This just proves the old adage you can't ever have enough antennas.
On 4/24/2011 3:06 PM, Robert Chudek - K0RC wrote:
> 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
> worked okay.
> 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
> enough antennas!
> 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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