How to pick the right antenna

12.27.2016 09:07, Tom Donovan

This is the first part of a two-part article – please also read part two – Installing an Antenna  – for helpful further information on how to connect your antenna to your radio and how to ‘tune’ your antenna for best performance.

Perhaps the easiest improvement you can make to a two-way radio is also one of the least expensive and definitely the one that will have the greatest impact on both your radio’s transmitting and receiving range.  This is the replacement of the antenna.

Although the concept of swapping one antenna for another sounds easy and simple, there are some issues and challenges associated with it.  But – keep reading – we’ll help make the challenges easy and issues easily resolved.

This article is designed for people using either Ham type VHF/UHF radios, or alternatively, MURS/GMRS radios.  Much of what we say applies to CB radios too, except that their antennas are ideally very much larger (five times larger than 2m/GMRS and 15 times larger than 70cm/MURS).

Note that FRS radios are not allowed to have external antennas, and if you have an HF or other less common Ham radio, then with your General or Extra license, you probably already know most of these things!

If you have a base station or mobile two-way radio, it almost certainly does not have an antenna provided with it, and so you can skip the next section (but not the other sections).  If you have a portable type walkie-talkie, then there’s a big question you first need to answer.

Can Your Radio Accept an External Antenna?

Okay, so the first consideration is whether or not your radio is even capable of accepting an external antenna.  Hopefully, you used our two-part article ‘How to Choose the Best Walkie-Talkie‘ to help you select your Handheld Transceiver (HT) and one of the very first things we recommend in that article series is to get an HT that has a removable/replaceable antenna.

If your radio has a fixed antenna, then you’re dead in the water and you need to start off by getting a better radio.  Fortunately, that’s not a major investment these days – about $40 or so will get you a Baofeng UV-5R at Amazon and that’s more than good enough for most ordinary purposes (if you want an appreciably better radio, you’d need to almost add another zero to the cost of the UV-5R series).

Measuring and Comparing Antenna Gain/Efficiency

Antennas can have their efficiency measured, so as to give you an understanding of how ‘good’ they are.  This is often referred to as the antenna’s gain.

This measurement is in decibels, and is either measured in dBi or dBd units.  What is the difference?  To convert from dBi to dBd you subtract 2.15 from the dBi rating to get the equivalent dBd rating.  For example, an antenna with a rating of 4dBi is the same as one with a rating of 1.85dBd.

(In case you wondered, the ‘i’ means it is a measurement relative to an isotropic antenna, and the ‘d’ means it is a measurement relative to a dipole antenna, and dipoles have a 2.15dB gain compared to an isotropic antenna).

Sometimes you’ll see an antenna that is described as having a certain dB gain, but the specification doesn’t indicate if it is in dBi units or dBd units.  If the rating isn’t specified, you can safely assume it to be on the least favorable scale, ie, dBi.

Choosing an External Antenna

There are three main families of external antennas.  There are short antennas designed to be used with handheld transceivers, larger mobile antennas suitable for mounting on a vehicle (either permanently or temporarily) and even larger antennas again for use with a fixed base station at your dwelling or retreat or office.

Slightly different issues apply to choosing a fixed antenna for a base station – you can consider issues such as directionality of your antenna as well as antenna style and, most of all, antenna location (and coax cable run length) and those issues are beyond the scope of this article.

Certainly, no matter what type of radio you have, you should have the best possible antennas at your main fixed bases, and these are issues we will consider separately.  But for this article, we are focused on antennas that radiate more or less evenly in a full 360° circle around them, albeit ideally in a flat pattern rather than wasting signal sent directly up into the sky or down into the earth.

Portable Antennas

The standard antenna your radio comes with – typically called a ‘rubber ducky’ – is not a very efficient antenna.  It was designed to be short and convenient (and hopefully moderately sturdy too).  But it was not designed for best performance.

Fortunately, there are many other after-market antennas out there that give massively better performance.  As we reported in our article on How to Maximize the Range of your Radio, swapping from the standard antenna to an after-market antenna improved the signal strength radiated by a small portable radio about eight-fold.  That’s a huge improvement in signal strength, for probably a less than $20 cost.

If the antennas you are selecting from quote their gain figure, then use that to help you evaluate the best antenna for your portable.  Otherwise, a generally rule of thumb can be that the bigger the antenna the better (but make sure it is designed for the frequency bands you are wishing to use).

And with antennas being such low-cost items, there’s no harm in buying two or three and then experimenting with them to see which works the best.  You could even probably sell the ones you didn’t want on eBay or Craigslist for close to what you paid for them.

Mobile Antennas

Having a separate antenna for a radio being used as a mobile (ie in a vehicle rather than handheld ) provides two major benefits.

