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Author Topic: "No ground radial" HF vertical antennas  (Read 15593 times)
K3MOV
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« on: February 24, 2005, 07:26:40 PM »

If you "google" dipole, G5RV, Zepp, or Windom antennas, you are overwhelmed with the amount of theoretical information indicating how and why these antennas work.

One of the most popular types of antennas today in the U.S. is the "no ground radial" HF vertical antenna such as the Cushcraft R8, R7, R6000, MA5V, the Hy Gain DX 77, AV 640, the Diamond CP6, and the MFJ 1798.  In spite of their popularity, other than sponsored sites, I have found next to nothing regarding the theory of these antennas.  I have the Champion Radio Products published "HF Vertical Performance" manual.  The tests in that work included some of the above antennas, but it really didn't go into the theory very much.

Is anyone aware of a non-sponsored site or book where I can learn more about these antennas??
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WA6BFH
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« Reply #1 on: February 24, 2005, 08:07:55 PM »

Yes, and you asked the singularly correct question -- because I am aware of NO simialr "web based" analog!

Try, William I. Orr's "Radio Handbook", and or Shrader's, "Electronic Communication". If your math skills are decent take a look at Kraus, "Antennas"

73! de John WA6BFH
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K0ZN
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« Reply #2 on: February 24, 2005, 08:13:28 PM »


Hi,

The key here is understanding basic antenna theory, and the ARRL Antenna Book is about the best broad source on this.

These antennas are basically half wave end fed radiators with a choke and small counterpoise to keep the RF from flowing down the outside of the coax. They work "OK" but there is no free lunch and they have their own limitations.

They are popular, but not necessarily the "best" type of vertical antenna. ALL antennas involve some compromise. 1/4 wave monopoles (ground mounted or ground plane) verticals generally offer equal or better performance due to full size ground planes, but this means a lot of WORK...installing radials, etc. and many people don't want to go that route...so the "no radial" antennas sell pretty well for marketing reasons. Both modeling and real world results tend to show that verticals with full size ground systems have a little lower radiation angle.

73,  K0ZN
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K4EQ
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« Reply #3 on: February 25, 2005, 05:13:33 AM »

I agree with everyone's comments. In fact, every antenna is a compromise of sorts. Because of the need for a lower profile at a new QTH several years ago, I purchased an R7. Despite its limitations, after 8 years of use I had worked 260 countries with it using 100 watts. I've worked over 100 countries with it on QRP. That's a compromise I can live with.  --Dale, K4EQ
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KE6VG
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« Reply #4 on: February 25, 2005, 07:26:10 AM »

Here are two sites that may answer some of your questions.

This one has the R7 and Force12 vertical dipoles described and shows how to home brew them.
http://www.iol.ie/~bravo/index.htm

This site has more antenna info than you can use.
http://www.cebik.com/radio.html

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WA7NCL
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« Reply #5 on: February 25, 2005, 10:40:25 AM »

Search on W4RNL and go to his web site.  You get a lot of good info on antennas.  He has a series on Verticals without vertigo.  You can read it.  Also I would suggest getting an antenna modeling program and experimenting.  W7EL has a good one.  EZNEC.

No radial antennas are ones that are not current fed (1/4wave).  They are voltage fed at the end usually.  They work, but do not eliminate all ground loss.  I have used them for years because I am too lazy to dig ground for radials.
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« Reply #6 on: February 25, 2005, 06:11:58 PM »

Hi Tom, I really liked your question and thought maybe we would learn something about these types of antennas and how they work but I guess we'll have to keep guessing? Nothing I have seen explains anything that the layman could figure out quite easily. It's like were supposed to be kept in the dark...Bill
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K0ZN
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« Reply #7 on: February 25, 2005, 07:45:32 PM »



AC6IJ:

There were TWO explanations. I will repeat...

Those types of antennas are VOLTAGE FED Half wave radiators. i.e. the RF energy is fed at one END ("the bottom", in this case) of a half wave radiator and a "choke type balun" is used at the feed point to keep RF from flowing back down the OUTside of the coax. The small radials are to reduce capacitive coupling to the ground and/or also help decouple the coax from the antenna. What question(s) does this leave unanswered?

There is not room here to go into great detail about the properties/math, etc. of end fed radiators. If this is still not clear, to satisfy your curiosity, you should pick up a copy of the ARRL Antenna Book and study the first few Chapters on basic antenna principals and theory.

