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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 55469 times)
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W2DU
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Walt, at 90, Now 92 and licensed 78 years


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« Reply #50 on: November 16, 2009, 07:48:48 PM »

Some excellent posts on this thread, indeed. The intelligence of people in this AMfone group is so far ahead of those on the QRZ group it is amazing. Don's posts are exceptionally good. And thank you Bruce, for the nice words--I feel honored to be accepted by this great group!

However, I'm a little concerned about Brian's problem with feedline radiation. Brian, how can be sure your 'balanced' feedline is really radiating? Have you measured it, and if so, how did you perform the measurement? Next, if the system is constructed correctly it will make no difference whether the line impedance is 600, 450, 300, or whatever, with respect to feedline radiation.

On the other hand, let's see what might cause the 'balanced' feedline to radiate. The feedline will radiate somewhat if it is WAY off center, causing unequal currents on the radiator, and thus somewhat unequal currents on the feedline. Another cause could be that one conductor of the feedline is making a poor or non-connection to its antenna terminal. Still another cause could be an open in one of the feedline conductors. As I said above, the impedance of the line has nothing to do with causing it to radiate. As I'm sure you know, feedline radiation is practically zero when the currents in each conductor are equal and out of phase, because the RF fields radiated from each conductor are opposite in polarity, and thus cancel.

Another point that is often misunderstood is that although antenna currents on the radiator result in radiation, antenna currents cease being antenna currents at the junction of the antenna and the feedline, and now become transmission-line currents. When the conductors of the feedline are sufficiently close to prevent radiation, transmission-line currents do not result in radiation. Consequently, with the spacing normally used in open-wire, or other ladder line, no part of the feedline becomes a portion of the radiator.

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. However, the 2nd ed contains a lot more material than the 1st, and the new 3rd edition contains a lot more than the 2nd, so you must be the judge of what to copy.

Walt
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« Reply #51 on: November 16, 2009, 07:53:15 PM »

Rob
I think the disadvantage would be that the 450 window line would change tuner settings in various WX conditions. I took a dive for the W7FG ladder and I like the concept of a continous wire that goes from ladder line to antenna wire without splices and a failure point from bad connections, which are plaguing me now.. The 450 ohm doesn't hold up very well in Western PA. Wx.
.......NEVER run ladder line indoors around house wiring or near anything! Talk about noise pick-up WOW!

Fred
Hi Fred,by dumb luck my ladder line comes in through plexiglass pane in basement casement window and ends about 12 inches later at the flashbox which sits right in front of the window.   Outside the plexiglass pane has banana jacks for the feed so I can pull it away outside if I want to.  So it's mostly low Z coax indoors.   I make my transfer from the W7FG line to the dipoles by using a big tip 150 watt Wahl iron to heat up the joint then I saturate it with silver lead free solder.  Never had a problem but for some reason soldering splices in the W7FG line is harder.  Got to use more flux on them I guess.  

Rob

P.S. Walt tnx for ur work with your FB book & looking fwd to the next edition
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« Reply #52 on: November 16, 2009, 08:21:36 PM »

Walt, Thanks for posting.  I wonder if you can comment on my situation:

I have a about 130 ft of wire 50ft up horizontal.  The ends are puilled down as my property is not wide enough. About 20 ft on each side of the antenn angles down.

I ran this with 450 ohm line for a year using the KW Johnson tuner.  The line ran out a plastic pipe in the wall the over wooden stakes until going straight up to the antenna.

I lowered the antenna, Cut the 450 ohm line off, Soldered on 600 ohm open wire line.  Ran this through the wall.  This line goes UP the house, over the roof and then arcs to the antenna.

To the locals on 40 meters I gained 20!!! DB.  These guys use Back yard verticals.  On other bands I cant honestly tell the difference.  Why the huge gain on 40? 

