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Radio Lowdown on the Down Low.


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So getting on the air is a matter of having a powersource, a transceiver, and an antenna. An important part of your antenna system, especially if you use the sort of compromise stealth antennas I've been discussing so far is your antenna tuning unit. Think of everything after the coax plug in the back of the radio as being part of a separate system. This system consists of your feedline and your antenna itself.
A simple truth about radio signals is that they sometimes bounce. Sometimes that's a good thing, other times that's a bad thing.
Bouncing signals are usually a good thing when the bouncing happens outside of your antenna system, and in the atmosphere. In this case the radio signal is on its way somewhere, going from your antenna to some other antenna. Bouncing is good and happy. Bouncing signals are a bad thing when the bouncing happens inside the antenna system, on its way to the atmosphere. This happens when there is a "mismatch" between the antenna, the feedline, the radio, or all of the above. The thing that is mismatched is called "Impedance" and it is a source of confusion and consternation for radio operators everywhere.
Simply put, impedance is a measure of how hard the system fights the current flowing through it. Impedance is to AC current what resistance is to DC current. Getting deeper, Impedance has a "real" part caused by the resistance of the circuit/feedline/antenna, and an "imaginary" part caused by reactance generated from inductors and capacitors in the system. In an ideal system, the impedance is all real (no reactance), and the impedance between each section of the circuit either matches, or is transformed so that it is matched.
This concept of "impedance" and "reactance" is essential to understand for the stealth radio operator more so than the guy who doesn't care how big or visible his antenna is because of the antenna choices the stealth operator makes. when there is an impedance mismatch between portions of the circuit, part of the signal travelling forward is reflected back to the source. This can be very bad for the source! Think of it as a very tiny amount of EMP in your system. You can fry (literally) part of your radio if there is an impedance mismatch. I've done that (unintentionally) more than once while building radios and antennas. At best, you wind up with a poor received or transmitted signal. The good news is that if you have a modern radio, your radio will likely reduce your output power if you transmit into a mismatched antenna. This won't protect your radio forever, but it will protect it long enough for you to realize you are an idiot
The stealth radio operator is more concerned with hiding his antenna than making sure that the antenna has an impedance match to the feedline and radio. The simple solution to this is to use an antenna tuner between your antenna and your radio, and let it do the job of making sure your radio is protected from impedance mismatches. Some side benefits of an antenna tuner are:
They help cut down interference from strong nearby radio signals.
They help prevent harmful interference from your radio on harmonic frequencies.
They act as a buffer between your radio and lightening (if the tuner is properly grounded)

They also have some disadvantages:
There is signal loss in inserting a tuner.
They are a 'weak point' in the circuit, improper usage can be hazardous due to the large voltages generated while matching signals, especially while transmitting.
Added expense for quality units.
Here's what it's like to use a tuner:

Part 1:

and Part 2 is here, but I can't post the video it is shorter:
So to recap:
1. GOTA - Get On The Air. Pragmatism over theory.
2. When using a compromise antenna keep your power down, especially if the antenna is inside
3. Invest in a good tuner.
4. Higher and longer are better ideas.

Next time we will discuss antennas for local communication.