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Author Topic: Nov QST Ladder Line loss  (Read 11128 times)
K3AN
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Posts: 787




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« Reply #45 on: October 19, 2009, 02:01:49 PM »

Thanks for those numbers Cecil. Now, is anyone willing to step up to the plate and duplicate the QST testing (with your own setup which may differ from theirs) and provide some numbers for old, dirty and/or wet line?

Or will the QST article become the new reference?
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G3TXQ
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Posts: 1529




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« Reply #46 on: October 19, 2009, 02:07:07 PM »

>>VK1OD wrote: Of course, if you plugged diameter in instead of radius, you would get the numbers that the ARRL spruiks.<<

Or, if you calculated the AC resistance of 100ft of #18 wire at 10MHz and forgot that there is 200ft of wire in 100ft of ladderline Wink

Steve G3TXQ
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N3OX
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Posts: 8847


WWW

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« Reply #47 on: October 19, 2009, 02:09:29 PM »

Cecil, not here, not now.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N3OX
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Posts: 8847


WWW

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« Reply #48 on: October 19, 2009, 02:19:26 PM »

"Sounds like I can probably skip the article"

No, don't skip it.  Read it.  The line attenuation for lines on the ground is very weird.  They admit it's weird and probably spurious.  But it would be interesting to see if it's TOTALLY spurious (measurement artifact) vs. something that has some information about that most insidious of engineering materials... dirt ;-)

I still don't think anyone should lay their ladder line on the ground, but at the same time pure RF curiosity leaves me wanting more.

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W5DXP
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Posts: 3630


WWW

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« Reply #49 on: October 19, 2009, 02:55:46 PM »

> K3AN wrote: Or will the QST article become the new reference? <

The 1980s ARRL Antenna Books had an obvious slope error on the line losses graph. In the late 1990's, the ARRL  corrected the *slope* of the graph but apparently did not correct the *magnitude* of the loss values.

Sometime in the past, I made a note that the loss value for 75 MHz (0.4 dB) was correct on the old graph - but I don't remember why I made that note something like 15 years ago.

Bottom line seems to be that window-line does NOT have lower matched line loss than 7/8" coaxial hard line.

Dare I ask? Do the ARRL open-wire graphs have the same problem?
--
73, Cecil, w5dxp.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
N5LRZ
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Posts: 0




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« Reply #50 on: October 20, 2009, 01:13:26 PM »

Do you know what you do when you get an increase of loss in transmission line....

You say screw it and just INCREASE transmit power by cranking up the big 1.5 K amp.

That is what you do, compensate by jacking up the power output--up to but not exceding max power allowed per the FCC Regs of course.
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W6RMK
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Posts: 657




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« Reply #51 on: October 19, 2009, 09:13:25 PM »

Wes Attaway did some tests with decent equipment and calibration some years ago:
http://users.triconet.org/wesandlinda/ladder.htm

shows "many dB/100ft" difference wet vs dry in loss at 50MHz with several commercial "window lines"

lots of analysis and modeling of the results to understand why the measurements are what they are.
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VK1OD
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Posts: 1697




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« Reply #52 on: October 19, 2009, 11:15:46 PM »

Jim,

I know N7WS as Wes Stewart, perhaps he is also known by the name you mention.

I, and I think others, have referenced his work earlier in this thread.

An interesting reconciliation between his measurements and theoretical prediction is his case of #16 wires at 0.75" air spacing. He reported Zo=399, A100(50MHz)=0.3dB, Er=1.01, and calculating that scenario with TWLLC (http://www.vk1od.net/calc/tl/twllc.htm) gives:

Parameters   
Conductivity   5.800e+7 S/m
Rel permeability    1.000
Diameter    0.0013 m
Spacing    0.0190 m
Rel permittivity   1.010
Loss tangent    0.000e+0
Frequency   50.000 MHz
Length   30.480 m
Results   
Zo   402.88-j0.43 ohm
Velocity Factor   0.995
Length   1839.19 deg, 5.109 wl, 30.480 m, 100.000 ft
Line Loss (matched)   0.297 dB

The W551-W554 dry characteristics are in TLLC (http://www.vk1od.net/calc/tl/tllc.php). The wet figures are there, but 'hidden' at Wes's request. I think I can understand why one set of wet figures aren't extensible to general scenarios, but the paper is certainly worth a read, it is credible, and enlightening on the reasons why ladder line behaves as we observe.

Owen
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G3TXQ
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Posts: 1529




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« Reply #53 on: October 20, 2009, 01:44:25 AM »

>> W5DXP wrote: Dare I ask? Do the ARRL open-wire graphs have the same problem? <<

No, they don't! In Table 1 and Fig 23, 21st Edition of the Antenna Book, the 600 ohm open-wire figures are consistent with calculated copper losses.

