Antenna Matcher

[Big Lou]

Can someone explain to me a antenna matcher ? Like the The PDC30 for example that a found on RedmanCB.com [Please login or register to view this link] Does this mean I can buy it, hook it up and get good SWR without messing with my antenna ? Sounds to good to be true so whats it do ?
Thanks ,
Lou

[4 cycle]

Google How to use an antenna tuner.

['Doc]

An antenna tuner/matcher only makes a mismatched antenna system appear better to the transmitter than it was. That allows the transmitter to produce full output instead of 'cutting back' because of the mismatch. Since the mismatch is still there, only a percentage of that increase in power output ever get's to the antenna. So while there can certainly be more power being radiated, it still isn't the total amount of power delivered by the transmitter. You only get the full amount when the antenna is resonant and matches the rest of the system.
So why bother with ever using a tuner? Because of two things. No matter what antenna you are talking about it's only going to be resonant on one frequency (or chunk of frequencies very close to the resonant one). That means you can sort of 'skootch' up or down a bit, retune using that tuner, and the transmitter things things are just fine and produces full power instead of a reduced power output because of non-resonance. the other reason a tuner is very nice is that you can change bands and still make a non-resonant antenna 'work'. Not as well as a resonant one, but something is almost always better than nothing. A tuner can make a non-usable antenna usable. They do have limits though. They do not do 'miracles'.
There are other factors that come into play, but that's a fairly good 'ball-park' explanation of a tuner. Another more descriptive name for a tuner is a variable impedance matching transformer. That's what it does, transforms one impedance into another impedance. Now, if you moved that tuner from just behind the transmitter/amplifier to just in front of the antenna at it's feed point, you change the name again, to something like a gamma, beta, 'hair-pin', whatever matching device. Like the ones you see on beams and other antennas. Of course, when you move that tuner to the base of the antenna, you make it a lot harder to adjust the thing, it's a little harder to reach, sort of. Same principle, just a difference of which end of that feed line it's on.
- 'Doc

[Idaho Annie]

That's a great explanation Doc! But I have a question, too....

If high SWRs are physically bad for the radio, doesn't a tuner 'protect' the radio from any damage? So even though you may not get the greatest power out, or resonance, at least by using a tuner you are protecting the radio from hurt?

Curious,

['Doc]

That's certainly one way of thinking about it. And while what you are thinking is true, high SWR can damage a radio, it usually takes more than just a very short time to do that harm, unless it's really, really outrageous. So, yes, it can make the transmitter 'happy' and protect it to some extent. The real problem is with doing damage to things between that tuner and the antenna, it won't do anything to protect there, feed line for instance. that's where most problems occur, the coax being damaged from a very high SWR and too much power. A tuner can be 'insurance', but it's never going to be the best insurance, and certainly not the cheapest.

One other thing you should be aware of with tuners. They are usually rated for power in Pep watts whether that's stipulated or not. That means that it may say it can handle oodles and gobs of power, but you'd better figure on about half of whatever it says. this is one area where bigger definitely is better. Why the Pep thingy? Bigger numbers, and advertising!
- 'Doc

[Circuit Breaker]

In addition, ideally, the best place to put a tuner is at the base of the antenna. This reduces the amount of signal coming back down the coax and also reduces the amount of loss...which is also dependent on how "out of tune" or resonance the antenna is. If your SWR is 2:1, then the amount of loss using the tuner to bring the SWR lower is negligible. In most cases, your antenna is probably already going to have a good match on the normal 40 channels and probably go below and above that...how much depends on the antenna. Of course one option, if you want to have a perfect match from 26 to 30 MHz is to get the SteppIR SmallIR vertical. It's the same length as an Imax or A99. At the base, there is a stepper motor that increases or decreases the length of the copper element inside the antenna so that it is the ideal length for any frequency from 14 MHz to 54 MHz. They aren't cheap though. I had the BigIR back in FL. It covered everything from 7 to 18 MHz as a 1/4 wave vertical and 21 MHz to 54 MHz as either a 1/4 or 3/4 wave vertical. The new versions of the BigIR now cover 3.5 to 54 MHz thanks to the addition of a loading coil.

[Night Crawler]

How can the PDC30 have a frequency range of 0-30mhz without a variable inductance? If that thing can handle 500 watts I'll eat my hat.

['Doc]

Night Crawler,
You ready for this??
It's possible! But, it's only possible in a very narrow range of possible circumstances. The likelihood of any usable antenna falling into those circumstances is almost 'zero', and when you factor in that 500 watts thingy, it's an even more rare set of circumstances... but, within the realm of things possible. Just like it's possible for me to win the lottery, like some of the emails I get say I've done. I can think of circumstances where that is certainly possible. (That's called imagination by the way, especially since I've never bought their lottery ticket.)
And when you stop and think about it, it's also something you see a lot of with advertising...
- 'Doc

PS - I do agree with you. I also couldn't resist... so what else is new?