Empirical evidence to confirm your analysis: When I replaced my plumber's
delight TB with a 20/40 dual monobander with elements insulated from the boom,
my 1/4 wave 80m sloper went from very satisfying to essentially non-functional.
Lots more metal was up there, but it wasn't at ground. Of course, my 20/40
results improved dramatically!
/Rick N6XI
"Rajiv Dewan, N2RD" wrote:
> I just did some quick modeling on Eznec using a 6m 30' boom yagi model I
> had:
>
> Case 1: Only mast (tower) 45' tall, 4" dia over perfect ground, 3.65MHz
> Source impedance 13.3 - 146j ohms, SWR (50ohms) 36
>
> Case 2: Mast with a 30' boom 6m yagi just above it, NOT touching
> source impedance14 - 137j ohms, SWR 31
> Max current in boom 0.03A (for 1A feed feed current)
>
> Case 3: Boom connected to mast, not insulated
> source impedance 30 + 5j ohms, SWR 1.7
> Max current in boom 0.3A (for 1A feed feed current)
>
> My bottom line - No connection - No good. There is some effect if the
> antenna is insulated but not much.
>
> Perhaps you could put in a relay to short the boom to tower/mast when
> needed.
>
> Regards,
> Rajiv, N2RD
>
> ----- Original Message -----
> From: <lsica@attbi.com>
> To: <towertalk@contesting.com>
> Sent: Friday, June 07, 2002 2:57 PM
> Subject: [Towertalk] is an LP a good sloper top hat?
>
> > I have a tower mounted half-sloper, with an log periodic
> > on top of the tower. Problem is, the log is completely
> > insulated from the mast on the tower. Does it still work
> > as a top hat to the tower for the sloper to work against?
> >
> >
> > _______________________________________________
> > Towertalk mailing list
> > Towertalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
> _______________________________________________
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--
Richard M. Tavan
TIBCO Software Inc.
3307 Hillview Drive
Palo Alto, CA 94304-1213
tavan@tibco.com
n6xi@arrl.net
650-846-5214 Office
408-896-0476 Cell
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