Hello everybody and welcome back to my blog! I hope that you have been enjoying my technician class series that we started last week. Today we are going to talk about antenna tuners and what they actually are.
One thing that we always have to think about when it comes to our radios is how much power we are putting out and how much power is being reflected back to our radios. This is called the Standing Wave Ratio or SWR for short. Most of the time, the SWR is corrected by fixing your antenna. However, there are times when you cannot “fix” an antenna. If the antenna is a long wire or inverted V or even just a Barbwire fence, you have to use a an antenna tuner. If you go by just the name it, it is a little misleading; An antenna tuner doesn’t actually do anything to the antenna. So what does it actually do, you ask? An antenna tuner is used to transform the impedance at the feedline input to a value that your transceiver can handle, typically this is 50 ohm. When the impedance value of your antenna system matches the correct impedance value of your transceiver, you will be able to transmit the maximum amount of power.
If you have an antenna tuner in your system, does your antenna, itself, need to be tuned correctly? Yes, it does. Even though the antenna tuner corrects for an incorrect or bad impedance or SWR between the tuner and your radio, you may still have bad SWR between the antenna and the tuner. So the bad SWR shouldn’t affect your transceiver but could potentially hurt your antenna tuner. Also, you will have transmit power loss at your antenna due to part of it being reflected back to the tuner.
What is the correct way to tune an antenna tuner?
If this is the first time using your antenna tuner you shouldn’t trust the knob markers. Disconnect the antenna tuner from your radio and power, if it is powered, remove the top cover and turn the knobs until the moving capacitor plates are only half meshed with the stationary plates. Once this is done, you will need to loosen the Allen nuts and rotate the knobs so that they are at mid-scale, then tighten the Allen nuts again and replace the cover.
Now let’s talk about the antenna tuner itself. Most antenna tuners have an induction rotary switch ant two capacitors. The capacitors are often labeled ANTENNA and TRANSMITTER. Some antenna tuners have a continuously variable induction, commonly known as a roller inductor, instead of an induction rotary switch
Once you have verified that the mid range on the antenna and transmitter knobs are correct, set both controls to mid-scale, hook the turner back up to your radio and power, if needed, and turn on your radio. Turn your induction switch until you hear the loudest noise or signal coming into your radio. Then, rotate the antenna and transmitter controls until you get the absolutely loudest signal or noise level on your radio. This should be close to your best tuning spot.
With your radio set to low power, tune it to an unused frequency. Listen for a little bit to verify that it is unused, then key up and say your call sign then transmit a continuous carrier while you tweak the antenna and transmitter controls for the lowest reflected power rating and highest output power as you read your SWR meter.
Once you have it tuned, it is a good idea to tune your radio up and down from the frequency that you tuned on; transmit every once in a while, until you find your range of acceptable SWR/Power output. Once you know the range of what is an acceptable SWR, then you will know how far you can generally tune in that band before you need to adjust you tuning.
So that about covers it. Thanks again for coming to my blog. Please leave any comments or questions you have in the comments below. Please share my heart with your friends, like me on Facebook, follow me on Twitter, Google+, and LinkedIn. Until next time…
73 de Curtis, K5CLM
UPDATE: This post was originally posted on Thursday, July 30, 2015. The grammar and spelling of this post was horrendous! I would like to apologize to all my readers for this. I broke one of the rules that I set forth for myself when I started this blog, to always proof read my posts several times out loud before I publish anything. Due to my internet being down the past couple days, and wanting to maintain my post schedule, I wrote this post on my phone, mostly using Speech-to-text, and it really butchered it! After I thought it was done, I failed to proof read it because I was doing multiple things at once, namely taking care of my 5 kids while my wife took a much needed mommy day. I hope that everyone will continue to come back to my blog.