I have made a dedicated 75 meter half-wave dipole.  The leg lenghts are not identical (don't ask please) but I would like to adjust them to be equal without taking the whole thing down.  I can adjust each leg, so I can tune for frequency, but I need to be able to determine which leg is longer.  I suspect that I can use a Smith chart to do this, but it will be trial and error for me.  Can anyone tell me how I can use my nanaVNA to balance my dipole legs?  Thanks.  73 de AI7JN  Rick

Can you reach feedpoint??

You could wind a 1 to 49 transformer and feed each leg as an endfed halfwave
(just to check its resonance/length)

If you tune both halves to the same resonance spot.. They should be electrical
the same length (mechanical they may still differ a bit if the legs are
influenced by surroundings)

Hth

Dg9bfc sigi



Am 02.07.2022 21:10 schrieb Richard Chism <rchism@weedranch.com>:

> I have made a dedicated 75 meter half-wave dipole. The leg lenghts are not
identical (don't ask please) but I would like to adjust them to be equal
without taking the whole thing down. I can adjust each leg, so I can tune for
frequency, but I need to be able to determine which leg is longer. I suspect
that I can use a Smith chart to do this, but it will be trial and error for
me. Can anyone tell me how I can use my nanaVNA to balance my dipole legs?
Thanks. 73 de AI7JN Rick



_._,_._,_

* * *

Good Day Rick.

I would expect using the TDR functionality of NanoVNA is answer.    There are a number of YouTube videos available where folks demonstrate the necessary steps to configure it.

In your case, I would expect you will need a special adapter that allows you to connect one leg of your dipole at a time to your nano.   Once the unit gives you readings that reasonably represent the expected approx length of one leg, you would switch over to the other leg and contrast difference.  When you observe that one leg shows its major reflection earlier than the other, you will have identified the shorter one.

I would be inclined to perform the tests directly at the dipole feed-point and avoid the effects of coaxial cable variables.  This should also make it easier to switch between the two legs.

Hope this helps.

KE8PLM

Hi Rick,

Let me start out by stating that I am *NOT* an expert with the nanoVNA. I’m just downloading some of my thoughts.

Unless you are measuring each leg ‘independently’ at the center insulator of your dipole, I’m guessing it will be a challenge. How are you feeding the antenna – ladder line, coax, with or without a balun/unun/matching transformer, etc.? Those would obviously introduce some electrical characteristics you’d have to work through. That’s why I think you’d have to measure each leg independently at the center insulator, with the feedline disconnected. I don’t think you’d have any success measuring each leg ‘through’ the feedline.

Other things that might complicate the measurements would be if one leg is higher above the ground than the other, if it runs closer to tress than the other leg, if it runs closer to buildings/utility lines/??? than the other, etc. Any of those *might* result in the leg appearing longer or shorter electrically than it really is physically.

I’m not saying it can’t be done, but just pointing out some things that come to mind that could potentially complicate your measurements.

Good luck and have a great weekend. 73

Ken -- WBØOCV

From: Richard Chism
Sent: Sunday, July 3, 2022 12:30 AM
To: NanoVNAV2@groups.io
Subject: [nanovnav2] Balancing dipole leg lengths

I have made a dedicated 75 meter half-wave dipole.  The leg lenghts are not identical (don't ask please) but I would like to adjust them to be equal without taking the whole thing down.  I can adjust each leg, so I can tune for frequency, but I need to be able to determine which leg is longer.  I suspect that I can use a Smith chart to do this, but it will be trial and error for me.  Can anyone tell me how I can use my nanaVNA to balance my dipole legs?  Thanks.  73 de AI7JN  Rick

This is exactly what I would like to do, but how can I make a measurement with only one connection?  Doesn't the nanoVNA need both the inner and outer conductors of the port connected to something?  I see how this would work for measuring a coax, but I can't find anything online for measuring a wire unless I can access both ends.  How would such an adapter as you describe be configured?

My thoughts were to measure the impedance of the antenna, then shorten one leg and see if the impedance increased or decreased.  If it decreased, it would mean that I had shortened the longer leg, and vice-versa.  Does that seem correct?

Another issue is that I am using a 1:1 50 ohm cube balun to connect my coax to the antenna.  What will this do to my measurements?  Would I have to tie the ends of the dipole dirfectly to a connector?  It would be much easier if I could make my measurements through the balun.

Comment
Assuming you have 1/2 wavelength long device and it has a fundamental
resonant frequency .
The feed point impedance varies depending on location of such feed pont.
The resonance does not change with location of the feed point.

As pointed out - the "legs " surroundings have bearing on the feed point
impedance too.

Hence In practice it would be (more) prudent to match the impedance
instead of adjusting the symmetry of the length.

Rick,

What is the goal of adjusting the dipole leg lengths? Current balance?
Pattern cleanup?

Brian K1LI

On Sun, Jul 3, 2022 at 12:30 AM Richard Chism <rchism@weedranch.com> wrote:

> I have made a dedicated 75 meter half-wave dipole. The leg lenghts are
> not identical (don't ask please) but I would like to adjust them to be
> equal without taking the whole thing down. I can adjust each leg, so I can
> tune for frequency, but I need to be able to determine which leg is
> longer. I suspect that I can use a Smith chart to do this, but it will be
> trial and error for me. Can anyone tell me how I can use my nanaVNA to
> balance my dipole legs? Thanks. 73 de AI7JN Rick
>
>
>

I just want the optimum performance from the antenna, and since I am using a 50 ohm balun I assume the best match would be when the legs are equal length.