The first benefit is that an antenna mounted on the outside of your vehicle is better than an antenna inside your vehicle.  Not only is it slightly higher up and free from the partial shielding, obstructions, and absorbent materials inside the vehicle, but it may also have a better ground connection (using your entire vehicle as part of its overall antenna configuration) than is the case for a portable antenna on the radio itself.

The second benefit is that it can be larger and therefore more efficient.

It is common to note that many mobile antennas are coiled in the middle.  There is one downside to such a design – the coil seems to act as a wind trap/musical instrument when driving down the road and particularly if your antenna is on your vehicle roof, you’ll get very much more wind noise inside the vehicle than you would with a different design of antenna.

If you find yourself unable to get an alternate style of antenna, then you can modify your coiled antenna either by placing something around the outside of the coil or something on the inside of the coil – in both cases, to make it a solid object that doesn’t make as much of a whistling noise in the wind.

Unfortunately though if you do this, you will increase the antenna’s wind resistance and may cause it to bend over more when driving down the road at freeway speeds, and the movement from vertical to angled will reduce the antenna’s functionality.  Better to either accept the wind noise or to choose an antenna that doesn’t have the center coil in it.

The best location for an external antenna is in the center of the vehicle’s roof.  Sometimes this is not practical, but it should be your first choice whenever possible.

Dual vs Single Band Antennas

You will probably have a multi-band radio – possibly with two, maybe even three ‘main’ VHF/UHF bands that you wish to communicate on.

It seems that the 2m band is the most popular ham band, closely followed by the 70cm band, although this seems to vary somewhat from region to region.

The 1.25m band is a very distant third – depending on your perspective you might see value in concentrating on popular bands or unpopular bands.  If you are hoping to use existing repeaters out there, you should focus most on 2m and 70cm bands, but if you want to use a band which probably has fewer other people sharing with you, then the 1.25m band may be a better choice.

One last comment about band choice.  The 70cm band has a very broad range of frequencies (from 420 – 450 MHz), with a 3.5% spread above and below the central point of the band.  The 2m band has only a 1.4% spread, and the 1.25m a 0.7% spread.  This has some implications with antenna design – it is harder to get an antenna that works well all the way from 420 – 450 MHz than it is to get one which works well from 222 – 225 MHz.  This is explained in the second part of this series, and we tell you how to turn this challenge into an advantage.

Back to antenna issues, you can get a single antenna that is designed to work on both 2m and 70cm, and you can even get tri-band antennas that will work reasonably well on 1.25m too.

This is normally the most convenient approach to adopt.  But in your home/base station environment, you might want to have separate antennas for each band, and possibly even in a mobile environment too.  Indeed, as well as having separate antennas, there is a lot of good sense in having separate radios for each band too – it can make monitoring and working on multiple frequencies much easier.

On the other hand, if you’re not wanting to use existing repeaters, do you really need the extra flexibility – and extra hassle too – of having multiple bands?  Why not then just concentrate on a few specific channels in only one band?

If you know you’ll only be using a radio in one band, get an antenna optimized for that band.  But if you want extra flexibility, then consider dual/tri band radios and dual/tri band antennas.

Directional Antennas

For portable and mobile use, you seldom want a directional antenna, because you have no idea what direction you’ll be facing or where you’ll be communicating to.  Instead, you want an antenna that radiates equally in all directions, 360° all around itself, but hopefully in a flat plane so the signal goes ‘straight out’ – ie perpendicular to the antenna mast itself, which you should generally hold as close to exactly vertical as conveniently possible.

There is one exception to this.  If you are only semi-mobile, and will be stationary at a particular location for a period of time, and if the person(s) you wish to communicate with are also at a known location, and if the reception is poor with normal omnidirectional antennas, perhaps you’d want to use a directional antenna in these cases.

Directional antennas are much larger than regular antennas.  The 70cm band is probably the most practical for directional antennas, because they can be much smaller and lighter than similarly directional antennas for the other two frequency bands (1.25m and 2m).

If you are establishing a fixed ‘base station’ you might then consider a directional antenna if you knew that you’d always be wanting to communicate with people in one direction and almost never in other directions.

There are many different types of directional antennas, with many different patterns of directionality, ranging from very tightly focused in one direction only, to broadly focused on perhaps about 270° which a relatively ‘blind spot’ for the other 90° (a cardioid pattern), to ones with a focus both front and back but not one the sides (a figure 8 type pattern).

Even only a moderately directional antenna might give you five times more power in its main directional focus – and note that this focus applies not only for sending power out primarily in that direction, but also to receiving weaker signals more readily from that direction, too.

The design and use of directional antennas is a fascinating subject but beyond the scope of this article.  If you can see a situation where a directional antenna would be beneficial, you should definitely consider it further.

Related Products

Stubby Heliflex Antenna Stubby Heliflex Antenna
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