Topband: DUAL BAND INVERTED L

[Tom Rauch]

> he described the construction of traps which looked like they could handle
> legal limit-type power. I believe the traps were constructed out of RG213.
> I'm certain that the information is contained in the 'topband' archives or

Be careful what you use for traps in a Marconi antenna, especially 
a bent antenna. The voltage is at least double that of a dipole, as is 
the current, through the trap. 

A 1 kW trap in a dipole only handles 250 watts in a Marconi 
configuration. If ground losses are high, it will handle more power of 
course because there is less "fire-in-the-wire".

Coaxial traps are also somewhat lossy compared to other 
systems. The Q, using some methods of measurement (delta 
frequency tests), is misleading because the trap "capacitors" are 
transmission line sections. Loss is higher than actual ESR and 
EPR measurements would imply, causing the false impression Q 
is high.

Rather than use a trap, I'd just add a second wire 1/4 wl long on 80 
meters spaced several inches from the 1/4 wl 160 meter wire. With 
some pruning, you should get reasonable SWR on both bands, and 
not have any worries about traps or remote tuning units.
    
73, Tom W8JI
w8ji@contesting.com


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