Howdy-

I couldn't agree more. You know what you're talkin about. And yes, it is illigal txmit over 4 watts in the US on the citizens band. At 52", the radiation pattern from 2 whips will just look like a flower with a lot of pedals and two lobes just slightly longer than the others. People, unless you are drivin a big rig with a trailer that blocks part of your signal, you're waisting your money.

Wattage?. . .hmmm. At one time, untill about 5 yrs ago, I used to have regular contacts with a gentelman on Midway Island on HF using around 15 watts. Now that kicks but.

 

Yea, propagation is cool..

That's the thing that get me. The CB band is so suited to long distance work, but rarely does anyone take advantage of it. It's not really the average persons fault. They get a CB and then need an antenna. Go to the store and there's dozons of options to choose from, but all mobiles and not much in the way of explination. Except, here's your antenna, you need a good ground plane and get your SWR as low as it will go and it'll be, "tuned". Want to spend more money? Here's the High Power model.

Everyone wants more range, so common sense says to get more power. It just doesn't work. You get power and range from your antenna.

The FCC sets the limits at 4 Watts - coming out of the radio. It doesn't set limits on the antenna gain. Every 3dB gain doubles your effective power. Hook your 4 Watt CB into a 3 dB gain antenna, you'll have 8 Watts directional coming out. Now you might say, "But, I can do the same thing with my linear hooked up to the old firestick." Yes you can BUT, it's at a price. Just because you can transmit doesn't mean you'll receive. It'll get to the point that with enough power, you'll say - Hey, anybody out there? Maybe 5 people will respond, but you can't hear them. A gain antenna will hear them.

You run power and the neighbors complain. They complain loud enough and the FCC will come to the door, take all your gear and fine you about $8 grand, (this is usually lowered if you say the kids gotta eat).

You run a high gain antenna with a 4 watt CB and don't transmit over a 172 mile radius, (right antenna, it's a piece a cake with a little practice - even with a Uniden 510), the FCC will come to your door, check out the old 510, then they'll go to your neighbors and suggest they get better shielded TV coax.

Firesticks twin array claim from the link in an earier post kind of bugged me. The 4 foot spacing they state is so close to a 1/8th wave I just figured it's what they meant. I did some reading at lunch today and found that twin 1/4 wave sticks spaced at 1/8 wave fed in phase, (like they come, store bought), have a 0.3 dB gain. Basically nothing, or the same as a single stick. However, if the same configuration of two antennas is fed 180 degrees out of phase, it'll endfire at 3.8 dB. (That means I'd have to have one stick in front of the truck and one in back somehow, for front and back gain. Wouldn't look as good as two mirror mounts, but the gain figure is very impressive.) I should email them and tell them I want one!

 

It actually doesn't look to bad. My buddy "squawk" had an `88 Ranger XLT 4x4. He mounted one dead center on his front and rear bumper.

I'll try to find a pic (most of them are in storage) of his truck from back then.

 

A few of the things that need to be under stood about the twin mount antennas.

Coax:
The length of the two coax lines running the antennas must be the same electrical length. This is not the same as the physical length in most cases, but usually it is with no modifications. To say there's lots of variables is to put it mildly. The reason you want them both equal is so that the split signals will be in phase when they reach the antennas, where the signals will combine and feed off each other and throw out a wave in the direction you want. The reason they tell you not to coil up the excess coax is because when you coil it, you're in effect, making a choke which slows down one side, the other or both. Sometimes you want a choke, but not when you're shooting for perfect phase. A lot of times this won't show up on your SWR meter, so everything appears to be working just fine. The , "T", arrangement of coax they give you with the twin sticks is called a Phasing Harness for good reason.

Antenna spacing:
The antenna spacing is just as critical as the coax. One of the things that make phased arrays difficult to make work is not only do you have to worry about getting a good ground plane for each antenna, you have to work to get the spacing between them just right. And the relationship between the two can make a difference, too. A fraction of an inch can make a big difference. When you transmit on an array the signals from each antenna energize the other antenna and go back and forth. Just like ping-pong. How they, "bounce" off each other is what gives you the gain or direction. Thinking about it DC current wise, the current does split at the base of the phasing harness, but meets up again at the antennas, so you don't really lose current - just direct it where you want.

For the end fire arrangement I wrote about in the last post to work, the antennas need to be spaced 1/8 wavelength apart - that's about 4 1/2 feet. The phasing on the coax needs to be 180 degree's out of phase, (in this case one side NEEDS to be choked perfectly). This is really difficult to do. You can't just buy it pretuned and expect it to work right. There's just too many variables. It's very hard to test for phase, (even the test equipment to attempt it can run into the 10's of thousands). The way to do it is to document all the variables, calculate phase, electrical length and the LC network, cut the coax a bit longer than needed - then cut, solder connectors, test, repeat. Then you just hope for the best.

When someone tells you it's easier to just run coax to one antenna and leave the other on dummy, please believe them. That goes for semi-tractor trailer rigs, too. The good news is, if you REALLY want to make it work, there's lots of info on the internet about it. Just search, "phased array antenna".

 

Howdy knows his stuff ya'll. I'm gusssin he's either an EE or a fellow Ham.

 

damonlan is definetly right. You definetly know your stuff Howdy, so can i ask ya a question. I too would also like to run dual whips but after reading all this, im gonna keep the whip on the passenger side just a dummy antenna. I want either mount them on my mirrors, or behind the bed on the cab. Since the one wont be hooked up, just there to look good lol, it cant interfere with the other one right? Thanks.

