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[Articles Home]  [Add Article]  

A Multi-Band 33 Foot Dipole

Cecil A. Moore (W5DXP) on February 26, 2014
View comments about this article!

A Multi-Band 33 Foot Dipole

Cecil Moore, W5DXP.com, Rev. 1.0, Jan. 23, 2014


This article describes a simple way to enable a 1/2 wavelength 20m dipole to work well without a tuner on 20m, 17m, 15m, 12m, and 10m. Although it applies to any 33 ft dipole, maximum performance will result when the dipole is made to rotate. The gain is almost as good as a two-element Yagi on 10m (9.5 dBi).

It is an accepted fact that a ladder-line fed 1/2WL dipole can work well on all higher frequency HF bands but it usually requires a wide-band antenna tuner. In a related article on his web page, W5DXP shows how to vary the length of the ladder-line to accomplish no-tuner operation on all of the HF bands using a 130 ft. ladder-line fed dipole.[1] That same basic technique can be utilized to enable 20m-10m operation for a 33 foot dipole.

The transmission line chosen for W5DXP's 33 foot dipole (height=40 feet) is the "300 ohm" transmitting ladder-line (#562) available from TheWireman.com. The estimated Z0 is actually around 288 ohms and the estimated velocity factor is around 0.83. The lengths of ladder-line suggested in this article assume those transmission line characteristics. Other transmission lines, e.g. 450 ohm ladder-line with a velocity factor of 0.9, will naturally result in slightly different optimum lengths and SWR values.

Decades ago, W5DXP wrote a DOS program, IMAXGRAF.EXE, that given the dipole length and velocity factor of the parallel feedline, will display the optimum feedline lengths.[2] The following display was obtained for a 33 foot dipole fed with ladder-line having a velocity factor of 0.83.

What we are looking for is a grouping of dots around a vertical line. We see one such grouping for 17m-10m around a ladder-line length of 108 feet but we are missing the 20m dot at that length. The best we can do is the grouping around 90 feet and that is the one we choose. The ladder-line length for 20m in that group is a no-brainer and is 3/2 wavelength, i.e. 3(29.5')=88.5', which will reproduce the resonant feedpoint impedance of the 33' dipole. W5DXP used EZNEC[3] & AutoEZ[4] simulations for the rest of the lengths, but his real world results are very close to those simulation values.

The SWR curves for each of the five bands can be viewed at SWR Curves

One can use the same method for varying the length of the ladder-line as was described in W5DXP's No-Tuner All-HF-Band Dipole article[1]. But since the length of the ladder-line needs to be varied by ten feet for the 33' dipole, only four short jumper lengths are needed. W5DXP has four lengths of 2', 2', 2.5', and 3' ladder-line with banana plugs/sockets on each end so changing bands takes only a few seconds in the shack.

Hams with built-in autotuners, like W5DXP's IC-756PRO, can get by with only one five foot jumper. A fixed ladder-line length of 88 feet puts 20m, 17m, and 15m all within range of the autotuner. Adding a single five foot jumper puts 12m and 10m within range of the autotuner. This is how W5DXP usually operates his multi-band rotatable 33 foot dipole.

Hams with wide-range external tuners, like the MFJ-949E, can use a fixed 90 foot length of ladder-line. Here are the impedances looking into an ideal 1:1 choke using 90 feet of 300 ohm transmitting ladder-line to a 33 foot dipole at 40 feet, according to EZNEC:

14.2 MHz, 64+47 ohms; 18.14 MHz, 113+180 ohms; 21.3 MHz, 69-j18 ohms; 24.95 MHz, 64-j159 ohms; 28.5 MHz, 153-j484 ohms

[1]w5dxp.com/notuner.htm

[2]w5dxp.com/goodbad.htm

[3]Free EZNEC demo available at eznec.com

[4]Free AutoEZ demo available at ac6la.com

Member Comments:
This article has expired. No more comments may be added.
 
