for dipole antenna,which is preferable ladder line or coaxial cable

[MITHUNVIMALAN SA]

I have some doubts regarding wires. Ladder wire has a high impedance level, but coaxial wire has 50 ohms. Ladder wire provides low loss, but coaxial is more user-friendly. Could you please suggest which one is better? regards mithun vimalan india

[Steve Cerwin]

Mithun,

A center fed HF resonant dipole at modest height above ground presents a feed impedance not far from 50 ohms. If all you wanted to do was use it on the band where it is resonant and perhaps the 3rd harmonic, just feeding it directly with 50 ohm coax cable is simple and easy to implement. A 1:1 BALUN at the antenna will strip antenna currents off the outside of the shield which helps cure a number of potential problems associated with a radiating or “hot” feed line. Using ladder line on this type of antenna would not make a lot of sense and would actually demand use of a tuner since connecting 450 ohm ladder line to a low impedance antenna guarantees a huge reflection at the antenna. .

But if you wanted to use the dipole on a number of bands where it does not always present a friendly low impedance, then open wire line has advantages. You will of course need to use a tuner. Open wire or ladder line has much lower loss than coax. When you use a tuner to make an untuned antenna resonant with a conjugate match you wind up with reflections at both the antenna and tuner end of the feed line. The back-and-forth reflections make the line look longer, which multiplies the losses. For example suppose you use coax with a total loss of 2 dB for your length and frequency on a non resonant antenna. You use a tuner to fix the impedance match at the transmitter end. You send power up the coax to the antenna and lose 2dB. Part is accepted and radiated and part is reflected back down the line where the conjugate match in the tuner turns it back around towards the antenna for another try. But by the time it gets there it has traversed the coax three times: up, back, and up again - each time incurring the 2 dB line loss. So the first-pass power returned to the antenna by the tuner is down 6 dB. The next iteration is down 12 and soon there is nothing left. Substitute ladder line with maybe 0.2 dB of loss and the up-back-up path costs only 0.6 dB.

Where do the coax losses go? Heat. Aside from efficiency, high power fed into coax that has a lot of standing waves can destroy it. (Don’t ask me how I know that). 

So one piece of advice is to use coax on antennas that present a fairly decent match on all the frequencies you use it on. Correctly designed center fed dipoles on fundamental and odd harmonics, some off-center fed dipoles, and many trap dipoles can give you matches on multiple frequencies that are good enough to operate with coax and a tuner without a lot of line loss. But if the antenna cannot give you a low feed impedance on all desired frequencies and you need to use a more aggressive conjugate match, then the ladder line will provide a far more efficient solution. 

73, Steve WA5FRF

On May 13, 2024, at 10:59 PM, MITHUNVIMALAN SA <mithunv...@gmail.com> wrote:

I have some doubts regarding wires. Ladder wire has a high impedance level, but coaxial wire has 50 ohms. Ladder wire provides low loss, but coaxial is more user-friendly. Could you please suggest which one is better? regards mithun vimalan india

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[MITHUNVIMALAN SA]

hey steve,Thank you for breaking down the considerations between coaxial cable and ladder line so comprehensively. It's fascinating to see how the choice of feed line can impact efficiency and performance across different operating scenarios. I particularly found the explanation about the reflections and losses in coaxial cable versus ladder line very insightful. It really highlights the importance of selecting the right feed line based on the antenna's impedance characteristics and operating requirements. Do you have any personal experiences or preferences when it comes in working with "S-band"

[Graham c]

A classic ( flat not inverted V ) dipole is closer to 75 ohms. Often overlooked is the use of RG-6 or similar cable particularly if your use is receive only although is just as easily used for transmit.  

As Steve commented, use BALUNS.

Also, something else to consider for receive only is the use of CAT5 or similar network cable. four twisted pairs ( use one pair with three spares or use one pair to provide DC power to a remote LNA or switch, etc ) each with an impedance around 100 ohms. Available with shielding, UV friendly outdoor or direct burial rated. Most of the benefits of ladder line with the convivence of coax. I have a receive only antenna based on Dallas Lankford's Low Noise Vertical design which has been in use for 10+ years using outdoor rated CAT cable that has proven very reliable and show little sign of wear; I live in Eastern Ontario Canada having moderate year round weather conditions. Use matching transformers or BALUNs as needed for your application i.e. my 100 ohm feed line is matched to my 50 ohm input distribution amplifier with a 100:50 ohm BALUN.

