Vertical yagi mounting
Jim Garver
> In a recent on-the-air discussion, I pointed out the error
>of mounting a two-meter yagi in the vertically-polarized
>position while using a metal mast (assuming that the antenna
>mounts from the center of the boom and not at one end...
> One of the on-the-air participants, admittedly a new ham,
>became very defensive and said that he used a Cushcraft
>A147-11 vertically polarized on a metal mast, and his antenna
>"had directivity."
According to my simplex pal across town, his Cushcraft yagi
manual actually says to mount them that way or at least it has
pictures of the yagi vertically mounted with the mast sticking
up only a couple of inches above the boom. Other weirdness in
the Cushcraft manual is a picture showing the coax routed across
the top of the insulated elements. Maybe the marketing folks at
Cushcraft took all the pictures. I've seen their collinear arrays
upside down in magazine ads.
>1) I assumed that a metal mast, being in effect a non-resonant
>"extra" element suddenly stuck in the middle of a parasitic
>array, would detune the antenna and probably throw the radiation
>pattern off by creating either more than one lobe or skewing
>the main lobe above or below the plane of the array by some
>noticeable amount. Is this assumption anywhere close to correct?
I've heard that if you have to do it, then stick the mast up
until its even with the top elements so as not to destroy the
symmetry so much. I've modeled both ways with the MN antenna
program and it screws up the pattern pretty good but mostly at
the expense of forward gain. My real experience is not so
easily measured but I know a 7 element 2 meter yagi improved
for both vertically and horizontally polarized signals after
I mounted it horizontal. Previously I had tried both metal
and wood masts but still ran the coax down the wood mast with
the yagi vertical. The coax will also become an unbalanced
and unwanted element this way.
My KLM 2M14C circular yagi manual says to mount the thing on
a non-conductive mast or boom and run the coax off the back
end. It works okay this way. I found a telescoping
fiberglass broom or window squeegee pole at the hardware store
that is pretty strong and about 6 feet long when collapsed.
You only need to get about 4 feet away from metal but 6 or 7
feet is better at 2 meters.
I don't know what others think about this but the only place
for a metal mast on a vertically polarized yagi is on the end
where it may act as a reflector.
Better yet, buy two yagis and cophase them on a horizontal
boom.
--
zar...@ornews.intel.com WA7LDV
Paul H. Bock
> One of the on-the-air participants, admittedly a new ham,
>became very defensive and said that he used a Cushcraft
>A147-11 vertically polarized on a metal mast, and his antenna
>"had directivity."
NOTE: My on-the-air comments did not suggest the antenna
had "no directivity", only a screwed-up pattern, but the
"defensive" ham took it that way.....
>pattern off by creating either more than one lobe or skewing
>the main lobe above or below the plane of the array by some
Poor choice of words; "above or below the plane of the array"
implies the antenna is horizontal when it isn't; what I mean
here is that the major lobe no longer points in the same direction
the antenna is pointed because of the deleterious effect of the
metal mast, which is now parallel to the parasitic directors and
has a detuning effect.
(|_|) * Paul H. Bock, Jr. K4MSG * Internet: pb...@melpar.esys.com
| |) * Senior Systems Engineer * Telephone: (703) 560-5000 x2062
"You can have my bug when you can pry my cold, dead fingers from
around it....." - anonymous radiotelegraph operator
Paul H. Bock
of mounting a two-meter yagi in the vertically-polarized
position while using a metal mast (assuming that the antenna
latter being common for 3- and 4-element yagis).
One of the on-the-air participants, admittedly a new ham,
became very defensive and said that he used a Cushcraft
A147-11 vertically polarized on a metal mast, and his antenna
"had directivity."
So, I have a couple of questions based on my assumptions
as follows:
1) I assumed that a metal mast, being in effect a non-resonant
"extra" element suddenly stuck in the middle of a parasitic
array, would detune the antenna and probably throw the radiation
pattern off by creating either more than one lobe or skewing
the main lobe above or below the plane of the array by some
noticeable amount. Is this assumption anywhere close to correct?
2) I once heard two hams testing a A147-11 which ham A had just
installed, and he was trying to figure out why station B was
stronger when the antenna was about 30 degrees off-azimuth from
Station B's known location (the antenna was vertical, BTW, and
the two stations were about 60 miles apart). Ham A was using
a - you guessed it - metal mast. Does this result sound
reasonable?
3) Has anyone out there ever purposely installed a yagi array
vertically using a metal mast and tried to measure the effects
(VSWR, azimuthal pattern accuracy, etc.)? I have a A148-10S
which is currently mounted horizontally, and have been toying
with rotating it into the vertical plane and trying to measure
the effects, but maybe someone else has tried it out of
scientific curiosity.....
Jan Chojnacki
>1) I assumed that a metal mast, being in effect a non-resonant
>"extra" element suddenly stuck in the middle of a parasitic
>array, would detune the antenna and probably throw the radiation
>pattern off by creating either more than one lobe or skewing
>the main lobe above or below the plane of the array by some
>noticeable amount. Is this assumption anywhere close to correct?
