# dipole

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KK4BYD, May 2, 2011.

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1. ### KK4BYDHam MemberQRZ Page

ok guys been reading up some on the dipole,and even the multiband dipole. I still have a question and I'm sure it depends on your location and where you want to talk.Does the direction of the antenna matter in any way. It looks like if you have a height of at least 50' the antenna is really omni directional anyways,then I hear people saying get a rotatable dipole. Have I skipped a paragraph or whole page somewhere in my reading.Guess it my be a stupid question to some,but I cant see purchasing a rotatable dipole if its going to be omni direction anyway. Maybe their design is for someone with limited space and height restriction,I dont know and want to know,so please explain this to me.I haven't bought the first radio yet cause I'm still trying to get my ducks in a row. With me being a South Alabama Redneck if I dont get my dipole up 50' my wife will be hanging clothes on it.Anyways if someone would explain this to me would be great,a dipole from my reading is the way to go.Thanks in advance !
Makitaman

2. ### KB4QAAXML SubscriberQRZ Page

In general terms, a dipole has directionality which can be quite useful by orienting it to avoid noise, or increase gain of weak signals.

-Rotatable dipoles can be handy, particularly if you don't have room;, or want a rotatable antenna, but a full size half wave wire dipole will beat small 'ham stick' types every day.

-The directional pattern of a dipole is shaped like a figure eight, and is at right angles to the antenna. In other words, the null (weakest signal) will be along the lenght of the antenna.

-Generally, higher a dipole is, the better the long distance performance is, because the Take Off Angle, decreases. Optimal height would be about 1/2 wavelenght (up to maybe 1 wavelength) above ground or better. (Someone can correct me or give more precise info, I'm too tired to drag out the antenna book at the moment).

-On the other hand as a dipole gets closer to the ground they interact, decreasing the directionality and increasing the take off angle. This can be useful for making close in contacts. In fact there is a whole interest group of users who use this effect on 80 and 40m, called NVIS, Near Vertical Incident somethingorother. Nine or ten feet is as low as you really need for maximum effect.-

-As far as washing clothes, my Southern Grandmother always recommended Mondays!

3. ### 2E0OZIHam MemberQRZ Page

Just point the end where there is nobody to listen to! Or in other words, broadside to the people you DO want to listen to! Here when I had a dipole it was north south as I wanted to point towards Europe from here in the UK. Your height of 50 feet sounds OK, and 40/20/10 might be the way to go. Too bad you dont say if you could stick a wire in a receiver and see where "the action" is at your QTH. Advice I took to heart at the end of last year was;

1. Decide WHEN you can operate regards time of day.
2. Work out what antennas are best in relation to what band will be active when you will be on the radio.
3. Build them yourself.

My setup wont win too many contests, but its cheap and flexible and it works. If it was higher it would work even better. (W3EDP antenna fed from a IC718 with a MFJ901B manual tuner).

4. ### W8JIHam MemberQRZ Page

Start thinking in terms of wavelengths, not feet, and things will be clearer. At heights less than about 1/2 wavelength above ground a dipole starts to lose directivity. This is because the earth reflection focuses the energy at high angles, and up above the antenna we can never be in a spot directly off an end!!!

By the way, you notice pretty much everyone uses take off angle. That's as bad as thinking in feet instead of wavelengths. Take off angle probably misleads people more than any other specification.

Even my friend who wrote the common programs EZNEC lamented a long time about including take off angle. He told me he just knew it would cause problems. But because K6STI had included it in his programs, it wound up in EZNEC. What really is of interest is the absolute gain over a range of useful angles, not take off angle which (by itself) is usually meaningless.

So avoid using take off using take off angle and feet when thinking or speaking in generalizations, and you will be ahead of the game.

A dipole at low height (in fractions of a wavelength, less than 1/2 wave high) starts to have more energy at high angles and less at low angles, but the low angle gain of a dipole is often much greater than a vertically polarized antenna. The reason is complicated, but the end result is a vertical even with a much lower "take off angle" usually has less energy at low useful angles than a dipole with a very high "take off angle".