A Multi-Band 33 Foot Dipole  
by RSHIRE22 on February 26, 2014 Mail this to a friend!
Seems to me using a wideband tuner is far easier than varying the length of ladder line. Especially since ladder line losses at HF are negligible. Also since the lengths you cut aren't always plug and play without trial and error.

So ignore and do what has always worked. It's called a multiband dipole with tuner.
 
A Multi-Band 33 Foot Dipole  
by RSHIRE22 on February 26, 2014 Mail this to a friend!
A more challenging question would be how to get a 33 foot dipole at 40 feet to rotate. Alas the weakness of the dipole.
 
A Multi-Band 33 Foot Dipole  
by KD8TUT on February 26, 2014 Mail this to a friend!
Thank you!!! Learning a lot!

73
 
A Multi-Band 33 Foot Dipole  
by W1JKA on February 26, 2014 Mail this to a friend!
Re: RSHIRE22

Perhaps some folks don't have the space for anything longer than 33 ft. or are not interested in working lower than 20 meters. As far as height/rotation,then best height possible and a rotation alternative is another 33 ft. dipole at 90* with simple 12V relay switch. If you have an alternate solution for a limited space antenna then post it in the appropriate Forum.
 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on February 26, 2014 Mail this to a friend!
> RSHIRE22 wrote: A more challenging question would be how to get a 33 foot dipole at 40 feet to rotate.<

"Shirley, you jest." From telescoping aluminum tubing, pop-rivet together just the driven element of a 20m Yagi. Then put it on top of an old Rohn 20G TV tower like I did. Tubing available from:

http://www.texastowers.com/aluminum/round.htm

And it doesn't have to be at 40'. It will work well at 30' or even at 20' on top of a telescoping pole rotated by hand. A friend of mine has one of the latter that he uses portable for field day.

On the subject of antenna tuners, I have a MFJ-949E tuner but I find it easier and more efficient to vary the length of the ladder-line than to fiddle with three knobs when changing bands. Switching a single five foot section of ladder-line out for three bands and in for the other two band puts the impedance in range of my IC-756PRO's autotuner.
--
73, Cecil, w5dxp.com
 
RE: A Multi-Band 33 Foot Dipole  
by W5LZ on February 26, 2014 Mail this to a friend!
Different strokes for different folks!
I find it easier (don't have to go outside and make changes) to twiddle a couple'a knobs. Keeping notes about those knob settings makes the whole thing a lot faster. The 'best' way of doing it? Nope, but it's certainly easier for us lazy people...
- Paul

If it fit's you life 'style' then it's good. If it don't, then try something else...
 
RE: A Multi-Band 33 Foot Dipole  
by N2EY on February 26, 2014 Mail this to a friend!
Just plain BRILLIANT, Cecil - as usual!

73 de Jim, N2EY
 
RE: A Multi-Band 33 Foot Dipole  
by K9QR on February 26, 2014 Mail this to a friend!
Yes...tuners are not a problem for us space challenged hams. I keep a note of the knob positions on my MFJ949 and use the autotune on my TS-590 for the fine tuning. Quick and easy. I know its not efficient but it works around the world with my 100 watts and homebrew vertical.
 
RE: A Multi-Band 33 Foot Dipole  
by K8AG on February 26, 2014 Mail this to a friend!
Very cool! Reminds me of an antenna I made a few years ago. Need to try this.

Thanks

73, JP, K8AG
 
A Multi-Band 33 Foot Dipole  
by RSHIRE22 on February 26, 2014 Mail this to a friend!
W1JKA,

I look to threads for information on how to do something better or easier. When I discovered this thread was showing how to do something easy more difficult I had to post. I apologize if it came accross as facetious.

The world is full of smart people who will try to convince you to make the easy difficult and they are smarter than you. Call it the weakness of being smart.