Antenna modeling software shows that the antenna performance will change
imperceptibly as a result of the leg length changes you propose. For
example, shortening the length of one leg of a 133-ft dipole (which
resonates at 3.6-MHz in free space) by 6-ft reduces the gain by 0.04-dB,
while increasing the resonant frequency to 3.78-MHz.

Brian K1LI

On Mon, Jul 4, 2022 at 12:03 PM Richard Chism <rchism@weedranch.com> wrote:

> I just want the optimum performance from the antenna, and since I am using
> a 50 ohm balun I assume the best match would be when the legs are equal
> length.
>
>
>

Hi Richard-
here's some advice from an old antenna engineer- you may already know all this but I hope it may prove useful.
I assume you are discussing a half-wave dipole fed at the middle.  As has been discussed, it is difficult to make a good measurement of an end-fed quarter wave because you don't know what the VNA sees as the counterpoise for the wire.  I suggest you not worry about the dipole balance, and I assume you cut the two halves to be about the same. If not, read on.

The impedance match of any antenna is not very important if it is below 2:1 SWR, because the power lost is about 1/2 dB, which is virtually undetectable in communications.  My only exception to this is that some modern transceivers want to see 1.5:1 SWR for full power out.  If you are getting 1.5 or less, you really don't need to do better.
If you need to do better, here's how the wire affects the impedance.  For the half-wave dipole, the resistance will be around 50 to 100 ohms at the center.  If you move the feedpoint off center, the resistance will increase slowly until you get near the ends, and at the end you will have a resistance of thousands of ohms.  So if your feedpoint is off by a few percent, it will make no practical difference.
The reactance is largely determined by the overall length of the dipole, so trimming either end to get the reactance to near zero will work, even if the two halves are unequal.
An example of this is the off-center fed dipole, where the two halves are unbalanced by 50% or so.  The resistance is higher, but the resonant length is about the same.
We engineers often have to decide what is good enough.
73  Ed  W2EMN

Ed,

That is VERY good to hear.  Now all I have to do is take a couple of
feet off of the leg that I suspect is longer in order to optimize it for
the frequency range I use most often, and if I'm wrong it sounds like it
won't matter.  Yes, it is a center fed (approximately) half wave dipole
cut for 75 meters, so the percentage difference won't be much.  Maybe 4%
at most. Thank you.  That simplifies everything.

73 de Rick AI7JN

On 7/4/2022 11:08 AM, djed1@aol.com wrote:

> Hi Richard-
>
> here's some advice from an old antenna engineer- you may already know
> all this but I hope it may prove useful.
>
> I assume you are discussing a half-wave dipole fed at the middle.  As
> has been discussed, it is difficult to make a good measurement of an
> end-fed quarter wave because you don't know what the VNA sees as the
> counterpoise for the wire.  I suggest you not worry about the dipole
> balance, and I assume you cut the two halves to be about the same. If
> not, read on.
>
> The impedance match of any antenna is not very important if it is
> below 2:1 SWR, because the power lost is about 1/2 dB, which is
> virtually undetectable in communications.  My only exception to this
> is that some modern transceivers want to see 1.5:1 SWR for full power
> out.  If you are getting 1.5 or less, you really don't need to do better.
>
> If you need to do better, here's how the wire affects the impedance. 
> For the half-wave dipole, the resistance will be around 50 to 100 ohms
> at the center.  If you move the feedpoint off center, the resistance
> will increase slowly until you get near the ends, and at the end you
> will have a resistance of thousands of ohms.  So if your feedpoint is
> off by a few percent, it will make no practical difference.
>
> The reactance is largely determined by the overall length of the
> dipole, so trimming either end to get the reactance to near zero will
> work, even if the two halves are unequal.
>
> An example of this is the off-center fed dipole, where the two halves
> are unbalanced by 50% or so.  The resistance is higher, but the
> resonant length is about the same.
>
> We engineers often have to decide what is good enough.
>
> 73  Ed  W2EMN
>
>
>
>
>

A dipole at resonance will have a resistance of about 73 ohms. If the length imbalance is small compared to the length of the dipole the change in performance will be small compared to the balanced length dipole.

> On Jul 4, 2022, at 09:03, Richard Chism <rchism@weedranch.com> wrote:
>
> I just want the optimum performance from the antenna, and since I am using a 50 ohm balun I assume the best match would be when the legs are equal length.
>

Performance does not change... You can feed a halfwave wire anywhere along its
length..

A good balun will keep the antenna well isolated from the cable...

So it will just work... Even if you feed at 48/52%split and not exact on 50
/50

Dg9bfc sigi



Am 04.07.2022 16:16 schrieb Richard Chism <rchism@weedranch.com>:

> I just want the optimum performance from the antenna, and since I am using a
50 ohm balun I assume the best match would be when the legs are equal length.



_._,_._,_

* * *

I'd vote for using the TDR function.

