Half Wave Dipole v Folded dipole

[piraterx]

Hi this has probably been debated at some point.

I have an NRG centre fed half wave dipole with 1:1 coax balun tuned for 98-108MHz.
I was given a half wave folded dipole which was built for around 100MHz or so.I added a 4:1 coax balun to match it for use with 50ohms coax.

Now can i ask is there any great difference between these two antennas? I think the Folded type is more broadband?

I have been playing with them earlier on RX only and its like the folded dipole pulls in that bit better than the other dipole? Both being mounted in near or less same place and same length coax etc.

Are radiation patterns the same?

Any thoughts welcome

[Albert H]

Both dipoles have the same radiation pattern. The folded one will have a feedpoint impedance very close to 300Ω, so you need 6 : 1 impedance conversion for a 50Ω coax feed. You also need unbalanced (coax) to balanced conversion.....

The single dipole will have a Pawsey stub, doing the unbalanced to balanced conversion, and Stephen always used to cut the antenna slightly long to bring the feedpoint impedance down towards 50Ω!

The "fatter" the elements of an aerial, the wider bandwidth it'll have. Jaybeam made an 87.5 - 108 MHz folded dipole that they claim gives <1.2 : 1 SWR right across the band. It uses very fat aluminium tubing!

Generally, a single frequency antenna can be better optimised for its frequency of use. I generally don't much like dipoles, but stacked and correctly fed, they can work quite well.

[radionortheast]

the folded dipoles you see on professional installations will still be tuned for the frequency in use, they use folded because its easy to match the impedance. Years ago I had a folded dipole that got out really well, thought it was horizontal & could only cope with 1 - 2 w, think it only worked well because it was on top of the roof.

They'll always be a slight loss with wide band aerials, you can get close, theres another problem more downward radiation, as an example with my wideband aerial I get 12 w either end of the band and zero reflected but a 1 w in the middle band, the more power you use the more it would cause a problem.