Adjustments for resonance

[Slowmover]

Do you actually speak like this, or is it just a forum persona or something?

It’s a gift to capture ones own “voice” in words since it implies character attributes are a harmonic just above or below the words the reader can follow.

The rest of us try for consistency, whether it comes off well or not at least it’s understood as humility.

Organization of information adeptly imparted is no mean feat.

.

 

[Handy Andy]

Do you actually speak like this, or is it just a forum persona or something?

Not sure what you're getting at but yes, sometimes a word or two is transposed into a before or after - even the after before the 'fore.

So, being what this thread is...unless you approach much of this subject with a sense of humor realizing that not many others are seeing everyone's' points of view - might as well be articulate about it.

IF you've ever visited Rec.radio.cb newsgroup in the years I was on it, you can see where and how I found my "voice" you read today.

It was never easy - nor was it fun, but it, being a learning experience- made it worthwhile to develop the skills needed to get points of view, references, or thoughts - across to the reader.

As we tend to segue from Monitors, Desktops and Laptops onto Tablets and iPhones - there is a segment of the population that will again be pushed aside for the lighter, less statistical or even less informative medium - onto a simplistic, socialized Herd mentality that in order to get heard, you need to keep it simple - in this fashion, the continuous dumbing down of data becomes the slippery slope.

We lose ourselves because of the forced simplicity from the complexity of having to make choices.

​

Occam's Razor looks more like a Fairy Tale when it comes to reading Twitter feeds and the general flow - you get more of the feeling of the emotions from posters than you do the factual efforts the society should be obtaining, as working knowledge to strengthen itself as a whole from the environment full of fluff from the emotional fellowships and followings can be.

• - so I chose this route as a LEGACY to offer information that whether it can be processed at the time or not - is left behind as a trail of bread crumbs. The flavor may be intense at times but overall can be helpful if only in providing nourishment for the use of vowels sprinkled in with consonants, making words, sentences, onto - creating metaphors.

At least, it can be used as a marker to identify the poster as a method of finding, searching and mining for data that can be obtained later, even if it's parsed down as a search function just to obtain an answer for a condition that many overlooked during the progression of the thread.

In fewer words,

I write with emphasis - biased upon the feeling of the train of thought. I write from the experience I have had that makes me give the effort - the donation of time and thought. Some might consider this an emotion, but to the end user, the emotional response they may have, is subjective, I can only say so much - so the interpretation is left to their experiences, not that of the poster.

 

[freecell]

The reflected power is not "lost". It reflects at the transmitter again and goes out the antenna.

"the only reflected power lost is the amount dissipated in the line because of
attenuation - the remainder returns to the load."

Another Look at Reflections Part 1
M. WALTER MAXWELL

 

[freecell]

Another Look at Reflections Part 1
M. WALTER MAXWELL

https://www.worldwidedx.com/attachments/reflections-walter-maxwell-pdf.36264/

 

[Handy Andy]

Now here;

Many authors are responsible for perpetuating the unscientific and erroneous viewpoint that the coax-fed antenna must be operated at its self-resonant frequency, by continually overemphasizing the necessity for its being matched to the line within some arbitrary, low SWR value to preserve transmission efficiency, and by implying that efficiency equals 100 minus percent reflected power. The viewpoint is unscientific because it neglects the most important factor in the equation for determining efficiency - line attenuation. And it is also erroneous because efficiency does not relate to reflected power by simple subtraction. Setting an SWR limit alone for this purpose is meaningless, because the amount of reflected power actually lost is not dependent on SWR alone. The attenuation factor for the specific feed line must also be included because the only reflected power lost is the amount dissipated in the line because of attenuation - the remainder returns to the load. These authors have so wrongly conditioned us concerning what happens to the reflected power that many of us have overlooked the correct approach to the subject. It is clearly presented in both the ARRL Handbook and the Antenna Book that transmission efficiency is a two-variable function of both mismatch and line attenuation. With this knowledge and by using a graph of the function appearing in these ARRL books, presented here as Fig. 1, the amateur can determine how much efficiency he will lose for a given SWR with the attenuation factor of each specific feed line.

He can then decide for himself what the realistic SWR limit should be.

That's from link - thank you.

I set off one key important factor I feel is being missed - and many are being misled - so yes, I agree with the need to understand X ≠ 0 in all cases.

But the limit to find that resonance - being practicality, that the Owners of such equipment being the station itself and all of it's equipment - will have to settle for best SWR - whether the system (or antenna or both) is Resonate or not - to save their equipment from damage.

