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Author Topic: 450 ohm ladder line or 600 ohm OWL?  (Read 15928 times)
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k7iou
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Johnson Viking Five Hundred


« on: January 27, 2015, 11:25:30 PM »

QTH in AZ where we get 11 inches rain a year. I have a 80M full wave loop with 450 ohm ladder line. I just installed a Johnson 1K Matchbox with 450 ohm connected to the balanced output. Seems to work great, better than with coax to balun under eve of house.
Question:
Will there be any noticeable improvement if I remove 450 ladder line and install 6" on center 12 gauge 600 ohm OWL?
Thanks
de k7iou

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de k7iou
KA0HCP
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« Reply #1 on: January 28, 2015, 12:42:44 AM »

Probably not.  It depends on what bands you use the antenna.

A full wave loop has an impedance of about 100 Ohms on it's resonant band.

If you are using it only on 80m, then you would be better off using 50 Ohm coax. with only a 50 Ohm mismatch.

By using 450 Ohm or 600 Ohm balanced line you are introducing losses.

*On the other hand, if you use it on non resonant bands, then a 300 or 450 Ohm balanced line may give you lower  losses.   You would need to do the calculations.

Bottom line: Balanced line isn't always better if you already have a well matched antenna for the band you operate!

b.
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KA2DZT
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« Reply #2 on: January 28, 2015, 01:00:39 AM »

I have a FW loop on 75M and I use coax.  I use a 1/4wavelegth of RG-11 (75ohm) coax off the loop with the rest being RG-8 to the xmtr.  The 75ohm 1/4W transforms the impedance up to about 100ohms to better match the loop.  Works FB.

Fred
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Ralph W3GL
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« Reply #3 on: January 28, 2015, 01:23:52 AM »

Yeah, Freddy, but it introduces a bit of FMing on your carrier... Grin Grin Grin
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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
k7iou
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Johnson Viking Five Hundred


« Reply #4 on: January 28, 2015, 11:00:12 AM »

Probably not.  It depends on what bands you use the antenna.

A full wave loop has an impedance of about 100 Ohms on it's resonant band.

If you are using it only on 80m, then you would be better off using 50 Ohm coax. with only a 50 Ohm mismatch.

By using 450 Ohm or 600 Ohm balanced line you are introducing losses.

*On the other hand, if you use it on non resonant bands, then a 300 or 450 Ohm balanced line may give you lower  losses.   You would need to do the calculations.

Bottom line: Balanced line isn't always better if you already have a well matched antenna for the band you operate!

b.

Sorry but I disagree as ladder line is not lossy. I use it on 40/80 and it works like a champ. Remember the Johnson Matchbox is a balanced tuner and works well with ladder line or OWL.
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de k7iou
W1ITT
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« Reply #5 on: January 28, 2015, 11:03:06 AM »

In Arizona, UV will take it's toll on the plastic in the Crappy Brown Stuff 450 ohm line.  I'd go with proper, manly, 600 ohm line, paying particular attention to the material used as spreaders.  Most formulations of Delrin are pretty good in that application, if you can't find the increasingly scarce ceramic spreaders of ages past.
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KA0HCP
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« Reply #6 on: January 28, 2015, 11:50:48 AM »

http://www.daburn.com/10-62feederspreaderinsulators.aspx

Daburn has a wide selection of ceramic insulators and other old time components.  I have never ordered from them.

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K3ZS
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« Reply #7 on: January 28, 2015, 11:59:29 AM »

Probably doesn't apply to you since you don't get rain, but rain changes the tuning on the 450 ohm brown stuff from 40M and higher in frequency.   I use the crappy brown stuff, been up since 1998 no problem with the UV, but then again, AZ gets a lot more than PA.  If I ever change it, I will use OWL.

