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Author Topic: Antenna efficiency  (Read 1208 times)
W5ARD
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Posts: 1




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« Reply #15 on: March 20, 2009, 05:38:05 AM »

After reading a number of posts by K0BG, I have a funny feeling that he has had some sort of bad experience with the ATAS antenna. It is almost as if he has a personal vendetta against them based on how often he takes the opportunity to criticize them.

I don't understand it though. I have one and honestly I think it does quite well. If I can work the stations I hear and I can get responses to a CQ call, and I routinely get favorable reports, why shouldn't I be happy with the ATAS? I have worked Iceland, Siberia, Tasmania, Costa Rica, Hawaii and all over the US from my mobile in Allen, Tx. And it is very easy to do given the design of the ATAS. Isn't that the point of all of this?

Sure I could be more efficient or get further if I had a horizontally polarized antenna with dozens of ground straps and carefully calculated distances and after spending tons of money on equipment and end up looking like a spectacle. But I (and many others) prefer to keep it discreet. Besides, discreet still works. Mind you, I think K0BG's site is wonderful and highly educational. But for the average HAM doing mobile work, I think it is more important that the process be easy. The ATAS makes it easy.

Cheers.
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K0BG
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Posts: 9879


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« Reply #16 on: March 20, 2009, 06:32:49 AM »

Al, you summed it up perfectly:

<If I can work the stations I hear and I can get responses to a CQ call, and I routinely get favorable reports, why shouldn't I be happy with the ATAS? I have worked Iceland, Siberia, Tasmania, Costa Rica, Hawaii and all over the US from my mobile in Allen, Tx.>

You've used the common methodology for justifying an antenna installation, whatever its quality or efficiency. The truth is, you cannot calculate, estimate, interpret, or validate efficiency from the entries in a log book.

The issue here is, you have nothing to directly compare the ATAS to, but if you did you'd know just how inefficient it is. Compared to an HS1800, or Tarheel 200A, the difference is about 15 to 20 dB depending on where and how they are mounted. Compared to a HiQ or Scorpion, the difference is typically 20 to 25 dB. You can argue that 20 dB is only 3 S units or so, but that's a really big difference when the bands are in poor condition.

Alan, KØBG
www.k0bg.com
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KE4DRN
Member

Posts: 3729




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« Reply #17 on: October 01, 2009, 08:35:01 PM »

hi Club Call K6UW,

Did you ever own a Tarheel antenna ?

I have two of the Tarheel models, both work fine
when installed properly.
Well built including Pittman DC motor.

Robert supports the Tarheel antena

Technical Support & Questions
Contact: Robert in North Carolina
919-552-8788

tarheelantennas@aol.com

73 james

by K6UW on March 1, 2009  
     
I'd stay away from Tarheel. They have been sold out to WB0W last year.
WB0W is doing the building.
There is no tech support from WB0W.
The quality of the Tarheel antennas has never been great.
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K5END
Member

Posts: 1309




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« Reply #18 on: October 08, 2009, 09:45:29 AM »

Alan's statement is true, in fact. Logbooks are not a valid "measurement." I agree with 100% on this point. Moreover, "more," or the great circle distance to DX contacts do not mean a better antenna.

But the ability to make contacts readily and consistently (or not) is a good indicator. This is not science; it is valid logic. It is philosophy.

Ad hoc LEMMA 1: A zero contact result "indicates" (but does not prove) a very, very bad antenna. For example, a perfect antenna and a bad coax (or LID operator) could result in zero contacts.

Ad hoc LEMMA 2: Easy and consistent contacts to stations thousands of miles away do prove that the antenna is working, to "some" extent. Maybe it's 2% efficient; maybe it's 11% efficient. But it works. So your radio outputs 100 watts, and your antenna is 5% efficient? Congrats. You're operating QRP, as far as ERP is concerned (but NOT QRP by contest rules.)

Let's not make the common mistake of comparing Apples to uh, well... (please pardon the pun, Alan. SRI!)

Last year I bought a used "original" Little Tarheel for a farthing. It was one of the first made. It's designed to operate down to 40 meters. I added a 2' mast extension below the assembly and a whip above the assembly (to the max height allowed by the DOT) with a capacitance hat at the top. And I put a LOT of ferrite on the control cable and the coax starting at the foot of the mast. At 20 m we had no RF in the cab. To my relief the ferrite rings didn't even get warm.

Wind load is not a problem for that configuration at 75 mph. Nothing broke in 600+ miles across Texas. With those add-ons it needs very little of the coil  to get resonance at 14 MHz. I've used it in OKQP and TXQP for 20 meters, and contacts on that band more than 600 miles away (because of the nature of 20 meters) are plentiful and easy.

With the LT in TXQP I found out what it is like to be at the bottom of international pileups when I crossed into counties of low QSO activity. What a rush! The code was thick and fast. But I worked them the best I could. After crossing into Jones County I worked nearly 30 (CW) stations from the Azores to California in just over 20 minutes. That says something for the LT.(That is not at all impressive compared to the OM Hams, but it's not bad for a brand new, no-code, newbie, eh?)
 
But is the LT a super efficient mobile antenna? That's not really a good or relevant question. I think the LT was designed to be small, convenient and affordable, with a low wind load--and still work. Everything in design and engineering is based on a trade off or compromise. Some efficiency was compromised for the design specs of the LT, and I'd say they did a good job of balancing convenience and performance.

Here is a good parallel example to illustrate the point. The MFJ-259B is a handy and useful instrument, especially for troubleshooting. But compare it to laboratory grade or service test equipment and it doesn't appear to be worth much. See where I am going with this? It met the design specs. That's it. It does a good job of its intended use and is priced affordably for the consumer market.

This buyer's approach is useful for all areas of design and purchasing. Decide what your requirements and limitations are, and shop (or build) accordingly. And if you don't like the result, go back to the drawing board and evaluate your requirements and limitations. This works for me.
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