 

[Slowmover]

3.0:1 is no go
2.0:1 is marginal
1.5:1 is acceptable

Where 1.5:1 is a given knowing where to go next has been — continues to be — an interesting read.

As my completed mobile installations have been of a temporary nature (maximum length 1-3/years) owning an Antenna Analyzer hadn’t been a priority.

VSWR has sufficed (though I’d have paid for knowledgeable analysis) and until my own vehicles feature permanent installations the possible remedies to obtaining “best” AA readings haven’t quite been applicable. I’m not an experienced Amateur Operator applying tech savvy to difficult semi-tractors; a reversal of approach.

I revived this thread as questions about tuning 102” whips were answered to the OPs satisfaction after he obtained an AA and worked to get “best”. This thread revival applied to another thread altogether; interesting to see it has taken new life.

Practicality is how I consider Reliability + Longevity to exist for my purposes.

A better Field Strength Meter plus an AA look good to me. Sort of like the numbers obtained in baseline performance car owners never obtain. Diagnosis later as time passes makes better tools worthwhile, IMO, as all sorts of mysterious or confusing faults can start to show up.

Starting again from scratch may not be an option. That’s the fallback for most folks as I see it. New car or new radio system. A bad thing if that’s the only option.

.

 

[338_MtRushmore]

But the limit to find that resonance - being practicality, that the Owners of such equipment being the station itself and all of it's equipment - will have to settle for best SWR - whether the system (or antenna or both) is Resonate or not - to save their equipment from damage.

It seems like you are saying resonance may be found where SWR is not the lowest. If this is true, why would a resonant antenna system reflect more power? Shouldn't it radiate more power since it is resonant?

 

[Slowmover]

It seems like you are saying resonance may be found where SWR is not the lowest. If this is true, why would a resonant antenna system reflect more power? Shouldn't it radiate more power since it is resonant?

They chart differently on an AA.

.

 

[338_MtRushmore]

They chart differently on an AA.

.

That is where the problem begins. The AA is reading correctly, but if the readings are interpreted incorrectly, what's the point?

Would you say your truck ran more efficiently in a lower gear if it burned more fuel? That is the exact argument for tuning for x by increasing swr.

 

[Shadetree Mechanic]

The ground plane or lack thereof will affect the impedance even if it is resonant. This is why the star duster has it's radials at the angle that they are.

This is why it was stated that the radiator length is adjusted for resonance. Then a matching network is used to fix the impedance.

 

[338_MtRushmore]

I'm not sure who's instructions you are following. Sirio says to tune with an swr meter?

 

[freecell]

the importance of resonance in an antenna system:

1.optimizes current in the antenna.
2.makes the antenna easier to feed.
3.indicates frequenc/y/ies where the load represents a pure resistance.
4.establishes the center of the band in reference to operational bandwidth
5.tracking changes in antenna systems due to modifications
(like raising and lowering radials in ground plane antennas of all types)

all of the above are considerations taken into account by antenna system
engineers.

bob85 & marconi take note, particularly point #5

https://www.worldwidedx.com/threads/sirio-2745.261582/page-2#post-761819

no one ever even knew anything about swr in the age of the "swinging link"
matching network. damage blamed on reflections is really caused by
improper output-coupling adjustment – not by SWR. even today in Land
Mobile Radio an swr of 1.5:1 is the industry standard for a flat line.

 

[freecell]

"The relative unimportance of low SWR
when feed-line attenuation is low is demonstrated
rather vividly in the following two examples of
spacecraft antenna applications. First, in the
TirosESSA-Itos-APT weather satellites, of which the
entire multifrequency antenna-systems design was
the work of the author, the dipole terminal
impedance at the beacon-telemetry frequency (108
MHz in early models) was 150 - j100 ohms, for a
VSWR of 4.4, reflected power 40 percent.
Matching was performed at the line input, where it
was fed by a 30 milliwatt telemetry transmitter.
(We can't afford much power loss here!) The
feedline and matching-network attenuation was 0.2 dB,
and the additional loss from SWR on the feed line
was 0.24 dB (5.4 percent), for a total loss of 0.44
dB (9.6 percent). On the prevalent but erroneous
assumption that all reflected power (40 percent) is
lost, only 18.1 milliwatts would reach the antenna,
and efficiency, determined on the same erroneous
basis, would be only 60 percent. But 27.1
milliwatts were measured; of the 2.9 milliwatts lost
in total attenuation, only 1.6 milliwatts of it was
from the 4.4:1 VSWR. So the real efficiency would
have been 95.5 percent if perfectly matched at the
load, but reduces to 90.4 percent by allowing the
4.4 VSWR to remain on the feed line. Second, in
the Navy Navigational Satellite (NAVSAT), used
for precise position indications for ships at sea, the
antenna terminal impedance at 150 MHz is 10.5 -
j48 ohms, for a VSWR of 9.8, reflected power 66
percent. Also matched at the line input, flat-line
attenuation is 0.25 dB, and the additional loss from
SWR is 0.9 dB, for a total system loss of 1.15 dB,
approximately 1/6 of an S unit. This is an
insignificant amount of loss for this situation, even
in a space environment where power is at a
premium. Why did we match at the line input?
Because critical interrelated electrical, mechanical
and thermal design problems made it impractical to
match at the load. Line-input matching provided a
simple solution by permitting the matching
elements to be moved to a noncritical location."

