Jim Brown, K9YC wrote: "BUT - in my experience, vertical dipoles don't work
very well on the HF bands."
My personal experience is a little different Jim!
I have a single self-supporting tower for all my antenna systems. When I
moved to this QTH (winter) about 15 years ago I hung some temporary
wires off the 90 foot tower in order to get on the air. One of those was
a 40 meter dipole with one end near the top and the wire sloping away at
a 60 degree angle. (I would consider it an 'almost' vertical dipole.) It
Later I installed a 40m Telrex dipole. This is a 70+ feet long, stout
aluminum horizontal radiator. I side mounted it on the tower about 80
feet above ground. My intention was to remove the vertical dipole,
although I had an empty switch position so I decided to hook her up.
Normally I can flip between these two antennas with no noticeable
difference in RX signal strength (not precisely measured, but eyeballed
on the IC756 Pro 3 analog meter).
However! There are times when one antenna or the other will provide a
readable CW signal while the other one will not. This is especially true
near the band noise floor, although sometimes 'booming' signals will
exhibit a 20 dB (approximate) different on the meter.
The one area where the vertical dipole works better for me is the QSO
Parties where the target stations are mobiles. The closer these stations
are to my QTH (border states), the more pronounced the vertical wire
shines. The difference in strength is not as apparent when working the
coastal stations (CA, FL, NY from MN).
As you might expect, my temporary vertical dipole has become a permanent
fixture in my arsenal of antenna choices. That said, with all the wires
hanging from this tower, it would be a modeling nightmare to determine
all the interactions! But even so, I don't think you can every have
73 de Bob - KØRC in MN
On 4/24/2011 2:00 PM, email@example.com wrote:
> Message: 2
> Date: Sat, 23 Apr 2011 21:28:48 -0700
> From: Jim Brown<firstname.lastname@example.org>
> Subject: [TowerTalk] Fwd: Re: Antennas for 80m
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> See responses interspersed.
> >Do any of your tech notes reflect on the problems of grounding a
>> >The problem, of course, is that the ground lead becomes part of the
>> >radiator and detunes the antenna and, unlike the feedline,
>> >decoupling the ground lead can be an issue.
> Your question reflects some serious misconceptions with respect to
> how the EARTH interacts with a vertical antenna. The earth is very
> lossy. If we allow the EARTH to be part of the antenna, it burns
> transmitter power, making transmitted signal weaker. We use radials
> to shield the fields produced by a a vertical antenna from the earth,
> and also provide a return path for antenna current so that this does
> not happen. It IS important to connect the coax shield at the base
> of the antenna to the earth, but this is for LIGHTNING PROTECTION,
> not to make the antenna work. There should NEVER be a choke in that
> lightning protection line.
> Radials also serve to decouple the coax from the antenna, but only
> partially. This is also the function of adding a coax choke at the
>> >Are the issues the same whether it's a radial-free antenna (R5,
>> >R8000 etc.) vs. a radial-dependent (HF2V, 5BTV, etc.)?
> What I've described mostly applies to quarter-wave antennas. A few
> antennas are designed to function as vertical dipoles, so they don't
> need radials to carry return current, or as a return for the fields.
> BUT - in my experience, vertical dipoles don't work very well on
> the HF bands.
> Bottom line -- verticals for 80 and 160 want to be on the ground and
> have radial systems or serious counterpoises or both. And, as others
> have noted, verticals much shorter than a quarter wave need loading,
> preferably top loading.
> There are good discussions of these issues in the ON4UN book, and in
> the ARRL Handbook and Antenna Book.
> 73, Jim K9YC
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