Since this is copper wire, set the velocity-factor to around 98%, but you
only need to disconnect the feedpoint end you don't need to touch the far
end (to measure at least).

Check both sides, then figure out the length you need to shorten by,
shorten, re-measure, and both legs should be the same.

There are good videos on YouTube on using the TDR functionality, I'd
recommend the video by Alan w2aew (albeit for coax).



73s,

Chris.

On Tue, 5 Jul 2022, 2:03 am Richard Chism, <rchism@weedranch.com> wrote:

> I just want the optimum performance from the antenna, and since I am using
> a 50 ohm balun I assume the best match would be when the legs are equal
> length.
>
>

...and answering in local morning just after waking up isn't always the
best idea :)

Yes you would need a current return.



Cheers,

Chris.

On Tue, 5 Jul 2022, 9:27 am Chris Keladis, <ckeladis@gmail.com> wrote:

> I'd vote for using the TDR function.
>
> Since this is copper wire, set the velocity-factor to around 98%, but you
> only need to disconnect the feedpoint end you don't need to touch the far
> end (to measure at least).
>
> Check both sides, then figure out the length you need to shorten by,
> shorten, re-measure, and both legs should be the same.
>
> There are good videos on YouTube on using the TDR functionality, I'd
> recommend the video by Alan w2aew (albeit for coax).
>
>
>
> 73s,
>
> Chris.
>
> On Tue, 5 Jul 2022, 2:03 am Richard Chism, <rchism@weedranch.com> wrote:
>
>> I just want the optimum performance from the antenna, and since I am
>> using a 50 ohm balun I assume the best match would be when the legs are
>> equal length.
>>
>>
>

A test transformer 1 to 49... Then endfed each leg (should be similar in
resonance on 40m)...that way very few is needed for a current return..(a bit
of capacitive coupling... Or a very short wire)

But overall you will not see any difference if you shorten one end.. Or both..

Sidenote.. Not cut the wire... Fold over and secure with a cable tie

Dg9bfc sigi



Am 05.07.2022 01:35 schrieb Chris Keladis <ckeladis@gmail.com>:

> ...and answering in local morning just after waking up isn't always the best
idea :)

>

>
>

>

> Yes you would need a current return.

>

>
>

>

>
>

>

>
>

>

> Cheers,

>

>
>

>

> Chris.

>

>
>

>

> On Tue, 5 Jul 2022, 9:27 am Chris Keladis,
<[ckeladis@gmail.com](mailto:ckeladis@gmail.com)> wrote:
>

>

>> I'd vote for using the TDR function.

>>

>>
>

>>

>> Since this is copper wire, set the velocity-factor to around 98%, but you
only need to disconnect the feedpoint end you don't need to touch the far end
(to measure at least).

>>

>>
>

>>

>> Check both sides, then figure out the length you need to shorten by,
shorten, re-measure, and both legs should be the same.

>>

>>
>

>>

>> There are good videos on YouTube on using the TDR functionality, I'd
recommend the video by Alan w2aew (albeit for coax).

>>

>>
>

>>

>>
>

>>

>>
>

>>

>> 73s,

>>

>>
>

>>

>> Chris.

>>

>>
>

>>

>> On Tue, 5 Jul 2022, 2:03 am Richard Chism,
<[rchism@weedranch.com](mailto:rchism@weedranch.com)> wrote:
>

>>

>>> I just want the optimum performance from the antenna, and since I am using
a 50 ohm balun I assume the best match would be when the legs are equal
length.



_._,_._,_

* * *

Thanks everyone for all the good advice.  I had used plenty of extra wire.  It was resonant at 3.750 so I took over 4 feet from what I thought was the longer leg and wrapped back more in case I needed to adjust the other way.  It was then resonant at 3.90.  I will probably take a few inches from the other leg, but it is working great!  Although I cut it for 75 meters, on 30 meters I talked  to a Russian about 35 miles east of Moscow using 100 watts and a cheap tuner.  I also heard clearly, but couldn't reach, a guy ferom Lithuania and another from Germany.  I am on the southern Oregon coast so that was ,pretty darned good!

I still don't understand how I can measure a wire using the TDR function.  A coax, yes, but for a wire do I just connect it to the center conductor of port 0 and leave nothing connected to the shield?

"Not cut the wire... Fold over and secure with a cable tie"

just to be picky again

should this need

*"assuming the wire is bare" *

I had plenty of wire.  I still have well over a foot wrapped back on each leg.  Thanks for the advice,.  I really do pay close attention to responses.  :)

Just for fun, I took and old set of rabbit ears and wired it with some RG58. And mounted it on a not-too-high wooden pole in the back yard. I extended the sections to make a balanced 100 MHz dipole and verified for a baseline. From there I proceeded to vary the angle and feed point [changing relative leg lengths]. With the NanoVNA, you can make some rapid real time observations on how those adjustments affect performance.

>
> I still don't understand how I can measure a wire using the TDR function. 
> A coax, yes, but for a wire do I just connect it to the center conductor
> of port 0 and leave nothing connected to the shield?

Exactly. You can measure resonance frequency directly and adjust length.
https://m.youtube.com/watch?v=WEdDAKJlriQ

With all the "commotion" on this thread, why not just drop the darn set of
wires and take care of the problem on the ground with mechanical rulers and
physical measurements????