Ron
 
A Multi-Band 33 Foot Dipole  
by RSHIRE22 on February 26, 2014 Mail this to a friend!
My tuner only cost $30. How much does ladder line cost these days? Read this first before you start cutting ladder line. Then if you still disagree go cut away!

http://www.arrl.org/random-length-multiband-dipoles
 
RE: A Multi-Band 33 Foot Dipole  
by WB2WIK on February 26, 2014 Mail this to a friend!
18 ga copperweld window line costs $0.135/foot in cut lengths, or $0.12/foot in 100' lengths.

So, it's pretty cheap.

The "patch panel" to do the line length changing needn't be outside, it can be inside (probably against an outside wall close to where the line comes in) and using banana jacks and plugs (the "dual" kind like Pomona sells, which plugs both conductors at once) takes about five seconds to make a change.

And, it can handle a kilowatt or more without fear of arching a component in a tuner.

I like this idea.
 
A Multi-Band 33 Foot Dipole  
by WA7EQX on February 26, 2014 Mail this to a friend!

Would adding a 31 ft or a 35 ft fan wire to the dipole would bring the dots together on the chart ?
 
RE: A Multi-Band 33 Foot Dipole  
by W6OGC on February 26, 2014 Mail this to a friend!
Where do you find it that cheap? Everywhere I've looked it is close to 50 cents or more a foot, unless you buy the whole reel, 1,000' or so, except MFJ at 35 cents a foot for 100'.
 
A Multi-Band 33 Foot Dipole  
by N8RAT on February 26, 2014 Mail this to a friend!
"The gain is almost as good as a two-element Yagi on 10m (9.5 dBi)."


Hmmmm. I highly doubt the claim that a 10 Meter, 2 element Yagi would exhibit that amount of gain.
 
A Multi-Band 33 Foot Dipole  
by F6GYY on February 27, 2014 Mail this to a friend!
Nice article, but very cumbersome the whole thing...

The best solution remains the 43 foot dipole
this time with 2 X RG-62 coaxial cable of 93 Ohms.
About 180-200 Ohms...

Only the central conductors are used . I Had Wireman 450 Ohm for a long time here, its impedance
is changing with the weather conditions : rain, frost and snow...

A must have is a very good symmetrical tuner like a Johnson , a Palstar , a Annecke or a homebuilt one.

Also works on 40 m quite well....but is primarely used for 20 m to 10 m.

Bertrand F6GYY
 
A Multi-Band 33 Foot Dipole  
by N2OBM on February 27, 2014 Mail this to a friend!
Cecil,

I am still amazed at using a RC-292 with extra elements in your 22'x 22' 'ground plane' design. LDG at the feedpoint...very good results; I would still like to see take off angle predictions.

Bertrand,

Is that a version of the To-Good-to-be-True antenna?
If I understand you...(1) center conductor of each coax run to each of the dipole elements, shields connected to each other but not grounded?

Not to take away Cecil's thunder, but please elaborate.

Cecil, could your program be 'tweaked' to replicate the TGTBT antenna? There were specific coax lengths that needed to be avoided...maybe your program could portray your 'dot alignment' based on dipole element length and various coax types (RG-58, 59, 8x) that could be used to feed the antenna? If I remember, one advantage was the 'dual coax feedline' could lay on metal gutters without all of the adverse 'lumps' that ladder or twinlead would introduce in the same instance.

Great article, good feedback...73
 
RE: A Multi-Band 33 Foot Dipole  
by F6GYY on February 27, 2014 Mail this to a friend!
Hi,

coupler is grounded, the two shields are bounded together and connected to the coupler's ground.

The 40 feet of feedline is well protected and can enter the house without problems...

Wireman 450 OHm is also very sensitive to the UV's of the sund and, with the time, will alter its caracteristics..!!!!!!!!!!!!!!!

Works nicely... Made a ssb Contact with the Philippines on 17 m , running 200 watts.
 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on February 27, 2014 Mail this to a friend!
> RSHIRE22 wrote: How much does ladder line cost these days? <

At TheWireman.com, seven cents a foot less than RG-8x with 1/3 the matched line loss of RG-8x.:)

> WA7EQX wrote: Would adding a 31 ft or a 35 ft fan wire to the dipole would bring the dots together on the chart ? <

Since I recently purchased AutoEZ from ac6la.com, it should be easy to explore that idea.

