Adding a linear amplifier?
First a couple of definitions of "dB":
A dB is unit used to measure the power of a signal, such as an electrical signal or sound, relative to some reference level.
An increase of ten decibels in the power of a signal is equivalent to increasing its power by a factor of ten.
As a measure of sound intensity, a zero-decibel (0 dB), reference is considered to be the lowest level audible to the human ear; the speaking voice of most people ranges from 45 to 75 decibels.
Another good definition:
dB....A term representing the ratio of two quantities.
For our purposes of this article, one ratio being the sound level that is measured and the other ratio being a reference sound level corresponding approximately to the faintest sounds detectable by the human ear. The greater the sound level measured in dB, the louder is the sound.
Generally, a change of 2dB is just perceptible, 5dB is clearly heard and audible, and 10dB "appears" twice as loud. All based on good hearing of the human ear.
The reverse is also true with the above numbers. A 10dB change lower in power would be 1/2 as "loud" as it was before the change was made. But....it is difficult for the human ear to tell just how loud "twice as loud" is...you do notice a change, but just how much change....how can your ears "measure" that change...it is a relative value based on your hearing.
The difference between running a kilowatt (1000 watts) and running 100 watts is 10 dB). That would "sound" 2 times louder if you could measure it accurately. Said another way in reverse, the difference between running 100 watts and a kilowatt is also 10dB.
So you might be thinking, "Well if that is true, then if I run a 500 watt linear instead of a killowatt, then this would make a 5dB change in my signal. Would'nt that make my signal sound almost 2 times louder?" The simple and mathematical answer is NO.
Remember, a 5dB change in power is audible and detectable by most ears, but it is not "mathematically" 2 times louder.
The reason is that the db "scale" is not linear and is based on a mathematical formula which we will not get into due to being somewhat complicated and is not needed for this article.
"Ok"...you say..."So how many db change to the better would I have if I added 500 watts to my transmitter? What if I was running QRP at 5 watts and then added 500 watts? I need help!
Enter the calculator below.
To use: Place your cursor into the first "Before" window.
Highlight the entire number and enter your power level.
Do the same with the next "After" window. Then click the "Calculate" button.
Read the result in the "dB" window.
Notes: It is accepted that most S meters require "about" 6 dB change
to equal 1 S unit difference. This may change from S meter to S meter and is not a standard but a commonly used value for reference purposes.
You are wanting to add a 500 watt linear to your 100 watt radio.
How much "dB" difference will that make? Place 100 in the first "Before" window. Then place 500 in the second window...click Calculate = 6.98070 dB difference,
(almost 7dB), or a little over 1 S unit.
The "QRP" Example:
Place 5 in the upper Before window, then place 500 in the lower After window. Click "Calculate' for your answer! 20 dB.....now thats a huge increase from your tiny signal and when using about 6dB per S unit on the other guy's S meter...thats about 3 S units on his S meter plus "some pocket change left over"!
Now let's go "illegal" for a moment with another example!
Let us assume that your running a kilowatt all the time and still not getting the signal reports that you want.
You decide to shell out those really big bucks for a 5 kilowatt linear added to your 100 watt radio! By using the calculator above, you will find that the change in db "power" will be only 6.98 dB difference.....now was all that money worth getting slammed by the FCC for just another 1 S unit on the other guy who may not have a calibrated S meter....maybe for you, but not for me!
In many cases, with poor band
conditions, high noise levels and heavy interference, etc, and if your
signal is just above the noise level at say S 3 as an example, then by
adding another 10 db to what you are already using (100 watts) you
would gain just a little over 1 1/2 S units and be "heard" (seen
on the S meter), at about S4 to 5 or said another way.....a
little above the noise level if all the variables involved did not
change. Your signal will be stronger on the S meter but you may or
may not be "heard" better than before! The signal level above the
noise level is what counts. If your signal is still down in the other
guy's noise level, you still can't be heard.
If your audio in the other guy's receiver is muffled due to a poor quality mic, improper mic techniques or audio settings on your transmitter, then adding more power, and changing nothing else, only makes the unreadable muffled signal stronger, not more intelligible. So it doesn't matter the distance of the receiver, they could be in Punta Cana or Cancun Mexico, it'll still be muffled.
Your goal is to strike a happy
medium between intelligibility and signal strength using only the amount
of power needed to establish the communications as per FCC rules. All that
is required by the station on the other end is to be able to understand
you clearly. If you have to continually repeat your call sign...you are
not being clearly understood! Ham radio is NOT intended to be broadcast
band FM quality! If the band is "dead", then no amount of power,
legal or not will help you!
I hope this has helped you in some way to understand the relationship between adding more power to your station or...NOT...You have to compare the difference in dB "gain" and how it is "heard" on the other station vs the expense of more power and hope for the best on the other end of your signal on the air! Adding an additional amount of power to your signal, (within your license privileges), may help you.......or not........mother nature and your audio quality if using voice modulation will decide!
73 Don, N4UJW