Hamstick Dipole for CB (is Balun Needed At All?)

[rbomba]

So out of boredom, I put together a hamstick dipole (more so a CB antenna dipole but haven't seen anyone use that term, so It's a Hamstick dipole for this conversation), and mounted it up in the backyard on an extendable fiberglass painter's pole so the antennas are approx 9' off ground. They are currently in the horizontal position. Using my Rig Expert AA-30 analyzer, I tuned each antenna to get an SWR of about 1.08 around 27.385 MHz as 38 LSB is an area of interest.

Would there be any reason a Balun is needed in this configuration?

If so, how would one go about adding it?

 

[prcguy]

A balun is not needed but probably not a bad idea. Two things going on here, one is the dipole on the grounded side of the coax is in parallel with the shield of the coax and the coax can become a radiating part of the antenna. If the match is really good then the vast majority of RF will radiate off the hamstick dipole and very little off the coax. As the match gets worse on the dipole more RF current will flow on the coax shield and it will radiate more. A good 1:1 choke balun, one made with ferrite and not a useless "ugly balun" made of coax will stop the RF currents on the coax and isolate it from the feedline.

Second problem I see is the height, 9ft off the ground is right at 1/4 wavelength making your dipole basically a two element beam pointing straight up with a fraction of the power being radiated at the horizon. If you can get the dipole at 18ft off the ground, the first 1/2 wave point, it will pull the radiation pattern down closer to the horizon. Not completely but enough to put most of the energy near the horizon and at a great take off angle for DX. If you could get the antenna several wavelengths up you can eventually get the pattern way down at the horizon, but that's usually impractical with a wavelength at 27MHz being about 35ft.

 

[rbomba]

A balun is not needed but probably not a bad idea. Two things going on here, one is the dipole on the grounded side of the coax is in parallel with the shield of the coax and the coax can become a radiating part of the antenna. If the match is really good then the vast majority of RF will radiate off the hamstick dipole and very little off the coax. As the match gets worse on the dipole more RF current will flow on the coax shield and it will radiate more. A good 1:1 choke balun, one made with ferrite and not a useless "ugly balun" made of coax will stop the RF currents on the coax and isolate it from the feedline.

Second problem I see is the height, 9ft off the ground is right at 1/4 wavelength making your dipole basically a two element beam pointing straight up with a fraction of the power being radiated at the horizon. If you can get the dipole at 18ft off the ground, the first 1/2 wave point, it will pull the radiation pattern down closer to the horizon. Not completely but enough to put most of the energy near the horizon and at a great take off angle for DX. If you could get the antenna several wavelengths up you can eventually get the pattern way down at the horizon, but that's usually impractical with a wavelength at 27MHz being about 35ft.

@prcguy - With respect to the second issue you see, would it matter if the orientation changed from horizontal to vertical (while keeping the height off the ground the same @ ~9'?

 

[prcguy]

Vertical would put a little more energy near the horizon but much of it will still be waisted up at a high angle. That's just how it works when the antenna is only 1/4 wave off the ground. There is no NVIS propagation at 27MHz to speak of and if this were a 40m amateur antenna, being horizontal and low to the ground would have some benefit of transmitting straight up and raining back down to saturate a couple hundred mile area around you when propagation permits during the day. NVIS is only useable below about 10MHz.

There is a chart on this site that shows the radiation pattern of a horizontal dipole at heights from .1 to 2.5 wavelengths above ground. You can see that even at 1/2 wavelength or 18ft high for CB, the pattern is not right at the horizon but pointing upwards above it. Its way better than 1/4 wave or 9ft above ground. A vertical will be similar at 1/2 wave and higher except for the extreme upward lobes. Radio Antenna Engineering - Radiation Pattern

@prcguy - With respect to the second issue you see, would it matter if the orientation changed from horizontal to vertical (while keeping the height off the ground the same @ ~9'?