never mind i got my answer the easy way....and I will be using this on my Spitfire427 beam....So this means for the gain well worth it)
Until next time SI-GIN...
I was convinced in those days that if I could just get another 20 watts of output from my transmitter that it would make all the difference in the world at the receiving end. If I could just get those extra 20 watts that rare DX operator in a distance land would see my signal jump from a pitifully weak whisper to a loud boom that he could not ignore, and I would get that contact. Today I know that little extra power would not have made any difference at all. However, I still have an intense desire to push my transceiver to its maximum power output to get a DX contact. But it doesn’t stop there. I want every db of gain that I can possibly get out of my antenna. As far as coax is concerned, I want that big, heavy, hard to handle, expensive coax because I don’t want to loose any of my valuable watts getting from my transmitter to the antenna. Does all of this pushing, shoving, and optimization really make a difference? Probably not!
It turns out that you must increase the output power of your transceiver by at least 3 db in order for the person you are talking with to notice any change in your signal strength. For your signal to sound twice as loud, you must increase your power out by about 9 db.
How much is a 3 db increase in power? A 3 db power gain is equal to a times 2 increase in power (3 db = x2). So, if your transceiver is running 100 watts, you must increase your transceiver’s output to 200 watts in order for the person you are talking with to notice any increase in your power. If you wanted your signal to sound twice as loud, you must increase your power to 800 watts (9 db = 3 db + 3 db + 3 db = x2 x2 x2 = x8)!. Clearly, increasing power by 20 watts, say from 100 to 120 watts, is not going to make any difference at all to the person receiving your signal. On the other hand, if you cut your power in half from 100 watts to 50 (a 3 db decrease in power), the other operator will hardly notice any drop at all in your signal strength. So why beat your transceiver into the ground by running it at full power? If you run at 75 watts instead of 100, your transceiver will run cooler and no one that you talk to will know the difference. There is someone who may notice the difference however, your neighbors. If you are having interference problems, cutting your power level in half could solve those problems without having any noticeable affect on your ability to make contacts. For example, when I operated on 10 meters at 100 watts, my lawn sprinklers would turn on whenever I keyed my transceiver. When I dropped to 50 watts, the problem went away. Running at 50 watts turned out to be a great water conservation technique.
What about antennas? The same 3 db rule applies. You can go to a lot of trouble and expense on 40 and 80 meters putting up phased vertical arrays to achieve 2 or 3 db of gain. But 3 db of gain will hardly be noticeable to anyone listening to your signal, so why bother? The threshold in antenna cost verses performance gain is around 6 db. If your antenna provides 6 db of gain, operators listening to your signal will notice a difference. Your signal will not be twice as loud, remember you have to get 9 db of gain for that to happen, but at 6 db the gain will be noticeable. The table below puts antenna cost verses performance gain somewhat into perspective. This table compares various yagi beam configurations to the performance of a dipole. The table shows the db gain, relative to a dipole, achieved by each of the antennas. The antennas get more expensive as you go down the table. The table also indicates the increase in signal strength observed by the S-meter on a distant transceiver that is receiving your signal.