> N8RAT wrote: I highly doubt the claim that a 10 Meter, 2 element Yagi would exhibit that amount of gain (9.5 dBi). <

Sorry, I should have said that gain figure was over average ground. A 1/2WL dipole over average ground has a gain of about 7 dBi. Adding one parasitic element increases the gain by about 3 dB for a total gain of about 10 dBi over average ground for a two-element Yagi or Hexbeam.

> F6GYY wrote: The best solution remains the 43 foot dipole this time with 2 X RG-62 coaxial cable of 93 Ohms.<

Is it a rotatable version?

> N2OBM wrote: Cecil, could your program be 'tweaked' to replicate the TGTBT antenna?<

Another interesting idea. As a first approximation, one could just adjust for the difference in velocity factor between the 0.85 300 ohm ladder-line that I used and the VF of the side-by-side run of coax. Side-by-side runs of coax have not been characterized as well as single runs so there seems to be some room for conceptual errors. I believe the outside braid of the coax could be considered to represent a virtual ground so the balanced antenna feedpoint impedance could be split into two parts and analyzed separately. But I could be wrong about that.
--
73, Cecil, w5dxp.com
 
RE: A Multi-Band 33 Foot Dipole  
by F6GYY on February 27, 2014 Mail this to a friend!
Hi,
my rotable version was
about 36 feet and a half long ( about 11 meters )

so 5.5 m X 2 .... it also worked on 40 m...
with a good symmetrical tuner...

Have got a legend here , the 250W Model from Alfred Annecke DJ6OO ( silent key )...


Bertrand
 
RE: A Multi-Band 33 Foot Dipole  
by F6GYY on February 27, 2014 Mail this to a friend!
Annecke lengendary symmetrical tuner

http://www.dj0ip.de/antenna-matchboxes/a-n-n-e-c-k-e/symmetrical-koppler/


Bertrand
 
RE: A Multi-Band 33 Foot Dipole  
by WB2WIK on February 27, 2014 Mail this to a friend!
W6OGC posted: Where do you find it that cheap? Everywhere I've looked it is close to 50 cents or more a foot, unless you buy the whole reel, 1,000' or so, except MFJ at 35 cents a foot for 100'.

RFC #551 from the RF Connection is $0.27/ft in cut lengths and $25.00 for 100 feet: http://therfc.com/balncd.htm

That's retail, of course (it's good stuff).

I buy from the same source he does (factory). :-)

 
A Multi-Band 33 Foot Dipole  
by K1DA on February 27, 2014 Mail this to a friend!
And which side of the ladder line to I jam into the center connection on the SO 239 of my transmitter? Or, is there some magic in that regard that I am missing, like a balun?
 
RE: A Multi-Band 33 Foot Dipole  
by N4JTE on February 27, 2014 Mail this to a friend!
Cecil tnx for putting this article out there.
I have learned so much from your website and open wire feeder configurations. Antenna articles on eham require a very thick coat of armor but your acquired knowledge and applications are proven winners, thank you for sharing with us.
Bob
 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on February 27, 2014 Mail this to a friend!
> K1DA wrote: Or, is there some magic in that regard that I am missing, like a balun? <

I said in the article that the same techniques used in reference [1] could be used for this antenna. Here's a picture of the balun:

http://w5dxp.com/121Choke.JPG
 
RE: A Multi-Band 33 Foot Dipole  
by AF4K on February 27, 2014 Mail this to a friend!
I tried what the ARRL suggests with 450 ohmm ladder line feeding a 100 foot center fed dipole. Results were not good. It failed to tune on 80m and some other bands too. Tried two different tuners, using 1 4:1 balun.

