any advantage with big diameter tube

[davev8]

I Read someplace a long time ago that a vertical antenna will have a wider bandwidth with bigger diameter tubing than one with small tube...i will guess that this is incorrect as a Imax works well and it only has a wire up it.....
But does anybody know if their is a performance advantage with using larger tubing for the radiator or for the radials ?

The obvious disadvantage will be the higher wind loading

 

[Captain Kilowatt]

Yes, an antenna with a wider cross section will have a broader bandwidth. How much wider that bandwidth is depends on the two diameters being compared. On HF frequencies it ammounts to a VERY small difference and is usually not worth the effort or wind load. You can however make a cage of several wires spaced several inches apart to simulate a large diameter tube to improve the bandwidth somewhat on HF but using solid tubing is not a great idea. On VHF or UHF it can make a HUGE difference. Also the larger the diameter is the shorter the overall length has to be.

 

[Marconi]

I Read someplace a long time ago that a vertical antenna will have a wider bandwidth with bigger diameter tubing than one with small tube...i will guess that this is incorrect as a Imax works well and it only has a wire up it.....
But does anybody know if their is a performance advantage with using larger tubing for the radiator or for the radials ?

The obvious disadvantage will be the higher wind loading

Dave, IMO most CB claims are bigger and better BS. There are technical differences of course, but very often such differences are hard to detect and even harder to measure.

However, if you come back later and tell me you doubled the diameter of your radiator, and you saw the bandwidth double as a result...I will have no reason to doubt your words.

 

[vkrules]

Bandwidth is definitely better with larger diameter tubing .I have a 1/4 wave made from 44 mm aluminium tube and 4 wire ground planes at 45 deg.The swr is dead flat on the 40 chs and the 1.5 to 1 points are 26 mhz to 28.4 mhz .I originally used 2.2 mm copper wire for the radiator ( on a fiberglass pole) on the same ground planes and mount . The 1.5 swr points were about 26.8 mhz to 27.430 mhz . As for performance , haven't noticed any difference ,the aluminium may have less noise on it in high wind and thats about it.

 

[vkrules]

Thats an extreme example 20x the diameter for a 5x increase in bandwidth and a big increase in cost.Hope the real world example helps.

 

[Marconi]

Good info vkrules, but my example was a simple doubling of the radiator diameter.

For example: if I used your idea on a 1/2" radiator...I would be using a 10" diameter radiator for the comparison. It's a frequency difference thing, but it is a good point.

 

[vkrules]

Good info vkrules, but my example was a simple doubling of the radiator diameter.

For example: if I used your idea on a 1/2" radiator...I would be using a 10" diameter radiator for the comparison. It's a frequency difference thing, but it is a good point.

True ! 1/2 inch to 1 inch wont double your bandwidth, but it will give you a couple of hundred hz extra( at 27 mhz) I wonder how broad a 10 inch radiator would be ,21 to 28 mhz,? At uhf we would be in discone territory !