Dave - WØLEV

On Sun, Jul 10, 2022 at 3:30 PM Dirk <dottensm@gmail.com> wrote:

> I still don't understand how I can measure a wire using the TDR function.
> A coax, yes, but for a wire do I just connect it to the center conductor of
> port 0 and leave nothing connected to the shield?
>
> Exactly. You can measure resonance frequency directly and adjust length.
> https://m.youtube.com/watch?v=WEdDAKJlriQ
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

I am an elderly disabled veteran.  I needed a lot of ,help getting them up and I cannot take them down, measure them, and put them back up without a lot of additionmal help.  Each leg is 60 feet long and in the trees.

You can feed a dipole off center. What is the SWR at the transmitter side of the coax?

Mike N2MS

> On 07/10/2022 4:52 PM Richard Chism <rchism@weedranch.com> wrote:
>
>
> I am an elderly disabled veteran. I needed a lot of ,help getting them up and I cannot take them down, measure them, and put them back up without a lot of additionmal help. Each leg is 60 feet long and in the trees.

Commotion? I have only seen an orderly path to understanding.
I have not seen any reason to complain.

On Sun, Jul 10, 2022 at 10:27 AM W0LEV <davearea51a@gmail.com> wrote:

> With all the "commotion" on this thread, why not just drop the darn set of
> wires and take care of the problem on the ground with mechanical rulers and
> physical measurements????
>
> Dave - WØLEV
>
> On Sun, Jul 10, 2022 at 3:30 PM Dirk <dottensm@gmail.com> wrote:
>
>> I still don't understand how I can measure a wire using the TDR
>> function. A coax, yes, but for a wire do I just connect it to the center
>> conductor of port 0 and leave nothing connected to the shield?
>>
>> Exactly. You can measure resonance frequency directly and adjust length.
>> https://m.youtube.com/watch?v=WEdDAKJlriQ
>>
>>
>
> --
> *Dave - WØLEV*
> *Just Let Darwin Work*
>
>
>
>

--




n_n

You do not need a Smith Chart – even a 50 year career engineering professional uses that chart for preliminary design purposes only.



Just use the VSWR function …. Good enough for your antenna.



All of my personal amateur radio antennae (2m, 6m & 10m Yagi; Screwdriver HF Vertical; 567 foot End-Fed Horizontal Long wire; VHF/UHF J-Pole) were tuned using VSWR readings only.



W4JDY

Rick is asking the common-sense things one does before putting the antenna up.



A balanced feedline or using a Balun at the feedpoint eliminates most problems. The other is simply measuring each leg to be the same.



Its just not all that hard folks.

4:1 – 1:1 are used to eliminate current in my feedlines in the shack.

Go online as the differential dipole leg length designs are well documented already.

And depends on the legs angle apart too.

Ed,



That was the most common sense reply to what engineers strive to achieve vice the purists in what is a hobby.



W4JDY

Unless you are at UHF and above, the TDR is not really a help.

There are many factors that materially affect the performance of any
antenna such as height above ground, closeness to other objects such as
metal gutters, ground properties, wire diameter, etc.

Unless you have very expensive equipment to measure radiation patterns I
assume by antenna "performance" you mean the lowest SWR. I suggest you
use the old formula of 468 / frequency in mHz and then divide by 2 to get
the length in feet of each half of the dipole. If you off + or - 5% of
formula length don't worry about it.

Many hams think the lowest SWR is the Holy Grail of antennas and that is
simply not true. As long as you have an antenna tuner that can match the
antenna impedance to about 50 ohms the antenna impedance matters little.
Use the best coax or ladder line you can afford as the feed line.

When a tuned 50 ohm signal is sent to a non-50 ohm antenna part of the
signal will be radiated and part is reflected back to the source. The
antenna tuner then reflects this partial signal back to the antenna. After
about 5 round trips about 99% of the original signal is radiated. For a
dipole substantially all the signal loss is the cable loss due to its
impedance which is converted to heat.

Bottom line. Measure close as you can with a messuring tape and get it up
as high as you can and don't worry about TDR measurements.

Good luck!

Hank, K5HHQ


On Mon, Apr 10, 2023 at 10:59 PM W4JDY <W4JDY1953@gmail.com> wrote:

> And depends on the legs angle apart too.
>
>
>
> *From:* NanoVNAV2@groups.io <NanoVNAV2@groups.io> *On Behalf Of *Richard
> Chism
> *Sent:* Monday, July 4, 2022 10:16 AM
> *To:* NanoVNAV2@groups.io
> *Subject:* Re: [nanovnav2] Balancing dipole leg lengths
>
>
>
> I just want the optimum performance from the antenna, and since I am using
> a 50 ohm balun I assume the best match would be when the legs are equal
> length.
>
>
>
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
> Virus-free.www.avast.com
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
> <#m_-2948354919653306_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>
>
>

On 4/10/23 7:49 PM, W4JDY wrote:
> And depends on the legs angle apart too.
>
> *From:* NanoVNAV2@groups.io <NanoVNAV2@groups.io> *On Behalf Of *Richard
> Chism
> *Sent:* Monday, July 4, 2022 10:16 AM
> *To:* NanoVNAV2@groups.io
> *Subject:* Re: [nanovnav2] Balancing dipole leg lengths
>
> I just want the optimum performance from the antenna, and since I am
> using a 50 ohm balun I assume the best match would be when the legs are
> equal length.
>
>

Everything affects the feedpoint impedance. But a lot of that has very
small effect on the antenna performance/efficiency, in either a
"effective aperture vs power presented at the feedpoint" for receive or
"radiated power for power supplied by transmitter" sense.

