DID I Blow up My RF Ammeters?

[W2VW]

It's #16 G 26 strand wire.
My configuration for the antenna is 125 feet of feedline and 240 feet antenna.
70 foot high VEE ends 40 feet high
Maybe these numbers help with what is happening in radio land.

Fred

Roughly a resonant doublet on 160. Your feedline is slightly longer than a 1/4 wavelength when velocity factor is applied and is transforming the low impedance at the feedpoint to a very high impedance at the antenna coupler. The ammeters won't budge. Many "tuners" wouldn't tune this config at all. Try it on 80. Those ammeters will read like you are in series with a cantenna.

EDIT. They won't read much on 80 either. Duh.

[k4kyv]

The total length of one feeder plus one leg of the antenna is what determines the resonant frequency of a balanced open-wire fed dipole.

Bingo, that's exactly what I have been saying. Each leg of my antenna is 65' and the open wire line is 80'. It's a center-fed Zepp.

So, 65' + 80' = 145 = 1/4 wave at about 1.6MC.

The total length of the antenna is now 290' = 1/2 wave at around 1.6MC.

So what does the surge impedance of the parallel conductor open wire line have to do with it?

I'm changing it to the close spaced #14  390-ohm cheap stuff. I've used it many times before and it doesn't react in the same way at all. The feedline will act more like feedline and not just lengthen each antenna leg as much.

Assuming approximately a half wave radiator,  that will happen only if the impedance of the transmission line approaches the impedance at the mid point of a half wave dipole, usually about 70 ohms in a real world installation.  Anything as high as 390 ohms will be a resonant feedline and the feeder length will add to the dipole leg length to determine the resonant frequency.  The added length is strictly a function of the length of resonant wire, even in the case of coax running at high SWR.  One factor that may make a difference is velocity factor.  Solid 300-ohm ribbon and even that crap with the rectangular holes punched in the ribbon will have a higher velocity factor than true open wire line, and will  lower the resonant frequency.  But real open wire line with two wires spaced together with plastic spreaders every 6" to several feet, will be minimally affected by the insulation over the wire or the spreader material and display a 97% wavelength velocity factor, even if it is el-cheapo stranded #16 wire with PVC tubing for spreaders.

[WA1GFZ]

Air is 1 any other material is lower than 1

[ke7trp]

Hi Fred,
   I originaly had 130 ft of 16G copper wire up with 450 ohm Solid conductor line. This was a factory made antenna given to me. It was made by Van Gorden.  Called the ALL BANDER.  It tuned wonderfull on every band of my KW matchbox. I had a BIG signal on all bands. 2 years in the AZ Sun made the ladder line turn white.
  I replaced the 450 ohm line with 600ohm True ladder line.  I ordered 200 Ft.  I used 85 for my feed.  Ran it up the house and over, then up to the antenna.

I had a HUGE increase on 40 meters.  About the same on 75.  I lost 20 meters.. Cant tune it below 2 to 1.  10 and 15 tune great.  I worked the world on 10 just last week.

I have checked the balance and I to cannot get an RF ammeter to read.  I only have one.  I ended up using light bulbs and they where the same brightness when tuned flat.  My old meter might be bad... I have not checked it.

I wanted to list out the lengths for 600 ohm line from Tip of antenna to end of open wire line for this antenna config. This info is listed in several books. I had Bill orrs on my desk:

L is the flat top measurement. 
S is the ladder line length.

L + S should equal one of FOUR measurements.

110 ft
133 ft
177 ft
212 ft


I think this is where people are having trouble.  Your antenna is the correct length.  Mine is not and Brians is not.  The book explains that if you dont have one of these four lengths, The antenna will have trouble tuning on some bands.

Clark

[ke7trp]

Brian,  YOU GOT F*&^(*.   

I just counted mine.. 26 Strands. 16AWG.   Oil resistant, 600 volts.


Clark

[ke7trp]

Yeah.. I agree.  I had 450 ohm line.. It tuned FLAT on every band, mid cap on my KW matchbox.

With 130 ft of line and 85 to 90 ft of this 600 ohm line, I just measured resonance at 3.990.  The 450 ohm line measured 3.600.


Clark

[K5UJ]

My 130 foot long center fed dipole is fed with around 90' of ladder line.  When I put up my new dipoles last summer I re-read the business about the "magic ladderline length" i.e. an odd multiple of 1/8 wave at the lowest frequency for the antenna and attempted to follow that just for the heck of it.  I never paid it much attention in the past figuring the tuner would deal with whatever length I used.  I decided there must be something to it because the matchbox tunes the dipole like a dream on 80 40 and 20.  I have not tried it any higher because I have a separate smaller dipole for the high bands, but I did the same thing with it re the length of the line, and the matchbox tunes it on all bands 10 to 20 including 12 and 17. 