Rotten experiment that took a lot of work time and resources. I went back to COAX feedlines and did much better. Not going to bother with ladder line or open wire feeders any more. Too complicated and did not get the job done.
 
A Multi-Band 33 Foot Dipole  
by N8TI on February 27, 2014 Mail this to a friend!
For some reason, I've never had good luck with ladder line. However, I did see this type of arrangement in QST.

The person had the ladder line on a drum or somehow rolled up. It looked pretty easy to change in and out the spliced pieces.

I think that the fact the length of the open line feed line changes impedence at the radio could be what gave me trouble. You can't just throw it up like coax. Obviously, when you work with this stuff you have to measure, which is what I did not do. This article explains why not measuring is not a good idea. It shows what having the wrong length of feed line can do to you.

 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on February 28, 2014 Mail this to a friend!
> AF4K wrote: I tried what the ARRL suggests with 450 ohmm ladder line feeding a 100 foot center fed dipole.<

What length of ladder-line did you use? For 80m, the ladder line length should be about 30' (G5RV) or 30'+1/2WL which would be 30'+118'=148'. If the ARRL suggested "any length" of ladder-line for 80m operation of a 100' dipole, they should have specified a very wide range tuner for any length of feedline between 60' and 120', with 90' being a worst case length. Those very high impedances not only tax an antenna tuner but also stress the balun. I have a web page that discusses good and bad lengths of ladder line:

http://w5dxp.com/goodbad.htm

 
Why not match your line and boost your power out?  
by ZL4AI on February 28, 2014 Mail this to a friend!
This is an outstanding article, and the point made ABOUT ELIMINATING LOSSES is absolutely correct.
The point is a tuner looses a lot of power.
If you do an analysis of the line, using "Transmission Line for Windows" (or similar programs) you will find as you incrementally step along the line the impedance, voltage and current vary tremendously with line length. They only match at few specific lengths which the article identifies. If you choose a line length that matches your band of choice you can then operate with very little loss on both transmit and receive. Have a look at the following web page where the line loses and tuner losses are estimated.

http://www.jking.netau.net/ZL4AI-N4GG_01.htm.

If you want to be heard on the air this approach is of matched transmission line length is very much a MUST DO.
 
RE: Why not match your line and boost your power out?  
by K8QV on March 1, 2014 Mail this to a friend!
<<< The point is a tuner looses a lot of power. >>>


I'm not an engineer, but I know from theory and practical application that this simply isn't true.
 
RE: Why not match your line and boost your power out?  
by W5DXP on March 1, 2014 Mail this to a friend!
> K8QV wrote: <<< The point is a tuner looses a lot of power. >>> I'm not an engineer, but I know from theory and practical application that this simply isn't true.<

The semantic problem is the difference between exclusive statements and inclusive statements. The above quoted statement at least implies an exclusive statement which is often false. We can make it a true statement by turning it into an inclusive statement.

The point is a tuner *sometimes* dissipates a lot of power.

One can estimate the losses in a tuner with the following tuner simulator.

http://fermi.la.asu.edu/w9cf/tuner/tuner.html

For instance, a 5 ohm load on 160m is a 50 ohm SWR of 10:1. The tuner simulator says the losses in the tuner will be 3.1dB, i.e. a loss of 51% of the source power and that's a lot of lost power.

But a 500 ohm load on 10.125 MHz is also a 50 ohm SWR of 10:1. The tuner simulator says the losses in the tuner will be 0.2dB, i.e. a loss of 4.5% which is not bad and a lot better than a folded-back power source.

