[Antennas] Would vertical be better than yagi? Maybe...
Charles Greene
[email protected]
Wed, 12 Jun 2002 20:55:43 -0400
Danny,
It's a 1/4 wave vertical, a 1/2 wave horizontal dipole and a Moxon
rectangle beam which is horizontal. One thing about the 1/4 wave vertical
is that its efficiency varies greatly as a function of the number of ground
radials. As this vertical was to be used for field day, I didn't use a lot
of ground radials and they were elevated. It is an actual 1/4 wave
vertical we use for field day, as I was evaluating which was the most
effective antenna for field day use. Sorry I neglected to mention this. I
wasn't trying to be tricky; I just had a senior moment. If you add more
ground radials, the antenna efficiency improves. Of course, there is a
limit, as you can't get more than 100% efficient. Never-the-less, with the
gain as stated, -.59 dBi, it is at a vertical angle of 20 deg, and it has
more gain than either the Moxon beam or dipole at 20 degrees vertical angle
and below and thus is a more effective antenna for DX. My actual vertical
I gave performance information on has 24 radials with an average length of
around 20 feet; and I haven't tried to model it. The performance figures I
gave are a result of trying to copy weak PSK31 or CW signals. If I am on
one antenna and I am having trouble, I first switch antennas, and more
often than not the G5 gives better copy. That, in my opinion defies
conventional wisdom. I would expect better performance on the vertical on
40 than the G5. It may have something to do with the lack of more and
longer of radials I have on the vertical. Both antennas have short, low
loss feed lines and both tune well with my antenna tuners. The G5 also
picks up more noise. It is parallel to the local area power transmission
line and is located about 50 ft from it, and I attribute a lot of the
increased noise pickup to that.
As the antennas are so close in performance I plan to replace the G5RV with
a 135' Ft Off-Center fed antenna to give me better performance on 80 meters
and some different coverage on the higher bands due to the lobes. There's
no point in having two nearly identical antennas. I put up the G5RV
because I thought it would give me more gain E W on 20, but it is so close
to the vertical in gain that it usually doesn't make any difference.
At 06:30 AM 6/12/2002 -0700, K6MHE wrote:
>Charles,
>
>I have been following this with some interest however I am wondering if
>you are comparing a *vertical* dipole to a *horizontal* Moxon Rectangle?
>If so I would expect the "takeoff angle" to be different. I wondering you
>modeled the Moxon in the vertical or horizontal position? In other words
>are you truly comparing a dipole and yagi in alike curcumstances?
>
>Danny, K6MHE
>
> At 06:55 AM 6/12/2002 -0400, you wrote:
>>Karl and All,
>>
>>I'm sorry I have to disagree with you Karl. One big advantage of a Yagi
>>compared to a dipole, is it's take off angle is lower. I modelled the
>>field day Moxon Rectangle antenna in June 2000 QST for 40 meters with
>>EZNEC, and also modelled a vertical and dipole at the same height for
>>comparison purposes. A Moxon Rectangle is a two element beam with the
>>ends folded toward the center. Results:
>>
>> Vertical angle
>> of maximum radiation Gain
>>
>>1/4 Vertical 22 deg -.59 dBi
>>
>>40 meter dipole 62 deg 6.61 dBi
>>at 37 ft.
>>
>>Moxon Rectangle 45 deg 9.55 dBi
>>at 37 ft
>>
>>The antenna is for 40 meters but a similar comparison can be made for
>>higher frequencies. Actual results may vary, but the advantage of the
>>beam with respect to gain and take off angle is readily apparent.
>>
>>For actual results, I have a G5RV at 30' and its gain is about the same
>>as my Hustler 6BTV vertical on 20 on US stations but slightly better on
>>DX. The gain of the G5 is slightly greater on 40. I don't have a
>>comparison on the other bands except to state that they both work about
>>the same.
>>
>>73's
>>
>>At 05:55 PM 6/11/2002 -0500, Karl Kanalz wrote:
>>>Actually, John, if you look at the elevation patterns ("take-off angle")
>>>of a Yagi antenna, you'll find that the take-off angle of a Yagi is the same
>>>as a dipole at the same height! The major difference is that the Yagi has
>>>(usually) a front-to-back and front-to-side ratio that the dipole *doesn't*
>>>have,
>>>and that's why it produces "gain" over the dipole.
>>>
>>>Your particular "... lack of height..." is why your Yagi is not performing
>>>as
>>>expected.
>>>
>>>If you'll read the appropriate sections of the ARRL "Handbook" or the
>>>ARRL "Antenna Book", you'll begin to understand the importance of
>>>height above ground for *any* antenna, and how it affects the radiation
>>>pattern, the "take-off angle" and so on......
>>>
>>>Karl K - W8TIF
>>>McKinney, Texas
>>>
>>>-----Original Message-----
>>>From: John Geiger
>>>Sent: Tuesday, June 11, 2002 3:04 PM
>>>To: [email protected]; [email protected]; [email protected]
>>>Subject: would vertical be better than yagi?
>>>
>>>I recently put up a 2 element triband yagi (full size
>>>tribander) but it is not up very high-maybe 25 feet or
>>>so. The lack of height is noticable in performance.
>>>It does show gain towards Europe vs my dipole (G5RV
>>>type, also not up very high), and it also showed gain
>>>over the dipole when working VK9LO the other day.
>>>SOmetimes the yagi is a couple of S units better than
>>>the dipole towards Europe. Most of this has been done
>>>on 20 meters. Have not found enough stuff on 10 to
>>>compare yet.
>>>
>>>However, the past few days been trying to work BQ9P
>>>for #298, and the yagi doesn't show much gain at all
>>>over the dipole towards the far east-observe the same
>>>with Japan. Did work DU3NXE on 20 cw this AM with the
>>>yagi, but he was about as loud on the dipole.
>>>
>>>THe way I understand it, the low height does not give
>>>me the low angle radiation lobes that the long haul DX
>>>often requires. So my question is: Given that I
>>>might not be able to get the Yagi much higher for some
>>>time (my yard is a nightmare of trees and power lines)
>>>would I be better off getting a vertical on the roof
>>>instead. I know that verticals hear equally poor in
>>>all directions, but would it allow me to get the lower
>>>angle-long haul stuff.
>>>
>>>I would appreciate any comments, especially from those
>>>who have been in the same boat.
>>>
>>>73s John NE0P
>>
>>73, Chas, W1CG
>>
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>
>
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73, Chas, W1CG