As an aside, Mr Lankford's writings make for some very interesting reading if you can find them.  A google search will find much.  This is the only web page I know of which has many of his writings  https://www.okdxf.eu/index.php/technika/80-antenarska-kolekce-dallase-lankforda    ( use Chrome to translate )

cheers, Graham ve3gtc

[Johnson Francis]

Graham, 

You have raised one of my interesting topics. Long back I used to use local 75 Ohms cable for my homebrew 120W vacuum tube CW/AM radio as 50 Ohm cable was not locally available. With a dipole antenna tied to tall coconut trees, I could work a lot of DX, including from the United States, which in those days was considered as one of the most difficult DX from this region. I did not use any antenna tuner, but the Pi tank in the final stage would have acted like one, I presume. Probably as you mentioned, 75 Ohms TV cable was a good match for the horizontal dipole antenna. 

In the present era with commercial 50 Ohm radios, I wonder whether it can still be used as most new radios can take up to 3:1 VSWR with built-in automatic tuners. After all, 75 Ohms cable presents a VSWR of only around 1.5:1 to a 50 Ohms radio. I also read somewhere about a cotangent matching transformer. Does any one know how the name 'cotangent transformer' came? Has it anything to do with the cotangent of the wavelength?

de Jon, VU2JO

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[Randy Frum]

Hi Mithun,

S-Band could be a whole different story...  I guess one question others might have is... "what length of feedline do you intend to run?".

Losses increase with frequency.  So at 2 - 4 Ghz and depending on line length and coax type you could suffer catastrophic losses. For example... at 2.4 Ghz with LMR 400, you would lose nearly 7 db of your signal at a 100 ft length. If you were above 10 Ghz... probably waveguides would be recommended... however at 2 to 4 Ghz waveguides start to get pretty big.  If you are only looking for a short run of Coax (25 ft or less) you could probably get away with LMR 400 or something similar without appreciable loss.  For longer lengths, you could go to hardline or there are some instances where open wire (450 or 600 ohm) may work but you would need to do the matching.

Regards,

Randy

AC4FD

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[Black Michael]

For a good comparison of cable loss....and for excellent cables that actually come with a testing sheet.

https://messi.it/en/comparison-chart-50-ohm-cables.htm

Mike W9MDB

[Graham c]

one way of matching 75 ohm to 50 ohm is with a 1/12 wave match. 

https://www.qsl.net/kx4om/TechSolutions/12th-WaveMatching/12th-wave_2019.html

https://pa0fri.home.xs4all.nl/Ant/Eentwaalfde%20golf%20trafo/One-twelfth%20wave%20transformer.htm

Older radios having tube finals having PI tank final would handle the difference easily - I have done so with my old Kenwood TS-520.  Newer solid state radios should easily handle that same 1.5:1 mis-match easily and those with a built in tuner even more so. 

Even the F type connectors used with the 75 ohm cable are quite capable of easily handling the 100w of typical ham radios. 

I have a vague recollection of an article from many years ago which described 50 ohm as better for power transmission and 75 ohm as better for voltage but the difference was minor - however,  I can not find it at the moment.  This is close but not the one of my vague recollection:

https://www.digikey.ca/en/blog/the-reasons-for-50-ohm-and-75-ohm-transmission-lines#:~:text=The%2050%20%CE%A9%20value%20is,%CE%A9%20is%20a%20better%20choice.

Everything is a compromise driven by your needs, wants, and resources.

cheers, Graham ve3gtc

[Steve Cerwin]

Hi Mithun,

At 2-4 GHz coax loss become truly horrific, I have built many an antenna there and my personal design philosophy has been to make the antenna be 50 ohms so it can be fed directly with coax (and not very much of it). For example RG-316 is a popular miniature coax. But at S band losses can be over 40 dB/100ft. Thats pushing a half a dB per foot!  “Antenna tuners” that attempt to fix a bad match at the transmitter end of the coax are simply impractical at VHF and up because of reverberant coax losses. 

