More Antenna Stuff
This entry is more a note to myself an anything else but it should be of interest to anyone interested in antennas. Realize that all of these comparisons are heavily influenced by what I can do physically with the yard I have and the effort I want to invest. Your situation may be different.
This is a comparison of several antenna types both single band and multiple band listing disadvantages of each approach.
The main disadvantage with a ATU free multiband antenna approach is lack of harmonic filtering. Normally a single band dipole is the equivalent of a very narrow tuned filter. This is not the case for dipoles that have been tweaked to perform on multiple bands. Not that I am particularly concerned about harmonics from the commercial gear, but I also have homebrew stuff that may not be as harmonic free.
A secondary disadvantage of ATU free multiband antenna systems is a lack of adjustment in the shack and relatively narrow bandwidth compared to operating with an ATU. Antenna systems characteristics change when it rains and snows as compared to when it is dry. If you can’t tune out those changes, you have to live with the mismatches. Besides, it always seems that I want to operate on a frequency that will not give me a decent swr when I use a no-tune antenna system.
DIPOLE - This is an excellent antenna all by itself but it requires proper installation. Meaning it should be installed as a flat topped antenna at a height not less than 1/4wavelength. I can do that on 20 meters but I have a four element beam for 20 so I am not about to rush outside and put up a 20 meter dipole.
INVERTED VEE - This is a dipole that has a high center support and is allowed to have its ends droop. I can manage a center support of about 50 feet and allow the ends to be up at around 15 feet. Not good for 80 and barely sufficient for 40. Also, with those dimensions, the included angle between legs is such that the antenna ends up being a cloud burner on ALL bands. Take off angle at 90 degrees.
G5RV - This is a 20 meter antenna. I already have and excellent beam for that band. I am not sure what form of mythology considers this to be an all band antenna. Oh sure, it could be all band with an ATU but then nearly anything could be all band with an ATU.
80/40 TRAP DIPOLE - Nearly all band but narrow (100khz) bandwidth on 80 meters. For my location it can only be installed as a cloud burning inverted vee. A poor solution.
WINDOM - Actually just an off-center fed dipole for 80 meters. The idea is to find a feed point that remains fairly constant over frequency, match to it, and enjoy ATU free operation. The main problem with this is that I can’t get this thing up high enough to do any good on 80 and 40 meters. Also, the low swr points shift when it rains.
DELTA LOOP - Works great on 40 meters but does not make a very good all band antenna even with an ATU.
INVERTED L - I can run a wire 50 feet up and 60 feet out but the end will only be 15 feet off the ground. Height problem.
SLOPING DIPOLES - Not enough yard to accomodate them on 40. Forget using them on 80.
SHUNT FEEDING TOWER - I did that for a while. It worked. Did an EZNEC analysis on the setup and found it had a -2.0 DBi gain. Close-in signal strength to a weekly sked dropped from 10 over 9 to 9.
88 FOOT NON-RESONANT DIPOLE - This needs an ATU to be able to work and requires open wire line of sorts to be able to run high swr with low loss, but it can be installed here as an almost flat-topped dipole, can be tuned for very low swr on nearly every ham band from 80 to 10 meters, will not limit me to any range of frequencies. I have been avoiding this antenna because it requires open wire line and there are installation requirements that I cannot meet. However, it can also be made to work with 300 twin lead and I can meet the installation requirements for twin lead.
So now I am back to the 88 foot dipole I was using back in November of 2006. Since then I have also added an L antenna. A 27 foot vertical with 27 foot counterpoise also driven with 300 ohm twin lead and a second balanced antenna tuner. All balanced line and tuners. No baluns. Seems to work fine. It is at least as good as what I was using before and has the advantage of offering operation at any frequency on any band.
If you have the ATUs, use them. If you don’t have the ATUs get some.