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Some words on the Ladderline vs. Coax issue...




 
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Author Topic: Some words on the Ladderline vs. Coax issue...  (Read 55499 times)
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Patrick J. / KD5OEI
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« Reply #100 on: November 17, 2009, 11:32:20 PM »

Started to scan the book. This project will take a while! Besides the time it will take, there will be a wide black line on the spine side of the page. This is because its a book......and I cant get it to lay flat on the scanner unless I pull the book apart page by page which I dont want to do. Even though the line is there, no text will be lost.

Bill

doing it that way - 2 sheets at a time, the aspect ratio will match the CRT screen better.
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« Reply #101 on: November 18, 2009, 12:31:25 AM »

So far, and over the past 38 years of ham radio, I have preferred coaxial feeders.

I use coax (helical - not solid dialectric) today on all of my antennas, and I suppose anyone who has talked with me knows I get out reasonably well  Cool   But, I do decouple the coax from the line using a whole lot of #43 ferrites over the coax, at the antenna feedpoint.  And I use low-loss, usually helical coax cable and nothing with a solid dialectric.

There's just a whole lot less equipment involved with coax feed, and also the RF is carried away from the shack in a convenient manner, without a problem, the coax touching whatever it wants, etc.

I do use a single coax feed for both 160 and 75 meters - with both antennas connected to the same feedline and it works out just great!

Regards,

Steve
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ke7trp
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« Reply #102 on: November 18, 2009, 12:50:37 AM »

Coax is easier:)  I wish I had room for big antennas.

All my verticals use Andrews Heliax. Half inch or 3/8s. I love it..

Clark
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k4kyv
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Don
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« Reply #103 on: November 18, 2009, 01:11:39 AM »

What about feeding that 72 ohm dipole with 300 (450, 600 etc) ladder line?  now you've got a BIG mismatch. So doesn't a lot of your power get reflected right back down the line? 

But then the reflected wave reaches the feed point end and is reflected back to the antenna where  a little more is radiated and the process repeats itself until all the energy is dissipated into the radiation  resistance of the antenna plus some feed line losses.  The  reflected power does not disappear, except for what is dissipated in the dielectric and the resistance of the wire.  Those reflected wavefronts oscillating back and forth from one end of the feed line to the other is what produces standing waves on the line.

This is equally true with coax, twin lead and open wire.  The solid dielectric stuff wastes the most energy in the process, the reason why it is OK to run open wire at high SWR, but solid dielectric coax need to maintain as low SWR as practicable.
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Don, K4KYV                                       AMI#5
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« Reply #104 on: November 18, 2009, 02:17:27 AM »

......................

Coming now to copying book material with respect to copyrighting. For those who have a copy of my book I encourage copying it for others. I'm not interested in royalty money, what concerns me most is that what knowledge I have I can communicate to others in a meaningful way.

....................

Walt


Wow! Walt is like the Jerry Garcia of Amateur radio!!  Freely share the goods!!  It's about the CONTENT not the money!  Love it!
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« Reply #105 on: November 18, 2009, 09:44:14 AM »

Rob, you can use a long pole with either a 1N34, 6" pickup wire, a .01, and mini coax to a microamp meter; or a NE2 at night as very basic line sniffers. Ive used maybe 20' of aluminum tubing (and old 10M boom) with a 4-5' wooden mop handle stuffed in at the hot end. It may be enough to give some meaninful indication at least over part of the OW run.


As far as ATU's there is an article in Feb 62 QST pg 39 that may be of interest. It also references a good 1942 IRE paper.

Carl
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Steve - WB3HUZ
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« Reply #106 on: November 18, 2009, 10:29:01 AM »

Yep. Two feet is not enough to make any substantial change on 20 meters. Two feet is only 0.03 wavelengths. Add something like an eight of a wavelength.


Try adding 6 to 8 feet and I bet you will be fine. I used to run 2 Vee beams in parallel with one about 10 feet shorter than the other to lower the q that fixed everything. You are just outside the matchbox tuning range on 20m so it could take close to a quarter wavelength change to get you out of trouble. You can even hang the extra feed line off the match box with the end open. Just be careful as there can be some high voltage at the end. You could short the end but it will change things a lot on other bands.
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Steve - WB3HUZ
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« Reply #107 on: November 18, 2009, 10:43:22 AM »

The other thing to keep in mind is that your dipole will probably NOT be 72 Ohms. That is the impedance of a dipole in free space. When a dipole is less than about 0.25 wavelengths above the ground, the impedance is usually less than 72 Ohms. Higher dipoles can have impedances above 72 Ohms, peaking out in the 80-90 Ohm range.