 

Oh i also forgot to mention, if i mount them on the bed behind the cab, i have a rollbar that will also have kc lights on it eventually. Could the rollbar affect the reception of the antenna at all. Thanks again for the great info.

 

Having one active and one dummy on your mirrors won't affect it noticeably. Of course, any time you have part of your antenna below the roof line or anyplace other than the center of your roof it will make your pattern somewhat directional. But for looks it's probably worth it.. In some cases your dummy can act as a passive reflector, but I wouldn't worry too much about it.

Down low, behind the cab is probably the worse place for an antenna, however; if you were to fab some kind of mount on your roll bar to attach them, it would work well. Height is always good.

damonlan - Back in the 70's I was in my teens and the family lived up in the mountains, where everyone had CB's and Handles. One old retired guy was the resident CB radio tech for the locals and log truckers. His wife had died years before and he turned the house into his own private CB museum. He must have had at least 40 or 50 old Browning Rx Tx tube sets lining every wall in the house, a 5 kW linear and a big beam on a his tower. All his feedline were strung right out the kitchen window. He told me I could hang out as long as I never bought anything from Radio Shack.

Since then I've built phasing harnesses for 50 meg lowband, hooked up 1.5MW TV transmitters to 6 dB antennas and tuned the wave guide, installed and tuned microwave systems up to 28 GHz, and a host of other radio site, two-way, cell, and broadcast stuff. Got my two year electronics degree and passed the General Radio Telephone Operators test years ago.

After years and years of prodding from people in the industry, last month I passed my Tech Class ham test. So I guess I'm newbie ham!...

The thing I like about RF stuff is you can never know it all. I'm still learning, like everybody else.

 

Thanks again Howdy. Cant wait to get my CB radio and whips eventually........

 

Howdy-
You've done the kind of stuff I have alwayse wanted to do. But I just can't seem to get into the RF world and make a living. For now, it's just a hobby. I agree with the old-timer, lay off the Radio Shack stuff. BTW. . Welcome to Ham radio.

 

Yes! welcome to ham radio !

W6EZ

 

i use a wilson 5000 mag mount on a van you could use a 102" stainless wip wilson makes a good antenna go to http://www.copper.com wilson makes a lot of different mounts plus you can take the stinger and load off quick

 

Howdy, where can I get one of those 3dB gain, 1/4 wave 109" stainless steel whip antenna's you mentioned earlier and what kind is best.

Thanks,
Jeremy

 

There is no such thing as a 3db gain 1/4 wave whip.
There are two forms of gain to be considered.
One is dbi ( gain over a isotropic (sic) radiator )
this is a gain figure for a paper antenna that radiates equally well in 360 degrees.
the other gain figure is dbd and that is gain over a dipole. A dipole is two quarter wave elements fed at the center point.
A quarter wave antenna is 1/2 of a dipole, so the BEST you can expect is to be 1/2 as good as a dipole.
1/4 wave antennas are at best, 50% effective.
So just buy ANY 1/4 wave antenna and know you are better off than ANY of those other antennas with a coil.
1/4 wave stainless is always good.
Radio shack is easy and cheap.

 

A 108" stainless whip has unity gain. That means it radiates in an omnidirectional pattern, (circular). The thing itself is really simple. It's a length of plain old rod. There's not really much to it, but the manufacter's try to make them better looking by tapering them and adding a little ball on top.

The nice thing about them is they perform well. They are a true 1/4 wave. I believe 5/16" is the standard diameter. This big diameter gives you a couple things. One, the bigger the diameter, the shorter the physical length needs to be to equal the elecrical length. Two, the thicker it is, the wider the band width it'll work well at. Tune a thick antenna at Ch. 19 and it will most likely show close to the same SWR at Ch. 1 and 40. A skinny antenna will still work, but not quite as well on the upper and lower freqs. Three, it'll handle pretty much any power you want to throw at it, (but power doesn't matter that much, so this point is added for trivia reasons only).

The problem we've always faced with trying to run a CB on a vehicle is the wave length. A half wave whip would be really great, but it would stick up 18 feet. 1/4 wave at 9' will have minimum SWR and still work, maybe not as well as a half wave, but acceptable and it'll fit on your rig without taking out power lines. It's still up there though. They used to be around all the time.

I can't remember the first year that Firestick came out with the wire wrapped around the fiberglass rod antenna. It wasn't as good as the full 1/4 wave, but it was an electrical 1/4 wave, so the SWR was down. Plus, it was short enough to fit on most anything and still drive in the parkade. Larson and Wilson do kind of the same thing by bottom loading, (adding a coil at the bottom).

Look at it this way. When you transmit, the signal you send out is really 36' high. That's your wave length. If your antenna is a fraction of that, (like 1/4 or 1/2) it'll still throw and catch, just not as well. If you shorten the physical length even more, you can only make up for it by increasing the elecrical length or you'll reflect back a bunch of your power. You trick your radio into thinking the antenna's longer, so it still works. It's just not as good performance wise, (you catch even less of that 36' wave).

There's only a couple things to remember about mobile antennas:

1. Make sure your physical stuff is right, (good ground plane, connectors, coax, power cables and tuned antenna).

2. Any antenna is better than no antenna at all.