"Mike (by way of Bill Tippett )" wrote:
> I have heard these arguments before about delta loops on the
> low bands (one of my DXing buddies at work keeps telling me
> the same thing about our 75M delta loop), but aren't we
> forgetting that you don't get something for nothing?
The important consideration in my view is that the Delta Loop allows you to
get up and running with a fair performing 160 or 80 meter antenna without
much effort. However according to the original testing I did on 80 meters
the inverted Delta beats the single support delta when it is fed at one
end. The impedance appears to be a bit lower allowing direct 75 ohm or
even 50 ohm coax. Decoupling ferrite and /or a balun at the elevated
corner feed point should reduce pattern distortion. Another important item
to consider is that the patterns appear much different when wooden supports
(power poles) or trees are used to support the inverted Delta and pattern
degradation can be reduced by sloping the feed line away from the end
support by 45 degrees.
I have never had the ability to model the different antennas but I would
expect that if metal towers are used to support the Inverted Delta, or the
Single tower "straight" Delta loop that the tower are contributing to
significant reradiation. I have even gone so far to say that a single
support straight delta on a single 120 foot metal tower is a loop excited
1/4 wave vertical. Having said that, the Delta Loop, in any configuration,
seems to be a quieter antenna than the straight shunt fed vertical. This
is determined by hundreds if not thousands of switching comparison between
both antennas.
Herb Schoenbohm, (ex-KV4FZ)
Box 4419
Kingshill, VI 00851
|