Another Look at Reflections Part 1
M. WALTER MAXWELL

 

[bob85]

The point of my post in this thread was Nick put his analyzer at the radio end of the coax then set about adjusting the antenna for x=0,
That is what many people do,

They don't read instructions for how to use analyzers, jump in feet first tuning for x=0,
its often why they bought the analyzer in the first place, swr is for mudducks & resonance is king,

When somebody posts that they tuned their antenna for lowest vswr people will jump on them saying things like
"but where is the antenna resonant" "you should be tuning for resonance" "vswr tells you nothing" or similar comments,

It turns out that the vswr tuning mudducks are doing it the right way because antenna self resonance = minimum vswr,
adjusting the antenna for x=0 at the rig end of a random length of coax means the antenna is not resonant & the reactance that introduces causes more reflected power / elevated vswr,

The mfj manual tells you about coax reactance shifting the system resonant point as does respected publications,

DB mentiond earlier that a good field strength meter can trump either of the other 2 methods for tuning your antenna, That's true,

radios & amplifiers rarely output maximum power into a 50ohm load,
changing supply voltage & nothing else changes optimum load impedance,

a good field strength meter allows you to find the best compromise for maximum signal,

Keydown champions have used field strength meters to fine tune their setup for many years.

NINE NINE NINE NINE

 

[338_MtRushmore]

"The relative unimportance of low SWR
when feed-line attenuation is low is demonstrated
rather vividly in the following two examples of
spacecraft antenna applications. First, in the
TirosESSA-Itos-APT weather satellites, of which the
entire multifrequency antenna-systems design was
the work of the author, the dipole terminal
impedance at the beacon-telemetry frequency (108
MHz in early models) was 150 - j100 ohms, for a
VSWR of 4.4, reflected power 40 percent.
Matching was performed at the line input, where it
was fed by a 30 milliwatt telemetry transmitter.
(We can't afford much power loss here!) The
feedline and matching-network attenuation was 0.2 dB,
and the additional loss from SWR on the feed line
was 0.24 dB (5.4 percent), for a total loss of 0.44
dB (9.6 percent). On the prevalent but erroneous
assumption that all reflected power (40 percent) is
lost, only 18.1 milliwatts would reach the antenna,
and efficiency, determined on the same erroneous
basis, would be only 60 percent. But 27.1
milliwatts were measured; of the 2.9 milliwatts lost
in total attenuation, only 1.6 milliwatts of it was
from the 4.4:1 VSWR. So the real efficiency would
have been 95.5 percent if perfectly matched at the
load, but reduces to 90.4 percent by allowing the
4.4 VSWR to remain on the feed line. Second, in
the Navy Navigational Satellite (NAVSAT), used
for precise position indications for ships at sea, the
antenna terminal impedance at 150 MHz is 10.5 -
j48 ohms, for a VSWR of 9.8, reflected power 66
percent. Also matched at the line input, flat-line
attenuation is 0.25 dB, and the additional loss from
SWR is 0.9 dB, for a total system loss of 1.15 dB,
approximately 1/6 of an S unit. This is an
insignificant amount of loss for this situation, even
in a space environment where power is at a
premium. Why did we match at the line input?
Because critical interrelated electrical, mechanical
and thermal design problems made it impractical to
match at the load. Line-input matching provided a
simple solution by permitting the matching
elements to be moved to a noncritical location."

Another Look at Reflections Part 1
M. WALTER MAXWELL

That is a very misleading quote. What he is saying is if the vswr dip indicating resonance occurs at 5:1, the antenna system will function great. No need to get to that magical 1:1, especially if it involves tuning further from the indicated resonance point.