The BeNevolent dbu wrote in
:

In article ,
Dave Oldridge wrote:

rocky wrote in
:

In article ,
Dave Oldridge wrote:

Big Endian wrote in
:


My center of a 3.8 Mhz doublet is at about 35 feet and am going
to drop the ends from 30 feet to about 10 to 15 feet. Just
wondering if it will make all that much difference if any?

There will be a marked improvement in the low angle performance in
the direction off the ends of the antenna (the flattop is very
poor at this). This will come at the expense of a sight loss
(about .8db) off the pattern's top (where you can most afford it).
You will also experience a slight deterioration in the SWR (based
on 50 ohm coax) from about 1.34 to 2.05, easily managed by any
tuner, including those built into many radios. You will also find
that you need to shorten the antenna very slightly to maintain the
same resonant frequency.

This won't make it into a superior DX antenna but it may allow you
to hear things you missed before. Basically, Bob Heinlein was
right. There ain't any such thing as a free lunch.

What I've read is that when the ends are dropped to an inverted Vee
configuration the feedpoint impedance drops closer to 50 ohms, but
the Vee bandwidth is more restricted. Hard to believe that
lowering the ends by 15 feet from 30 would make all that much
difference on 75 meters.

It's only really noticeable on low-angle (about 30 degrees or so)
signals from the direction off the ends.

I am going to have both antennas up at the same time. I'll switch
between the two and see if there is any difference on close in
(100-300 miles) stations hearing me. The antennas will only be a few
feet apart, one will be a dipole cut for around 3.8 and fed with 52
ohm coax, the other is a 130 ft. center fed doublet using 450 ladder
line. This may take a while because we're still in winter.

Assuming the mean RF CURRENT heights are the same and the two antennas
are not violently interacting, you shouldn't see much difference. There
will, of course always be some phasing differences between two different
antennas, even if they are otherwise equal. This cannot be avoided where
signals are being reflected off the ionosphere and the ground.

--
Dave Oldridge+
ICQ 1800667