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Thoughts On The ATAS-120 Ham Radio “Screwdriver” Antenna

November 27, 2010

In the ham radio world bigger is generally better.  This, contrary to the belief of some, has to do with the basic laws of physics.  It’s just how things work.  Those with radio communications as a hobby seem to put a premium on communications at a distance.  The bigger the distance the more amazing the ability to communicate.  And to communicate at those larger distance generally requires bigger antennas and bigger power levels.  True – you CAN talk around the world on a minute amount of power.  But for those that want to do it ANYTIME and under ANY CONDITIONS – well, they run amplifiers.

Why are bigger antennas needed for longer distance communications?  Propagation phenomenon.  Certain wavelengths bounce off of various levels of the atmosphere and return to earth.  Others are absorbed by the atmosphere.  Still others punch through and just keep on going.  Generally, the lower the frequency in Megahertz the better it is for longer distance communications under certain conditions.  Under certain conditions is the critical term.  Conditions (earth weather and space weather) are constantly changing.  Thus, one day a certain frequency may be great at a certain time while a bit later a different frequency may be better.  Things change.

Ham radio operators would like to own just ONE antenna that can DO IT ALL.  While it’s not quite that simple, the “screwdriver” antenna comes close in many respects.  The antenna gets it’s name from the way it works.  There is a motor inside the antenna (or at the base) that changes the physical and electrical length of the antenna by turning the antenna like a screwdriver turning a screw.  Either up or down.  Part of the magic is that some screwdrivers (like that ATAS-120) have the ability to turn the antenna just the right amount every time without the user telling it how much to turn.  This is pretty cool when you watch it.  It does this by repeatedly measuring the electrical match of the antenna to the frequency selected by the user.

In practice it takes maybe 15 – 30 seconds at most to tune the antenna.  As screwdrivers go though, the ATAS-120 antenna is a pretty small antenna.  Gordon West, legendary ham radio FCC license preparation book and audio expert says that you know that you’re a “real ham” when you neighbors come outside, point at your antenna and gasp… “What the HELL is THAT???”.  In that respect the ATAS-120 barely qualifies as a “real” screwdriver.  I have seen some screwdriver antennas that make one want to believe that a Special Forces team surely has landed!  The ATAS-120 screwdriver antenna is not known as the highest “Q” antenna (read “efficient”).

With that said, and after a year or two of use of the antenna, the ATAS-120 antenna is a great little antenna.  Yes – it will probably become corroded after a few more years of use.  But for the price and ease of mounting it is a lot of antenna for a little price.

One thing that the antenna is very good at, with attention to good grounding, is the ability to allow you to work a number of different frequencies very quickly for a low price.  While it won’t do the best job in the world on any given frequency, it does allow the new ham to experiment a bit with each frequency and determine which frequencies s/he would like to use most of the time.  While some people can get this information from a book, nothing completely substitutes for experience.  My wife, Jane (ke8krs) and I have used this in the following ways.  We have used her ATAS-120 to determine what good HF mobile frequencies are.  Then I have acquired single band antennas (a 20 meter ham stick is my latest) for use on my car.  The ATAS-120 will also help us determine what frequencies we want to target for a base station antenna farm.

Some people use the ATAS-120 for a base station antenna by itself.  I have heard both good and bad things from it.  Some mounting height helps.  A great grounding system is absolutely required.  One fellow used his metal fence as a mounting structure and got great results.  Another ham used his apartment porch railing and got poor results while other have gotten good results.

Mounting structure support is one major advantage of the ATAS-120 screwdriver antenna.  Compared to it’s bigger brothers, the ATAS-120 does not require much of a mount at all.  I have seen some of the “dream screwdriver” antenna mounts – and they require a major investment of money, time and metal.  Now – if you absolutely demand (or want) the best performing antenna and can afford the time and cash required to install the big screwdrivers – then by all means do so.  But – if you are on a limited budget, want something that will work quite nicely and realize the limitations of it – then by all means do not be afraid of the ATAS-120 antenna.

Stay tuned!

Jon Kreski, AB9NN

http://www.HamRadioResources.com

http://www.Twitter.com/AB9NN

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