And there was some humor in the typo in that statement. "Looses" means the opposite of "loses".:)
--
73, Cecil, w5dxp.com
 
RE: Why not match your line and boost your power out?  
by W5DXP on March 1, 2014 Mail this to a friend!
I should also state the real reason that I developed this method of varying the ladder line length to achieve a no-tuner match. I was using an MFJ-949E tuner with my IC-745 when I bought an SG-500 amplifier which is designed for a fixed 50 ohm load. I could either build or buy an antenna tuner capable of handling 500 watts or I could come up with some other method that didn't require the big bucks layout for a higher power tuner. That's when I came up with the idea of varying the length of the ladder line to achieve a match. "Nece$$ity is the mother of invention." Not that I invented the idea, but developed it using digital switching techniques described at:

http://www.w5dxp.com/notuner.htm
--
73, Cecil, w5dxp.com
 
A Multi-Band 33 Foot Dipole  
by N6JSX on March 2, 2014 Mail this to a friend!
This article is interesting but it appears to be solely based on PC mathematical projections. The assumptions sound reasonable with merit BUT where is the 'beef' --- the actual measured results of a real installed/operational antenna to verify these PC values?

 
A Multi-Band 33 Foot Dipole  
by K1DA on March 2, 2014 Mail this to a friend!
There has been a fair amount written of late about "balance" on parallel line fed antennas and if such a simple antenna DOESN'T work for you it's worth looking at. The problem is that not only that the currents in the two conductors have to be equal, but they have to be in proper phase as well in order to achieve a cancel of line radiation. An RF amp meter in each side of the line tells you whether or not the currents are equal but nothing about the phasing. I suggest paying attention to the physical symmetry of the installation and the use of a good size balun, not the tiny thing many "tuners" have internally installed. In most cases 1 to 1 is better than 4 to 1 as tuners usually do a better job transforming high values DOWN than they bringing a very LOW value UP. On a particulay band one might end up with only 20 or 30 ohms at the transmitter end of the feedline (despite the line itself being "450 " ohms) divide that by 4 or 6 and problems in tuning can result for which the antenna and feedline are blamed.
An open wire fed antenna which produces a lot of RF in the shack is probably NOT in balance. I've learned a lot over the years from a good old field strength meter in the shack. A strong reading on the meter does not ALWAYS mean a strong signal going out.
 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on March 2, 2014 Mail this to a friend!
> N6JSX wrote: This article is interesting but it appears to be solely based on PC mathematical projections. <

Quoting the article: "W5DXP has four lengths of 2', 2', 2.5', and 3' ladder-line with banana plugs/sockets on each end so changing bands takes only a few seconds in the shack."

Why does "it appear to be solely based on PC mathematical projections."? I am not sure that 88.5' is an exact measurement for 20m operation but I am sure about the above jumper lengths because they are what I actually use and the SWRs are actual measured values from which the feedpoint resistances were calculated. In fact, I tweaked the values entered into EZNEC so that the EZNEC results would agree with my real-world measurements.
--
73, Cecil, w5dxp.com
 
RE: A Multi-Band 33 Foot Dipole  
by W9AC on March 2, 2014 Mail this to a friend!
"This article is interesting but it appears to be solely based on PC mathematical projections. The assumptions sound reasonable with merit BUT where is the 'beef' --- the actual measured results of a real installed/operational antenna to verify these PC values?"

This question shows a lack of understanding of simple transmission line mechanics. W5DXP is not showing us anything that wasn't managed by hams extensively back in the '30s and '40s. He will be the first to tell us so.

What W5DXP did was to formulate typical line values to achieve a 50-ohm SWR as close to 1:1 as possible on the bands of operation when using non-50-ohm lines. On some bands, that may not be exactly achieved, but certainly 1.5:1 is possible at any point on the band of operation. Fine R and X compensation is needed for a 1:1 value but changes in as little as 1 ft. of line length is a reasonable way to achieve a low SWR(50) objective.

In a nutshell, changing the line length results in a changing line input Z when the load to line is not perfectly matched. We should know that the SWR of line's characteristic Z does not change. But the 50-ohm SWR (SWR[50])indeed DOES change and that's what allows us to find a length of line that gets us close to 50-ohms resistive (50+j0). The SWR(50) value is attained on any line not just coax. It's possible to adjust the length of 600, 450, 300, 75 ohm lines types and get close to a 50-ohm resistive value.

