[Antennas] Butternut Vertical

2002年8月18日 11:50:13 -0500

Folks, it is a well known and daily demonstrated fact that anything will
radiate whatever r-f power you can put into it. Some things radiate better
than others. A good operator can do much more with a poor antenna than a
poor operator can do with an excellent antenna.
Having said that, the physics of the matter is that the less ground-return
loss you have with a vertical, the more efficient it is and the less
transmitter power goes into heating up the Earth around the antenna,
regardless of its height. Within a circular area centered on the vertical
and with a radius about equal to the height of the antenna, displacement
current flows from the antenna to the Earth and back via the coax braid to
the transmitter. 
Any resistance/loss in that path simply converts r-f into heat - rof that
doesn't get radiated. An adequate radial field will "collect" the majority
of this ground-return current and thus minimize the loss. Lack of such a
field causes the current to seek whatever path it will to return to the
transmitter - and such a path is inevitably lossier than that provided by
the radial field.
The success of ground rods is highly dependent upon local soil conditions,
etc. But even in this area of North Texas where we have some of the most
conductive soil in the entire country, the r-f resistance of even several
ground rods is much greater than that of even a minimal radial field.
Most ground rods actually make poorer contact with "Earth" than one might
expect, considering the effort involved in sinking an 8 ft rod in the
ground. Such a ground rod is excellent for a-c safety grounding and is
required by the National Electrical Code. But most ground rods exhibit
relatively high resistance to Earth when used for r-f "connections" to the
ground.
Note that radials (elevated or on the ground) and ground rods, etc. all
have *nothing* to do with the radiation pattern of the antenna. It will
radiate all the power it gets with whatever radiation pattern its design
provides. A good ground system - adequate radial field or fortuitous ground
rod(s) - simply allows the antenna to radiate more of the power entering
the coax at the transmitter end. 
(I know that with only one radial there is some directivity involved but
that is because a true radial field is symmetrical and all radiation from
its components cancels. A single radial does not meet this requirement so
its radiation adds to that of the "antenna." This is frequently seen with
mobile installations in which the strongest signal is radiated in the
direction the car is headed.)
So, I stand by my original statements regarding the need for an adequate
radial system; the convenience (to me) of a ground-mounted antenna with a
ground radial field; the inconvenience (to me) of an tuned, elevated
antenna and radial system. No amount of successful anecdotal evidence
changes the basic physics that 1/4-wave verticals will radiate more power
when provided with an adequate radial field.
I admire the skill and determination of the operators who can achieve great
success working DX with minimal vertical installations, but such success
does not invalidate the demonstrated requirement for adequate radial
fields. As one gentleman remarked, adequate radials just make the job
easier. 
In re-reading my postings on this topic, I cannot find anywhere where I
have stated or implied that the beginner must have a fully professional
radial installation, etc. as was exaggerately reported in one posting. My
comment for any operator, newbie or old-timer, is that the antenna will do
what it will do regardless of the age or experience of the operator. If the
newcomer wishes to put up an antenna and disregard the manufacturer's or
designer's instructions, then the results will follow accordingly.
C'mon, folks, it isn't rocket science to put a vertical on a short mast
stuck into the ground and lay out 6-8-10, however many radials one can fit
into the space available. Of course, 120 1/2-wave radials are not required!
That's nonsense . . . and maybe a ground rod or two will help - it is worth
trying. But the "sure" way is just to lay out a few lengths of wire and
help to ensure that your operating time and effort will pay off with an
antenna that is radiating all that the transmitter is sending it.
BTW, it has been long known and understood that a lot of short radials -
0.15 to 0.2 wavelengths - work better than fewer, longer radials. So, if
you don't have a lot of room, just put out as many short radials around the
base of the antenna as you find energy and wire for, and then go operate
and have fun.
One last bit of practical advice: how do you know when to stop putting down
radials? Measure the input impedance of the antenna . . . if it is a
1/4-wave, it should show an input Z of about 36 ohms resistive at its
resonant frequency, and thus a 50-ohm SWR of about 1.4:1. If the SWR is
lower than that, the difference is being caused by r-f loss in the ground
return path. So add a couple of radials and measure again. Keep doing this
until adding a couple of radials produces no significant increase in the
SWR or reduction in the input impedance. Another good indication is 2:1 SWR
bandwidth. The HF9-V has a bandwidth on 80 meters of about 30 KHz at the
low end of the band per Butterworth if an adequate radial system is used.
Finally, the instruction manual for the HF9-V says in capital letters on
the first page:
"NOTE: HIGH PERFORMANCE BUTTERNUT VERTICAL ANTENNAS REQUIRE A RADIAL SYSTEM
FOR ALL INSTALLATIONS."