By the way, 20 is very hard to tune.. I can get it to 1.8 to 1 but the tuner is out of range and reads 0 and 1 on the Caps. 
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« Reply #53 on: November 16, 2009, 08:29:25 PM »

Quote
I have both a quarter wave vertical (with radials) and a dipole @ 110' average height.  The dipole is a half wave for 80m, and thus a quarter wave for 160m.  I get much better results all over N. America with the vertical, except for within a 100 mile or so radius, which is limited by the skip zone.  In Nashville, roughly 50 mi. as the crow flies from here, I am 30 dB stronger with the shortened dipole.

But for receiving, the best solution when using a vertical (or any other antenna for that matter) is to have available one or more separate receiving antennae.  Besides my beverage, I have a rotatable indoor loop for 160.  Nearly every time, the vertical is the worst of the 3, but occasionally it outperforms the rest.  I  have a rotary switch for all my receiving antennas, and when I first contact a station, I always try all the antennas to see which one performs best on receive.

Thats fine for you, myself and others that have the room for a Beverage farm. I'll be the first to admit my DX totals would plummet real low if I was stuck with the TX antenna only. My station has been known for its ability to hear on 160/80.


Quote
If the horizontal antenna is fed at the mid point, the feeders come off at 90 from the antenna for at least a 1/4λ run and the feedline is kept a reasonable distance away from large metallic objects, the feeders should be essentially balanced.  The frequency of operation has nothing to do with it.

The feedline has to drop vertically and not in the plane of the antenna otherwise antenna mode RF will be coupled. In the real world not many have 130-140' available for 160 and even 60-70' is not an option for 80.  Any deviation from the ideal can have an effect and cause feed radiation.

Quote
"Unbalance" in open wire feeders actually translates to balanced currents in he feeders plus common mode currents.  Eliminate the common mode and the current in the feeders is perfectly balanced.

Easier said than done which is the problem. When you stop spouting strictly theory and then try to apply it to a typical hams yard things fall apart fast.


Quote
If the antenna and feedline are configured as described above, the primary cause of common mode currents and therefore unbalance is that the open wire feeders are trying to function as a Marconi antenna.  This happens most often because the output from the tuner is not isolated from ground.



Id say it contributes to a large degree but just bringing the line into a house and thru a part of a basement full of electrical wiring and copper pipe will cause unbalance. If the shack is at an upper level or attic and right next to the outside wall it is minimized or a non issue. Coax doesnt care where it is run.


 
Quote
A Marconi antenna has to have some kind of ground plane to function.  If the open wire feeders are isolated, or "floating free" from ground, there is no opportunity for them to behave like a Marconi.
 

Thats true for an efficient Marconi. However the basement scenario mentiond avove allows plenty of capacitive coupling to grounded and ungrounded metal.

Quote
The most effective way to float the feeders from ground is to use a balanced link-coupled tuner, and do not directly ground the midtap of the secondary coil.  To drain off static discharges from the antenna, ground the mid-tap of the coil through an rf choke.

Those contemporary, bogus, "balanced" tuners that use an unbalanced L, T or Pi-network, feeding a balun that is inserted between the tuner and open wire line, are just begging for common mode currents, feeder current unbalance and feedline radiation.


The more elaborate the tuner the less efficient it can become and becomes a chore to tune and is rather narrowband. Unless you live on a net frequency it becomes a royal PITA to QSY. I tried several iterations of open wire antennas and tuners and always went back to coax. Ive no use for tuners period.

QST finally got off their dead butts in the 90's and did the first indepth evaluation of the commercial tuners. Some with poor LC ratios lost substantial power and MFJ's were notorious for catching on fire when on 160M.  And that was coax to coax!


Quote
There will be no more RFI in or nearby the shack with OW line than with coax, if there are no common mode feeder currents, either at the fundamental or harmonic frequencies.  Coax can just as easily have radiation from common mode currents circulating on the outside of the braid.

True but the sleeve balun aka common mode choke has been around for around 40 years now and there is no excuse for coax line radiation.

