Adjustments for resonance

[freecell]

Shadetree Mechanic posted:

"I think the biggest thing to learn here is to tune it to resonance, then use a matching network to fix the swr. I have to go write that down now...."

anyone who has ever lengthened or shortened an antenna who believed that they were in any way directly affecting any form of impedance matching has been fooled.

" then use a matching network to fix the swr."

every feedline that exhibits reflection and attendant standing waves, either from a mismatched source or load, is also a potential matching network.

 

[Shadetree Mechanic]

Shadetree Mechanic posted:

"I think the biggest thing to learn here is to tune it to resonance, then use a matching network to fix the swr. I have to go write that down now...."

anyone who has ever lengthened or shortened an antenna who believed that they were in any way directly affecting any form of impedance matching has been fooled.

" then use a matching network to fix the swr."

every feedline that exhibits reflection and attendant standing waves, either from a mismatched source or load, is also a potential matching network.

But changing the length of the radiator can change the impedance, right? It is just the wrong way to change impedance?

 

[freecell]

Shadetree Mechanic:

load impedance changes with frequency and you see a frequency or range of frequencies where the swr is reduced. the swr changes because you changed the frequency at which the antenna is resonant. the only thing that's changing while remaining at a predetermined, fixed frequency is X / Reactance.

the usual instructions provided by antenna manufacturers to: "adjust the length for the best or lowest swr" will more times than not leave the antenna resonant far from the intended operating frequenc/y/ies.

 

[The DB]

I think you two are beyond stage 3, and I'm not even certain I want to fiddle with the next step. It seems like massively diminished returns for the effort in most situations.

Thank you.

I have a stage system of my own, I use it to categorize what someone is likely to understand or not. Each stage is based on a conceptual leap from the stage before, and the further you get the harder it is to jump from one stage to the next. Your stages one and two are essentially the same as mine, although I would use a different name for them...

That doesn't mean I wouldn't play with a remote receiver if someone else put their effort into installing it.

I do plan to get something like that up in time, but I doubt you live near me... I guess you could test how DX is between your area and my area with that setup...


The DB

 

[HomerBB]

I do plan to get something like that up in time, but I doubt you live near me... I guess you could test how DX is between your area and my area with that setup...

I just went out and tried it...
I think my antenna sucks.

 

[freecell]

here's what happens when you look around the band with an mfj analyzer connected to an antenna that is too short for resonance inside the cb band,

we see R 50 jX=0 @ 27.500 mhz.. 103" is too short to achieve resonance inside the cb band, let alone the center of the band @ 27.185 mhz. this one ends up 95 khz, above channel 40. this is the result of sirio using the free space formula for calculating the length of the driven element. these cb antennas are seldom if ever operated high enough above the ground to qualify for operation in "free space." if the formula for operation over real ground had been used instead the radiator would be another 5+ inches longer and would actually be resonant at some frequency inside the cb band. sirio seriously needs to get their act together. where the cb band is concerned, free space is at least 1.5 wavelengths above the ground and that can vary depending upon the resistivity and dielectric permittivity of the soil directly underneath the antenna. that's approximately 54 feet from the feedpoint to the earth ground beneath the antenna. if the feedpoint is no where near that height then you're not even close to "free space."

https://www.worldwidedx.com/threads/sirio-2745.261582/#post-760800

 

[HomerBB]

My Imax2k is 49' from feedpoint to the ground. But I don't see any free space beneath it. There's a mast right below it, and then some grass, which I have to mow, and that sure ain't free... mower, gasoline, sweat...
I guess I need to get it up another 6'. But it seems to work okay with no tuner needed from 15m to 10m.

 

[bob85]

Walt maxwells reflections tells us

"Any reactance added to an already resonant (resistive) load of any value for the purpose of com-pensation to reduce the reflection on the line feeding the load will, instead, only increase or worsen the reflection. It is for this reason, although contrary to the teaching of several writers, that the lowest feed-line SWR occurs at the self-resonant frequency of the radiating element it feeds, completely independ-ent of feed-line length. Any measurements that con-tradict this indicate that either the measuring equip-ment or the technique (or both) are in error"

Instructions for analysers and other sources tell us that when you measure through a length of coax you are looking at system resonance not antenna resonace & the coax will add reactance to the system moving the resonant point to a frequency other than the antennas self resonant frequency unless the coax is cut for the same frequency as the antennas self resonant frequency.

so it seems to me that the antenna makers instructions to tune for minimum vswr are correct & the reason resonance looking from the radio end of your coax is not the same frequency as lowest vswr is due to reactance in random length coax,

That's why I tune for minimum vswr,
& providing you have no common mode on the braid effecting vswr you can shift system resonance to the same frequency as lowest vswr by trimming the coax after you set the antenna for minimum vswr,

imho tuning for resonace through coax won't get you the lowest vswr or a resonant antenna unless you are incredibly lucky,

Are Walt Maxwell & Analyser makers wrong & if you think they are how do we prove or disprove it ? where is the source of info that says they are wrong ?

