new dipole antenna

[shakuna]

greetings all. i recently purchased a new dipole antenna. on ebay. its called the amazing cb antenna. for 11m use.
i was curious to see how this is gona work when it arrives sometime next week. has anyone ever used a dipole for a base antenna and how good or not good does yours work. i,ve read where alot of ameature ham operators use them and had great results. this new type is suposed to handle 2k w. easly and be able to talk great distance.

lol maybe it might work or not, but i do like to experiment with new antenna types to see which works well and doesn,t.
any opinions or ideas on how to set it up for proper use is much appreciated and helpful.

if you like i can pm you the link and see what you think about it? i have a few ideas on how to put it up , but geting it to work right will be a challenge for me lol. thanks and bless you all.

[the dutchman]

hello,
ive not used one, but i read over at cbradiomagazine.com that you can tape the ends in to tune the swr. dont know if this helps, but you can check out his article on the website.

-john

['Doc]

Shakuna,
Dipoles have been around for a lot of years, they work well. In fact, they are the 'standard' that other antennas are compared to (when you see 'dBd', that 'd' refers to a dipole) in relation to gain and radiation pattern shape (directitivty).
The things people use to compare antennas are resonance, SWR, directionality, gain, and power handling ability. (Those things are listed in the order of they're importance, by the way.) So in reverse order...
Power handling capability
Is primarily determined by how 'good' the insulators used to make an antenna. The actual size of the conductor isn't all that important, within reason. If that conductor or wire or tubing is large enough to hold up it's own weight, and/or the weight of the antenna, it'll handle just about anything an average person is ever likely to feed it. You shouldn't expect #32 wire to handle much. Something like 14 gauge wire will handle anything you are likely to feed it (1500 watts isn't even gonna make it sweat, assuming everything else is close to being right).
Gain
Since a dipole is the 'standard', it doesn't have any gain, as such. That doesn't say anything about how well you might hear things with a dipole, just that there's no 'gain' involved. If you compare it with a typical 1/4 wave vertical, it will have some gain. With a typical 5/8 wave vertical, a little less gain. But only when the dipole is hung vertically (same polarization). Other wise, the differences possible can go in either direction depending on propagation.
Directionality
Dipoles are like all other antennas, directionality depends on height above ground (dirt). At something like it's own length above ground, that dipole starts to be bi-directional in the directions off the sides of that dipole (doesn't matter if it's horizontal or vertical, but if vertical, it just means it's omni-directional). At something close to twice it's own length above ground, it becomes noticeably directional. That does NOT mean that it won't hear things off of the ends, it still will, but just not as strong as off of the sides. And of course, it's gonna depend on what's around the antenna, that affects directionality too.
SWR
The input impedance of a dipole, if it's hung as a 'flat-top', no 'droop', is something on the order of 70-75 ohms. So, an SWR of 1.5:1 is very typical. That's normal and not a big deal at all. As the angle between the dipole's 'legs' starts to decrease from 180 degrees, it's input impedance starts to go down. Make it a little 'droopy' and seeing an input impedance of 50 ohms isn't unusual at all. In fact it's probably the easiest way to 'adjust' input impedance matching (SWR). Hang a dipole vertically and you get something like a 1.5:1 SWR. Start raising that bottom leg towards horizontal, and the SWR starts going down. That's why you can get a good match with a 1/4 wave vertical by the way, it's just a vertical dipole with one raised leg. (Sounds sort of dog-ish, don't it? Still a fact.)
Resonance
This is the biggy! If it ain't resonant, it just isn't going to work as well as it could if it were. Resonance means that there are no reactances present in the antenna, not too long or too short. What's the big deal with that? Reactances do not produce any radiation, only resistance does. So if there's any reactances present it means that some 'power' just isn't being radiated. Bummer, right?
Reactances are not always 'bad'. It depends on 'where' that reactance is and why it's there. Keep it out of the antenna. Or, since reactances come in both (+) and (-) kinds, they react with each other and can add up to 'zero', which can be good! And is why a loaded antenna works (coil = inductance = (+) reactance, which when 'added' to the (-) reactance produced by a 'too short' antenna = resonance. That "too short" = capacitive reactance.). And that brings us to the really -good- part! An SWR meter doesn't know a reactance from a jelly-bean. Reactance + resistance = impedance, which that SWR meter does recognize. It doesn't know what proportion of that impedance is reactance or resistance. There are quite a few impedances possible which appear to be 'good', but aren't because there's reactances present in them. Which means some signal/power is not being radiated from what appears to be a nice SWR. ... Always a 'catch', ain't there? Yep, always is, in everything, not just radio stuff.