That's why we never want to use feet unless we are talking about a specific band, and we never want to use take off angle.

5. ### K3STXHam MemberQRZ Page

If you are a new Ham, just put up a wire dipole and play around. Of course everything W8JI said is true, but for us mere mortals there is theory and there is reality. The REALITY is that I have two dipoles for 40 meters, one for NW/SE stations (South America and over the North Pole) and one for NE/SW stations (Europe and Australia). They are each about 40 feet high, just a little over 1/4 wavelength. I can tell a difference when working a station in Europe when switching between the two antennas, but its not THAT dramatic.

I have another dipole that is 100' long and 60' high and on bands like 15 meters there should be lots of nulls where I should NOT hear stations well. I have not noticed them! Tom is right, the pattern might predict "a null here", but that null might only be for an angle of 11 degrees, the null might be much less prominent at 25 degrees and THAT is where the signal arrives to me.

Put up a simple antenna and THEN play around with changing things. Don't overthink it at the beginning.

paul

7. ### W5DXPHam MemberQRZ Page

EZNEC sez that a 20m 1/2WL (33') dipole at a height of 1/2WL (35') has a maximum gain of 7.4 dB with 12.5 dB nulls off the ends. That is quite directional. I have a 33' rotatable dipole and it works well.

8. ### KK4BYDHam MemberQRZ Page

Thanks guys, yeah I'm new to ham and trying to put my money in the best places. Got plenty of wire, just going to experiment a little. I'll. Print off all the suggestions here and put them to good use. Thanks again!

9. ### EI4GMBHam MemberQRZ Page

Hi There,

A well installed horizontal dipole is a good antenna to start off with. You might also consider a G5RV Jr.(51ft). This can be matched on 40m,20m &10m using a rigs internal tuner - handy! After that see what you want to do. Best of luck.

Fred EI4GMB

Last edited: May 2, 2011

A random thought on rotatable dipole. Say you have a 40m rotatable dipole. That means, you have sufficient unobstructed space for a ~210' horizontal loop antenna (40m half-wave is ~67', rotatable implies circular swing space is available, circumference of circle with 67' diameter is pi x d = 67 x 3.14 = 210 feet). A little more gain than a half-wave dipole, possibly quieter, less maintenance, easier to put up and multi-bander.

11. ### W8JIHam MemberQRZ Page

A dipole that can be turned 90 degrees, or two crossed dipoles, is really hard to beat.

A loop only has more gain than a dipole when it has multiple nulls. If it has multiple nulls there can be problems with holes in covering certain directions.

The multibands aspect is a nice feature, but then a dipole can be a fan dipole or a trap dipole or a ladder line fed dipole.

It really all depends on what the user wants to build. What ever people build and use is always the best, no matter how it actually works.

12. ### WA1BHam MemberQRZ Page

Hi Makitaman,

You can spend (waste) a lot of time considering the ultimate, best or compromise of a dipole or, any antenna for that matter. I see you don't list a call sign so, I consider this antenna a SWL or listening antenna. First you can put as much wire as you can as high as you can get it and use an antenna tuner. Tune to a unused frequency. Adjust the tuner to get as much back ground noise. You can then try moving the antenna orientation and note your results. A good rule of thumb is make the dipole for the lowest frequency (longest wave length) you intend to use.

My dipole is cut for 160m. It works out for me to use 257 feet 16 ga wire center fed with 25.75 feet of 470 ohm ladder line. The highest point is 30 feet and it slopes down to 4 feet off the desert floor. The feed point is about 20 feet off the ground. All of this is a compromise. I do have the antenna orientated North-South just as a starting point. I may tweak that a bit in the next generation of test.

