How many times have you heard someone on the amateur radio bands expound upon what they believe is sound amateur radio antenna theory when in fact it is a myth? Terms like “SWR is flat”, “vertical antennas radiate poorly in all directions”, “this vertical antenna doesn’t require radials”, and on they go. Some amateur radio operators are so dogmatic about their beliefs in these antenna myths that they won’t even accept facts by proven amateur radio antenna theories presented by knowledgeable antenna experts.
So what we have done is to bring a few of these antenna myths to our page here for you to read up on. Before the ‘flames’ start it might be nice to define the word ‘myth’:
myth – An anonymous tale emerging from the traditional beliefs of a culture or social unit.
Half-wave Antenna Myths in Ham Radio
Grant, KM5KG has an excellent article about half-wave antenna myths on his web site ( http://www.km5kg.com/halfwave.htm). His article addresses long held beliefs about standing near HF antennas running under power levels of say 100 watts which some erroneously believe to be a safe power level.
VK1OD brings up one of the most popular myths there is concerning amateur radio antennas – flat SWR. Fat SWR is better known as 1 to 1 SWR, no SWR and so on. This article on amateur radio antennas SWR is an excellent one for those that have struggled to reached the elusive flat SWR stage with their antenna but can’t. Hot link to the page: http://vk1od.net/transmission line/VSWR/VSWRMyths.htm
The Myths of Low Band DXing
This article delves into the sometimes mysterious world of low band DXing which is held as an art by some. Gerry, VE6LB and he has an excellent article about low band DXing on his web site at: http://www.telusplanet.net/public/telwest/LBDX.html
Perhaps one of the best sources for amateur radio antenna myths is that of the article by Marc, N4UFP. Parts of his article on ham antenna myths is presented below.
Urban Legends from the world of Antennas
Marc C. Tarplee Ph.D., N4UFP
ARRL South Carolina Section
Myth Number 1 :High SWR is bad – Antennas that show high SWR are inefficient and do not radiate well.
* False!!!!! – an antenna’s efficiency is determined by the ratio of its radiation resistance to its total input resistance. Power reflected by the antenna travels back to the transmitter and is re-reflected back to the antenna.
Myth Number 2 :Low SWR is good – Antennas that show low SWR radiate better.
* False!!!!! – a dummy load has an SWR of 1.0 and it doesn’t radiate at all. A short vertical antenna with a radiation resistance of 0.1 ohm and a loss resistance of 49.9 ohms radiates only 0.2% of its input power but has an SWR of 1.0
Myth Number 3 :A vertical antenna is an antenna that radiates “poorly in all directions”.
* False!!!!! – A properly installed vertical antenna can radiate very well at low takeoff angles. A good ground system is a must for a vertical to work well.
Myth Number 4 :A quad array is better than a yagi.
* Yes, maybe – If a quad and yagi have the same number of elements and are installed at the same height, the quad usually has a slightly lower angle of radiation and will have slightly higher gain, because each element is an actually an array of dipoles.
Myth Number 5 :My antenna has to be resonant in order to work.
* False!!!!! – The antenna radiates because a varying current flowing through it creates an electromagnetic field. Resonance only simplifies matching the antenna to the transmission line.
Myth Number 6 :To connect 450 ohm ladder line to my matchbox, I need a 4:1 balun.
* False!!!!! – Commercially available baluns are designed to convert 200 ohms balanced to 50 ohms unbalanced. Unless the input impedance of your antenna system is 200 ohms, the impedance the matchbox sees is not 50 ohms and there are additional losses in the balun.
Myth Number 7 : The most cost-effective improvement to an amateur station is a good antenna.
* True – A simple 3-element HF yagi can provide a gain of 6 – 8 dB on transmit and receive and costs $400 – 600, which is about $100/dB. A good linear amplifier can provide 10 – 12 dB gain on transmit only and costs $1500 – $6000, which is at least $150/dB.
Myth Number 8 : The SWR of my antenna system can be improved by changing the length of the feed line.
* False!! – SWR depends only on the line and antenna impedances, not on line length. If changing the line length changes the SWR, there are probably unwanted currents flowing on the outside of the coax and the varying SWR that is measured is not the true antenna SWR. A balun may be required at the feedpoint, or the coax may have to be re-routed.
Page tags: SWR, antenna, baluns, matchbox, yagi, antennas