Thursday, September 06, 2007

Where'd he go?

I have not blogged for about ten days. Miss me?
During this hiatus I have been trying to finish a draft of a white paper entitled Antennas for 100 Pound DXpeditions. You can find this in my download area. The file to download is named "Antennas-for-100.pdf" and it is approximately 26 MB in size so be patient.
I was not entirely happy with things I had done on Montserrat. Further, some of the "conventional wisdom" I received on various Buddipole configurations did not make sense to me (though I was reluctant to argue at the time). I decided not long after returning home that what was needed was a disciplined and scientific approach to this problem. What do these antennas do? How well do they perform? What configurations work? Which configurations are unsatisfactory?
I begin to answer some of these questions in this white paper. Here are some conclusions I've drawn on the Buddipole, for example:

  • No short whips -- The standard Buddipole configuration sold comes with stainless steel whips just under 6 foot long. They are too short for reasonable HF work. I will still use them for my 6 meter Yagi made from Buddipole parts, but I'll not use them again for HF. Period.

  • For 20 meters and up, no coils -- The standard Buddipole configurations specify coils and particular taps for the bands. I believe it makes more sense to remove the coils from the bag and substitute long whips (9 foot 4 inches) and two extra antenna arms. That can be used to make the antenna described below.

  • Only full-sized verticals for the Buddipole -- In the end, after looking at configuration after configuration for the Buddipole, the only one that really performs well is the full-size vertical with no coils and four radials. The 20 meter version requires four arms and a fully extended long whip, but it is great on that band.

  • At least 4 radials -- I've read lots of discussions about using just one sloping radial for the Buddipole. After extensive modeling, I am convinced this is a very bad idea. At least four radials are needed. Four elevated radials help create an antenna that performs very well. The one radial approach gives you a bizarre pattern with deep nulls.


I also analyze two other antennas: the Force-12 Sigma-5 and the TW Antennas Traveler. For their size, both antennas performed very well. The fact that they are multiband antennas (5 bands 10-12-15-17-20) fed with a single feed line means significant savings in coax weight. Instead of running five runs of small coax for five single band antennas, one could run a single length of high quality coax, reducing signal loss and still saving weight. It is important to assess whole systems of things, not just the pieces like the antenna.

I have presentations to give to local clubs beginning in about two weeks. My new slides are not done. So, I will likely disappear again for a while. Comments on the early draft of this white paper are encouraged. Let me know what you think.

3 Comments:

Blogger Scot said...

An outstanding post, yes, your blogging was missed. But, it reads that the time away from the keyboard paid handsome dividends. My best to you throughout your research and experimentation. Thank you for sharing your results with the broader blogging community.

73 de Scot, KA3DRR

September 06, 2007 8:26 PM  
Blogger David said...

Wow.

I'm going to need some more time to re-read through that paper. There's an awful lot of good info in there and it's going to take a bit of digesting to better understand it.

As you can probably surmise, I was interested in the single vs. four radial analysis on the Buddipole (even though I had a Buddistick), and I may try to play around again and see if I can replicate my results from ZF and then "fix" things by adjusting the radials.

And yes, you were missed. :-)

September 06, 2007 10:32 PM  
Blogger Richard said...

Scott,
I'm looking forward to reading your antenna paper and giving you feedback. However, I'm having problems downloading the file for some reason. And yes, you have been missed!

Rich

September 08, 2007 7:06 PM  

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