K0ZN
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K3MOV
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« Reply #8 on: February 26, 2005, 01:00:25 AM »

K0ZN, please don't blow a gasket.  Below are several questions that I have been researching but for which I still have not found satisfactory answers.  Any input you can provide will be appreciated.

1) From what I can determine, the Cushcraft R5 vertical was the first commercially available antenna of this type.  It was reviewed in QST in October, 1990.  What happened around that time at Cushcraft to allow them to manufacture what I assume was a rather unique concept in vertical antennas?  Had it ever been tried before commercially or non-commercially?

2) What determines the length of the counterpoises / radials?  I have seen them range from 4 feet to 6 feet.  

3) Why are all of the radials the same length, even though the antenna covers several bands?  Normally, would not ground plane radials be different lengths for different HF bands?  If these radials perform a completely different function than those used on a standard vertical, where is the "mirror image" that one usually looks for in vertical antenna ground systems?

4) How high should these antennas be mounted above the ground?  I have read that 8 to 9 feet is an ideal height.  I have also read that like beams and wire and most antennas, the higher they are mounted the better they perform.

5) Why do some of the verticals of this type use tuned radials while others simply use the "standard" 4 to 6 foot rigid radials?

6) What is the advantage, if any, of Hy Gain's using: "Quarter wave stubs on 6, 10, 12, and 17 meters and capacity hats on 15, 20, 30, 40 meters instead of typical lossy can traps.  And the AV-640's resonators are placed in parallel not in series"?

7) The Hy Gain manual describes the AV 640 as: The center radiator of the AV-640 supports 1/4 wavelength stubs for 6 , 10, 12 and 17 meters.  For 20, 30 and 40 meters, a coil and capacity hat are used on each band to create a 3/8 wavelength radiator.
Do most off these antennas with which you are familiar use half wave radiators?  I assume they would have slightly more gain than 1/4 and 3/8 wavelength radiators.

Thanks in advance for your help.  I assure you that I have checked all of the references that you and others have mentioned.  I have come up with better guesses but not answers.

73, Tom
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WB6BYU
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« Reply #9 on: February 28, 2005, 12:59:07 PM »

1)... Cushcraft R5... 1990...

Actually they came out with the R3 in 1984 or so.
But single-band versions had been around for much
longer than that: the "Ringo" series (available from
440 MHz down to at least 10m) are half-wave, end-fed
verticals.  The ring is a coil, and the tuning capacitor
in parallel with it is formed by the end of the radiator
passing into (and being insulated from) the mounting mast.
This makes a parallel-tuned circuit to match the high
impedance of the end-fed half-wave element, and the coax
is tapped onto the coil with a sliding bar.

A J-pole is also an end-fed half-wave radiator.  They've
been around for 50 years, and the original Zepp antenna
design behind this was patented in 1908.

One difference is that the R3 used a motorized capacitor
to tune the matching network to the operating frequency.
The radiator had two traps so it was resonant on 10/15/20m.
What was radical about this design was that it managed
to tune the antenna (remotely) on multiple bands:
previous designs were primarily single-band antennas
(with the occasional harmonic operation.)

A matching network to go from 50 ohms to several thousand
ohms generally requires a tuned circuit of some sort.
(Thus the motorized capacitor on the R3.)  The important
leap on the R5 (I think) and later versions was that
Cushcraft managed to broadband the matching system.
I think this was done by using a broadband ferrite
transformer to step up 50 ohms to 450 or 600 ohms (or
somewhere in there), then moving the antenna feedpoint
in from the end until it matched at this intermediate
impedance.  Since it was inconvenient to have the
feedpoint physically in the middle of the element, the
lower portion of the radiator below the feedpoint was
replaced by a capacitive "bottom hat", which appears to
be a set of radials.


2) length of counterpoises/radials
3) why are radials all one length

This is simply a matter of design.  As described above,
this is a "capacity hat" at the bottom of the driven
element, and do not act like normal radials.  As such
they are not "resonant" by themselves, but rather they
bring the whole antenna into resonance in conjunction
with all of the various traps, tubing lengths, etc.
If you think of it as providing capacitance, rather than
each radial being individually resonant, then you can
see that what is important is the TOTAL capacitance of
all the "radials", not the individual length of each
one.


4) How high should they be above the ground

The ends of the "radials" are a high impedance, just
like the ends of a dipole.  Thus they are sensitive to
detuning from surrounding objects - including the earth.  So my answer would be, high enough that the
base of the antenna is clear of other large objects.
Since the earth is a large object, I suspect that
4' to 8' is a typical minimum practical heigth, though
I haven't tried it.