Many times gain is a requirement at S band and panel arrays have been a personal go-to choice. Here you can set the antenna impedance by correct standoff distance above the ground plane. E.g., a dipole is 50 ohms at 0.17 wavelengths and a full wave loop is 50 ohms at 0.11 wavelengths. A long antenna like a Chiriex-Mesny (zig-zag) array is better at a spacing to give a 200 ohm match that is easily transformed to 50 ohms with a 4:1 BALUN. Other useful matching tools are shunt feed schemes like a gamma or T match. The venerable quarter-wave, open wire transmission line transformer can transform almost any nonreactive impedance to 50 ohms with judicious tap location (e.g., a J-pole). The point is to make the antenna feed point be 50 ohms by design. Then choose the coax very carefully for the length you need. 1 dB coax loss reduces range ~10%. 3 dB puts half of your power into heat. 6 dB means only one fourth of your power makes it through the coax to the antenna and this cuts range in half. 

73, Steve

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[Johnson Francis]

Thank you Graham.

de Jon, VU2JO

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[MITHUNVIMALAN SA]

Thank you so much for your guidance. I am currently attempting to convert a 1GHz yardstick into an SDR and am building my own receiver S-band antenna. I am undergoing a lot of research based on the doublet antenna and am trying to create the perfect design in HFSS. If you have any knowledge regarding this, kindly assist me.
guys your guidance means a lot|
You might wonder why I am building this. Essentially, I am a CubeSat developer, and we are a team of 45 teenagers, all under 19, dedicated to constructing India's first neuromorphic CubeSat named ULOG3.

The sad reality is that there is no one to help us; however, your assistance enables us to develop a keen sense for our future goals.

thank you

regards

mithun vimalan

india

[Nicholas Hall-Patch]

Hello Graham,

Another site, and the only one so far as I know, that has permission from Dr. Lankford's family to host his publications, is the IRCA Reprints:

http://dxer.ca/images/stories/2019/irca-reprint-index.pdf

For his own reasons, he had taken down his writings from various sites before he died, making them difficult to find.  And, when a copy can be found, there is no guarantee that it was his "final word" on the topic, as there were sometimes many different versions of a single article.  IRCA has been working on publishing only the final versions.



73

Nick

[Johnson Francis]

Glad to see that you are developing a CubeSat, Mithun. There is an active LEO Satellite Repeater Contact WhatsApp Group of which I was a member some time ago. There were many in that group quite knowledgeable about previous amateur satellite projects launched from this region by ISRO. You may be aware that there is a good number of VU operators on QO 100 Geostationary Satellite with uplink on 2.4 GHz and downlink on 10 GHz band. Many have homebrewed their own setup. I am sure there will be some near you as well. May I know your callsign please?

de Jon, VU2JO

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[David Eckhardt]

If you are relatively new to the hobby, I'd recommend coax with an appropriate 1:1 current balun or common mode choke at the feed point. 

Dave - WØLEV

On Tue, May 14, 2024 at 3:59 AM MITHUNVIMALAN SA <mithunv...@gmail.com> wrote:

I have some doubts regarding wires. Ladder wire has a high impedance level, but coaxial wire has 50 ohms. Ladder wire provides low loss, but coaxial is more user-friendly. Could you please suggest which one is better? regards mithun vimalan india

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Dave - WØLEV

[Bill Mader]

One common misunderstanding is the idea that a BALUN (acronym for BALanced to UNbalanced) chokes common mode current--it does not.  It transforms a balanced antenna to an unbalanced (coaxial) feedline.

A common mode choke (quite different in design from a BALUN) provides a high impedance to common mode current flowing on the shield of the coaxial feedline.

Even those who sell both often confuse them.  Although, some maker sell a combination of the two in one box (Balun Designs) but they are two devices in one package with two different purposes.  We should not call them by the same name, whichever is convenient at the time.

BTW, the Sun in New Mexico rapidly destroys network cables used outdoors.  YMMV.

One more point is the impedance of a dipole varies dramatically with its electrical height above ground--dramatically.  Check out the first chapter of the ARRL Antenna Book.  Most of the technical details in that publication are like a sentence passed around the dinner table.  By the time a handful of folks repeat it, the result has little to do with the original sentence as facts turn into lore.

73, Bill, K8TE

[Terry Bullett]

I use 450 ohm ladder line to feed my nominal 450 ohm traveling wave dipole.  I can't afford the weight of the 50:450 broadband impedance transformer at the feed point.  The ladder line is light. 

