[HCARC] 10 meter Loop
Gary and Arlene Johnson
qltfnish at omniglobal.net
Mon Aug 13 09:49:01 EDT 2012
So if I take the 2 foot copper plated steel antenna sections I have that are
approx 7/16" inch in diameter tapering down to a point with a bead on the
end and construct a 33 foot tall vertical antenna and a good aluminum fence
wire ground plane, with an added induction tuner (wire coil with a roller
that changes the antenna length) I should be able to get it to tune up
somewhere in the 40 meter band. It terminates in an so-235 connector
already so that won't have to be modified. So the question that begs an
answer would be would the same length antenna made from heavier gauge and
larger diameter aluminum sections be better, worse, or about the same??
Gary J
N5"BAA"
----- Original Message -----
From: "Dale Gaudier" <dale.gaudier at windstream.net>
To: "'Gary and Arlene Johnson'" <qltfnish at omniglobal.net>
Cc: <hcarc at mailman.qth.net>
Sent: Monday, August 13, 2012 7:16 AM
Subject: RE: [HCARC] 10 meter Loop
> Gary:
>
> I'm sure Kerry will have his views on this, but here goes:
>
> 1. Antennas that use full size elements for their particular design will
> be
> more efficient at radiating their signal and therefore will produce
> maximum
> gain for that design. "Size" refers to the size (length and diameter) of
> the radiating elements of the antenna and the spacing of any parasitic
> elements, such as the reflectors or directors used in Yagi-type antennas.
>
> Most common ham antennas are built around a dipole driven element that is
> 1/2 wavelength at its resonant frequency (dipole, Yagi, etc.). Even the
> 1/4
> wave vertical is a variation of this model in that the "missing" half of
> the
> dipole is made up by the ground or ground plane. There are a few other
> common designs that use 5/8 wave and full wave radiating elements. A few
> specialized types of antennas, such as Beverages and rhombics, may be
> multiple wavelengths in size.
>
> As I mentioned in my previous post, Yagis and other types of directional
> antennas will also have a physical length due to the spacing of the
> elements
> along the boom. The spacing and number of elements is dictated by the
> amount
> of gain desired. However, the adage that "bigger is better" is subject to
> the law of diminishing returns - doubling the size of an antenna doesn't
> necessarily double its gain. And bigger antennas are more difficult and
> expensive to construct.
>
>
> 2. The type of metal an antenna is constructed of has only a minor effect
> on
> its electrical characteristics, at least at HF and VHF frequencies. That
> is
> because the alternating voltage and current which sustain the
> electromagnetic field that radiates from an antenna is located within a
> very
> narrow layer on the outer part of a conductor. This is the so-called "skin
> effect". That is why a popular type of antenna wire has a copper coating
> over a steel core. Of course, you also need to consider the mechanical
> aspects of the conductors and cost. That's why copper and aluminum are the
> conductors of choice for most antenna designs.
>
> 73,
>
> Dale - K4DG
>
> -----Original Message-----
> From: Gary and Arlene Johnson [mailto:qltfnish at omniglobal.net]
> Sent: Sunday, August 12, 2012 10:24 PM
> To: Kerry Sandstrom
> Cc: hcarc at mailman.qth.net
> Subject: Re: [HCARC] 10 meter Loop
>
> Kerry and others as needs be,
>
> Time to be careful with us new guys again!!!
>
> "Physics says the maximum gain you can get is determined by the physical
> size of the antenna."
>
> I assume by physical size you are talking about length or are we talking
> about diameter of the antenna, or are we talking about a combination of
> both???
>
> What does the metal that the antenna is contructed from have to do with
> its
> abilities - IF ANY???
>
> Gary J
> N5"BAA"
>
>
>
>
> ----- Original Message -----
> From: "Kerry Sandstrom" <kerryk5ks at hughes.net>
> To: <hcarc at mailman.qth.net>
> Sent: Sunday, August 12, 2012 8:08 PM
> Subject: Re: [HCARC] 10 meter Loop
>
>
>>I agree with Dale.
>>
>> You have to be very careful when you see gain figures. Over the 50 years
>> that I have been a ham, there have been many many magic antennas.
>> Generally
>> they are around for a few years and then they disappear never to be heard
>> of
>> again. Most of my memories are of VHF antennas. Some of the designs
>> that
>> have come and gone are the old Cush Craft colinears, basically 8 half
>> waves
>> fed in phase and backed up with reflectors. The basic design is sound
>> but
>> Cush Craft had unique mechanical design in which the ends of adjacent
>> half
>> wave elements are embedded in a plastic insulator for there support. The
>> problem is the insulator added capacitance at a high impedance point and
>> they were impossible to match over a reasonable frequency range. KLM had
>> HF
>> and VHF antennas which had 2 or 3 driven elements in parallel. This was
>> supposed to increase the bandwidth. The idea I first saw published as
>> the
>> Swan multi drive beam and was designed for 2 meters. It worked but not
>> that
>> much better than normal yagis and the design hasn't been seen in years.
