Some Basic HF Antennas

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Antennas

Along with a radio, you'll need an antenna. It's best to put them outdoors, where you can more easily get away from noise sources within the home. There is one cardinal rule with outdoor antennas; NEVER EVER put them where they could fall on power or phone lines. Apart from being a source of noise, there are considerable (and potentially lethal) shock and fire hazards.

Indoor antennas tend to be much less effective - you have to contend with picking up noise from any number of sources within the home, as well as shielding from the home's construction. There are options for indoor antennas that work, but keep in mind that they are far less effective than their outdoor cousins

This article is not intended to be comprehensive - there are many books on this subject. Some of the most authoritative are written by the ARRL (American Radio Relay League) and the Radio Society of Great Britain. Check out dealers such as Universal Radio for their availability.

Whip antenna built into the radio

Most portable radios include a small built in whip antenna. While this is often satisfactory for listening to high powered shortwave broadcast stations, it is usually insufficient for listening to lower powered pirate stations, except under the best of conditions.

Active Antennas

These antennas often consist of a short whip element tied to an amplifier. For this reason, they are often referred to as E Field antennas. As such they are problematic at best; they are often prone to hear more noise than signal, and if the receiver hasn't got a particularly good front end, overloading may be an issue. If the unit has a gain control, this will help to some degree. See the Active Antennas article for a more complete discussion of this topic. Examples include the Bonito Boni-Whip and the MFJ-1020C

Random wire Antennas

As the term implies, a Random Wire is a wire antenna of random length. A random wire generally works well for signal reception, and is an improvement over the built-in whip antenna that is included with many portable radios. The king of random wire antennas is the Vibroplex PAR EF-SWL antenna which is widely available. This antenna features a box with various methods of connecting and grounding; it takes some experimentation to figure out which combination works best in a given environment. While the 45 foot length would be fine for most portables and SDRs, to really be efficient at 4 Mhz (the lowest HF band currently used by pirates), the antenna needs to be lengthened. Fortunately you can easily replace the antenna wire.

Dipoles

A dipole is perhaps the most basic radio antenna. The most commonly used dipole is the half-wave, so named because the total length is approximately one half of a wavelength long at the desired center frequency. The antenna is made up of two wire elements, each about a quarter of a wavelength long. Coaxial cable is used to connect the wire elements to a radio or transmatch. Dipoles are usually cut to a specific frequency, and will be most efficient there and on odd wavelengths from that point; hence a 4 Mhz dipole will work well on 12 Mhz, a 5 Mhz dipole will work well on 15 Mhz, and so on. Outside these ranges, the efficiency of a dipole can drop off. There are more wide banded dipole designs, although such antennas can take up a good deal of space - these include the classic fan dipole and the T2FD

Using dipoles in a listening mode really doesn't require much retuning; in fact some dipoles are actually close enough to pirate frequencies that they are still relatively efficient. A dipole cut for the 75 meter ham band will work just fine to hear 4 Mhz pirates; A 60 meter dipole will also work with the 5 Mhz pirates, and a 40 meter dipole will work with the pirates that are just below 7 Mhz

Multi Band HF Amateur Radio Antennas

If there is one antenna that hams use that is wide banded, the G5RV would fit the bill. This antenna has many variations, and a good Google search will turn them up. For receiving only, a transmatch may not be needed. While normally used with HF amateur band transceivers, this antenna would also work well for desktop receivers. It might be too much for low end SDRs (such as the Funcube Dongle and the RTL-SDRv3) and portables without some front end protection (in the form of a passive preselector). The same could be said of using this antenna on a wideband receiver such as the AR8600 mentioned elsewhere, depending on your local RF environment, of course.

Another popular wide banded HF antenna is the Carolina Windom - one version of this takes up only about 66 foot, and is shown here

What do you do if you don't have the space (or understanding neighbors?)...

Loop Antennas

Loops have been around in one form or another since the birth of the broadcast industry. An argument can be made that they are one of the oldest known types of antennas. They are resistant to noise, and on frequencies below about 3 Mhz or so, have directional properties in a very small space. The resistance to noise often makes them an attractive choice for indoor installations. They can easily be hidden to avoid the scrutiny of a HOA. These antennas work best close to the ground, unlike wire antennas that often need to be high up and in the clear. Experiments have shown that some loops become omnidirectional if mounted horizontally and higher up, instead of mounting vertically as is the norm.

Loop antennas come in many varieties. Some are passive - meaning they have no amplifier. Others are active (they have an amplifier to overcome the low signal pickup that is typical of these antennas). Some examples of these antennas are:

Passive Loops
Active Loops

There is even a type of antenna called a Skyloop. These antennas are not small and require a considerable amount of space to erect.

You can find an extensive list of many different types of loops here (offsite wiki).


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