Quote
Think of coax as a three-conductor feedline.  You have the central conductor, the interior of the shield braid and the exterior of the shield braid, each functioning as an independent feedline conductor.  The currents in the central conductor and the interior of the shield braid must be equal and opposite and thus balanced at all times.  Common mode currents reside at the exterior surface of the coax, and the whole thing may radiate as a large-diameter copper tube serving as a Marconi antenna.


Im well aware of the issue and wrote a few articles on the subject in the 80's aimed at obtaining high impedance from the sleeve balun as well as being broadbanded.

OTOH OW is a 2 way street having both modes on the surface which often defy removing the common mode.

Quote
Unless you are equipped to measure feedline radiation over its total length (read Maxwell, Krause, Jasik, military publications, etc about voltage and current peaks and nulls) dont say it doesnt exist.
It doesn't exist if there are no common mode currents on the feeders


Which brings us full circle. The Army Signal Corps spent years trying to attain perfection at comm centers during WW2 and after. Bringing OW into the TX building didnt work no matter what they tried for tuners. Why do a few hams with less credentials think they are better?

Quote
Regarding efficiency, I use 140' of coax to run between the shack and the antenna  tuner shelter at the base of the tower, and open wire line up the tower to the antenna.  When I first installed it, I used some very expensive N.I.B. RG-214/U coax, with silver plated central conductor and double silver coated braid, and supposedly extremely low-loss dielectric.  I got a good deal on it from a satellite TV dealer; I never could have afforded to pay full price. Because of its reputed low loss, it was used in big dish satellite systems to run at microwave frequencies from the LNA in the dish to the down converter.  I ran an efficiency test, assuming that for 160m it would be nearly 100% efficient.  Using a 50Ω dummy load at the far end and after checking to make sure I had 1:1 SWR at the transmitter end, I loaded the transmitter up to exactly 100 watts.  At the far end, the power into the dummy load measured only 93 watts.  I was losing 7% of power at 2 mHz in a 140' length of that super-efficient coax. (It became much worse after rodents chewed holes in the jacket and it became contaminated with water.)

Many fell for that trap and before RG-214 it was RG-9B. The dielectric is the same as RG-8/213 and that is what determines the loss. And silver plating does squat at HF and even most VHF. All the dual shield offers is close to 100% shielding effectiveness. To eliminate the rodent problem I use all CATV hardline including the 750' run to the Beverage switching center.

Quote
...open wire can have its uses for some, such as very long runs to an antenna...


Quote
Actually, open wire line is most useful for long runs only if it is operating at a relatively low SWR.



Agree. The literature is full of installation details from MF to VHF, past and present. I know a few running in the 750' to a quarter mile range to get to antennas on top of a hill, and in a swamp.


 
Quote
A  long, resonant feedline tends to be very high Q and sharp tuning. The reason is that the long line is a series of quarter-wave resonant sections end-on-end.  The length of the quarter-wave section varies with frequency.  These changes in length are additive over the total length of the line.  What might amount to a small percentage of variation across an entire band with a quarter-wave or half-wave resonant feeder system, will amount to a substantial fraction of a wavelength over a feedline several wavelengths long.

Many of the vintage installations were to feed rotary antennas when OW was used right to the feed point. They reportedly worked very well. My contemporay comments are for those monoband antennas that switch to coax thru a stub and balun or thru a LC network. Im sure the balance is far from perfect but a little feedline radiation at almost ground level way out thru the woods is of little consequence. Since those antennas are used by serious contesters and DXers a transition to coax is also done at the house. Nobody wants the hassle of a tunner in those situations.

The feed to my 160/80/75 Inverted vees is about 450' of 3/4" CATV hardline where losses are measured in tenths of a dB even when the 160 VSWR gets to around 3:1 at the high end as its cut for low end DXing. Any pi network can be adapted to the situation at hand as it is, in reality, a tuner.

Quote
Here is an example:  You have on 80m antenna fed with open wire tuned feeders, and you want to operate on one frequency on the CW band and one in the phone band, so you choose 3563 and 3938 kHz (numbers chosen here for easy approximate calculation).  Centred on the middle of the band, 3750 kHz, that range of variation represents 10% of the total frequency/wavelength (3750 kHz plus and minus 5%). 