So don't worrry about the mismatch Ed. The loss will be negligible, unless you are using very lossy coax and/or a very long run of it,. Even if your dipole was 72 Ohms, this would only amount to a SWR of 1.44. This SWR results in a whopping 0.01 dB more loss than if you had a perfect match when using 100 feet of RG8 on 3.8 MHz.

You can check you exact situation at the link below.

http://fermi.la.asu.edu/w9cf/tran/index.html


What about feeding that 72 ohm dipole with 300 (450, 600 etc) ladder line?  now you've got a BIG mismatch. So doesn't a lot of your power get reflected right back down the line?  

But then the reflected wave reaches the feed point end and is reflected back to the antenna where  a little more is radiated and the process repeats itself until all the energy is dissipated into the radiation  resistance of the antenna plus some feed line losses.  The  reflected power does not disappear, except for what is dissipated in the dielectric and the resistance of the wire.  Those reflected wavefronts oscillating back and forth from one end of the feed line to the other is what produces standing waves on the line.

This is equally true with coax, twin lead and open wire.  The solid dielectric stuff wastes the most energy in the process, the reason why it is OK to run open wire at high SWR, but solid dielectric coax need to maintain as low SWR as practicable.
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k4kyv
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Don
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« Reply #108 on: November 18, 2009, 01:28:35 PM »

A neon lamp will not give a reliable indication of radiation from the OW feeders.  All it will give is an indication of the intensity of the near field of each of the wires.  By the time you get far enough away to detect the radiated field, it will be far too weak to light up a lamp.

The neon lamp is most useful for determining where the maximum and minimum voltage points are along the feeders.  You might get some idea of feedline balance at a high voltage point by carefully moving the lamp between the feeders,  preferably by sliding it over a spreader, and noting if the null point appears exactly equidistant between the two wires. 

Something I have found with mine is that even the glazed commercial EF Johnson ceramic spreaders are NOT perfect insulators.  I can hold a neon lamp up to a spreader, and a bright spot appears in the bulb where the glass envelope touches the surface of the ceramic, just as it does when touching a metallic conductor that is hot with RF.
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Don, K4KYV                                       AMI#5
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« Reply #109 on: November 18, 2009, 01:29:18 PM »

So far, and over the past 38 years of ham radio, I have preferred coaxial feeders.

I use coax (helical - not solid dialectric) today on all of my antennas,


Steve, doesn't that run of heliax up to the dipole feedpoint weigh a lot?

73

Rob
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« Reply #110 on: November 18, 2009, 01:30:17 PM »

Rob, you can use a long pole with either a 1N34, 6" pickup wire, a .01, and mini coax to a microamp meter; or a NE2 at night as very basic line sniffers. Ive used maybe 20' of aluminum tubing (and old 10M boom) with a 4-5' wooden mop handle stuffed in at the hot end. It may be enough to give some meaninful indication at least over part of the OW run.


As far as ATU's there is an article in Feb 62 QST pg 39 that may be of interest. It also references a good 1942 IRE paper.

Carl
KM1H
hi Carl, thanks -- I have a few fiberglass poles I can use.

73

rob
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kc6mcw
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« Reply #111 on: November 18, 2009, 03:23:16 PM »

Here is a test I have done to find out what caused the RFI in my shack when using balanced line. The test was made on 75m. It made a big difference where the ground was on my link coupled tuner and after installing an ugly coax choke at the tuner input. It didn't make a difference if the transmission line was balanced or unbalanced thus acting as Marconi antenna, a conjugate match was obtained in both scenarios. Also, upon using the SLC, Utah reciever on smeter.net as a remote recieving site with an S meter, I noticed that my signal didn't change much when I went from a balanced to an un-balanced state on my transmission line by changing the ground location and retuning, etc. That would make sense due to my wire antenna is only 40' high and acts as a NVIS system. And when it was in an un-balanced state, the transmission line acted as a Marconi antenna using everything including the neighbors home as the counterpoise causing RFI havic, also performed as a NVIS system! So would it be safe to determine that both antenna systems were efficient but with different side effects?


* balancedlinedemo1.jpg (182.46 KB, 800x600 - viewed 518 times.)
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Steve - WB3HUZ
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« Reply #112 on: November 18, 2009, 04:24:17 PM »

What was the time period of the tests? Did you quickly switch back and forth while watching the remote S-meter?

Consider this - if your antenna system is producing RFI in your neighbor's stuff, that's RF energy that is not making it to the ionosphere.
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kc6mcw
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« Reply #113 on: November 18, 2009, 04:27:25 PM »

Not if the neighbors "stuff" is now part of your antenna system per sei, see it wouldnt really be RFI, but RF voltage/current that is on the other half of the antenna/counterpoise/neighbors home.... and the tests were very fast and over a 2 hour test period to average out the test results due to the changing propagation. I am very confident in the signal results in other words.
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The Slab Bacon
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« Reply #114 on: November 18, 2009, 04:47:08 PM »

well,
       Here is another thougt to ponder................... Is the RFI coming from your feedline or your antenna Huh  Huh If it is definately coming of of the feedline, then you have some tweeking and testing to do. But.................