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-- 
Dr. Terry Bullett          WØASP 
NOAA National Centers for Environmental Information (NOAA/NCEI)
Cooperative Institute for Research in Environmental Sciences (CIRES)
Terry....@noaa.gov    720-446-9775 (google voice)  978-337-9092 (cell)   
"Life is Complex.  It has a Real part and an Imaginary part." 

[Jay Underdown]

A center fed resonant antenna has an impedance of about 73 ohms.

When not at resonance is varies from about 10 to 5000 ohms impedance. We are talking RF impedance NOT D.C. resistance. Coax is handy because solid state radios have an output about 50 ohms. Old Tube radios could match 50-5000 ohms. If you replace the coax with ladder line,  the loss is less (not important below 10 meters), BUT with an antenna tuner, it will work well at ANY frequency. It is now called a center fed Zepp antenna. Since downsizing homes. I have a single 80m center fed Zepp (about 135ft long) for 1 radio and an end fed zepp (about 65ft long) for my other radio. I feed each with an air core Balun and an antenna tuner. Some tuner have built in baluns. Both antennas load, tune and radiate on all H.F. ham bands. If you email me at W0...@juno.com. I can send you more info. Put antenna in the subject line. Also look me up on QRZ.com 73. Jay W0PS

[Wes Stewart]

I believe this link still works:  http://users.triconet.org/wesandlinda/ladder.htm

Wes  N7WS

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[Johnson Francis]

Wonder how the term 'Center Fed Zepp' came? I have read that the original Zepp antennas were the end fed antennas of the Zeppelin airships which trailed the airships.

de Jon, VU2JO

--

[David G. McGaw]

It is considered a misnomer.  Similar to calling an Off-center Fed Dipole a Carolina Windom.

David N1AHC

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[Jay Underdown]

Hi Dave. Yes a True ZEPP is an end fed non reasonant voltage antenna. It is a Zepp as that what was used in the German Zepplins in the days of spark. It was just a looong wire with a weighted cone at the end.  In the dayd of spark, everythimg was non resonant as spark was a number of frequencies at the same time. In modern days, most any non resonant center fed wire can be called a Zepp. 73, Jay. (Licensed since 1958).

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[David Eckhardt]

Just a note on "resonance":  Any feed / hunk of wire no matter how its configured is resonant somewhere and harmonics of the primary resonant frequency.  Just because it doesn't "ring" in the ham bands or where you want it, doesn't mean it's not resonant. 

Dave - WØLEV

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Dave - WØLEV

[Darrel]

From https://www.qikzepp.com/support/technical-information.html

Zepp Antenna History

Zepp antennas derive their name from the antennas used on the Zeppelin Airships. An early patent by German Hans Beggerow from 1909 illustrates the concept of an antenna equipped balloon.


Early fixed installation Zepp Antennas were a half-wavelength long(or multiple) and fed with a 1/4 WL (or multiple) open wire feed line which uses only one of the wires. The feed line provided a matching section for the transmitter.




I think the true, end-fed Zepp antenna had to be a half-wavelength (or multiple) long, to give a high impedance match at the end of the 1/4 wl open wire feed line, to minimize radiation from the feed line.  So not quite a non resonant antenna.  A centre-fed dipole doesn't have that limitation.

Cheers
   Darrel aa7fv

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[Jay Underdown]

H Darrel. I have a question. What is the resonant frequency of a spark (FCC Class A) transmitter?  CW transmitters are Class B (damped wave)

Is this for regular spark (Old Ford Spark coil), Rotary Spark (what speed), large air gap, Quenched gap?

If an antenna needs to be resonant we need to know the frequency of the transmitter.

Voltage fed antennas do NOT need to be resonant to work. They also do not need matching stubs if using a matching network at the transmitter. In the old days (spark and vacuum tube) a "swinging link" was used to match for maximum R.F. Current. R.F ammeters were popular back then. Vacuum tube transmitters either used fixed (link coupling) (See Heath AT-1 transmitter), or a PI network in the output tank circuit (see Heath DX-35 transmitter). Home made "L" network antenna tuners were also common and easy to build. When we were kids with not much money, we used a home made "L" network into a random piece of wire (long wire antenna). Worked great.

The nice thing about H.F. antennas is that they are very forgiving. On H.F. almost any piece of wire with a tuner will work.

73, Jay W0PS

P.S. and yes, what little hair I still have is Grey.