If you use a quarter wave resonant feeder, when you go from the CW to the phone frequency, the tuner has to compensate for a change in resonant wire length of only 5% of a wavelength (10% of the quarter-wave leg of the antenna plus another 10% of the quarter-wave feeder = 10% of a total wire length of half a wavelength = 20% of a quarter wavelength). 

But say you move the antenna farther away so that now a 1 3/4λ feedline is required.  Adding in the quarter-wave leg of the antenna, we now see that each half of the symmetrical system now consists of two wavelengths of wire. So now, when going from the CW to the phone frequency, the tuner must compensate for a change in resonant wire length of 20% of a whole wavelength.  This calculates to 80% of a quarter wavelength.

Looking at the standing waves on a resonant line, voltage and current loops are exactly a quarter wavelength away from voltage and current nulls.  So in the first case, changing between the two frequencies moves the relative position of the feedpoint 20% along the way between a current loop and a current null. Almost any link coupled balanced tuner could handle that much variation by changing the setting of the split-stator tuning capacitor, without having to tap down on the coil or change from series to parallel tuning. 

But in the second case, the feed point has moved 80% of the relative distance between a current loop and a current null.  Therefore, you would have to toggle between series and parallel tuning to cover those two  frequencies in the same band.  Since any change in frequency moves the loops and nulls a relative distance that  is multiplied by the number of quarter waves between the transmitter feed point of the open wire line and the ends of the antenna,  as the length of the tuned feeders is increased the tuning becomes increasingly more critical, and eventually series or parallel tuning won't hold across the entire band.

The  same phenomenon occurs when using the same feedline and antenna on harmonics to cover higher frequency bands.  You might be able to use one tuner configuration on 160m, but using the same antenna on 10m you might have to change from series to parallel tuning to cover the entire band.

Ive tried OW at several QTH's over the past 54 years as a ham, none were what I called satisfactory and were mostly something to get up quick after moving that worked to some fashion on many bands. The only tuner that really worked well was a series/parallel affair from a late 40's QST and switching was a Rube Goldberg affair that was part patch panel and part plug in coil swapping. Not exactly QSY convenient.

The bottom line is that OW works for some who remain a minority. You learn to work with what you have with OW or coax. And the last thing that is needed is trying to jam opposing views down anothers throat.

We dont need another war on here.

Carl
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« Reply #54 on: November 16, 2009, 08:48:39 PM »

Quote
Another point that is often misunderstood is that although antenna currents on the radiator result in radiation, antenna currents cease being antenna currents at the junction of the antenna and the feedline, and now become transmission-line currents. When the conductors of the feedline are sufficiently close to prevent radiation, transmission-line currents do not result in radiation. Consequently, with the spacing normally used in open-wire, or other ladder line, no part of the feedline becomes a portion of the radiator.


Walt, That only holds when either a current or voltage peak is at the feedpoint. Otherwise the antenna will attempt to be down at some point on the feedline This will be true if say the antenna is cut for 3900 and you decide to work at 3550. Its more pronounced in the G5RV where feedline radiation is a part of the design and the bottom of the required length feedline usually goes these days into a ferrite balun with choke beads on the coax to the shack.

Then there are tuned feeders and untuned (nonresonant) feeders to contend with and there are pros and cons to both.



Quote
To the locals on 40 meters I gained 20!!! DB.  These guys use Back yard verticals.  On other bands I cant honestly tell the difference.  Why the huge gain on 40?

Id say that you now have a large vertical component to the radiation.

