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Author Topic: Buddipole horizontal dipole  (Read 1427 times)
K3ZL
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Posts: 124




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« on: December 14, 2009, 05:04:04 PM »

Have any of you had any experience with the buddipole antenna?  I see one on eBay, and also looked at the website.  Would like to know how it would compare to a 1/2 wave 40 meter dipole, if both were up at say 40 ft.
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KF6A
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Posts: 214




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« Reply #1 on: December 15, 2009, 01:55:37 AM »

I have not used a Buddipole but a full sized 1/2 wave 40m dipole should outperform it no problem. If you can get the wire dipole up I would do that instead of using a loaded/shortened antenna.
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AA4PB
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Posts: 12688




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« Reply #2 on: December 15, 2009, 05:06:45 AM »

I wouldn't put up a Buddipole as a permanent antenna. The loading coils and taps are not weatherproofed. First choice would be a full sized 1/2 wave wire dipole. If that won't fit then get some loading coils and put of a shortened wire dipole. You can go down to about half size without having a terrible amount of loss. It'll have better performance than the Buddipole on 40M and it'll cost a whole lot less.

The Buddipole is a good antenna for what it was designed - a temporary transportable antenna.
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K6TFZ
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Posts: 36




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« Reply #3 on: December 15, 2009, 04:05:56 PM »

Yes, I have had one for a couple of years. The longest mast it comes with is 16 feet. The tripod, mast, arms, coils, and whips need to be assembled and guyed. The coils may need to be tuned. It takes time (minimum 20-30 minutes each, up and down). Instead, I now use inverted Vees, one cut for each band and held up in the center with a 31 foot telescoping mast (see "Jackite"). Takes 5-10 minutes. Works very well.  Jeff, K6TFZ
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WX7G
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Posts: 5920




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« Reply #4 on: December 16, 2009, 06:44:59 AM »

The Buddipole and other short dipoles can work well but are often tuned up such that the real antenna is one short dipole arm and the coaxial (external)shield.

If the dipole arm connected to the coax shield is resonant it can present a lower impedance than the coax shield. This minimizes shield current. But sometimes during tune-up a lower VSWR is found with the shield side arm detuned such that the shield is now the 'real' antenna. This isn't necessarily bad but can be. A clamp-on RF current probe (MFJ) can be used to aid in tune-up. The dipole arm connected to the shield is adjusted for minimum shield current.
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WX7G
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Posts: 5920




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« Reply #5 on: December 17, 2009, 07:35:45 AM »

An example of intentional 'shield tuning' is the Taktenna. The instruction manual says to adjust the shield side coil differently than the hot side. The result is that the shield side spiral has little RF current. The shield becomes the antenna.

This results in an antenna that consists of the shield and a small spiral. It can work quite well but is not the short dipole that is advertised.
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VK1OD
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Posts: 1697




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« Reply #6 on: December 17, 2009, 01:34:35 PM »

Have any of you had any experience with the buddipole antenna?  I see one on eBay, and also looked at the website.  Would like to know how it would compare to a 1/2 wave 40 meter dipole, if both were up at say 40 ft.

There are two main issues that impinge upon peformance of the Buddipole wrt a half wave dipole on 40m. I will assume that they are both fed with coax and an effective balun.

The Buddipole is a loaded antenna, and efficiency is reduced somewhat by the loading coils. The Buddipole is most commonly used at lower heights than a typical permanent half wave dipole configuraion. This increases losses by heating the soil, and reduces the feedpoint impedance somewhat which may increase line losses and matching losses. Buddipole offer a variable ratio balun which helps to reduce the line loss on lower bands.

I studied the Buddipole for the purpose of field strength measurement of ambient noise and BPL emissions, particularly to compare the Buddipole response (as would be used in field survey) and that of a 'typical' half wave inverted V dipole on 40m, the article is at Field strength measurement - Buddipole and FSM.

