antennas

This section will over time become a very comprehensive resource for antenna theory and practice.

ANTENNA BASICS

Antennas, to quote a friend, are one of life's eternal mysteries. "All I'm totally certain of is that any antenna is better than no antenna and the antenna should preferably erected as high and be as long as is possible or desirable". Here I have discussed at some length the very basics of antennas. Later I will add more content as time permits.

A FEW "RULES OF THUMB" FOR ANTENNAS

From my old site comes this gem from Jim Duffey. "Every now and then somebody asks the list for antenna suggestions. Quite often these people asking are beginners who are afraid of making the wrong choice. In order to help QRPers choose antennas wisely I have compiled a few "rules of thumb". As with any rules of thumb, these are general and there are some exceptions to them. A few may be somewhat controversial and I am sure alternate views will be given by those with opposite views. However I intend these guidelines to point one in the right direction rather than providing a detailed map of what to do..."

Reprinted with the kind permission by my friend, James R. Duffey KK6MC/5, a.k.a. "Dr. Megacycle".

CHOKE BALUNS

Essentially, a choke balun is designed to "divorce" your antenna from the feed line. If your feed line is coaxial cable then you don't want it to be part of your antenna. You want to be able to deliver all your power to the radiator itself, i.e. "the antenna". A choke balun does this admirably.

ACTIVE ANTENNAS

In a much earlier tutorial (November, 1999) on my old site I discussed Active Receiving Antennas at some length. I commenced by saying "An active antenna is sometimes used for receiving purposes in instances where a normal antenna would be impossible to accommodate in a physical sense. Such an antenna is sometimes called an aperiodic antenna, other people refer to it as an antenna booster. Here on the much newer topic of Active Receiving Antennas where I discuss some possible solutions.

ANTENNA DIPLEXER

Sometimes with receiving Antennas, problems arise with interference from out of band frequencies. One possible solution is an Antenna Diplexer. Here we make extensive use of our knowledge of both Low Pass Filters as well as High pass Filters to incorporate both types into one combined filter I call an Antenna Diplexer.

ANTENNA PRE-SELECTOR FILTERS

I'm asked every so often to produce a page on antenna pre-selector filters. An antenna pre-selector filter is nothing more than a narrow band filter, a topic already covered at some length on another page. Some confusion results because the narrow band filter topic contains no provision for variable tuning. There are several reasons for this. Contrary to your immediate impressions I find no particular benefit in introducing variable tuning to an antenna pre-selector filter. I can see a number of drawbacks however.

PASSIVE ANTENNA RE-RADIATORS

Passive Antenna Re-radiators - Again in response to some considerable interest I had in the past posted some project ideas for receiving difficulties for you to construct passive antenna re-radiators or "sort" of Q multipliers.

FIELD ANTENNA HANDBOOK - USMC

"Of all the variables affecting single-channel radio communications, the one factor that an operator has the most control over is the antenna. With the right antenna, an operator can change a marginal net into a reliable net. Marine Corps Reference Publication (MCRP) 6-22D, Antenna Handbook, gives operators the knowledge to properly select and employ antennas to provide the strongest possible signal at the receiving station of the circuit".

HUMOUR - AERIALS AND WHERE TO STICK THEM

There are a great many types of antenna and most of them function best when they are erect. This is because of 'standing-waves' which produce energy in a vertical plane. Energy in the horizontal plane requires 'lying-down waves' and this is why most of the radiated and received energy is termed 'ecstatic' rather than 'magnetic'. (Kirchhoff's fourth and fifth laws of self-immolation present a heated argument on this subject.)
http://www.hamtastic.co.uk/page3.html

PRACTICAL ANTENNA HANDBOOK

Designed for use by the novice as well as the professional, this book/CD- ROM combo gives the reader all kinds of projects with material that explains why they work.

A wide variety of antennae are covered: high frequency dipole, vertically polarized HF, multiband and tunable wire, hidden and limited space, directional phased vertical and directional beam, VHF/UHF transmitting and receiving, shortwave reception, microwave, mobile, marine and emergency.

This third edition has new material on wire antenna construction methods, antenna modeling software, antennas for radio astronomy and Radio Direction Finding, and antenna noise temperature.

ANTENNAS