5) Why do some use "tuned" radials...
6) Quarter wave stubs vs. capacity hats...
7) gain of quarter, 3/8, or half wave radiators...

Trying to get such an antenna to have a low SWR on 7 or
more different bands is quite difficult, since there
will be a lot of interaction amoung the different parts.
So each manufacturer makes different tradeoffs and
design decisions of how to get there.  Then the Marketing
department invents some fancy words about how it works
to make it seem even more magical, mysterious, and
desirable.  (I remember the big hoopla that one
manufacturer made when someone discovered that their
HF vertical had a low SWR on 2m - even if it was due
to a long lossy feedline - and he could hit a local
repeater.  Now Marketing could add another band to their
claims about the antenna.)

The first step, though is to realize that an antenna
is not "a half wave on 40m" unless it is 20m long.  And
none of the commercial antennas I have seen of this type
are 60 feet tall, so clearly this is stretching a point.  Generally, the longer the physical length of an
antenna, the better it will work, at least on those bands
where the antenna has to be smaller than full-sized.

At this point it is very difficult to summarize all of
the different techniques that manufacturers have used
to make their antennas work on as many bands as possible
(which is important from a Marketing point of view.)
Some use conventional LC traps, some use quarter wave
"decoupling stubs" to do the same thing (where space
permits), and others may use totally different modes of
operation on different bands.

But, from a practical point of view, the more bits and
pieces stuck on the antenna, the harder it may be to
tune up, and the greater the likelyhood of mechanical
failure.  Focus on choosing an antenna that will do
well on the bands of particular interest to you, rather
than one that is mediocre on many extra bands.  For
example, I'd suggest putting up separate VHF ground planes
rather than worrying about whether my HF vertical will
work there.
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K3MOV
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Posts: 504




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« Reply #10 on: February 28, 2005, 05:37:59 PM »

Thanks to all for the recent replies.

Dale (WB6BYU), you went above and beyond the call of duty, and I sincerely appreciate it.  Actually, I used to have a Cushcraft R7000 with which I was a little disappointed.  I now have the Hy Gain AV 640 and am just amazed at how well it works.  The only thing that troubled me about the AV 640 was WHY did it work so well.  You have set me straight.

I also posed my question to the ARRL.  I received this response from them today:
======================================================
    L.B. Cebik looks at the most basic case--the vertical dipole.
http://www.cebik.com/gp/vdgp.html
 
http://www.n6rk.com/ground.pdf
some experimental data
Rick found that ground is still a factor in obtaining that elusive low angle of radiation.
You also might want to read "The Effect of Ground in the Far Field," ARRL Antenna
book 20th ed page 3-1
 
    I'd suggest visiting W8JI's site
 
http://www.w8ji.com/end-fed_vertical_j-pole_and_horizontal_zepp.htm
He advocates modeling antennas with the feedline system as part of the model.
73--Zack Lau W1VT
ARRL Senior Lab Engineer
=======================================================
I will check out the new references as soon as possible.  Again, thanks to all for the helpful information.
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KC0WMN
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« Reply #11 on: April 28, 2011, 07:10:47 AM »

I recently came across a rigid dipole Comet H422 4 band, manual say's this unit wrks at 12ft. I agree it works very well, I decided to put a HF vertical on my trvl trlr so I put a metal rib lath frame around the roof, took one side of the comet and monted it to my antenna lifter and it raises the base to be approx. 15ft. I to do not wish to mess with radials being mobile and portable but understand ground plane is most important. The ant. is at the back of trlr., trlr. is 40ft wid da truck hooked up,( theory is the trlr es trk act as counter poise) 4.5ft on ea side of ant. and i throw a 35ft. counter poise off the back bumper, quick, easy, and wrks great. No radials but a ground plane fer sure.
73 KC0WMN
Ray
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KB4QAA
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« Reply #12 on: April 28, 2011, 07:45:25 AM »

A radial is a ground plane is a radial. 
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N6AJR
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« Reply #13 on: April 28, 2011, 01:23:47 PM »

some like the Gap series( titan, voyager etc) are actually a center fed half wave verticle dipole.
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W0BTU
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« Reply #14 on: April 28, 2011, 10:42:53 PM »

  What determines the length of the counterpoises / radials?

The laws of physics do. :-)

There is no free lunch. For maximum efficiency, an end-fed antenna requires a a good RF ground, period. Here's some info that you may find helpful: http://www.w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html
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