If it is coming off of your antenna it could be a "good" thing. This could mean that you have gotten rid of some of your losses and more RF is getting to the antenna.

If you dont have "RF in the shack" problems, but your neighbor is pissing and moaning about your RFI, it might mean that more RF is going to the antenna and not being wasted heating the feedline.

just something to ponder.....................
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« Reply #115 on: November 18, 2009, 06:33:43 PM »

A quick note.......
My post about complicating this thread was not meant to belittle anybody.........Its just if u read the original post....in my opinion the post was meant to "uncomplicate" the whole idea of coax vs balanced line.
The technical info posted here is first rate.
No harm intended folks.........I love ya all Grin   
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kc6mcw
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« Reply #116 on: November 18, 2009, 10:14:02 PM »

Yes, while there are multiple ways to correct the issue I have presented, the point I was attempting to make was that my signal didnt seem to change either way. Only that I had severe RF in the shack when the transmission line was acting as a Marconi antenna as Don pointed out. It makes perfect sense. The open wire transmission line works ONLY in a balanced configuration and is not possible to operate un-balanced as Walt said. BUT, when the tuner and ground is configured incorrectly, the transmission line becomes a Marconi antenna and no longer functions as a balanced transmission line carrying the RF to the real antenna in the sky. I realize this is getting way off the original topic but I find it very interesting learning to understand what this "RFI" really is. I personally dont believe it is RFI at all but simply just RF on the "other" half of its' antenna aka station cabinets, neighbors home, etc... Smiley
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« Reply #117 on: November 18, 2009, 10:33:21 PM »

So far, and over the past 38 years of ham radio, I have preferred coaxial feeders.

I use coax (helical - not solid dialectric) today on all of my antennas,


Steve, doesn't that run of heliax up to the dipole feedpoint weigh a lot?

73

Rob

It is fairly heavy... The center is held up by a tower and a pulley system.  I am guessing the antenna and feedline (with the type 43 cores up there also!) probably weigh at least 25 if not possibly 50 pounds.  The center is somewhat hard to hoist up when near the end.

Regards,

Steve
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Steve - WB3HUZ
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« Reply #118 on: November 18, 2009, 10:35:28 PM »

Quote
I personally dont believe it is RFI at all but simply just RF on the "other" half of its' antenna aka station cabinets, neighbors home, etc...

Technically true, but will your neighbors see it that way.  Grin  I know mine didn't at a previous location. I often tied the two conductors of my open-wire fed dipole together and ran it as a vertical-T against 16 radials. This configuration was superior to the balanced-fed dipole configuration for contacts greater than 300-400 miles on 160 meters.
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kc6mcw
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« Reply #119 on: November 18, 2009, 10:42:46 PM »

Steve,
I havent tried that yet on 160 but will soon. BTW, We might be able to hear you out here on the west coast tonight but might have to wait another few hours. I am listening out for you and Tom.

Joe
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Steve - WB3HUZ
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« Reply #120 on: November 18, 2009, 10:54:04 PM »

Listen this weekend, Friday or Saturday night. I'm off to bed now. That four letter word, WORK comes up in the morning.



Steve,
I havent tried that yet on 160 but will soon. BTW, We might be able to hear you out here on the west coast tonight but might have to wait another few hours. I am listening out for you and Tom.

Joe
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« Reply #121 on: November 23, 2009, 01:31:10 PM »

Listen this weekend, Friday or Saturday night. I'm off to bed now. That four letter word, WORK comes up in the morning.



Steve,
I havent tried that yet on 160 but will soon. BTW, We might be able to hear you out here on the west coast tonight but might have to wait another few hours. I am listening out for you and Tom.

Joe

Steve,
So you do work? I thought you were a prfessional Ham radio operator/mentor/DX op/pile-up cracker.

Fred
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Steve - WB3HUZ
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« Reply #122 on: November 23, 2009, 06:59:36 PM »

I go to a work place......



Listen this weekend, Friday or Saturday night. I'm off to bed now. That four letter word, WORK comes up in the morning.



Steve,
I havent tried that yet on 160 but will soon. BTW, We might be able to hear you out here on the west coast tonight but might have to wait another few hours. I am listening out for you and Tom.

Joe

Steve,
So you do work? I thought you were a prfessional Ham radio operator/mentor/DX op/pile-up cracker.

Fred
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