With an understanding of basic transmission line mechanics, we shouldn't be questioning if W5DXP's method works or not.

Paul, W9AC

 
A Multi-Band 33 Foot Dipole  
by RSHIRE22 on March 3, 2014 Mail this to a friend!
I built a multiband dipole with ladder line some years ago. It tuned and worked fine except one band was 2.5:1. On that band I just powered down to 30 watts. My teansceiver was fine with it.

RS
 
RE: A Multi-Band 33 Foot Dipole  
by KA4KOE on March 5, 2014 Mail this to a friend!
An old Eham tradition…..let me revive it here and now…Two words: FAN DIPOLE.
 
RE: A Multi-Band 33 Foot Dipole  
by F6GYY on March 8, 2014 Mail this to a friend!
Hi,
I do come back again... Your eastern states are under snow... so open Wireman 450 Ohm ( I had for years )
wont be weatherproof.

Forget it....Impedance will change quite often....
with rain, with snow....

We are several people using 2 times 93 Ohm coax cable
now... Only the 2 internal condeuctors are used...

It is called RG-62.......



Bertrand

 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on March 8, 2014 Mail this to a friend!
Unfortunately, RG-62 has more than ten times the matched line loss of 600 ohm open-wire feedline.
 
A Multi-Band 33 Foot Dipole  
by KJ6ETL on March 8, 2014 Mail this to a friend!
Use a Transmatch to tune the antenna. For the lower frequencies short the end of the feedline and use it as a vertical with top capacity against a ground plane...

Works like magic!
 
RE: A Multi-Band 33 Foot Dipole  
by K2WH on March 20, 2014 Mail this to a friend!
Two Words: Auto Tuner

Length of Feed Line: Inconsequential

Length of Dipole: Inconsequential

Operating Enjoyment: +10

K2WH
 
RE: Why not match your line and boost your power out?  
by K2WH on March 20, 2014 Mail this to a friend!
RE: Why not match your line and boost your power out? Reply
by W5DXP on March 1, 2014

I should also state the real reason that I developed this method of varying the ladder line length to achieve a no-tuner match. I was using an MFJ-949E tuner with my IC-745 when I bought an SG-500 amplifier which is designed for a fixed 50 ohm load. I could either build or buy an antenna tuner capable of handling 500 watts or I could come up with some other method that didn't require the big bucks layout for a higher power tuner. That's when I came up with the idea of varying the length of the ladder line to achieve a match. "Nece$$ity is the mother of invention." Not that I invented the idea, but developed it using digital switching techniques described at:

http://www.w5dxp.com/notuner.htm
--
73, Cecil, w5dxp.com

Why not just use a Balun, 4:1 and coax to your ICOM and use the internal tuner?

K2WH
 
RE: A Multi-Band 33 Foot Dipole  
by K2WH on March 20, 2014 Mail this to a friend!
A Multi-Band 33 Foot Dipole Reply
by N8TI on February 27, 2014 Mail this to a friend!
For some reason, I've never had good luck with ladder line. However, I did see this type of arrangement in QST.

The person had the ladder line on a drum or somehow rolled up. It looked pretty easy to change in and out the spliced pieces.

I think that the fact the length of the open line feed line changes impedence at the radio could be what gave me trouble. You can't just throw it up like coax. Obviously, when you work with this stuff you have to measure, which is what I did not do. This article explains why not measuring is not a good idea. It shows what having the wrong length of feed line can do to you.

I have used ladder line for the most part for 30+ years. Not once have I measured its length and I have used it on various wire dipoles of various lengths.

When using a tuner, the length of the dipole or ladder line basically becomes immaterial.