Carl
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« Reply #55 on: November 16, 2009, 09:13:28 PM »

Very interesting thread.......
As for feedline radiation......u will see in the picture that my feedline is within 5 ft. of my operating position and no rf problems. I run a 4x1 by 833'3 with no problems. In the pic u will see a relay at the top of the picture and its used to switch the balanced line between the tooner on the dryer and a KW matchbox. The spacing of the home made line is 4 inches in the shack and increases to about 7 inches up to the antenna. U can see the change where the feedline goes thru the window. It aint pretty but it works and I didnt use any complicated math the build it Wink

Bill  

BTW.....someone told me that  the feedline spacing had to remain the same or else I would have problems. Looks like nobody told that to the feedline... Roll Eyes


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« Reply #56 on: November 16, 2009, 09:47:56 PM »

Bear,

I will attempt a crude answer to ur question but a caveat:  I am not a physicist or E.E.:

It's important to understand that the virtues of parallel feed can only be enjoyed in a balanced system.  In the visual physical sense, that means antenna symmetry across the feed point, symmetry between the sides of the feed with respect to each other, and a genuine low Z unbalanced, to high Z balanced, matching network.    In my opinion, you can fudge some of this a bit -- maybe the spacing on the feedline wires is something other than 3 inches when making some turns outside, or one side of the dipole is a few feet closer to ground than the other -- these things are not a big deal.  If your current on one side is 97% of the other side the system is essentially balanced.   I get the sense from balanced feedline detractors (elsewhere!) that anything other than total perfection is a useless disaster.  Not true.

In the balanced system, the RF current exciting the dipole is moving in equal but opposite directions.  Because of this the electromagnetic fields, one on each wire oppose each other in their rotation and collapse.  Therefore, the line does not radiate.  Because of the physical construction and design of the line, there is this equal but opposite symmetry, even with high standing currents and voltages, so line loss is still very small.  The air dielectric prevents flashover and damage due to heat (except that Fred seemed to do some window line melting so it might be a good idea to stick with the 600 ohm stuff).   The currents in the line oppose each other because each side takes a turn handling return current with each RF cycle (see http://www.tfcbooks.com/special/antenna.htm for a visual diagram of this with the field lines of force about the dipole).

With coaxial cables the RF current flows on the surface of the center conductor and the inside surface of the shell.  The electromagnetic field is propagated through the dialectic and this works fairly well if there are no high voltage and current standing waves on the line although if the line is high quality it may withstand them.  The line is unbalanced because the shield is grounded.   It can work well when the antenna feedpoint Z is relatively close to the coax characteristic Z but there is more loss with high standing waves due to the coax design which has some leakage and resistance losses (how it works here:  http://en.wikipedia.org/wiki/Coaxial_cable ).  I'll freely admit to fudging on this last part because I do not intimately understand the inner workings of coax and to be sure, a large air dielectric coax such as heliax may handle an extreme missmatch between it and an antenna without much loss.  In fact LDF6-50A with a vswr of 6:1 has a swr loss of 0.194 dB for 300 feet on 160 meters.  Not bad, but feeding a high dipole with LDF6-50A may be difficult  Grin  My feedline loss calculations were done with this online calculator:  http://www.ocarc.ca/coax.htm

It's important for AMers that even under ideal condx on low frequencies, a long run of common ham coax such as RG213 can have unacceptable losses (to me at least).   For example, 300 feet of 213 on 160 meters to a 50 ohm load has a loss of 0.78 dB.  That may not seem like much but it is part of accumulated system losses such as loss in the tuner at the feedpoint, and antenna inefficiencies most of us can't avoid.   Unlike some modes such as PSK31 where a ham can get by with a poor antenna, I think for AM losses have to be reduced as much as possible because we are handicapped to begin with due to the power limit.

After doing some thinking about coax v. ladderline, I concluded that there is really not much need for argument because I looked at the pros and cons of each and, assuming a dipole fed with coax and a feedpoint choke balun really does not pick up any common mode noise, the advantages of a balanced system seem to pertain to transmitting (sw bc stations don't have to do any receiving  Wink ) and the advantages of coax seem to favor receiving.   Don sort of beat me to the punch on this but before anyone takes down their ladder line fed dipole and puts up a coax fed one because of RFI, why not use the balanced antenna for transmitting, and set up a separate coax fed rotatable rx loop or small low rx dipole?   I'm going to give one a try -- perhaps that will save me from having to walk around the neighborhood with a noise sniffer.  

