Hi Ford,
> Question:
> Is it better to feed this type of tower at a high impedance or low
> impedance?
In most cases ground losses will dominate system losses, and so
feed system errors won't make a noticeable difference. But if you
are splitting hairs the following is true.
The system will have less loss and more bandwidth when a simple
series C gamma with very high capacitance is used. This is
accomplished by placing the tap on the correct point of the tower,
using the right spacing, and using a fat conductor or cage of
conductors for the feedwire. This makes the Q of the feed system
the lowest possible value, and reduces reactive power in the
system. Reactive power causes loss, does not contribute to
radiation, and reduces bandwidth.
An omega match has more loss and less bandwidth, all other
things equal, than a simple gamma match with only a series C. A
gamma with a high value of series C has more bandwidth and
higher efficiency that one with a lower value of C, all other things
equal.
73, Tom W8JI
w8ji@contesting.com
--
FAQ on WWW: http://www.contesting.com/FAQ/topband
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|