax Calculator
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Old 01-08-2010, 02:31 PM
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Let's say that you plug in some values into this calculator - OK?

Belden 9201 RG -58 coax
70 ft coax length
Frequency - say 27.205mhz (ch.20)
Good antenna match of 1.2
Power out of your amp ~600 watts

What did you get out/lose?

Results
Matched Loss: 1.391 dB
SWR Loss: 0.017 dB
Total Loss: 1.408dB
Power Out: 433.819W

So, you lost 1 1/2 db transmitting (it takes 6db's for a single S-unit; but it also can be considered 1 1/2db receive loss as well)
But - you lost 166 watts and 1 1/2db output to boot - more than 1/4 of the linear's output!
Still think cheap coax is the way to go? This calculation used Belden RG-58 coax. If it was a cheaper brand of the same type of RG-58 coax - your losses would even be greater still!

The resistance, capacitance, and inductance in what wire you choose to buy is what will make a difference. Use that coax calculator, and see for yourself. The Belden/Davis/Times-Microwave RG-8 is about a +/-$1 a foot. Buy only as much as you need by measuring; then add 5-8 to have some room for error to that length.

As a reference, even the BEST coax would take 15 watts and only a small fraction of a db (Andrew/Heliax LDF6-50A - but EXTREMELY EXPENSIVE) when applying 600 watts into it. The Belden 9913, Davis BuryFlex 213, and the Tiimes/Microwave LMR-400 brands would lose about 60 watts and 3/4db - to be fair.
SO - how much do you want to lose?
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Old 07-28-2011, 05:04 PM
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ROB,
These post are great, can give you an example of a station I setup in LV, NV and ran for 13 years using low a Cobra 2000GTL a R/S Archer .64 ground plane antenna using 100' of R/S RG8U coax the base of my antenna was at 18' hooked to the AC on the roof and my antenna was grounded to three 8' grounded 10' apart, for the first 5 or six years the station was bare foot the had the option of running a Cobra 250XL kicker it out put was 100+ watts on am. I could talk to and hear Big Trucks that used Big Radio in them on a good night in Prim NV, the state line between NV an CA about 55 air miles my my QTH. I myself would would talk to my wife when I was coming back to NV from CA about 15 miles into Ca on SSB when I would be coming down the last big hill in Ca before I got to the state line every time I came home. That .64 had a very low angle of transmit and receive, much like the 5/8 wave antenna you described in your post, years after I did a this stuff met a guy that worked out there in Prim and he told me that I was the only station he every heard when he worked out there from LV from his mobile, but there was a guy that lived about 4 blocks from me that had another Cobra 2000 that was using a A99 at 50' that could hear a lot more SKIP when it was running that I could never heard using my .64 so that also proves out what you said about 1/2 wave antennas. I now use a A99 at 36' for my wife to talk to me when I go from Sun City to Phenix about 35 mile and it does a good job if there in not any SKIP.............Oldtimer

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Old 07-28-2011, 05:19 PM
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ROB,
These post are great, can give you an example of a station I setup in LV, NV and ran for 13 years using a Cobra 2000GTL a R/S Archer .64 ground plane antenna with 100' of R/S RG8U coax and the base of my antenna was at 18' hooked to the AC on the roof, my antenna was grounded to three 8' grounded 10' apart, for the first 5 or 6 years the station was bare foot an I had the option of using a Cobra 250XL kicker that had an output of 100+ watts on am. I could talk to an hear Big Trucks that used Big Radio in them on a good night in Prim NV, the state line between NV an CA about 55 air miles from my QTH. I myself would would talk to my wife when I was coming back to NV from CA about 15 miles into Ca on SSB when I would be coming down the last big hill in Ca before I got to the Prim NV. That .64 had a very low angle on transmit and receive, much like the 5/8 wave antenna you described in your post, years later after I did this I met a guy that worked out there at the time, he told me I was the only station he every heard when he worked out there from LV from his mobile, but there was a guy that lived about 4 blocks from me QTH that had a Cobra 2000 that was using a A99 at 50' that could hear lots more SKIP when it was running than I could using my .64 so that also proves out what you said about 1/2 wave antennas. I now use a A99 at 36' for my wife to talk to me when I go from Sun City to Phenix about 35 mile and it does a good job if there in not any SKIP............Sorry about not checking my spelling before that last post!.........Oldtimer

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