[Johnson Francis]

Thank you

de Jon, VU2JO

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[Wes Stewart]

What is your definition of will work?

[David Eckhardt]

QUOTE:  H Darrel. I have a question. What is the resonant frequency of a spark (FCC Class A) transmitter?  CW transmitters are Class B (damped wave)

Is this for regular spark (Old Ford Spark coil), Rotary Spark (what speed), large air gap, Quenched gap?

If an antenna needs to be resonant we need to know the frequency of the transmitter.

A high frequency spark with infinite rise time illuminates the entire electromagnetic spectrum.  One could say from DC (not possible) to light.  Actually well beyond light frequencies (wavelengths).  The old spark transmitter took advantage of this.  They narrowed the emissions by feeding a high-Q network consisting of an inductor, wire feeder, and ultimately, the "antenna" (a hunk of wire).  They did so by adjusting the inductor for maximum current in the "shack".  That formed the only resonant circuit of the spark transmitter.  My Uncle (8BZX) used a spark transmitter in his early days in Cleveland, Ohio.

Dave - WØLEV 

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--

Dave - WØLEV

[Black Michael]

And "spark transmitters" have been the bane of rocket programs at Cape Canaveral as the broadband pulse can hurt sensitive satellite payloads. 

Those transmitters were simply vehicles with noisy distributors....many of you may remember hearing them but doesn't happen as much any more with computer controllers.

I created a spark direction finder for NASA....

Mike W9MDB

On Thursday, May 30, 2024 at 11:40:56 AM CDT, David Eckhardt <davea...@gmail.com> wrote:





QUOTE:  H Darrel. I have a question. What is the resonant frequency of a spark (FCC Class A) transmitter?  CW transmitters are Class B (damped wave)
Is this for regular spark (Old Ford Spark coil), Rotary Spark (what speed), large air gap, Quenched gap?
If an antenna needs to be resonant we need to know the frequency of the transmitter.

A high frequency spark with infinite rise time illuminates the entire electromagnetic spectrum.  One could say from DC (not possible) to light.  Actually well beyond light frequencies (wavelengths).  The old spark transmitter took advantage of this.  They narrowed the emissions by feeding a high-Q network consisting of an inductor, wire feeder, and ultimately, the "antenna" (a hunk of wire).  They did so by adjusting the inductor for maximum current in the "shack".  That formed the only resonant circuit of the spark transmitter.  My Uncle (8BZX) used a spark transmitter in his early days in Cleveland, Ohio.

Dave - WØLEV 


On Thu, May 30, 2024 at 12:09 AM Jay Underdown <jay...@gmail.com> wrote:
>
> H Darrel. I have a question. What is the resonant frequency of a spark (FCC Class A) transmitter?  CW transmitters are Class B (damped wave)
> Is this for regular spark (Old Ford Spark coil), Rotary Spark (what speed), large air gap, Quenched gap?
> If an antenna needs to be resonant we need to know the frequency of the transmitter.
>
> Voltage fed antennas do NOT need to be resonant to work. They also do not need matching stubs if using a matching network at the transmitter. In the old days (spark and vacuum tube) a "swinging link" was used to match for maximum R.F. Current. R.F ammeters were popular back then. Vacuum tube transmitters either used fixed (link coupling) (See Heath AT-1 transmitter), or a PI network in the output tank circuit (see Heath DX-35 transmitter). Home made "L" network antenna tuners were also common and easy to build. When we were kids with not much money, we used a home made "L" network into a random piece of wire (long wire antenna). Worked great.
> The nice thing about H.F. antennas is that they are very forgiving. On H.F. almost any piece of wire with a tuner will work.
>
> 73, Jay W0PS
> P.S. and yes, what little hair I still have is Grey.
> On Wednesday, May 29, 2024 at 6:01:25 PM UTC-5 demers...@gmail.com wrote:
>>  
>>  From https://www.qikzepp.com/support/technical-information.html
>>
>> Zepp Antenna History
>>
>> Zepp antennas derive their name from the antennas used on the Zeppelin Airships. An early patent by German Hans Beggerow from 1909 illustrates the concept of an antenna equipped balloon.
>>
>>

>> Early fixed installation Zepp Antennas were a half-wavelength long(or multiple) and fed with a 1/4 WL (or multiple) open wire feed line which uses only one of the wires. The feed line provided a matching section for the transmitter.
>>
>>
>>
>>

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