>
I've installed a Yagi vertically mounted on a metal mast and I experienced
detuning. I couldn't tell you how the radiation pattern was affected since at
the time I had no way of determining that - but since I was operating on 2m, I
installed a horizontal counterbalanced boom and remounted the antenna a few
feet away from the mast. That seemed to help a good deal, although there was
still a little bit of detuning remaining.
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William P. Osborne
Paul H. Bock <p...@syseng1.melpar.esys.com> wrote:
> In a recent on-the-air discussion, I pointed out the error
>of mounting a two-meter yagi in the vertically-polarized
>position while using a metal mast (assuming that the antenna
>mounts from the center of the boom and not at one end, the
>latter being common for 3- and 4-element yagis).
Paul: This is an excellent problem for testing with the newer versions of
MIninec or NEC on the market. I have done a good bit of modeling of
stacked and interlaced 10/15/20 meter yagis and can confirm that a 20 meter
element in the middle of a 15 meter yagi is bad news in that it can cost
you 1 to 1.5 dB of gain, change the input Z some and cause most anything to
happen to the front to back. I have not tried a random length mast but I
would expect the same sort of results. 73 Bill
John Boyer
: On Thu, 28 Apr 1994 20:55:12 GMT,
I did a little modelling with NEC. I first constructed a rough 4 ele yagi
and got a resonable pattern. Then I added a long vertical pole roughly in the
center of the yagi. This really buggered the pattern. Ok so I did this at
Band II where I have a good idea of the size of things off the top of my
head, but it still applies to 2m. Here is my NEC input file.
CM vertical Yagi
CM
CM
CE
GW1,25,0.,0.,-.9,-.,0.,.9,.01,
GW2,25,.76,0.,-.76,.76,0.,.76,.01,
GW3,25,1.3,0.,-.6,1.3,0.,.6,.01,
GW4,10,1.9,0.,-.6,1.9,0.,.6,.01,
GW5,25,1.,0.,-2.65,1.,0.,.35,.03,
GE0,0,0.,
EX0,2,13,00,1.,0.,
FR0,1,0,0,96.,0.,0.,
RP0,1,359,1010,90.,0.,0.,1.,0.,0.,
EN
So I guess the answer is don't use a metal pole with a vetical yagi.
John B
Robert Casey
>
>So I guess the answer is don't use a metal pole with a vetical yagi.
>
out "what about the coax running up the wooden pole to get the radio
connected to the antenna?". He figured that, yes, it will have some
effect, but the coax being smaller than a metal mast, would not be
as bad. Don't really know. Would it help if we used ferrite beads
on the coax spaced something like one every 1/6 th of a wavelength
(or some such smaller than 1/4 wavelength) to be nonresonant? Idea
is to "break" up the coax into many short pieces to RF on the outside,
so it looks like non-significant short pieces of wire. ?
Zack Lau (KH6CP)
: 3) Has anyone out there ever purposely installed a yagi array
: vertically using a metal mast and tried to measure the effects
: (VSWR, azimuthal pattern accuracy, etc.)? I have a A148-10S
: which is currently mounted horizontally, and have been toying
: with rotating it into the vertical plane and trying to measure
: the effects, but maybe someone else has tried it out of
: scientific curiosity.....
Kent Britian measured a 2.2 wavelength 435 MHz DL6WU yagi
on his test range.
With the mast all the way through the yagi, the gain varied by
+1 to -10 dB.
With the mast half way through the yagi, the gain varied by +1
to -6 dB. There appear to be more spots to put the mast in
without degrading it too much, but this might be yagi specific.
He varied the spacing between the driven element and the mast.
The results appear in the 1993 AMSAT-NA proceedings (11th)
--
Zack Lau KH6CP/1 2 way QRP WAS
8 States on 10 GHz
Internet: zl...@arrl.org 10 grids on 2304 MHz
Jim Grubs, W8GRT
> In article <Cp83z...@bbc.co.uk> bo...@rd.eng.bbc.co.uk (John Boyer) writes:
> >
> >So I guess the answer is don't use a metal pole with a vetical yagi.
> >
> My father used a wooden pole to mount a vertical yagi, but I pointed
> out "what about the coax running up the wooden pole to get the radio
> connected to the antenna?".
Why not make the radiator a co-axial sleeve antenna and rotate
directors amd reflectors around it?
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Paul H. Bock
>My father used a wooden pole to mount a vertical yagi, but I pointed
>out "what about the coax running up the wooden pole to get the radio
>connected to the antenna?". He figured that, yes, it will have some
>effect, but the coax being smaller than a metal mast, would not be
>as bad. Don't really know. Would it help if we used ferrite beads
This problem has occurred to me as well. Your father is probably
correct about the effect being less than that of a metal mast; but
I think that if optimum performance was my goal, I'd run the coax
along the boom to the reflector, then tape it to the back of the lower
half of the reflector and let angle away from the antenna downward to
the mast. Not a nice, clean installation, to be sure, but probably
minimizes the effect. The alternative is the counterbalanced
horizontal boom idea suggested by someone else, but if I were going
to do that my "counterbalance" would be another antenna so I could
pick up the extra 3 dB gain.