Which Antenna Should I Purchase?
40 years ago when I first started sourcing radios for the mountaineering community, options were much more limited. You got a big heavy radio with no display, a steel antenna, that at best had a dial that would allow you to select from a maximum of perhaps a dozen channels. The frequency for each channel was determined by a crystal that resonated at the appropriate wave length for that channel. If you wanted a new channel, you ordered a new crystal for it. As the range of frequencies were usually targeted to one area, it was easy to tune an antenna to match that range without falling outside of the antennas capability to transmit without creating a standing wave. NiCad battery technology was one among many technological improvements that would revolutionize these radios. Fast forward to today, and we have radios that can monitor and transmit on multiply bands, talk to you, play music, easily store more than 200 channels, encode and decode codes, encrypt signals, connect to the internet or to your phone via BlueTooth, and cover at least a range of 30 mHz while being ultra light, producing a full 5 watts of power and, providing the right antenna is used, do so without creating a standing wave when they transmit. That one caveat is the reason why we've had to introduce the 'antenna packs', and why with every order, we get he question, "which antenna should we be using?".
The answer is not that easy, but in this, and the other related web pages on this site we attempt to de mystify some of the aspects of choosing the correct antenna when you are trying to effectively work through a huge range of possible radio channels and multiple bands. Here are a few laws and rules of thumb, starting with some seat of the pants generalizations that are important to remember (indeed, memorize!) as you consider the increasingly esoteric aspects of the art of antenna use:
• Telescoping antennas can cover a 30 mHz spread of the band (UHF or VHF) they are intended for because you can field tune them by adjusting their length (if you know what that length should be).
• Rubber Duck antennas can only cover a maximum of a 10mHz range of frequencies without the creation of an undesirable standing wave because you cannot change their length (at least not easily in the field).
• A VHF Rubber duck will not work effectively on a UHF frequency, and vice-versa.
• Dual band rubber duck OMNI antennas that supposedly will 'do everything', in fact accomplish the opposite because they simply cannot be designed to perform effectively due to the constraints imposed by the laws of physics. I love reading reviews of them where the hopeful HAM was disappointed in their performance - the equivalent of buying an eagerly anticipated Chinese moped from Kijiji and then complaining to anyone who will listen that you subsequently lost a 0-60 sprint competition with your neighbour who was riding his Yamaha crotch rocket.
• 5" 1/4 wave antennas might be conveniently short, but in comparison to a properly tuned 10" 5/8 wave, beyond serving for communication amongst close proximity stations (such as a landing helicopter) their performance could best be summed up as 'hopeless'.
• Your antenna choice is much more important than the make, model, or power of your radio. For example, a Baofeng UV-5R at 4 watts with a properly tuned 5/8 wave antenna will perform MUCH better than a more expensive Yeasu or Motorola* with stock antenna (*this is not an opinion, I have seen this happen personally at work on three occasions when I've been with other staff in the field and they could not hit a repeater with their issue Motorola HT1250, the first was below Badger Pass, and the last time being below Alymer Pass and trying to trip the Borgeau repeater. I then pulled out my Chinese HT and with the proper antenna could not only trip the repeater, dispatch reported a 2X3 signal index on simplex, and that was without the additional advantage of a counterpoise wire on my antenna. As the inability to check in with dispatch for a scheduled safety check would have meant a helicopter would have been dispatched if no contact was made, a $100.00 radio saved $2,000.00 in helicopter fees, because it performed better than a radio with a stock antenna that cost more than $1,000.00.)
• Look at the frequencies you plan to use. It's the Transmit one that is important, more so than the receive side which does not have the standing wave to worry about. Match the antenna that is closest to it within 5 mHz. Let's say your Tx frequency is 166.050. You would then purchase a 165 antenna. As each antenna has a 5 mHz spread on each side you could also use a 170 antenna but it would not perform as well as the 165 which is closer to 166 than 170 is. A 165 antenna covers the range of 160-170 mHz. If a factory supplied 1/4 wave antennas comes with the radio it is usually tuned for about 158-162, but it is not nearly as able to achieve long range propagation as the 5/8 wave Smiley Search and Rescue antennas. Hence the reason that 1/4 wave antennas should only be used for short range 'close in' communications. Professional Mountain Guides typically have up to 4 antennas (3 VHF, 1 UHF), plus a 'Rat Tail', in their Quiver.
The typical HT antenna doesn’t deliver any gain.
What? How come almost every manufacturer claim they do? First of all, manufacturers measure the gain of their antennas in dBi, which means that they compare it to an isotropic radiator. This is a more of a theoretical antenna than anything else. Such an antenna radiates (wastes) its energy into every direction: left, right, up, down and every direction in between. For some frequencies even a paper clip would deliver more gain than an isotropic radiator (but our Rat Tail works better). If you see something like 2.15 dBi, you’ll know that you’re being conned.
Ham radio operators measure gain in dBd. This measurement compares an antenna to a 75Ω half-wave dipole, or a 50Ω 1/4 wave ground plane. These antennas deliver a gain of exactly 0 (zero) dB. The approximate length of a 1/4 wave antenna, measured in centimeters, is easy to calculate: divide the wavelength by 4. So, an antenna for 2 meters would be about 50cm in length.
If you look at the stock antennas which come with dual-band HT’s, you will notice that none of them are 50 centimeters long. They’re much shorter! Yet they are a 1/4 wave or 1/2 wave in length, depending on the frequency. This is done by coiling up the necessary length of wire around a non-conducting core. This has two advantages: the antenna can be shorter and sturdier. Unfortunately there’s no such thing as a free lunch. By coiling up the antenna wire, the efficiency of the radiating element decreases considerably.
The real gain of a good dual-band helical antenna
So we learned that gain should be measured in dBd, not dBi. If we do that, the average dual-band helical antenna delivers a gain of minus 5 – 6 dBd on 2 meters, and something in the range of minus 3 dBd on 70 centimeters. 6dB or 3dB doesn’t sound like much, but don’t be fooled. -3dB will set you back by a factor of 2, and -6dB by a factor or 4. A Baofeng UV-5R is capable of delivering 4 Watts on 2 meters. But the stock antenna will eat up most of that power, radiating only 1 Watt into the air. Bummer, huh?
Single-band antennas always outperform dual- or triple band antennas.
More bands = more compromises. Sometimes it’s easy to make an antenna perfectly suitable for 2 bands, such as 4 meters and 2 meters. In this example the 1/4 wave for the 4 meter band will be a near-perfect 1/2 wave for 2 meters. It becomes trickier when you combine 2 meters and 70cm. In most cases antenna designers have to revert to ‘traps‘ in order to keep the SWR on both bands within reasonable limits. This system works well, but will decrease the efficiency of the antenna even further.
All the above is why we DO NOT recommend using the antennas that ship with the dual band radios and using VHF antennas for VHF, and UHF antennas for FRS channels. Also you can see why we use a longer 5/8 wave rubber duck antenna that matches your frequency range to increase your potential dBd by improving the efficiency of the radiating element, and recommend using a Rat Tail to reduce signal loss.
How to improve range:
Antenna height. The higher, the better.
Radiation pattern. Antennas should not waste energy by radiating it in unwanted / useless directions, this is why a Rat Tail is recommended.
Free space loss can be partly compensated by increasing power output. Doubling the output power will not double the range, the theoretical improvement is about 35-40%.
The use of repeaters at high elevations, which will compensate for the radius of the earth.