conductor diameter and bandwidth of dipole?

[towerdog]

Increasing the diameter of the elements increases the bandwidth of a dipole, but how much? I have searched all over for a formula or table showing what the bandwidth will be with a given size element at whatever frequency.
I was thinking about making a dipole out of scrap 1-5/8" (2"od) or 2-1/4" (3") coax using the copper jacket as an element if it would significantly increase the bandwidth, or would I just be wasting my time.

 

[GnG8d]

Try some of this coax ........

 

[wavrider]

Size of the radiator does increase band width.

Using coax will work, there is actual antennas made from coax, google bazooka or double bazooka.

On the other hand it is heavier than regular wire.

I use 12 or 10 gauge, target center freq and let the band width fall where ever it may.

Some use smaller diameter, 14 or even 16 gauge.

Use what you have get it resonant and start making some contacts.

I have not found any formula either for diameter vs band width.

 

[Beetle]

Build TWO dipoles. One the usual way, with ~ #16 bare copper wire. The other one with your scrap coax, tubing or whatever. Do some testing with one, then lower it and put the other one up in EXACTLY the same configuration, height, etc. and do the same testing, concentrating on determining what the BW difference is between the two. You might notice a significant difference; you may not.

But learn what works.

 

[W5LZ]

Do the experiment that Beetle suggested.
I think you will find that while the diameter of the conductor has some influence on the length of an antenna, it has little influence on the usable signal band width of that antenna. Or, for that usable band width to be significant, the increase in diameter of that conductor has to be a significant percentage of the wave length for the frequency of use.
That length/diameter thing is much easier/practical to do at VHF frequencies than at HF. And if you look hard enough, there have been a number of experiments dealing with it. One of those experiments dealt with 'bazooka' antennas and was in one of the earlier ARRL 'Antenna Compendium' series. While the apparent usable band width of a 'bazooka' antenna seems fairly wide, it's efficiency drops off significantly the further you get from the design resonant frequency.
There have been a number of antenna designs that use the conductor's apparent diameter as a basis. A 'cage dipole' is one of them, and so is the classic 'butterfly' beams.
The biggy in this sort of experiment is how/what you use to do the measuring. SWR is a particularly useless measurement in this sort of thing, it only deals with impedance matching and is NOT very definitive/useful by any means.
Try it! See what happens.
- 'Doc

 

[Henry HPSD]

Hello,

Oeps..wrote at the same time as w5lz...so appologize for the "double" things.


Roughly from 1mm to 10 mm will have 200khz increase
Roughly from 10mm to 100 mm will have 500 Khz increase.

Besides the wider bandwidth, the antenna will also be a bit lower in resonant frequency if diamter increases and length remains equal.

There are probarbly a couple who could show you the exact change in bandwidth by using enzec or so.

There are many forms of dipoles who are more "wide-banded" than a conventional.
Any search on google will give you loads of examples.
The bowtie-antenna was very popular in the old days..etc.etc.

Besides the correct ways...it is quite possible to make a dipole with a very wide bandwidth. Though wide bandwidth doesnt mean the antenna is good...
Often antennas with a very wide bandwidth migth have losses..and due to those losses the bandwidth is wide.

It is quite possible to use coaxcable to make a dipole.
But also in coaxial dipoples there are often losses.
And to those who think by using coax the length of the entire dipole is shorten with the verlocity factor...that is incorrect.
Though the dipole made out of coax will be slightly shorter this has nothing to do with velocity factor.

Regards,

Henry

 

[Captain Kilowatt]

Hello,

Oeps..wrote at the same time as w5lz...so appologize for the "double" things.


Roughly from 1mm to 10 mm will have 200khz increase
Roughly from 10mm to 100 mm will have 500 Khz increase.

Besides the wider bandwidth, the antenna will also be a bit lower in resonant frequency if diamter increases and length remains equal.

There are probarbly a couple who could show you the exact change in bandwidth by using enzec or so.

There are many forms of dipoles who are more "wide-banded" than a conventional.
Any search on google will give you loads of examples.
The bowtie-antenna was very popular in the old days..etc.etc.

Besides the correct ways...it is quite possible to make a dipole with a very wide bandwidth. Though wide bandwidth doesnt mean the antenna is good...
Often antennas with a very wide bandwidth migth have losses..and due to those losses the bandwidth is wide.

It is quite possible to use coaxcable to make a dipole.
But also in coaxial dipoples there are often losses.
And to those who think by using coax the length of the entire dipole is shorten with the verlocity factor...that is incorrect.
Though the dipole made out of coax will be slightly shorter this has nothing to do with velocity factor.

Regards,

Henry

Based on what frequency? The above numbers of 200 KHz or 500 KHz are NOT applicable to all bands. Any additional bandwidth gained is a percentage of the original bandwidth. You might gain those numbers on 10m but no way on 80 or 160m.

 

[towerdog]

Finally I got all the bugs out of my station and dipole up in the air as of about 15 minutes ago.
The dipole I constructed is fed by about 100' of LMR-240 double braided coax, and the dipole is constructed of 3/4" diameter coax, using the solid outer conductor. No balun. It is polarized horizontally, about 6 to 8 feet above ground. About 50 feet of the coax is laying on the ground, (original plan put antenna 80 feet up in a tree with line launcher that failed)

What I have is an vswr of under 2:1 from around 24.9 mhz up to 28.5mhz. I figure something else must be radiating or I just built something that uses magic.

I may run some RG-58 and relocate the antenna closer to house and see what I get tomorrow and if I get the same results I may build another one out of 1-5/8" (2" OD ) next weekend.

 

[towerdog]

Try some of this coax ........

That is the largest coax I ever did see, although I have personally decom-ed and scrapped 5", that is amazing. I wonder how you run such a line, as I doubt rope and cathead would pull it. Installing a connector, what a pipe wrench and 6' cheater bar. I woulda loved to seen the spool it came on, am sure it had to have been at least 400 feet of it. Guess it would be quicker to put up than solid hardline but its still going to give me nightmares when i go to bed tonight.