>> Currently there are a rash of dipoles with special properties and
>> verticals
>> with unique designs which make them wider band or they don't require a
>> ground. The latest rage seems to be verticals that are 40 feet tall
>> instead
>> of 33 feet (1/4 wave for 40 m). Physics says the maximum gain you can
>> get
>> is determined by the physical size of the antenna. Two well designed
>> antennas the same size should perform the same no matter how different
>> they
>> look. Unfortunately the reverse is not true. While there is a limit to
>> the
>> maximum gain, there is no limit to the minimum gain: you can design large
>> antennas which just don't work!
>>
>> Unless you know the operator on the other end, I wouldn't believe any
>> signal
>> report I receive. Too many ops just give you a 599 and not just in
>> contests. Such a report is useless. The best way to compare antennas is
>> to
>> switch back and forth between them and compare the received signal
>> strength,
>> but be aware that much of the difference you see may be because the
>> antennas
>> are optimized for different elevation angles and the signal is mainly
>> coming
>> in on one angle.
>>
>> Gain is the product of the directivity of an antenna and its efficiency.
>> Its efficiency is a complex concept that includes losses in the antenna
>> and
>> the efficiency of the way the antenna aperture is illuminated. Note that
>> yagis and dipoles and vertical are not particularly efficient. Several
>> years ago there was a lot of discussion about "supergain" antennas in the
>> professional antenna literature. What actually was happening is you
>> could
>> design antennas which had directivity higher than the conventional rules
>> of
>> thumb allowed, however, they were very narrow band, There impedance had
>> large reactive components and there losses were high. The end result was
>> you ended up with an antenna which had a narrow beamwidth and hence high
>> directivity, but its efficiency was so low that its gain was lower than
>> equivalent sized conventional designs.
>>
>> A dipole has approximately 2 dB gain over a (mythical) isotropic. Many
>> antenna manufacturers like to specify their antenna's gain compared to an
>> isotropic antenna. Sometimes they will use dBi to show its gain in dB
>> relative to an isotropic antenna. Others will use dBd to signify their
>> gain
>> is relative to a dipole. Unfortunately most seem to use just dB and it
>> could be either. For many years QST would not permit the antenna
>> manufacturers to include gain figures in their QST ads because the
>> numbers
>> were so unreliable.
>>
>> Dale mentioned that there is antenna modeling software available. He
>> mentioned EZNEC. I use NEC2 with 4NEC2 as the interface, myself. It is
>> available for free on the internet. NEC2 was developed over the last ~50
>> years by the US government, Primarily the DoD laboratories and the
>> national
>> nuclear laboratories. The current available version runs well on modern
>> PC's. Any model requires a knowledgable user. Be prepared to spend some
>> time learning how to create the input, run the model and interpret the
>> output data. I think the effort is well worth it.
>>
>> I have been to several antenna ranges. They have been for UHF and
>> higher.
>> Typically they have a transmitter site on a high hill overlooking a
>> valley
>> and second site on a high hill on the other side of the valley for the
>> receiver site. The goal is to elimante as much of the ground reflections
>> as
>> possible. If you get the idea that setting up an antenna range is an
>> expensive proposition, you are correct. It is only worse at HF. I don't
>> believe that any of the amateur antenna manufacturers have an antenna
>> range.
>> In years past, a couple of them that also did work for DoD had a range or
>> access to one, but those guys are long gone I think.
>>
>> The local ten meter net actually provides an excellent oppurtunity for us
>> to
>> play with antennas. There are a few participants located at varying
>> distances with different terrain between us. We should be able to make
>> reasonable estimates of how we have improved our stations from week to
>> week.
>> It should be a lot of fun.
>>
>> I don't like long e-mails, but unfortunately there is no way to discuss
>> some
>> of these topics in one sentence. Playing with antennas is a lot of fun.
>> Most only require some wire and insulators a some rope. You can learn a
>> lot
>> for very little money. When all is said and done there are really only a
>> few different types of antennas. The ones of most interest to hams is
>> dipoles (which includes vertical which are just half a dipole and its
>> image), travelling wave antennas (rhombics, vees, Beverage, etc),
>> log-periodics, and at the higher frequencies, aperture antenna (parabolic
>> reflectors, corner reflectors, etc).
>>
>> Have fun and see you on ten,
>>
>> 73,
>>
>> Kerry
>>
>>
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