What's all that got to do with using a dipole antenna? The same as it does with all antennas, if it ain't acting right, you got a chance of figuring out why, and fixing it.

The predominant type antenna for CB radio is a vertical. That's because of lots of mobile's with CB radios, and also because if done just slightly less than optimum, they take up less room than a horizontal antenna does. If you've got the room, and if the majority of the stations you talk to are fixed, a horizontal antenna is very cheap, easy, effective. Those aren't the only reasons for different polarity of antennas, but it's definitely part of it. A dipole is handy in that regard because it's polarity depends only on how it's hug up.

Get your mind around all that... that ought'a use up a few minutes.
- 'Doc

[shakuna]

thanks doc. this has been very helpful and most apreciated. it gives me a few ideas on how i should try droop efect and adjusting the antenna to get swr matched up to the radio. i look foward to trying out the new anetnna when it arrives. it will be like a kid having a new toy exploring ways to have fun, but in my case lol. it will be like ameature wana be tech, learning the trick of the trade or so speaking lol.

but yeh i agree, from what i heard from others they all love there dipole antenna and many use those over conventional antenna's . i saw one where he had it in a star sorta postion high up from the ground almsot like a beam antenna setup and he would turn it accordingly to adjust to the person(s) he was talking to. hard to expalin how he had it. but was realy neat. he had the swr to around 1.1 almost and he could talk skip for miles daily. though he was a licensed tech. he was very knowledgable back then. not sure if he still alive since i move years ago. haven,t heard from him since.

but again thx so much. i will let you know when i get it up and how its setup. and see if i can talk out farther then.

[shakuna]

i,ve installed the antenna and the swr is so low that its almost a 1.0. on both meters ist reading 1.2 to 1.3 on channel 40. and my transmit is much better now. sofar i,ve hadn,t had a chance to talk skip. not many have been on in the past several days. so i wait until the good skip returns. i put it in the inverted v postion, so its sorta omni directional now.

hope i won,t be disapointed on this.

['Doc]

Now that you see what the thing looks like, next time just make one!
- 'Doc

[shakuna]

yeh now i could make dipole for 10m 11m and 20m hopefuly soon. only problem is where to put them up lol. i want to add a good vertical as well for talking local and etc. a99 is good but alot of belldover often unless grounded well and tuned good. maybe a omni directional beam or so might do me well.

since i,m studying for ham license. i,ll always love cb no matter what though. just ham gives me a second option when cb airwaves are to quiet lol.

appreciate all the info and help you given me doc.

let me ask you a tech question sir please. after i retuned my dipole and goten it to nearly a 1.0 . my transmit went from a 9 deadkey to a 10 swinging 20db. not sure why that did, i thought i had a radio problem for so long as it keyed lower than my base and its not been altered in any way. the statis is so low now and i,m geting better power as well. does the dipole increase any of those? or did i just somehow made the galaxy dx 919 work right? i,m happy its doing that, just alil confused why it took so long to work right. thanks and blessings.

[ussixtysix]

Great info on the dipole antenna Doc'. Thanks a lot!

[ussixtysix]

Oh yea! What do ya' fellas think about putting one on the side of my apt. building. Five stories up?

['Doc]

ussixtysix,
If you can get around the physical limitations, it ought to work okay. Just depends on what you have to work with and how you go about it.
One method is to just stick a 1/4 wave out the window as some sort of angle, and drop a 8.5 - 9 foot wire down the side as the 'other leg'. Using a loading coil on that 'tilted' part can shorten it, but the other 'leg' still should be something around 9 feet give or take a few inches. I think that's how a lot of the 'apartment' antennas are made, or at least used to be. Will it work well? Depends on your definition of 'well' . It'd certainly work better than no antenna at all!
- 'Doc

(And as with any 'close', or inside antenna, count on there being interference problems.)

[ussixtysix]

Hey Doc' Thanks for the info. Been really thinking hard about the options here on the fifth floor. Sorry I don't quite understand. Are you saying one side should be inside the apt. and one side out?...Joey

[ussixtysix]

Oh...and ..sorry to pick your brain clean! You seem to be one of the guys that know their stuff around here. I need a 35 or more amp power supply. What would be a good place to start
in looking for a good deal on a quality DC power supply. Any type I should steer clear of? thank you........ Joey

['Doc]

About that antenna sticking out the window. All of it should be outside. No particular reason why at least part couldn't be inside, but there's no electrical benefit to that. One method of making one is to mount a flag pole 'holder' on a board towards one end. The 1/4 wave or pipe, or whatever would mount by sticking it in that flag holder. The center conductor of the coax would go to that part. The 8.5 - 9 foot wire would connect to the braid of the coax and just dropped down the side of the building. It amounts to a bent vertical dipole, and you tune it accordingly.