K2WH
 
RE: Why not match your line and boost your power out?  
by W5DXP on March 21, 2014 Mail this to a friend!
> K2WH wrote: Why not just use a Balun, 4:1 and coax to your ICOM and use the internal tuner? <

You quoted the reason why. I would not have been able to use my brand new SG-500 amplifier. The internal tuner only works between the ICOM and the SG-500 amp. It does not work between the SG-500 and the antenna.
--
73, Cecil, w5dxp.com
 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on March 21, 2014 Mail this to a friend!
> K2WH wrote: When using a tuner, the length of the dipole or ladder line basically becomes immaterial. <

In a typical system, the impedance encountered by the suggested 4:1 balun has a ballpark range of 50-5000 ohms.

(1) If the 4:1 balun sees 50 ohms on the output, it takes that already perfect match down to 12.5 ohms causing a 4:1 mismatch which results in additional losses in the tuner. Why would anyone want additional losses?

(2) If the suggested 4:1 balun sees 5000 ohms, it is nearly impossible to design a balun that is effective against common-mode problems. Why would anyone want common-mode problems?
--
73, Cecil, w5dxp.com
 
A Multi-Band 33 Foot Dipole  
by K8NQC on March 21, 2014 Mail this to a friend!
Throw those baluns out. A good balanced tuner is fine but the iron core baluns and SWR meters have been the bane of antenna work.

The ratios of voltages and currents are changing with each frequency and at each point along the feedline if it has any SWR. There is no place to interrupt the parallel balance except after the tuner without bad effects.. Did you ever wonder where the energy source is for the balun heating?

This antenna is a good design since the SWR is lowered before the circuit is changed to unbalanced.


 
RE: A Multi-Band 33 Foot Dipole  
by K8NQC on March 21, 2014 Mail this to a friend!
A simple 1:1 balun after the stub would be ideal. Air core would be near perfect.
 
RE: A Multi-Band 33 Foot Dipole  
by AF4K on March 22, 2014 Mail this to a friend!
I would respectfully disagree that measuring with SWR meters is a bad thing to do. The are very helpful in my opinion and I just don;t see what is so bad about using a balun! Perhaps some well reasoned explanation could help convince me otherwise, but I have found both to be extremely helpful and important at my station.
 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on March 23, 2014 Mail this to a friend!
I wasn't knocking baluns in general, just 4:1 voltage baluns used on multi-band ladder-line fed dipoles. A husky 1:1 current-choke-balun is usually the balun of choice for such an antenna.
--
73, Cecil, w5dxp.com
 
A Multi-Band 33 Foot Dipole  
by K4YZ on March 27, 2014 Mail this to a friend!

Interesting article, Cecil, but is it necessary to refer to yourself in the third person throughout the article as if someone else is writing the piece and singing your praises...?!?!

73

Steve, K4YZ
Winchester, TN
 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on March 28, 2014 Mail this to a friend!
W5DXP is too old to change his writing style which was common in the 1950's.:)
--
73, Cecil, W5DXP
 
RE: A Multi-Band 33 Foot Dipole  
by K5AF on March 31, 2014 Mail this to a friend!
Ladder line does have some losses, so do tuners and baluns. Depending on the feedline length, you might have a very low impedance at the tuner, which neither the tuner nor the balun is well-suited for.

I say get the best of both worlds, measure for a tuner-friendly load per W5DXP, then tweak it with the tuner for optimum power transfer!

Paul, K5AF
 
RE: A Multi-Band 33 Foot Dipole  
by N8RAT on April 6, 2014 Mail this to a friend!
"Sorry, I should have said that gain figure was over average ground. A 1/2WL dipole over average ground has a gain of about 7 dBi. Adding one parasitic element increases the gain by about 3 dB for a total gain of about 10 dBi over average ground for a two-element Yagi or Hexbeam."

I'd be very interested in any credible source that claims a 1/2 wave dipole has 7 dBi gain above average ground. Please educate me.
 
RE: A Multi-Band 33 Foot Dipole  
by W5DXP on April 7, 2014 Mail this to a friend!
Here's the elevation radiation pattern per EZNEC for my 33 ft rotatable dipole at a height of 33 ft over average ground used on 20m. Gain is 7.14 dBi.

http://w5dxp.com/20mDip.png
 
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