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KA0HCP
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« Reply #8 on: January 28, 2015, 12:38:14 PM »

Rather than 'debate' feedline losses, here is a calculator. 
http://www.qsl.net/co8tw/Coax_Calculator.htm

https://web.archive.org/web/20120129210132/http://vk1od.net/calc/tl/tllc.php
Here is a more advanced calculator from Owen Duffy, ex-VK1OD, on the Wayback Machine.

https://web.archive.org/web/20120424223706/http://www.vk1od.net/calc/tl/twllc.htm
And one for two wire transmission line.

http://www.smrcc.org.uk/tools/OpenWire.htm
Open Wire line Impedance Calculator
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KA2DZT
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« Reply #9 on: January 28, 2015, 12:40:20 PM »

In Arizona, UV will take it's toll on the plastic in the Crappy Brown Stuff 450 ohm line.  I'd go with proper, manly, 600 ohm line, paying particular attention to the material used as spreaders.  Most formulations of Delrin are pretty good in that application, if you can't find the increasingly scarce ceramic spreaders of ages past.

I have hundreds of them, problem is they're all about 12" long and weight a ton.  Make a OWL with them and you'll need a crane to get it up.

Fred
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WA2SQQ
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« Reply #10 on: January 28, 2015, 01:06:38 PM »

Here's what I use - cheap, easy and very reliable!

http://www.w1aex.com/owl/owl.html
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K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #11 on: January 28, 2015, 01:49:11 PM »

The W1AEX method posted above looks like an excellent and inexpensive way to make quality open wire line.

Some general OWL comments:

"Homemade" 600-800 ohm open wire line is more environmentally stable than the 450 ohm brown plasdick stuff.  Rain will sheet on the 450 ohm stuff... or snow or ice can make its inter-lead capacitance soar. Chase the ant tuner settings around.

The ultimate OWL has no spacers at all - just pull the two leads taunt. It helps to have a tower to anchor it to. I have done this it and it works FB, even with 1 foot spacing up to 20M.

Using the calculator posted above, I see that on 14 Mhz, 100' of 450 plastic line shows about 3.3 dB loss at 100:1 swr.   So if 1KW, then over 500 watts would be dissipated in the line.  200' would lose 6.6 dB.   That is an extreme swr case, like running a 75M dipole on 160M, but a rough guideline.

Loss will depend a lot on the particular impedance (or swr mismatch) we are dealing with.  If we are using it on all bands from 160-10M, then probability says there will be plenty of situations where we have   30:1 +  SWR situations on the higher bands, thus VERY high and very low impedance spots along the OWL.  The  low spots are the problem, since the currents peak and can start to warm up the line if it is small diameter. The heat will also depend on the power level, of course.

I know of a few instances where guys were running a KW and using the 450 ohm line (#18 wire?) as a multiband dipole. The plastic actually started to melt at the low impedance points.  Loss is still loss, and even at 1 watt the dB loss is there.

In contrast, the #12 or larger OWL homemade line would never notice it.

One more point: If matched into its characteristic impedance, the cheap 450 ohm OWL is fine. For example, a friend of mine once terminated 100' of it into a 450 ohm non-inductive resistor. He put in 100 watts at 14 Mhz and measured the power at the other end. IIRC, he measured about 98 watts. This shows that the brown 450 ohm line works FB IF it has an SWR of say 5:1 or less.  But for the big swr found on multiband dipoles using ant tuners, stick with the larger diameter wire, like #12 or larger.  Same goes for the ant tuner - use reasonable coils and connections to mimic the openwire line in size.

T

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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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w7fox
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« Reply #12 on: January 28, 2015, 02:04:49 PM »

I have used home brew OWL for a long time with good results.  My current center fed zepp uses #12 wire spaced 4 inches, with spacers at 4 foot intervals.  The spacers are acrylic plastic aka plexiglass.  They have been up for 30 years and show no detrimental effect from the weather.  You can get 5/8 inch acrylic rod from McMaster Carr, and it isn't expensive.  Good luck.

73
Chris
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ka1tdq
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« Reply #13 on: January 28, 2015, 03:26:08 PM »

I live in Arizona and have found that the life expectancy of any wire antenna will be about 5 years.  I had a dipole up for a year and the sun wore off the clear plastic stuff on the THHN wire I was using.  I would probably just use 450 ohm cheap stuff since it is "temporary."  I wouldn't put a lot of money into building decent OWL.

As for matching a full wave loop, the 1/4 wavelength matching section of 75 ohm coax seems to work amazingly well.  I put my first wire loop up recently doing just that.  I must've cut it exactly because the antenna was perfectly resonant on the first try.  