What does change is things like sensitivity to nearby (<1 wavelength)
noise sources, coupling to other structures, and to a lesser extent, the
radiation pattern.

In my opinion - "not to worry about (whatever)..." should not be the
objective of amateur radio enthusiast - quite a contrary. Being satisfied
/ impressed by minimal knowledge or just plain "here say" about the subject
is what is dumming this fascinating hobby. It is not the internet or cheap
HT -
"we have met the enemy and it is us ".

On Tue, Apr 11, 2023 at 9:59 AM Jim Lux <jimlux@earthlink.net> wrote:

> On 4/10/23 7:49 PM, W4JDY wrote:
> > And depends on the legs angle apart too.
> >
> > *From:* NanoVNAV2@groups.io <NanoVNAV2@groups.io> *On Behalf Of
> *Richard
> > Chism
> > *Sent:* Monday, July 4, 2022 10:16 AM
> > *To:* NanoVNAV2@groups.io
> > *Subject:* Re: [nanovnav2] Balancing dipole leg lengths
> >
> > I just want the optimum performance from the antenna, and since I am
> > using a 50 ohm balun I assume the best match would be when the legs are
> > equal length.
> >
> >
>
> Everything affects the feedpoint impedance. But a lot of that has very
> small effect on the antenna performance/efficiency, in either a
> "effective aperture vs power presented at the feedpoint" for receive or
> "radiated power for power supplied by transmitter" sense.
>
> What does change is things like sensitivity to nearby (<1 wavelength)
> noise sources, coupling to other structures, and to a lesser extent, the
> radiation pattern.
>
>
>
>
>
>
>
>

Well put, Anne!

"Equal dipole wire length": All this is fine, but the devil is in the
details. Once the equal-length wires of the dipole are hoisted into place,
the question remains: How do surrounding objects and earth characteristics
beneath the dipole affect that effort to make the wire lengths equal
lengths to the nearest mm (or less - another obsession)? Chances are you
have absolutely no idea. So, suddenly all that effort is for naught? Yes,
unless you carefully, rigorously, and professionally characterize the earth
characteristics within 5 (or so) wavelengths surrounding your antenna and
eliminate all surrounding objects within a 5-wavelength radius of the
antenna (numbers are empirical and not rigorously determined).

So, do the best we can. Any antenna is better than no antenna or a
well-sealed dummy load (even a dummy load radiates just a bit of
energy.....😊).

Dave - WØLEV

On Tue, Apr 11, 2023 at 3:58 PM Anne Ranch <anneranch2442@gmail.com> wrote:

> In my opinion - "not to worry about (whatever)..." should not be the
> objective of amateur radio enthusiast - quite a contrary. Being satisfied
> / impressed by minimal knowledge or just plain "here say" about the subject
> is what is dumming this fascinating hobby. It is not the internet or cheap
> HT -
> "we have met the enemy and it is us ".
>
> On Tue, Apr 11, 2023 at 9:59 AM Jim Lux <jimlux@earthlink.net> wrote:
>
>> On 4/10/23 7:49 PM, W4JDY wrote:
>> > And depends on the legs angle apart too.
>> >
>> > *From:* NanoVNAV2@groups.io <NanoVNAV2@groups.io> *On Behalf Of
>> *Richard
>> > Chism
>> > *Sent:* Monday, July 4, 2022 10:16 AM
>> > *To:* NanoVNAV2@groups.io
>> > *Subject:* Re: [nanovnav2] Balancing dipole leg lengths
>> >
>> > I just want the optimum performance from the antenna, and since I am
>> > using a 50 ohm balun I assume the best match would be when the legs are
>> > equal length.
>> >
>> >
>>
>> Everything affects the feedpoint impedance. But a lot of that has very
>> small effect on the antenna performance/efficiency, in either a
>> "effective aperture vs power presented at the feedpoint" for receive or
>> "radiated power for power supplied by transmitter" sense.
>>
>> What does change is things like sensitivity to nearby (<1 wavelength)
>> noise sources, coupling to other structures, and to a lesser extent, the
>> radiation pattern.
>>
>>
>>
>>
>>
>>
>>
>>
>
>

--

*Dave - WØLEV*

@ Anne Ranch,
I would appreciate it if you would clarify the point you are trying to make. What exactly was said that you interpret as "dumming" <sic> down our hobby or "Being satisfied / impressed by minimal knowledge"?

In my opinion all the responses to the initial question have been good. Each touches on something that affects antenna performance to a lesser or greater degree. To point out that some things are not worth obsessing over in a real world antenna is very helpful. A beginner might not know these things.

There is nothing wrong with engineering to a standard of "good enough", in fact it is impossible to do otherwise. Ask a machinist to cut you a 1 meter piece of steel and they will tell you it can't be done, you must specify the acceptable tolerance. +/- 1mm will be much less trouble and expense than +/- one micron. Which one do you really need?