But, as I have said before, the figures in Table 1 for 600 ohm open-wire and their 405 ohm "Generic Window Line" are totally inconsistent. At 10MHz the open-wire (#12 gauge) loss figure is quoted as 0.06dB/100ft which compares well with a calculated figure of 0.057dB/100ft. Now halve the wire diameter to #18 gauge and drop the Zo to 405 ohms for their Generic Window Line figures, and you'd expect to see 0.057*2*600/405=0.17dB/100ft; instead, they quote 0.08dB.

At all points on the Fig 23 graph, the loss for Generic Window Line is 1.5 times the loss for open-wire, instead of the 2.96 times you should expect.

73,
Steve G3TXQ
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VK1OD
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Posts: 1697




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« Reply #54 on: October 20, 2009, 02:28:50 AM »

Steve,

The fundamental problem with Fig 23 is that as far as I can see, they are all straight lines.

If you accept that a good model for lines is that loss=(k1*f^0.5+k2*f)*l where k1 relates to copper loss and k2 relates to dielectric loss, then at low frequencies, most lines will approach a straight line with position dominated by k1 and slope by the 0.5 f exponent, and at extremely high frequencies, slope dominated by the f exponent 1, and in between, a curve transitioning from one to the other.

It is unlikely that the representation of different cables with straight lines of different slopes in Fig 23 is a good approximation at all, since below 1GHz, copper loss dominates in most practical cables (ie slope dominated by the exponent 0.5).

One would expect that the lines for RG213 and a foam version of RG213 will have identical slope at low HF (since copper loss dominates), but the line for foam type will be displaced downwards (by virtue of its larger diameter centre conductor), and that at much higher frequencies, RG213 tends to increase in slope due to increasing significance of dielectric loss (f exponent of 1), and the foam type also increases, but at a lower rate. None of this is evident from Fig 23, though the effects of dielectric loss are not very pronounced below 1GHz for most practical cables. None of the curves are for CCS cables that show higher losses at low HF than pure copper conductors.

This graph has been in ARRL publications for a very long time, and with little change, but it doesn't convey some key characteristics of different groups of cables, eg the effect of foam dielectric versions of some standard PE cables, and CCS conductors in some RG6, RG59, miniature coax, and ladder lines.

Owen
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G3TXQ
Member

Posts: 1529




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« Reply #55 on: October 20, 2009, 03:28:29 AM »

Owen,

I agree that the variations in slope are very strange - even more so when you see that directly opposite Figure 23 is a Table 2 containing the relevant formulae!

73,
Steve G3TXQ
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G3TXQ
Member

Posts: 1529




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« Reply #56 on: October 20, 2009, 03:39:01 AM »

I believe that Wes Stewart's work was published in Antenna Compendium VI. Perhaps ARRL might be invited to comment on the very different conclusions reached in two of their publications!

Steve G3TXQ
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VK1OD
Member

Posts: 1697




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« Reply #57 on: October 20, 2009, 12:11:03 PM »

Steve,

I have created a figure similar to Fig23 using the data that underlies TLLC.

The figure is at http://www.vk1od.net/lost/Fig23.png .

You will see the effects that I spoke of, that at low frequencies the slope of all lines is the same as losses are dominated by copper losses, the 0.5 f exponent.

Have a close look at 8262 and LMR-195 which are normal RG58C/U and a low loss foam dielectric version. You can see the effect I spoke of in my earlier post.

The same of 8267 and LMR-400.

The *only* straight line here is 'Open / air dielectric (150/2.00)' as it models copper conductors in a lossless dielectric.

Note that this loss model assumes that skin effect is fully effective, and does *not* capture the effect of thin CCS or SCS coatings at low HF frequencies (such as some ladder line, RG6 and thin coaxes.

Owen
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W8JI
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Posts: 9296


WWW

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« Reply #58 on: October 20, 2009, 12:30:48 PM »

The MATCHED measured transmission loss of 100 feet of 450 ohm 18 ga solid CCS conductor ladder line suspended in air using a currently calibrated network analyzer with the transformes normalized out is:

2 MHz .08 dB
3.7 MHz .0817 dB
14.2 MHz .2336 dB
28.4 MHz .2854 dB

That's quite different than QST.

When that line is laid flat on short grass in damp soil the line impedance goes from about 435 ohms down to 315 ohms. I do not have loss for that just yet, but there isn't going to be any question the loss won't be nearly as good as in air. Even if the earth and grass dielectric is lossless (which it won't be)the impedance is lower, which would increase losses by virtue of increased current in a fixed conductor resistance.

I'm not quite sure how to measure the wet loss or on-the-ground loss, because the line would be greatly mismatched. Should I just measure it like it is matched and back out the mismatch losses manually?
 

Tom
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VK1OD
Member

Posts: 1697




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« Reply #59 on: October 20, 2009, 12:52:53 PM »

Tom,

Your recent measurements straddle my extrapolation of N7WS's measurements of Wireman 551, as used in TLLC, plotted at http://www.vk1od.net/lost/W8JI-N7WS.png .

Owen
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