This antenna works fine on 160m 40m 20m and 15m. It is a little fussy on 80m. By fussy I mean I move 20 KHz and I have to re-tune. The smaller the antenna (higher frequency or shorter wave length) the easier to move the dipole around. Try different set ups and use the one that best suits your needs.

Have fun.
Best Regards,
Keith

13. ### G0GQKHam MemberQRZ Page

Quite a lot of good advice for you Makita Man. I take it you use something of their range, like a drill ?

14. ### KK4BYDHam MemberQRZ Page

No,still waiting on my call sign,just took the Tech,then the General back to back almost 2 weeks ago,keep checking the database no posting yet.I promise as soon as I get it I'll post it.Just trying to get things in order and know what direction to go. Getting a lot of good info here,if it wern't for these guys I would have done threw money away.The list so far looks like a multiband dipole, for my first build,I'll grab a few cheaper pre-built antennas also to get on the air, a Yaesu FT 950,and a Icom 718,I already have several power supplies,may still grab another just so it will have the new smell, I already have most test equipment I may need,except a good analyzer not sure yet maybe the mfj-269. I'm sure I'll get some hits on my choices but thats okay, I have to check out there suggestions,and ideas, cause I want to know from the people that have the knowledge that I'm still trying to get.Thanks yall keep it rolling in.

Agreed. I am only suggesting that with all that space available, there is more than one design that can be experimented with

16. ### KK4BYDHam MemberQRZ Page

Got to print this off, yeah still waiting for them to post my call on the database.I slowly picking up stuff all along. I still got my antenna book but it doesn't compare to the info I get here. Nothing beats hands on and past experience. Thanks guys.

17. ### K3STXHam MemberQRZ Page

You seem to suggest you are going to get an FT-950 AND and IC-718. No need for both, the FT-950 will blow away the IC-718! If it were me I would hold-off on gettting the antenna analyzer till you really need it. I have been a Ham 30+ years and somehow managed to do without one!

If there is one think you will probably want that was not on your list it would be an antenna tuner. I personally like the small MFJ units like 941E, but other people will say "don't buy MFJ junk, buy a Palstar.". Palstar is good, but pricey. An antenna tuner will allow LOTS of flexibility for years, "tweeking" coax-fed dipoles with moderate mismatch to work and also will allow ladder-line fed-dipoles to work multiband. I think a dipole as long as possible, and as high as possible, fed with ladder-line to an antenna tuner (and then your rig) is an excellent first antenna. If it is 60 feet long it will work just fine for all bands 40-10 meters. If it is 100' long it will also work fine on 80 meters.

And don't forget a straight key, CW is the best part of Ham radio. I am also surprised it has taken weeks for your call to show up, I thought it would be a matter of days from VE testing?

paul

18. ### WA1BHam MemberQRZ Page

Hi Makitaman,
I'm happy you have the general. My elmer always said, "The hobby starts at General." I have recently gone through the return to the hobby. Many things have changed in the 8 years I was off the air. Many things are the same. There are a lot of opinions floating around and free advice is abundant.

I still listen more than I talk and plan more than I do. Using Morse Code to communicate is a skill and like any skill will diminish as it is unused. I wish you many years of fun and friendship in the hobby. I'll be happy to set up a sked when you get your station up and running. You can PM me anytime.

Best Regards from The Wild Wild West of Tucson

Keith

19. ### W1VTHam MemberQRZ Page

I agree with Tom--I operated a DX contest on a hill in Honolulu with nothing more than a pair of 15M dipoles and a QRP CW rig--I did really well and got a nice certificate for my efforts!

20. ### KK4BYDHam MemberQRZ Page

I was going to pick the 718 up for a back up,not a 100% sold on it yet. Yeah I'm suppose to have a tuner somewhere, have no idea where I don't even remember the brand. Got start digging things out, I sold some things 8 or 9 years ago, but it was mainly duplicate stuff I had picked up here and there. I have never had any problems with MFJ equipment. I know I'm getting some great info here, I've got a file started from threads I posted, and some other topics on other threads. Thanks again !