freecell said:
why is the larger gamma not as efficient at the lower power levels?
I don't know. I hope you can shed some light on it!
A local here has a M-106C. He also has a bowl box (that's not a good thing) running 6 3-500s (shoot me now!). He smoked his first gamma and got a replacement. We did a few minor upgrades to the 106 and installed the replacement stock (2KW) gamma.
The antenna tested fine and he ran that with just the driver for a while. The urge to flip the big switch was just too much but he knew he had to have a larger gamma or he would arc it also.
He went out and bought the 10KW gamma. We were surprised that there was a drop in signal on the receive. We tested the antenna and all was good.
Over a bit of time he was still unhappy with the performance of the antenna so we took some time one weekend to do some tests.
We swapped out the gamma for the 2KW version and bang, his receive was back on track. I have a Bird 4030 field strength meter so we took a couple of field strength readings; up close, approximate 1 wave length away, and a couple of miles away. Nothing scientific, but very repeatable. Then we installed the 10KW gamma and did it again.
With all other parameters being the same and using approximate 100 watts, we were surprised that there were consistently better field strength numbers using the 2KW gamma.
Obviously the 2KW gamma would not survive the big amp. The (for lack of a better term at this point) plates of the gamma were too close on the 2KW and would arc. The 10KW has more spacing. In order to compensate for the larger spacing, the 10KW gamma uses larger tubes.
It is my OPINION, that the increased spacing lowers the effciency of the feedpoint matching network. In other words, a lower amount of signal is making it to/from the driven element.
The fact is, something IS lowering the efficiency of the feedpoint matchin network as proven by the field strength readings. Remember, the ONLY change was the gamma.
I've talked to other people who have seen the same thing when going to bigger gammas. They however did not take any test measurements.
So now its your turn! You are a respected man on this forum (although your people skills suck at times) and your opinion and teachings carry some weight! So test away and prove me wrong. Don't use your books and keyboard however, do a real world test and let us know what you've learned!
Antenna
THEORY amazes me and I learn more and more every day! Even the great ones out there say its a best guess when it comes to antennas and like me, they too learn more every day!
Screamn' whitewall tires and a guitar by his side
Billy's got the fever as he rolls on thru the night
Some were born to listen, some were born to play
He was lightning on the highstrings and thunder on the bass
He could play it high, he could play it low
He could make it cry, he could make it moan
He knows when push comes to shove
The proof's in the pickin'
The PROOF's in the pickin' !