For a part going into space "good enough" might mean "the best the state of the art can provide". For ham radio it usually means "a human can't tell the difference". You may demand and strive for unobtainable perfection and of course that is your right, but in general I think comments that allow us to put resources where they do the most good are helpful, not dumb.

JJ W0FAA

Sent with [Proton Mail](https://pr.tn/ref/NV8FZHYH5PG0) secure email.

------- Original Message -------
On Tuesday, April 11th, 2023 at 10:23 AM, Anne Ranch <anneranch2442@gmail.com> wrote:

> In my opinion - "not to worry about (whatever)..." should not be the objective of amateur radio enthusiast - quite a contrary. Being satisfied / impressed by minimal knowledge or just plain "here say" about the subject is what is dumming this fascinating hobby. It is not the internet or cheap HT -
> "we have met the enemy and it is us ".
>
> On Tue, Apr 11, 2023 at 9:59 AM Jim Lux <jimlux@earthlink.net> wrote:
>
>> On 4/10/23 7:49 PM, W4JDY wrote:
>>> And depends on the legs angle apart too.
>>>
>>> *From:* NanoVNAV2@groups.io <NanoVNAV2@groups.io> *On Behalf Of *Richard
>>> Chism
>>> *Sent:* Monday, July 4, 2022 10:16 AM
>>> *To:* NanoVNAV2@groups.io
>>> *Subject:* Re: [nanovnav2] Balancing dipole leg lengths
>>>
>>> I just want the optimum performance from the antenna, and since I am
>>> using a 50 ohm balun I assume the best match would be when the legs are
>>> equal length.
>>>
>>>
>>
>> Everything affects the feedpoint impedance. But a lot of that has very
>> small effect on the antenna performance/efficiency, in either a
>> "effective aperture vs power presented at the feedpoint" for receive or
>> "radiated power for power supplied by transmitter" sense.
>>
>> What does change is things like sensitivity to nearby (<1 wavelength)
>> noise sources, coupling to other structures, and to a lesser extent, the
>> radiation pattern.
>
>

Engineering allows for "good enough", so long as the limits are set.
Physics requires solutions where "good enough" is not good enough!

And, yes. Our ventures into space are the best our technology can offer at
the time. Nearly everything addressing that challenge is well over
designed but still to the best and latest engineering standards and
practices at the time. After all, the Voyagers are still ticking and
sending back data well beyond the spacial influence of our star, the Sun.
Were/are our efforts "good enough" to enter and navigate space? I'd
venture an answer to that question in the positive, yes. But they're not
exact.

Does physics understand gravity? Absolutely not. But,...... engineering
can deal with the effects of gravity. We can write all kinds of
tensor-based equations which do an excellent job of describing the observed
behavior of gravity, but we still don't understand that force. But
engineering can deal with the force.

Dave - WØLEV

On Tue, Apr 11, 2023 at 6:58 PM W0FAA - JJ via groups.io <W0FAA=
protonmail.com@groups.io> wrote:

> @ Anne Ranch,
> I would appreciate it if you would clarify the point you are trying to
> make. What exactly was said that you interpret as "dumming" <sic> down our
> hobby or "Being satisfied / impressed by minimal knowledge"?
>
> In my opinion all the responses to the initial question have been good.
> Each touches on something that affects antenna performance to a lesser or
> greater degree. To point out that some things are not worth obsessing over
> in a real world antenna is very helpful. A beginner might not know these
> things.
>
> There is nothing wrong with engineering to a standard of "good enough", in
> fact it is impossible to do otherwise. Ask a machinist to cut you a 1 meter
> piece of steel and they will tell you it can't be done, you must specify
> the acceptable tolerance. +/- 1mm will be *much* less trouble and
> expense than +/- one micron. Which one do you really *need*?
>
> For a part going into space "good enough" might mean "the best the state
> of the art can provide". For ham radio it usually means "a human can't tell
> the difference". You may demand and strive for unobtainable perfection and
> of course that is your right, but in general I think comments that allow us
> to put resources where they do the most good are helpful, not dumb.
>
>
> JJ W0FAA
>
>
> Sent with Proton Mail <https://pr.tn/ref/NV8FZHYH5PG0> secure email.
>
> ------- Original Message -------
> On Tuesday, April 11th, 2023 at 10:23 AM, Anne Ranch <
> anneranch2442@gmail.com> wrote:
>
> In my opinion - "not to worry about (whatever)..." should not be the
> objective of amateur radio enthusiast - quite a contrary. Being satisfied /
> impressed by minimal knowledge or just plain "here say" about the subject
> is what is dumming this fascinating hobby. It is not the internet or cheap
> HT -
> "we have met the enemy and it is us ".
>
> On Tue, Apr 11, 2023 at 9:59 AM Jim Lux <jimlux@earthlink.net> wrote:
>
>> On 4/10/23 7:49 PM, W4JDY wrote:
>> > And depends on the legs angle apart too.
>> >
>> > *From:* NanoVNAV2@groups.io <NanoVNAV2@groups.io> *On Behalf Of
>> *Richard
>> > Chism
>> > *Sent:* Monday, July 4, 2022 10:16 AM
>> > *To:* NanoVNAV2@groups.io
>> > *Subject:* Re: [nanovnav2] Balancing dipole leg lengths
>> >
>> > I just want the optimum performance from the antenna, and since I am
>> > using a 50 ohm balun I assume the best match would be when the legs are
>> > equal length.
>> >
>> >
>>
>> Everything affects the feedpoint impedance. But a lot of that has very
>> small effect on the antenna performance/efficiency, in either a
>> "effective aperture vs power presented at the feedpoint" for receive or
>> "radiated power for power supplied by transmitter" sense.
>>
>> What does change is things like sensitivity to nearby (<1 wavelength)
>> noise sources, coupling to other structures, and to a lesser extent, the
>> radiation pattern.
>>
>>
>>
>>
>>
>>
>>
>>
>
>
>