And on page 16 under Tech Notes:
"It should be noted that a ground rod is useful only as a d-c ground or as
a tie point for radials. It does little or nothing to reduce ground losses
at r-f regardless of how far it goes into the ground."
I rest my case . . . and I suspect that we are all tired of this topic so
let's just shut it down.
73/72/oo, George W5YR - the Yellow Rose of Texas 
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe 
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437
Dave wrote:
>> Yes what you say is partially true .....
> But between Jan 2000 and Apr 2000 (just 4 months) I worked 5 Band DXCC and
> 210 countries with a ground mounted HF6-V with thirty two 66' radials. Yes
> you can work em without the radials but it is a whole lot easier and a
> WHOLE LOT LESS FRUSTRATING with the radials 8^)
>> The moral is spend your time catching the last rays of summer and plant
> some radials , you won't sit in line as long when it comes to working the
> pile up later and you just might work one of those rare ones that you would
> chance missing when your signal is down another 10db (at least) with out them .
>> As a long time planter of radials I've never been able to understand
> peoples aversion to doing it.
>> Dave
> PS: I gave up on raised ground planes years ago not because of they were
> better or worse performance wise (please lets don't open that debate
> again...although its been a while) but because they became a maintenance
> nightmare every time the wind blew, not to mention deer and large birds and
> the occasional human who got garreted!
>> At 10:09 AM 8/18/02 -0400, Jim Dockery wrote:
> >Well put.
> >
> >Jim, WB2HBZ
> >
> >
> >-----Original Message-----
> >From: [email protected]
> >[mailto:[email protected]]On Behalf Of Nelson Moyer
> >Sent: Sunday, August 18, 2002 10:09 AM
> >To: [email protected]; George, W5YR
> >Cc: Jim Boyd; Antenna Net
> >Subject: RE: [Antennas] Butternut Vertical
> >
> >
> >While I grant you that ground mounted verticals operate most efficiently
> >with radials, I think it's a stretch to state to a new HF operator that they
> >MUST have radials to work. I worked 305 countries on the DXCC list and
> >5BDXCC in 10 years using the Butternut HF6V, mostly ground mounted, with
> >nothing but one 8 foot ground rod driven all the way into Iowa clay. I would
> >love to have 120 radials attached to my vertical, but the reality of living
> >on a 60'x120' town lot preclude the luxury. I didn't let that stop me from
> >working DX. I mounted my HF6V on a roof tripod with a counterpoise for two
> >low band seasons, and it didn't work any better elevated than when it was
> >ground mounted. Because ground mounting makes maintenance easier, I moved it
> >back off the roof. Most of the time I operated running 100 watts, with up to
> >500 watts for major pileups. Most antennas are compromised by tradeoffs,
> >e.g. gain vs. front to back, etc. The same applies to verticals; efficiency
> >is improved, and bandwidth is narrowed, using radials, but you can work a
> >lot of DX with nothing but a ground rod. Let's not discourage new HF ops by
> >telling them they need to start at the top, i.e fully optimized radial
> >system, no surrounding metal objects or trees, etc. Could I have worked
> >5BDXCC faster using radials on my vertical? Maybe. Could I have worked it
> >faster with a yagi at 70 feet? You bet!. It's OK to use suboptimal antennas,
> >the point is to get on the air.
> >
> >Nelson, KU0A
> >
> >-----Original Message-----
> >From: [email protected]
> >[mailto:[email protected]]On Behalf Of [email protected]
> >Sent: Saturday, August 17, 2002 10:45 PM
> >To: George, W5YR
> >Cc: Jim Boyd; Antenna Net
> >Subject: Re: [Antennas] Butternut Vertical
> >
> >
> >All ground mounted verticals must have radials....BUT a vertical
> >mounted at or >.07wl above ground will work 99% as well with only
> >FOUR radials that are AT LEAST 1/4wl long at lowest freq...
> >This was stated on a web site by W4RNL and I have confirmed it at home
> >with a vertical mounted 20ft off the ground and it only has 4 60ft
> >radials...works great on 80-10 and bandwidth/resonance is EXACTLY as it
> >was on the ground with 32 radials...
> >
> >Also BC stations with AM sticks on top of bldgs have reported the
> >same thing...though the antenna has few radials there, being above
> >earth ground allows it to work well with only a min compliment of
> >radials...(one AM station here in Houston had that with its antenna
> >atop the old Rice Hotel!)
> >
> >Chris
> >WB5ITT
> >Houston