73

Rob
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« Reply #57 on: November 16, 2009, 09:53:04 PM »

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I get the sense from balanced feedline detractors (elsewhere!) that anything other than total perfection is a useless disaster.  Not true.

How true.....how true.....
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« Reply #58 on: November 16, 2009, 10:03:34 PM »

Quote
Another point that is often misunderstood is that although antenna currents on the radiator result in radiation, antenna currents cease being antenna currents at the junction of the antenna and the feedline, and now become transmission-line currents. When the conductors of the feedline are sufficiently close to prevent radiation, transmission-line currents do not result in radiation. Consequently, with the spacing normally used in open-wire, or other ladder line, no part of the feedline becomes a portion of the radiator.


Walt, That only holds when either a current or voltage peak is at the feedpoint. Otherwise the antenna will attempt to be down at some point on the feedline This will be true if say the antenna is cut for 3900 and you decide to work at 3550. Its more pronounced in the G5RV where feedline radiation is a part of the design and the bottom of the required length feedline usually goes these days into a ferrite balun with choke beads on the coax to the shack.

Carl
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Carl, I'm sorry, but I have to totally disagree with you concerning the antenna attempting to be down at some point on the feedline. That is one of the mistakes Louis Varney made in describing the action in his G5RV antenna, and which has been repeated over and over by those who swallowed his misleading explanation of the voltage and current distribution along the antenna and feedline. I'm preparing a post concerning the misleading aspects of his presentations that appear to make the G5RV something that it is not, especially the 34 ft open-wire section that he erroneously calls a 'matching section'. It is his incorrect explanation of the current distribution in the OW section of the G5RV feedline that has helped give that antenna a reputation as a superior radiator that it doesn't deserve. The G5RV will not radiate any more RF energy than any other single-wire radiator of the same length when fed with the same power.

In addition, as I've said in previous posts, when the antenna system is truly balanced, radiation from the feedline is insignificant, the G5RV included.
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« Reply #59 on: November 16, 2009, 10:08:46 PM »

Walt,
If u dont mind.......as u said in an earlier post......I will start to scan your book in pdf format. This will take a LONG time........its a big book!!!

Bill
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« Reply #60 on: November 16, 2009, 10:31:53 PM »

Suggestion Bill. Why not review the chapters already in pdf on my web page, and then download them. It'll save you a lot of time and effort compared to scanning every chapter. Consequently, I'd only scan the portions of the book that don't appear on the web page. In addition, if you're copying from the 1st edition, there has been some rhetorical editing between that edition and the 2nd. And further, there are more chapters in the 2nd ed than in the 1st.
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« Reply #61 on: November 16, 2009, 10:32:07 PM »

Walt, I look forward to your post on the G5RV antenna, lots of folks use those, but they never made much sense to me as it was explained. Quite interested in what you have to say.

Bill, good to see you here and thanks for the effort!
As someone else pointed out Walt shares a good amount of his book online, so some the chapters are already in digital form. Will save you some trouble, see w2du.com/Reflections2.html.
Seems that chapters 4 - http://w2du.com/Chapter04.pdf, 7 - http://w2du.com/Chapter07.pdf, and 20 - http://w2du.com/Chapter20.pdf address many of the questions the fellows are asking in this thread.

And thanks Walt for being so magnanimous with sharing the info.
I sure wish the W4RNL site was still "open", I find the current situation confusing to say the least.