Brian it sounds like you got a bad deal on that ladder line.  I guess it is too late to get a refund.   I ordered 200' last summer and got the right wire, the 26 strand no. 16.  My hunch is that the new guy who took over the business after W7FG went sk probably didn't know what he was doing at first and used the wrong wire until someone set him straight.  Just a theory; doesn't make it any better.  You never know until you try--I'd call them up and explain what you got for your money and see if they'll offer some kind of credit, or refund or something.  You have nothing to loose.

Rob

[Opcom]

Thanks for showing the cheap-o ladder line. I had no idea such cheezy line was being touted as full bore product.

[KF1Z]

Number of strands is irrelevant, except in flexibility.

Stranded wire is available in many different strand/lay configurations.

For #16 that can be anywhere from 7 conductors to about 445 conductors.

The nominal OD of the conductor will be anywhere from 0.0508" to 0.0670"

Could also be noted that some strand/lay configurations of #18 wire, will be larger in diameter than some strand/lay configurations of #16 wire.

And then, if we're talking about tinned, plated  (sucha as copper clad steel) then there's another whole set of parameters that gets thrown in.


If you can tell you didn't get #16 wire, just by looking at it.... your doing pretty darn well.
Most people would have to mic the strands.

However, since it's advertised as "16 guage 26 strand..."  you may well find it easy to get your money back INCLUDING any shipping costs, as the product was definately misrepresented.


I don't see though, how it would be possible for the impedance of the line to be over 1000 ohms .. it would take more than a 0.01" change in wire diameter to make that kind of difference!

[WA1GFZ]

or the load Z and the right length of feeder that transforms the input Z higher. This is why you have to terminate the line to test it.
I suggest you plug in your numbers to the HUZ provided transmission line site and see what happens.

[Ed/KB1HYS]

If you are using 600 ohm line (say 12 awg spaced 6 inches which is 586 ohms) to feed a center fed antenna then depending on the FREQUENCY you measure it at you can see an impedance anywhere from 70-5000 ohms at the transmitter end of the line!   If you are using 300 ohm line the impedance seen at the transmitter end drops to 75 -1200 ohms - depending on the frequency you measure it at.

This is a function of the transmission line making an impedance transformation (based on the electrical length of the line - which is frequency dependant) of the impedance seen at the antenna feed point.

The simplest example of this is a quarter wave stub. At the fundamental frequency (the one that determined the length) a dead short on that stub will appear as an open (and vice versa). At the second harmonic of that fundamental frequency, this same line is now a half wave long and will show a short when shorted and an open when open.  So this same line, terminated the same way, will have an impedance varying from zero (short) to infinity (open) based on frequency.
 
This same transformation occurs regardless of the termination impedance. So if you have a simple dipole at around 72 ohms or so at the feed point, the transmission line will transform this impedance to something else, unless you are feeding it with an exact electrical half-wave long feeder.  This means that (almost) any multiband antenna that does not use some type of matching system at the Antenna Feed Point will see widely varying impedance based on frequency. The combination of antenna feed point impedance change (due to being on a different frequency than it was cut for) and the feed line transformation (due to varing frequency changing the electrical length) results in the impedance range we see at the transmitter end of the feed line.

The smith chart was created to simplify the calculations for feedline impedance based on electrical length (it can do a lot more too!) Down load a Smith Chart Simulation and run scenarios and you can see this effect quiet clearly. If your a book person, there is a good smith chart chapter in Practical Microwaves by Laverghetta with simple examples you can work for your self.

This is also covered quiet well in some of the older handbooks that deal with balanced line with much more detail.

[Ed/KB1HYS]

attached is a chart from Bill Orrs Radio Handbook, 15th ed. This shows the effect on the impedance at the transmitter end for a multiband antenna with feeder and element lengths vs frequency.

The chart is for 300 ohm line, but the ratios are true for 600, just the impedance values change due to the higher Zo.