Owen

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WB6BYU
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Posts: 13029




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« Reply #7 on: December 17, 2009, 02:16:23 PM »

I would expect the Buddipole to be slightly less efficient than a
full-sized wire dipole due to the shorter length and the loading
coils, but probably not enough to make a significant difference
in operational capability.

The most noticeable difference will be the narrower bandwidth:
a wire dipole should cover the whole band at a reasonable SWR,
while the Buddipole will cover just a part of the band.  If you
are only operating over a narrow range of frequencies, this
may not be a problem, though it will take more attempts at
tuning to get it centered where you want it. 

I carry a wire dipole for portable operation - I tuned it up once
almost 30 years ago and haven't had to fuss with it since.
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WX7G
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Posts: 5920




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« Reply #8 on: December 18, 2009, 08:17:04 AM »

VK1OD you have written a great article on the Budipole. 10% efficiency.
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AA4PB
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Posts: 12688




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« Reply #9 on: December 18, 2009, 08:52:34 AM »

I don't see how you get useful information by comparing a dipole high in the air to a Buddypole mounted near the ground. I could take two identical 40M 1/2 wave dipoles, one mounted at 10 feet above ground and the other at 50 feet above ground and report that the one at 50 feet is a much more efficient antenna.

The free space model shows the Buddypole less than 2dB down (on 40M) and I expect that is about what you will get in actual practice when you operate the two antennas at the same height. At 20M the difference will be a lot less because in terms of wavelength the size difference will be a lot less.

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VK1OD
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Posts: 1697




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« Reply #10 on: December 18, 2009, 12:20:22 PM »

VK1OD you have written a great article on the Budipole. 10% efficiency.

I am not sure that extraction of a single figure of 10% efficiency (which I assume you calculated from average system gain) is, in isolation, a fair picture.

The article discusses a specific Buddipole in a specific context, and principally its response to broadband non-directional signals.

I mentioned earlier that there were two main factors that influenced performance.

The modelled free space average gain on 40m is less than 1.5dB behind a half wave inverted V dipole, so resistive losses in the dipole and loading coils is not extreme.

The modelled free space average gain over ground on 40m is about 8.7dB behind a half wave inverted V dipole at greater height, so the effect of losses in the soil is much higher.

The message to take away is that the biggest performance disadvantage comes from the low mounting height (2.85m in this case).

In terms of a reality check, could I hear DX with it? Yes, I could copy DX in the afternoon opening to Europe quite well, albeit at lower S meter deflection. Lower system efficiency reduces both the desired signals and the noise and interference, so S/N is pretty much the same. Could I work them with 100W? No, lower system efficiency means my EIRP is down, and it would be even less if running lower power.

Back to the original question, I do not have a comparison of both a dipole and Buddipole at 40', but I do have a comparison of them in free space and at typical mounting heights. It doesn't strike me that the Buddipole was intended for permanent exposure to the weather, nor that it would survive high wind speeds... so those factors might make its deployment as a permanent station antenna at 40' impractical rather than poorer performance, not to mention the lack of convenience for adjusting the antenna for band changes.

It is a case of horses for courses, and my own opinion is that the Buddipole is not suited to mounting at 40' as a permanent multi band station antenna.

Owen

PS: for AA4PB, the purpose of the study was to discover how field strength measurements of noise and BPL emissions made on a public street with a Buddipole could be extrapolated to a typical ham backyard dipole. The studies performed fed into the standards bodies working on emission standards for BPL, and they seemed to understand and accept the approach. Whilst the traditional approach is to use EMC receivers and portable loops, they typically do not have a sufficiently low noise floor to measure ambient noise on all of our HF bands, so a better antenna is required.

Whilst the EMC reciever / portable loop allows a scan of all of HF in three axes in just minutes, the collected data often just documents the instrument's own noise floor rather than the ambient noise. The Buddipole was much slower, needing to be tuned to each measurement frequency, but we could and did measure ambient noise above the system noise floor.
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