--

*Dave - WØLEV*

On 4/11/23 8:23 AM, Anne Ranch wrote:
> In my opinion - "not to worry about (whatever)..." should not be the
> objective of amateur radio enthusiast - quite  a contrary. Being
> satisfied / impressed by minimal knowledge or just plain "here say"
> about the subject is what is dumming this  fascinating hobby. It is not
> the internet or cheap HT -
> "we have met the enemy and it is us ".

That's hardly what I wrote. It is the observation from decades of
experience designing, modeling, building, and using antennas in a
variety environments, both terrestrial and in space.

For antennas that are low gain (doublets and the like), the physical
configuration of the antenna, in particular, the feed point impedance,
does not change the *efficiency* of the antenna unless it's extreme.

Whether the antenna is resonant at the operating frequency doesn't make
much difference *as a radiator* - it might make a difference for match
in a particular system, it might not.

Sure, the pattern might be perturbed a small amount. Or you might have
untoward interactions with the environment or feedlines, and the
measured Z might give an indication of that, but then, it might not.

Sometimes people get wrapped up in minutia that have small effect on the
performance (however measured) for simple antennas: dipoles, loops,
monopoles.

Where it gets trickier is when you have things like a Yagi - where
there's significant interaction among elements, and the mutual Z and
physical configuration has a large influence on the pattern
(particularly nulls and back/side lobes). And even there, you can spend
a lot of time on unnecessary precision in some aspect, when other
aspects dominate. How many modelers model the droop in a yagi element?
What's the effect of mis alignment? Or bending of the elements in the wind?

Now, it is fair that since amateur radio is by definition unpaid, it
doesn't hurt you if you want to dive down multiple rabbit holes. One
might learn something unexpected, or at least, unanticipated by
conventional models. And there's a whole world of mechanical engineering
aspects to antennas - finding inexpensive compromises is the name of the
game.

The OP was asking about performance - I interpreted that as "antenna
efficiency" - They could just have well be asking about withstanding
wind or ice, about which I am substantially less well qualified to comment.

In particular, the OP was talking about matching to 50 ohms. As it
happens, equal leg lengths would be the best match - The feed point
impedance is around 70 ohms. In all other positions for the feed point
impedance is higher.

However, there was another comment about angle - and that is probably a
really effective way to adjust the impedance lower. But then, does it
make a difference? And those are all for "ideal doublet in free space".

Again, one shouldn't be optimizing the fine details when the gross
things are dominant. And more to the point, one should learn how to
tell the difference. It's not always easy... that's why I love modern
modeling tools that are fast - you can try a bunch of weird things
quickly, without having to "commit to a build", and you can tell what
makes a big difference, and what makes a small difference.

>
> On Tue, Apr 11, 2023 at 9:59 AM Jim Lux <jimlux@earthlink.net
> <mailto:jimlux@earthlink.net>> wrote:
>
> On 4/10/23 7:49 PM, W4JDY wrote:
> > And depends on the legs angle apart too.
> >
> > *From:* NanoVNAV2@groups.io <mailto:NanoVNAV2@groups.io>
> <NanoVNAV2@groups.io <mailto:NanoVNAV2@groups.io>> *On Behalf Of
> *Richard
> > Chism
> > *Sent:* Monday, July 4, 2022 10:16 AM
> > *To:* NanoVNAV2@groups.io <mailto:NanoVNAV2@groups.io>
> > *Subject:* Re: [nanovnav2] Balancing dipole leg lengths
> >
> > I just want the optimum performance from the antenna, and since I am
> > using a 50 ohm balun I assume the best match would be when the
> legs are
> > equal length.
> >
> >
>
> Everything affects the feedpoint impedance. But a lot of that has very
> small effect on the antenna performance/efficiency, in either a
> "effective aperture vs power presented at the feedpoint" for receive or
> "radiated power for power supplied by transmitter" sense.
>
> What does change is things like sensitivity to nearby (<1 wavelength)
> noise sources, coupling to other structures, and to a lesser extent,
> the
> radiation pattern.
>
>
>
>
>
>
>
>

I like Dave's take, and the Darwin Awards, but thinking about it gets me to a question. A cut to simplification, if you will. You may have asked it as well. A dipole antenna is ambiguous from the standpoint of longitudinal physical symmetry. If you were to simply rotate it in azimuth around 180deg in free space (near your house may be quite different), it's pattern would rotate with it but any measurement from your nanoVNA (I have one, and they're great for finding fminVSWR and actual impedance vs freq!) would show no difference. I think this will be true no matter what the variance of your antenna's overall length is from a half wavelength (or any resonance circumstance, say a la velocity factor). Could this be true? If so, yours may be an unanswerable question, by a VNA at least.
--
AI7SI

There should be a distinction made , and I did not make / mention it,
between carrying-on social discussion , in style "so what , it works for
me...", and attempting to explain a subject based on some knowledge.
Unfortunately a simple / single "just contribute something" post cannot
always cover the subject on readers' terms. The reader is STILL allowed
(?) to interpret the post to his / her opinion / liking.
The forum is not a court where each word should be scrutinized / analyzed /
interpreted to meet lawyer's OPINION.