[Ed/KB1HYS]

Ok, if we look at a case where your transmission line is an  odd multiple of quarter wavelengths (simplest case) the input impedance is given by

Zin = Zo^2 / Zload  where Zo is the characteristic impedance of the line, and Zload is the load as provided by the antenna.  So if your antenna impedance is  72 ohms where your Feed line is also an odd multiple of quarter wavelenght the input impedance becomes:

(600^2) / 72 = 5000 ohms.  So if you have a half wave dipole (72ohms) fed with 600 ohm line that is 3/4ths wavelength long (or any odd 1/4 wave multiple) you will see 5000 ohms at the end of the feeder in the shack.

If you know both the real and imaginary values you can calculate the impeadance at the transmission end for any length of line.  The formula for that is:

Zin = Zo ((ZL+jZotan(betaL)/(Zo+jZLtan(betaL))   (sorry I can't do symbols here)
Where Zo = characteristic impeadance of the line
         ZL = load inpedance
      Beta = 2PI / wavelength (in the transmission line used NOT free space this is called the wave number)
and L = length of line between the Load and the point you are calculating to.

The only time a transmission line will ever measure as it's characteristic impedance (Zo) is when it is terminated in a purely resistive value equal to Zo.


Also, all these equations assume a zero-loss or lossless transmission line. It's a handy assumption that doesn't effect accuracy too badly but makes the calculations much simpler (my calculus is sooooo rusty).

[flintstone mop]

Brian,  YOU GOT F*&^(*.   

I just counted mine.. 26 Strands. 16AWG.   Oil resistant, 600 volts.


Clark

DATS what I has.
Brian you musta gotten the discounted model or the economy version.....geesh
 The length of the antenna part of the system must be the key.
Do you have the real estate to expand your antenna length? It's too short for 160M or is there no interest in 160?

Fred

[ke7trp]

YEah..  I have spent hours and hours on this subject this week.  It seems that its important to get the Top and the feedline set in the octaves of the ham bands.  This way, The tuner wont have to match over 1200 ohms. When this is done,  All bands will tune.

I am going to have to lower my Antenna and measure the feedline out. Once I know that, I can refer to the chart and add or cut until its right.

The big screw up for me happened when I read Lou McCoys book. He states, The feedline and top length does not matter.. String it up and use the most wire you can. 


C

[Jim, W5JO]

The big screw up for me happened when I read Lou McCoys book. He states, The feedline and top length does not matter.. String it up and use the most wire you can. 
C

Lew McCoy made other big mistakes beside this one.

[ke7trp]

So whats best?   There seems to be a line deviding people on this..


Throw up long wires, Run open wire down, Make your own tuner that will tune ANYthing. 

Cut the flat top and feeder so it is in the octaves of the ham band with the goal of not going on 1200 ohms on any band.


People really seem to be devided on this..  I have  a KW matchbox so I cant adjust the coil.  I require an antenna that works with this tuner.. that means 1200 ohms or less.  Others just keep modifying the tuner so what ever antenna they have, Tunes.  If you do this, Are you inducing loss?

C

[Ed/KB1HYS]

There's no one size fits all solution. you put up the best antenna system you can for your situation and adapt.  A dipole cut for the lowest frequency of interest and fed with ladder line works well as a multiband antenna. A fan dipole off off coax also works well.  The much maligned trap dipole fed with coax also works.  Of these three options, the only one that should require a tuner would be the ladder line fed antenna, unless your rig uses a link coupled balanced output tank. (P-P triodes).
A well designed robust tuner will have minimal loss, but some guys don't like having the extra controls of a tuner in the shack, so the go for the simpler options.  Some folks go with a resonant coax fed dipole for each band of interest and just use a switch in the shack no tuning.

the simple truth is nearly any conductive thing can be made into an antenna (trees, gutters, downspouts, wires lying right on the ground, etc. have all been used with success). The rest of the system is up to the wants or needs of the designer.  The "Best" antenna is a beast that has a different face for every station/operator.  You have to ask yourself what are the most important parameters for you at your station?   All band use?  Directivity and Gain? effciency? Compact size for a small lot?  DX (low takeoff angle) use? Local QSO's?   Once you identify the requirements that are imporant to you, and figure out which are the most important (you can't have your cake and eat it too!) you can design an antenna system.

In the end if you are happy with how it work, it is a good antenna!

[ke7trp]

If that is true, then adding length to my Feeder is not going to help.

C

[KD6VXI]

So whats best?   There seems to be a line deviding people on this..


Throw up long wires, Run open wire down, Make your own tuner that will tune ANYthing. 

Cut the flat top and feeder so it is in the octaves of the ham band with the goal of not going on 1200 ohms on any band.


