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Author Topic: back your post with mathematics  (Read 1944 times)
WX7G
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Posts: 5977




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« on: January 10, 2010, 10:27:10 AM »

Can you back up your answer mathematically? If not, you are quessing. As an old engineer once told me, if you cannot mathematically model your circuit you don't know what you're talking about.

The answers at eham can have a big impact on the questioner's life. Some advocate extensive radial systems for verticals. This is easy to advocate yet difficult and expensive to implement. Back up your recommendation with some numbers; how many decibels will be gained by going from a modest to an extensive ground? Let the questioner decide decibels versus cost and effort.  

The "low antennas are no good" respondents have been busy. They state that DX can not be worked with a low antenna. Tell us how many dB will be gained by a high antenna. Let the questioner decide decibels versus cost and effort.

Providing numbers allows the questioner to make his decision. He can make the decision to trade off so many decibels of signal strength for ease of installation.

Try to be positive and not negative. Our nattering nabobs of negativity - and you know who you are - can do great harm.
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KA5N
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« Reply #1 on: January 10, 2010, 12:58:56 PM »

What happened to the notion of having the questioner study up a bit before asking questions?  A little reading would do most newbies a great deal of good.
It is obivious most have never even Googled their question before going on eHam and asking them.
Allen
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KE3WD
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Posts: 5694




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« Reply #2 on: January 10, 2010, 04:12:03 PM »

I wanted to respond to this post mathematically but kept generating a large negative number...
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W7ETA
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« Reply #3 on: January 11, 2010, 02:03:50 AM »

One could wonder where the math is to back up your post?

You know the difference between Mythology and fact?
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WX7G
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« Reply #4 on: January 11, 2010, 03:25:21 AM »

Where is the math to back up my post? It is contained in the posts I have answered using math.

What I am getting at is that answers at eham tend to be subjective when they should be objective.

There are three kinds of answers:

Incorrect, no answer, correct.

Better no answer than an incorrect answer.
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AA4PB
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Posts: 12788




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« Reply #5 on: January 11, 2010, 05:30:17 AM »

The problem is that often you cannot give absolute answers using numbers because there are too many unknown variables. For example, the difference in dB between a "modest" and an "extensive" radial system. What is modest and what is extensive? What are the soil conditions, etc. All you can do is give some general rules of thumb like "more radials is better" and "a single 8-foot ground rod is generally not enough".

The problem with **most** of the questions is that they don't provide enough detail to provide an absolute answer.
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K0OD
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Posts: 2546




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« Reply #6 on: January 11, 2010, 07:09:36 AM »

Nothing, NOTHING, N-O-T-H-I-N-G! kills ham myths. A year ago some poster mentioned that an S-unit was 6 dB. I pointed him to extensive research showing how erroneous that belief was. Two weeks later he posted the same 6 dB nonsense in regard to another subject.  

The pursuit of mathematical precision in antenna comparisons is a major reason I recently purchased a Flex 5000 with its calibrated S-meter rather than an Icom 7600.

Myths about radials abound. How is that possible after all that has written on the subject over 30 years by W2FMI and others? Recently N6LF copper plated half his ranch to run real world tests on radial configurations.

http://www.antennasbyn6lf.com/design_of_radial_ground_systems/
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K0BG
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« Reply #7 on: January 11, 2010, 10:06:22 AM »

David, N6LF's set of articles Jeff mentioned, should be required reading by every amateur, whether or not he installs a vertical. If they are nothing else, they are an axiom of the correct way to accomplish a meaningful, and supportable, testing procedure. A follow up article by Bob Zavel, W7SX, should also be a requirement.

As I replied to you in the Tower Talk forum, you cannot accurately measure some antenna parameters. One of those is ground loss. As both white papers allude to, when you have intrinsic attributes in series, changing one effects the other. Even modeling isn't as definitive as most believe. Mathematics aside, proper field testing is a great way to prove (or disprove) a theory. What we have to be careful of, is using anecdotal references in our reporting of same (i.e.: number of DX contacts made and/or rote adjectives).

Alan, KØBG
www.k0bg.com
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K5END
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Posts: 1309




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« Reply #8 on: January 11, 2010, 10:46:24 AM »

There are three kinds of answers:

Incorrect, no answer, correct.

Actually, there is one more type of answer: the rambling, irrelevant, ambiguous vague answer that spouts B.S. statements that seem to refute some other comment, but that don't really address the original question.

There are many like this, and I think they are worse than incorrect answers. At least an incorrect answer sets itself up for correction.

The best response to this 4th type of answer is "whiskey tango foxtrot?"
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W7ETA
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« Reply #9 on: January 11, 2010, 06:53:45 PM »

I am unanimous in this assertion: I wouldn't understand the math based answer to the question of how an antenna radiates RF.
73
Bob
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KE3WD
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Posts: 5694




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« Reply #10 on: January 11, 2010, 07:06:15 PM »

How can a single entity be "unanimous"?

Why do some hams always have to make rules?

Why do the pileup police do what they do?

Mutha, may I?

F.E.C.E.S  

Of the bovine sort.
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WX7G
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Posts: 5977




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« Reply #11 on: January 11, 2010, 07:34:07 PM »

K0OD, the widely accepted definition of an S-unit is indeed 6 dB.

Long ago it was a subjective number but then came S-meters and the industry defined the S-unit as 6 dB. One reference says that the Millen company first proposed this.

In 1981 (that's 29 years ago) the IARU officially  defined the S-unit as 6 dB with S-9 being 50 uV on the HF bands and 5 uV on VHF.

Here is a link:
http://en.allexperts.com/e/s/s/s_meter.htm
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WX7G
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« Reply #12 on: January 11, 2010, 07:35:47 PM »

From the IARU:

STANDARDISATION OF S-METER READINGS
1. One S-unit corresponds to a signal level difference of 6 dB,  

2. On the bands below 30 MHz a meter deviation of S-9 corresponds to an available power of -73 dBm from a continuous wave signal generator connected to the receiver input terminals,  

3. On the bands above 144 MHz this available power shall be -93 dBm,  

4. The metering system shall be based on quasi-peak detection with an attack time of 10 msec ± 2 msec and a decay time constant of at least 500 msec.
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K0OD
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Posts: 2546




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« Reply #13 on: January 11, 2010, 10:17:40 PM »

"One S-unit corresponds to a signal level difference of 6 dB,"

What power does the IARU have to enforce their definition? Does it even try to get the makers to comply?

Marketing departments know that hams prefer radios with 'juiced' S-meters. Radio buyers want to give out big signal reports. They want to believe that 5 S-unit F/B on their yagi means 30 dB, not 20 which may be closer to the truth. Aside from the Flex, does any radio at any price even attempts to comply with the IARU definition?

Texts have shown that as little as 1 dB separates S-unit markings on some receivers. Reading vary wildly by band and along the meter scale.
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K5END
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Posts: 1309




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« Reply #14 on: January 12, 2010, 05:30:36 AM »

The first time I heard "s" units, I thought it referred to the "s" in differential equations, Heaviside formulas, etc.

And I thought, "man, these hams are really hip to the math."

I thought.



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