It's very broadband too.  The SWR doesn't go above 1.2:1 across the entire 40 meter band.

Jon

PS:  As for my peeps back in New England who just went through a major snow storm yesterday, it's warm and sunny here.

Go Patriots
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KA9EGW
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« Reply #14 on: January 28, 2015, 06:51:50 PM »

I'm very happy with my OWL using 73cnc.com Ladder Snap spreaders.  73, Brian KA9EGW
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aa5wg
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« Reply #15 on: January 30, 2015, 10:24:52 PM »

Sir,

Home brew ladder line is by far the best way to go.  Rain, snow, etc. has much less effect on home brew ladder line.

450 ohm line will provide lower voltages at the tuner.  600 ohm line will provide higher voltages at the tuner.

Home brew 300 ohm 4-wire ladder line provides lower voltages than 450 and 600 ohm systems.

Good luck.

Chuck
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N6YW
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« Reply #16 on: January 31, 2015, 07:25:27 AM »

Here's the direct link to the Fi-Shock "Zareba" insulators.
I bought the 73CNC black snap on insulators and they are perfect, but these are a better value for the quantity offered:
http://www.fishock.com/store/high-tensile-electric-fence/bht4fti200
73 de Billy N6YW
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KJ4OLL
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« Reply #17 on: January 31, 2015, 12:02:10 PM »

Hi,
I messed up on my ladderline rebuild.
600 ohm feed line into two 125ft wire runs.
A "Balun Designs" 4:1 between the LMR-600 from the shack and the feed line.

The original #14 AWG was too easily broken, and I had a few hundred feet of #10, and
so rebuilt all w/ the #10 for added strength.

AFTER I had it all installed, noticed in a 1960's ARRL handbook that the gauge of the feedline is
important.

Should have left the #14 in place for the feed line, to maintain 600 ohms.

By using #10 for the feed line, and retaining the 3" on-center spacers, the feed line is now 475 ohms.

According to the chart on page 349 of the 1963 handbook, for #10 feed line, the spacers need to be 8.5" for 600 ohms!!!

Ordering some UV resistant Acrylic to make the correct spacers........

http://www.mcmaster.com/#catalog/121/3609/=vpgtyk

73
Frank
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K1JJ
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« Reply #18 on: January 31, 2015, 01:29:48 PM »

Hi Frank...

I'm curious... are you using an openwire fed design that requires a balun?

Why not use what you have, eliminate the balun and build up a simple antenna tuner?  It doesn't get any better than that.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
k7iou
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Johnson Viking Five Hundred


« Reply #19 on: January 31, 2015, 04:29:33 PM »

This looks good
http://www.ebay.com/itm/LADDER-LINE-600-OHM-13-AWG-80-FEET/131395049773?_trksid=p2050601.c100262.m3457&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20140813130114%26meid%3Dcd6b746c48644e4298052cc547d89053%26pid%3D100262%26rk%3D1%26rkt%3D4%26sd%3D131395049773%26clkid%3D3755490377702621809&_qi=RTM1963929

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de k7iou
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« Reply #20 on: January 31, 2015, 06:32:00 PM »

K7IOU,
Yes it looks really nice!!

Fred
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Fred KC4MOP
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« Reply #21 on: February 01, 2015, 02:39:32 PM »

K1JJ,
I wish it was practical to connect the OWL to my tuner!

Would have to use a remote tuner, due to the distance and geometry
between the tower and the shack.

Lightning is a major problem @ this QTH, so an external tuner would require regular repairs.

http://www.nasa.gov/centers/kennedy/news/lightning_alley.html

To encourage the strikes to find a path to ground that does not involve 7000 degree plasma
in the shack, I have implemented all I could afford from this paper:

http://www.hamuniverse.com/groundingbypolyphaser.pdf

Plus built and installed a very nice static drain as described in ER, #284

http://i180.photobucket.com/albums/x257/fish1_07/am/ladder_line_protection/ER_ladder_line_protector_zps5ab54f14.jpg

Thus the compromise between optimum OWL deployment and flaming boatanchors!
73
Frank
KJ4OLL
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