Hi,
Preparing for "retired man countryside QTH" I am trying to understand some
topics related with Beverages.
I hope you can advise me and clear my doubts.
Thanks in advance!
Let assume, the only possible configuration for 8 directions Beverage farm
is a "star" configuration.
All Beverage antennas will meet at central point, where the switching box
will connect one particular Beverage as On-Line antenna.
My question is: what about rest of Beverage antennas?
I have seen designs where all other antennas are connected to ground.
From theoretical point of view I disagree with such solution.
Let me explain why:
1) we can see Beverage antenna as open-wire transmission line with the
ground as one conductor and the antenna wire as second line. At the further
end of antenna the wire is grounded through 450 Ohm resistance,
2) to avoid re-radiation from un-used rest of Beverage antennas (in star
configuration) and picup of re-radiated RF by Beverarage antenna actually
On-Line, closer ends of un-used Beverages are grounded.
On my mind that is mistake. If we have long open-wire transmission line:
- at one end connected through 450 Ohms to ground
- and grounded directly at the closer end
that WILL CAUSE MISMATCH in that line and such line WILL RE-RADIATE RF
energy pic-upped by un-used antenna.
3) Beverage is called "wave antenna".
The wave antenna is performed only WHEN PROPERLY MATCHED AT BOTH ENDS of
the line.
When such open-wire transmission line (with the ground as one conductor and
the antenna wire as second line) will be matched at both ends and WILL NOT
RE-RADIATE?
On my mind, only when, it will be terminated at BOTH ENDS with their
characteristic impedance, i.e. 450 Ohms.
We can do it implementing additional relays at impedance matching transformer:
- at the primary winding: to connect 50 Ohms resistors to all un-used
Beverages
- or, at secondary windings: to disconnect "cold" ends from ground and
grounding "hot" ends of all un-used Beverages through 450 Ohm resistances.
Can anyone cleare my doubts?
Will be grateful
Tadek, SP7HT
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|