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Author Topic: Antenna question  (Read 3238 times)
KC8IUR
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Posts: 156




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« Reply #15 on: January 21, 2011, 06:15:45 AM »

No matter what is done for an antenna, there are some hams that will INSIST that it will not work just because the figures on a piece of paper concerning its effiency says it will not work.  To those hams, I have before--and still do make just one statement.  It has been proven mathematically that a bumblebee cannot fly, yet the bee doesn't know that--and it keeps on flying.

I know it is often quoted that mathematically, a bumblebee or egg-beater helicopter cannot fly. How many people know or understand that math? Is it still even true? If math proved something could not fly, but obviously it can, then your starting suppositions are incorrect. At that point, you can find where your math is flawed and fix it.

With antennas, you can directly measure power input and power output at the antenna. There's no calculus with which to arrive at a flawed conclusion.
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AA4PB
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Posts: 12899




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« Reply #16 on: January 21, 2011, 06:25:51 AM »

"With antennas, you can directly measure power input and power output at the antenna"

Not really. You can directly measure the power input and you can measure the field strength at some given distance. What we are usually really interested in however is the field strength at some great distance (thousands of miles) and in between is "propogation". Propogation loss can change way more in a couple of seconds than the dB difference between two antennas. In addition, things like horizontal and vertical radiation pattern of the antenna come into play. There are many variables involved that make a practical comparison between two HF antennas very difficult.
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KI4SDY
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Posts: 1452




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« Reply #17 on: January 21, 2011, 06:31:44 AM »

What is a "tune can QRP unit?" How do you tune a can? Is that supposed to be a tuna can QRP unit?  Roll Eyes
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K0BG
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Posts: 9879


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« Reply #18 on: January 21, 2011, 07:13:08 AM »

Sorry about that, I didn't catch it.
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W3LK
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Posts: 5639




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« Reply #19 on: January 21, 2011, 10:41:41 AM »

I've said it before and I'll say it again ...

In the so-called antenna shoot outs, unless the ONLY difference is the antenna, the results are suspect, at best, and useless, at worst. Unless the same mount and mounting location on the same vehicle, as well as the same radio, is used for all measurements, the variables introduced by the differing mounts, locations and vehicles will make the results essentially meaningless.
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
ZENKI
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Posts: 960




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« Reply #20 on: January 21, 2011, 01:49:06 PM »

Thats why it would be nice if someone ran a professional mobile antenna shootout that eliminated all these variables and reported the real performance differences of these antennas.

I have found on my vehicle, especially on 20 and 40 meters that the performance advantage of the "super screwdrivers"to have an marginal advantage. I have found reason to bolt a 20 pound heavy weight contraption on my car yet. When I can see a real 6 db advantage on either 20 meter or 40 meters I might take a second look. I still own a High Q 5-80 and a Scorpion and they sit in the garage gathering dust!


I've said it before and I'll say it again ...

In the so-called antenna shoot outs, unless the ONLY difference is the antenna, the results are suspect, at best, and useless, at worst. Unless the same mount and mounting location on the same vehicle, as well as the same radio, is used for all measurements, the variables introduced by the differing mounts, locations and vehicles will make the results essentially meaningless.
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WB6BYU
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Posts: 13341




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« Reply #21 on: January 21, 2011, 10:21:54 PM »

Quote from: K1CJS
...there are some hams that will INSIST that it will not work just because the figures on a piece of paper concerning its effiency says it will not work...


Pointing out that some antennas are quite inefficient is not the same as saying they won't work,
for some definition of "work".  Saying that hamsticks for 80m are at best a few percent efficient
doesn't mean that they can't make contacts, or that hamsticks for higher bands won't have
much better efficiency.

Same with coax - using RG-58 with 3dB of loss isn't the end of the world if that is what you have
on hand.  In most cases the antenna will still work better up high with a lossy coax than indoors
at the rig with zero coax loss.

There is a continuum of trade-offs.  I make plenty of contacts running 5 watts or less to a dipole,
and someone running 100 watts to a 5% efficient antenna can expect to do about as well.  You
just won't be as strong as you would be if your antenna was radiating more of the power fed to it.
Twisted pair might not be the most convenient feedline, but when you are living in a remote
logging camp and the only wire available is what you can salvage  from the blasting operations,
it is better than any amount of LMR-400 sitting hundreds of miles away that you don't have access to.

You do what you can and live with it.  Don't assume that everyone has the same trade-offs among
convenience, cost and performance that you do.  There is no "one right way" to do things, and
anyone who insists otherwise is somehow missing the big picture.
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