-Bruce
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« Reply #62 on: November 16, 2009, 10:42:15 PM »

I look forward to the post also.  I was talking to Timtron one night last winter.  We talked until 3am.. LOL.  He switched between 4 antennas.  To our amazement the G5RV beat them all to Arizona.  He said he found it in the trash at a hamfest and through it up about 30ft in the air. 

c
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« Reply #63 on: November 16, 2009, 10:47:03 PM »

Clark, to answer your question about why you gained 20 dB on 40m when you changed to open-wire feedline, I can only think of one reason. You said the radiator is 130'. On 40m this is approximately a full wavelength, which means that the feed-point impedance at resonance will be in the neighborhood of 4000 to 5000 ohms. This impedance presents a huge mismatch to feedlines of 450 ohms or less with plastic insulation, which have much greater attenuation loss than open wire at high values of SWR. On the other hand, going to open-wire the attenuation loss is reduced very significantly, hence the greater signal. But 20 dB? That seems greater than I would expect for that change. There may be another reason that escapes me at the moment.
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« Reply #64 on: November 16, 2009, 10:50:45 PM »

Walt, that's extremely generous of you to provide permission to copy your book, and truly in the amateur spirit!

And kudos to you also, Bill, for volunteering to copy it; that's very generous of you as well.  As Walt said there's already a fair amount of it already on his website, so save yourself a bit of work  Grin
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« Reply #65 on: November 16, 2009, 10:57:52 PM »


I sure wish the W4RNL site was still "open", I find the current situation confusing to say the least.


All you have to do is register....
No more difficult than to register with this site.

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« Reply #66 on: November 16, 2009, 11:22:18 PM »


To the locals on 40 meters I gained 20!!! DB.  These guys use Back yard verticals.  On other bands I cant honestly tell the difference.  Why the huge gain on 40? 


This is a VERY simple question to answer, Clark.

Cross polarization = approximately 20 dB.

You now have power being radiated in the vertical plane, and the horizontal plane.

When you said the guys where using verticals, that made sense of it.

Now, the question is, did you have the SAME length, and approximately the same path, or is it both completely different? 

--Shane
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Patrick J. / KD5OEI
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« Reply #67 on: November 17, 2009, 01:23:16 AM »

I should have mentioned in the earlier post that the 3rd ed will have everything that appears in both the 1st and 2nd eds, plus several new chapters. So why don't you all wait for the 3rd? As I said, I'll keep you informed.

Walt

It'll give me something interesting to read over the holidays. No telling when III will come out. Good new books are scarce, the rest all seem dumbed down these days.

ah but never mind, Bill may scan it. I can download the existing chapters and read them off the site as well.

thanks,
Patrick
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Don
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« Reply #68 on: November 17, 2009, 04:28:05 AM »


To the locals on 40 meters I gained 20!!! DB.  These guys use Back yard verticals.  On other bands I cant honestly tell the difference.  Why the huge gain on 40? 


This is a VERY simple question to answer, Clark.

Cross polarization = approximately 20 dB.

Polarization would make a big difference for local ground-wave coverage, but ionospheric propagation is so turbulent that the polarisation of the signal becomes random at the receiving end.

As for the balanced line coming off the antenna at 90, I say if everything is truly balanced, it doesn't make any  difference whether the feeders run horizontally, vertically or slanted as long as they remain perpendicular to the antenna. If the antenna and feed line are indeed configured symmetrically, there would be negligible coupling between the radiating antenna and feeders.  Nearby metallic objects such as plumbing, overhead electrical wiring, house wiring, smokestacks, etc may upset the balance, but if there is reasonable separation between antenna system and stray objects, those unbalances would be too negligible to worry about.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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This message was typed using the DVORAK keyboard layout.
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« Reply #69 on: November 17, 2009, 07:17:59 AM »

Anyway, I walked outside with a field strength meter the other day and the feed line is radiating. I knew something was wrong as soon as I hooked the antenna up and turned on the receiver. The feed line makes the antenna sound just like an ungrounded 1/4 wave 160 meter Marconi antenna.

   I have been reading this thread with an awe of fascination while I am learning from you antenna gurus. This has been great. That said, I think everybody has it wrong. The solution is far simpler, and on the sinister side. Let me explain. My dear XYL of nearly 25 years has learned how to get me out of the hamshack. She knows which electrical appliances in the home cause RFI such that my joy of listening to the ham bands turns into a maddening session of frustration. I eventually turn off the equipment and come back into the house. There is the wife sitting at the couch looking all pretty and innocent. She asks me if i want to watch a DVD (a chick flick). So in the end, she was not so innocent, and she has smoked me out of the ham shack by creating RFI.