People really seem to be devided on this..  I have  a KW matchbox so I cant adjust the coil.  I require an antenna that works with this tuner.. that means 1200 ohms or less.  Others just keep modifying the tuner so what ever antenna they have, Tunes.  If you do this, Are you inducing loss?

C

Since you can't change the coil, why don't you change the spacing on a section of your feedline.  That would act as an impedance xformer, allowing your KW box to see a different impedance.

Might be a PITA, but could actually get you on the band thats hard to tune now...?  Go from 6 inches to 4 inches for 20-40 feet or so....  You could even play with the location of the xformer to get different impedances AT the tuna.

Add in enough length of existing line, and you'll get something similiar, but I think changing the spacing, AND KEEPING IT IN BALANCE would do you quite well.

--Shane

[ke7trp]

what a major pain. But you know what?   That is a hell of a suggestion..  I bet if I cut that space down, It would work..

C

[K5UJ]

The big screw up for me happened when I read Lou McCoys book. He states, The feedline and top length does not matter.. String it up and use the most wire you can. 
C

Lew McCoy made other big mistakes beside this one.

I got led astray (maybe not the best way of putting it) by an article on horizontal loops in QST around 2002.  One of the things it advised was to just make the balanced feed any length and let the tuner deal with it.   I had a tuner with the range needed to make my feed work okay so I thought that was good sage advice. 

Then on AM, I found that on some frequencies I had a lot of sustained current in the tuner or a lot of voltage at the end of the antenna  feedline (or maybe it's both?) and things were not very good with a 300 w. carrier.   

Some of this advice on antennas and feedline and tuners may work for SSB and CW but not for AM.  I think that may be part of the problem--the HF technical material in the ham literature for the past 30+ years has been written with low duty cycle in mind?  I'm sure the author of the article I read never operated AM, or he didn't mention it if he did. 

Anyway I got rid of the tuner with its toy inductors and put in the KW matchbox.   Now the range was less so I did the thing with making the feedlines an odd multiple of 1/8 w. on the lowest frequency.   On 3.6 MHz (what my dipole was cut for) that turned out to be around 97 feet (3/8 w.).  I fudged some and it is really more like 91 or 92 but it's close enough.  The MB tunes it no problem.   So I advise trying to get the feed 1/8, 3/8, 5/8...wavelength.   In my case 92 feet was longer than I needed so I had to loop it out over the back yard in a wider loop to get it to fit.  The length matters to the matchbox but handles my level of AM power so well that I don't mind adjusting the feed length. 

You can of course build a tuner to tune any Z at the end of the feedline, but if you have a far out Z that the MB won't handle it might be better to work on the feed length because your loss may be high otherwise, in a big tuner with high current on the coil(s).   

Rob

[Ed/KB1HYS]

Putting a switchable section of feed line in the shack is not that hard. There are some guys on the list that do it to enable them to tune the band that gives them trouble.  I think the easiest way is that once you determine how much line you need to add, (often just 1/8th WL of the freq in question) simply put some bannana jacks on the ends and plug it into/out of the system as needed. 
If you want old-buzzardly, you could use a beefy knife switch araingment.

Either way would work FB.

The line transfomer using different feedline spacing does work, look up using shorted stubs as impedance transformers.  I think switching in a few feet of the original feedline is simpler.

[flintstone mop]

So whats best?   There seems to be a line deviding people on this..


Throw up long wires, Run open wire down, Make your own tuner that will tune ANYthing. 

Cut the flat top and feeder so it is in the octaves of the ham band with the goal of not going on 1200 ohms on any band.


People really seem to be devided on this..  I have  a KW matchbox so I cant adjust the coil.  I require an antenna that works with this tuner.. that means 1200 ohms or less.  Others just keep modifying the tuner so what ever antenna they have, Tunes.  If you do this, Are you inducing loss?

C

Clark and others,
I'm thinking that the ops of the past were just happy to get a signal out. THey did not have the sophisticated gadgets we have now to see the shortcommings of improper lengths of feedlines or antenna lines and the impedances and reactance, etc.
Throw it up and tune it up.
Today we're going for the most we can get to be channel masters....yeah!!!

Fred

[KD6VXI]

what a major pain. But you know what?   That is a hell of a suggestion..  I bet if I cut that space down, It would work..

C

Clark,

To test this theory, try throwing 20-30 feet of windowline or something else in line with it.  Then you'd just have to make a support to keep the additional line from flexing or waving in the breeze and coming up on a gutter or downspout.  If it works, change the ladderline your using to have the transformer in it.  If it doesn't, throw the windowline in the garage above the car, and you've lost nothing.


--Shane