Power supplies. I'd recommend getting the biggest one you can afford. Two or three times the size you think you really need. You never have too much power supply. How many different 12 volt thingys do you have around the radio? See where that's going? As for bargains, just look around, see what you can find. I can't give you any recommendations about brands, I just don't know them like I used too. I'm sure others will have recommendations.
Good luck with it.
- 'Doc

[ussixtysix]

Thank you Sir' You are a wealth of knowledge. You are sooo right about the Power supply. I should have been using my noodle on that one. If you get the best you have room to grow!...Joey

['Doc]

And what I didn't say (no idea why) about that antenna is that the whole thing is stuck out the window which is then shut on the board, holding the whole thing in place. Helps if you take the screen off of the window first.
- 'Doc

[420Snowman]

Have a dipole in an inverted V in my garage attic and I love it!! I talk DX all the time on that puppy, it works better than my vertical about 95% of the time.!! Congrats on the new antenna, you are on the air now!!

Snowman

[Radio 75]

Another type of dipole is the coaxial dipole, sometimes called a Bazooka or Double Bazooka. I made one for 75 meters and another for 40 meters on the same feed point in the inverted Vee configuration. The 40 meter antenna had a less than 2>1 SWR curve for the entire phone portion of the band. The 75 meter antenna covered the general portion of the band with the same SWR curve. They worked very well, and were extremely quiet antennas!

It's been a long time since I've made one but if I remember correctly, you figure a full wavelength of coax at your center frequency of interest times the velocity factor of the coax you're using. In the exact middle of this length of coax strip about an inch or two of the outer jacket, and cut the shield all the way around and seperate them. DO NOT CUT THE CENTER WIRE OR INSULATION! The two ends of the separated shield is your feed point.

Now at the ends of the coax, strip back and inch or two of the outer jacket and the inner jacket and connect the shield to the center conductor. Measure from your exact center feed point to either end and figure out how much regular antenna wire you will need to add to each end to make an electrical full wavelength at your center frequency.
Put it up in an inverted vee configuration and trim the ends for lowest SWR at you operating center frequency and enjoy.

Virtually static free in the very dry winter months up here in the great frozen north!

Radio 75

['Doc]

A bazooka antenna is basically still a 1/2 wave dipole that uses a different matching arrangement. it's total length will be slightly shorter than the same 1/2 wave dipole made with wire. If I remember correctly, you use '460' instead of '468' as the 'magic' number to divide by the frequency in Mhz for the total length. And the really fun part is that the length of the center section from the center feed point to the 'short' on each leg is found by using the velocity factor of the coax used to make the thing! Multiply the length of each leg of that bazooka by the velocity factor, measure that distance from the center feed point and short the coax at that point (same for each side). Another 'fun' thing is that you should move that shorting point by the corresponding amount is you have to shorten the total antenna length to make it resonant (tune it). In most cases, the difference in where that shorting point won't make much difference at all, and most people don't bother.
Oh! And the best part about that bazooka antenna is that while the SWR stays fairly constant over a very wide range of frequencies, it's efficiency starts dropping the further you get away from it's design/resonant frequency. Meaning that while that SWR stays 'nice', it starts not being the best radiating antenna in the world. That's been a proven fact for quite some time, it just isn't advertised much. There was quite a good article about all that in one of the earlier ARRL 'Antenna Compendium' book series. Made for some very interesting reading.
- 'Doc

[Radio 75]

Oh! And the best part about that bazooka antenna is that while the SWR stays fairly constant over a very wide range of frequencies, it's efficiency starts dropping the further you get away from it's design/resonant frequency. Meaning that while that SWR stays 'nice', it starts not being the best radiating antenna in the world. That's been a proven fact for quite some time, it just isn't advertised much. There was quite a good article about all that in one of the earlier ARRL 'Antenna Compendium' book series. Made for some very interesting reading.
- 'Doc

Didn't notice that so much at the frequencies I was working, but it certainly makes sense. They are a great alternative for those on a tight budget. (don't need an antenna tuner)
My favorite part of those coaxial antennas is how quiet they are, virtually static free in the winter months.