   So Brian, is your noise issue in any way similar to mine? Maybe it is the XYL running a hair dryer for a timed duration after you enter the hamshack? The wife of a ham has to get creative you know.... Grin

73,
Jim
WD5JKO


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The Slab Bacon
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« Reply #70 on: November 17, 2009, 08:25:58 AM »

BTW.....someone told me that  the feedline spacing had to remain the same or else I would have problems. Looks like nobody told that to the feedline... Roll Eyes

Good one, Bill
this reminds me of a situation we did a few years ago.....................

the last year that we did the W3F special event station from the Howard County Fairgrounds in West Friendship, Md. Dave (K3ZRF) brought a W7FG complete ladder line fed diaperpole. Al (KZ3AB) shot us up some lines with his easy-hang and the antenner itself went up fairly easily. However............ it left us with another problem. The feedline would only reach the very back of the building (a 100' horse shed)

With no additional feedline in our arsenal, Gary(W2INR), Joe (N2YR) and myself stood there and scratched our heads for a few minutes and came up with "ladder line on the fly" Luckily, Joe had brought a full spol of #12 THHN wire. We spliced it in with wirenuts, and stapled it to the wooden support posts for the building, spacing it at an eyeball 6".

Many of the "ricebox hams" looked at and swore it wouldnt work, and really laughed at wirenut splices. And especially the 100' run of it.

It took my 4x1 transmitter at full strap, noone ever told the feedline that it would'nt work,
the RF didnt care, we had no problems with RF geting into the audio and....................
WE PUT OUT A STRAPPING SIGNAL!!

So the bottom line is that the feedline will work as long as no one tells it otherwise! !   Shocked  Grin

                                                                  The Slab Bacon
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"No is not an answer and failure is not an option!"
Steve - WB3HUZ
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« Reply #71 on: November 17, 2009, 09:45:45 AM »

I told my dipole that it was a four-element beam. I have the signal reports to prove it works.   Wink


http://www.amwindow.org/pix/htm/fallfest02/ff4.htm
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The Slab Bacon
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« Reply #72 on: November 17, 2009, 10:35:35 AM »


Steve, those pix were from '02. that was the first year at How Cow. Do you have any from '03? ?  that was the second year up in the barn. Someone took some pix of the feedline, but I dont rememba who it was.
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« Reply #73 on: November 17, 2009, 10:37:02 AM »

I have run mostly resonant dipoles fed with coax for the last 30 years, but have tried the open wire line, g5rv, trap dipoles, verticles, the B+W folded all band disaster, and other setups.
The G5RV was tunable to a lower swr, but not a great performer on 80 meters.

A well built dipole fed with coax is quite broad banded, has no real power limit, does not need a tuner if run into tube gear, and if put up well, is a maintance free antenna.

In my case, not having much ground, the antenna's are close to the house, so coax runs are under 75 feet.

I really like the no tune part, pick a band, pick a rig (its already tuned up), pick and antenna and go.

No tuners or baluns to worry about or waste any power, no rfi in the shack.
Rain, snow, ice, does not seem to change the swr.

I suspect there are better receive antenna's from a noise standpoint, there are antenna's with gain, and 160 meters is its own thing, and DX is another thing, but for the usual 80 and 40 meter AM operation I do, it seems hard to top a dipole.

If I had room, I would like to try a good 160 meter dipole fed with open wire line and a balanced tuna.
But I dont.

Brett


 
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« Reply #74 on: November 17, 2009, 11:14:55 AM »

I have always preferred a matched dipole cut and tuned to the frequency band. They always work well.

I have had many problems with multi-band wire antennas fed with open wire, usually due to poor tuner design and high voltage breakdown.

Pat
N4LTA
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