In "closing " - when subject is covered "good enough for government work "
- such "opinions" will obviously wary....
... unless "proper" reference to ARRL publication , in case of an antenna -
such as Windom, is mentioned *SARCASM *

..._._ ..

In my opinion, balancing legs of a dipole is completely unnecessary, and you will get the same results provided the dipole is properly cut for the frequency, and the feedpoint matches the impedance at that point.
Have we ever heard of an end-fed antenna? Or an off-center-fed dipole?
The impedance of the dipole at the center is roughly 50 ohms, and at the end is ideally infinite. (It's not 50 or infinite, but we won't discuss that.) At any point between the center and the ends, the impedance increases. If we feed it at some point, and have a matching transformer, balun if you will, and proper common mode choking (which you should have at any feedpoint), the antenna will work just the same as if you feed it exactly in the center.
As has been mentioned, anything outside the antenna including different ground conductivity will make a difference. This includes which way you run the feedline back to the shack. Or a water pipe under the ground...
I'll provide a couple references here that might provide more insight. I don't have any association with these sites, but there is practical information. DJ0IP actually goes out and tests stuff.
https://www.dj0ip.com/balanced-antenna covers we we have been talking about, but the background information I believe is in
https://www.dj0ip.com/ Common Mode Current and OCFD and probably some other places.

There is a bunch of technical stuff buried in the text of this site:
https://hamwaves.com/cl-ocfd/en/index.html
His intent is to make a multiband HF Off-center-dipole, and has some insight into basically the how and why off center works, and what many people do wrong and why.

If you take a look at both of these sites, I think you will quickly discover that perfectly balanced is not important, but resonant is.

Good luck with your project.

Arnold
KQ6DI

Arnold,

Nicely written and I agree with you.

Hank
K5HHQ

On Wed, Apr 12, 2023 at 12:32 AM Arnold Harding - KQ6DI <kq6di@comcast.net>
wrote:

> In my opinion, balancing legs of a dipole is completely unnecessary, and
> you will get the same results provided the dipole is properly cut for the
> frequency, and the feedpoint matches the impedance at that point.
> Have we ever heard of an end-fed antenna? Or an off-center-fed dipole?
> The impedance of the dipole at the center is roughly 50 ohms, and at the
> end is ideally infinite. (It's not 50 or infinite, but we won't discuss
> that.) At any point between the center and the ends, the impedance
> increases. If we feed it at some point, and have a matching transformer,
> balun if you will, and proper common mode choking (which you should have
> at any feedpoint), the antenna will work just the same as if you feed it
> exactly in the center.
> As has been mentioned, anything outside the antenna including different
> ground conductivity will make a difference. This includes which way you
> run the feedline back to the shack. Or a water pipe under the ground...
> I'll provide a couple references here that might provide more insight. I
> don't have any association with these sites, but there is practical
> information. DJ0IP actually goes out and tests stuff.
> https://www.dj0ip.com/balanced-antenna covers we we have been talking
> about, but the background information I believe is in
> https://www.dj0ip.com/ Common Mode Current and OCFD and probably some
> other places.
>
> There is a bunch of technical stuff buried in the text of this site:
> https://hamwaves.com/cl-ocfd/en/index.html
> His intent is to make a multiband HF Off-center-dipole, and has some
> insight into basically the how and why off center works, and what many
> people do wrong and why.
>
> If you take a look at both of these sites, I think you will quickly
> discover that perfectly balanced is not important, but resonant is.
>
> Good luck with your project.
>
> Arnold
> KQ6DI
>
>
>

My commentary was on opinions in style " I do not care how it works, but it
works for me ..."
Since this "discussion" continues , I like to use the attached as an
example of colorrary of such "opinion"... in MY OPINION, such statement
shows minimal knowledge of dipole and how VNA works.
In simpler terms - comparing apples and oranges. But that is my uneducated
opinion.






it's pattern would rotate with it but any measurement from your nanoVNA (I
have one, and they're great for finding fminVSWR and actual impedance vs
freq!) would show no difference.

A TDR as we use it in military systems is for opens or shorts in a multi-conductor transmission line. It is easier to measure the resonance of a single wire, and then compute its physical length from that.





WJDY

Because in free space or however one has the system physically located, the measurements will be different.



But then depending on one’s frequency, doing it before erecting the system is the smart play too.



If the system is already erected, and one is seeing if it has degraded, then I understand this effort.

It is far better to use an endfed wire with a 9:1 balun and avoid all of this balanced line business esp. if disabled.

W4JDY