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HF Amplifier Or AntennaHF Amplifier Or Antenna
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Subjects > Electronics (Search for Electronics) > Amateur Radio (Search)
Almost all newcommers to the hobby of Ham Radio (Search for Ham Radio) confront this dilema at some point. "Should I buy an amplifier, or improve my antenna system, or both?"
It's a reasonable question to ask after you get hooked on the hobby. You will want to increase the number of conversations (QSO?Create|Search's) you have, improve your ability to understand what you are hearing, and help others understand you. You'll probably want to work stations farther away, and maybe you'll compete in contests where you'll want to get higher scores.
What is the most important thing that a radio transmitter must do? It must cause a signal to be radiated that allows the operator to be understood in some remote location. What is the most important thing a radio reciever must do? It must select a certain signal from among all the other unwanted signals present (Selectivity?Create|Search), and then amplify that signal so that it can be understood (Sensitivity (Search for Sensitivity)).
One thing that is used during the tuning of transmitters, and setup of amplifiers is the [Dummy Load]?Create|Search. A dummy load is designed to absorb a signal, and radiate little or none of the signal. It is designed to be a perfect match for the output of a transmitter or amplifier so that none of the signal reflects back into the output of the radio or amplifier. Any reflected signal turns into heat, and risks burning up the output (the final) of the transmitter or amplifier. Is a dummy load a good choice to use for communicating? Of course not, since it doesn't radiate.
So the obvious answer is that an antenna that radiates as close to 100% of the signal is better choice. However, there are still some other issues to content with.
Angle of radiation can be important since very long distance communications will require the use of skip. Skip is the bouncing of signals off of layers in the upper atmosphere, allowing them to reach farther locations than the immediate vicinity of the signal.
Another issue that is important to radio transmission is the polarization of the signal. The signal can be horizontally polarized (such as from a horizontal dipole), vertically polarized (such as from a vertical antenna), or even circularly polarized (which is often used for communication with satellites). The transmitting and receiving antennas should have similar polarization, otherwise a reduction in signal strength will occur, called attenuation?Create|Search.
It can be very expensive to purchase an amplifier to more than double your current output power. Also, depending on your license crab, there will also be limits to the maximum transmitted power you can use.
There are also other considerations in the choice between antenna and amplifier improvements.
Amateur Radio (Search) is licensed and regulated by the governments of the world as a radio service. There are lots of rules and regulations, more than any "hobby" would have. When someone becomes a licensed ham, they are agreeing to follow these rules.
One of the most important rules is to not cause unnecessary interference, which goes hand in hand with the requirement to use a minimum amount of transmitted power to maintain the communications.
If it is OK to use 5 watts to talk across town, you should not use the high power 40 watt setting of your radio. Many hams would be surprised at how they can probably maintain most of the communications with half the power they ordinarily transmit. Besides the regulatory reasons to use low power, you can also extend the life of your batteries, and maybe even your transmitter.
About the only time when you wouldn't need to worry so much about using the most power possible is during an emergency involving threat to someone's life. However, even in this case, something the ambulance, police, and fire fighters are involved in all the time, even they try to avoid using more power than neccessary to avoid interfering with the communications in other jurisdictions.
Doubling your signal power output will cause receiving stations to hear an increase in your signal of just 3-dB, or half an S unit! To move the receivers signal meter on the other end a full S unit, you must quadruple your power!
So perhaps you need to multiply your signal by 8 times, in order to get just under a couple of S-units increase in receiver strength. Guess what? Increasing your 100 watt signal to a kilowatt will cost about $1500. And if you get a legal-limit amplifier, the 1500 watt signal will only be slightly more than 2 s units stronger, and will cost $2500 or more. Definitely a law of diminishing returns here.
There are other hidden costs too... You'll need a more powerful tuner. More expense, maybe about $500. You may need better wire to connect your your antenna. You'll also use a lot more electricity. Your "barefoot" amplifier with it's 100 watts of output could probably comfortably run for 8 hours or more from a standard deep cycle marine battery. But if you want to run an amplifier, you'll need a good source of 120V AC. For more than 500 watts, amplifiers require 240V of AC, which might mean having to run a new electrical outlet to your amplifier.
One other big draw back: All of this work to boost your output signal will do nothing to help you receive better. Since amateur radio is all about two communications, (broadcasting without listing is against the rules of Amateur Radio), what good is it to be able to talk farther than you can hear? You will only be causing unnecessary interference.
Think about your antenna. How can you improve how much signal your are effectively radiating? Any improvement in your antennas ability to radiate will likely improve it's ability to pick up signal, helping you to receive weaker stations too.
One way to improve almost any antenna is to raise it higher. Put it up in a tree, or on a taller mast, or put up a tower.
Another kind of antenna that is very effective is a full wave horizontal loop. This one inexpensive solution can increase your signal by 2 to 10 dB! Remember, your receive will improve also, letting you hear stations you might not have heard before too.
450 ohm open wire can also help you get back some of the losses you might have in your current antenna feed line. These loss can be anywhere from 6 to 25 dB.
Another possiblity is to by a multibeam antenna known as a yagi. You will want to have a rotator to be able to point it in various directions. This kind of antenna can result in a 30dB signal enhancement! Plus, stations off to the side of where you are pointing will not be as strong in your radio, helping you to hear better also.
Using the speech processor on your modern transmitter may also improve your signal by as much as 3 dB.
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