 

[Handy Andy]

@bob85 - none of this is what I would consider "wrong"...

One major aspect of using this information, is how you approach the "Use what works for you" notion.

Much of this information is being explained by book to encyclopedia; to help others try to grasp the issues that form - is skewed and edited by people being told (including myself here) that "You do this - the rest doesn't matter" or "You need to do this to obtain this"

So considering the lengthy discussions and the degradation of communication afterwards in attempts to shore up such subjects, I gave up trying to even promote the Keep it Simply Simple" (K.I.S.S. method) because of the bandwidth it causes in further explanation and emphasis.

We just have to help those whom editing function went into truncate mode.

So for the issue of SWR and your Sanity - the best response I have ever read regarding any effort in explanation - teaching, explaining or simply opening your eyes to see the light efforts - was this...

Instructions for analyzers and other sources tell us that when you measure through a length of coax you are looking at system resonance not antenna resonance & the coax will add reactance to the system moving the resonant point to a frequency other than the antennas self resonant frequency unless the coax is cut for the same frequency as the antennas self resonant frequency.

Many people see SWR as an end to a means - which in trying to make them NOT overthink this, is to look at the antenna and coax to the radio - when you're measuring at the radio - using the Built-in SWR meter or and analyzer type of one in line at the radios' connector - it's a SYSTEM - not "just" your antenna

Many "generalize" the Antenna as meaning their system - which then the Koax Kops tends to pound such a hapless individual senseless with facts - figures, figurines and trombones - to a point of where, in embarrassment; the budding (now nipped in the bud) enthusiast will sell their entire system to the first bidder on eBay - swearing, wishing they never did such a thing in the first place...Only to buy a Cobra 19 ESD/XXVII+ (or whatever generation it is at the moment) A Lil'Will glued to a pie plate tin and drill it to the sheds' roof and harass operators every night until the Solar Charged batteries go dead.

• Relax! It's only Radio!

The subjects of Mag mounts and coax lengths, and how permanent mounts offer more options than many realize, things tend to fall into place better once they see - and understand - the differences between them...

I'm no expert...

But...
Thank you!

 

[bob85]

Andy
what usually happens is people buy a basic analyzer hook it up at the radio end of their coax then dump vswr measurements & start chasing that magic word RESONANCE or x=0 as seen in this thread,

putting your analyzer at the radio end of your coax & tuning for x=0 on your chosen frequency is not the way to tune your antenna for resonance or least reflected power because random length coax adds reactance that shifts where x=0 will be,

Tune for lowest vswr then if x=0 is not on the same frequency as lowest vswr you can trim the coax until its no longer a random electrical length & not adding reactance to the system to bring x=0 inline with lowest vswr,

If trimming your coax causes vswr to change more than what can be attributed to the small reduction in coax loss of the trimmed shorter coax you very likely have common mode on the braid & you should fix the cmc before going any further,


You don't need anything more complex than a good basic vswr meter to tune your antenna for resonance & least reflected power since lowest vswr will always occur at the self resonant frequency of the antenna regardless vswr been 1.2:1 or 1.7:1 or whatever,
mistuning the antenna to move system resonance adds reactance to the load that will increase reflected power.

Analyzers are ok so long as you use them correctly but many people misuse their analyzer.

 

[freecell]

analyzers can be more accurate than you realize when looking at the complex impedance presented at the feedpoint of the antenna only when the following are observed.

stay out of the induction field of the antenna when making measurements.

to translate (repeat or mirror) the exact values of radiation resistance + loss resistance + reactance present at the feedpoint of the load and positively impact the accuracy of the analyzer the line used must be a 1/2 wl. @ the operating frequency and the velocity factor of the line must be factored into the calculations to arrive at a length of line which is electrically a 1/2 wl. at the target frequency.

"either the measuring equip-ment or the technique (or both) are in error."

"what usually happens is people buy a basic analyzer hook it up at the radio end of their coax then dump vswr measurements & start chasing that magic word RESONANCE or x=0 as seen in this thread,,,,"

that's the beginning of the entire problem.

see more: https://www.worldwidedx.com/threads/sirio-2745.261582/page-2#post-761802

 

[338_MtRushmore]

It doesn't help that people tend to consider reflected power as lost power. As long as my feedline losses are reasonable, and I'm tuned at the vswr dip, I could care less if I have a 3:1 vswr. It's just not significant.

 

[Shadetree Mechanic]

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

 

[Handy Andy]

Hmm...

Ok, I'll throw this out there, because no one else seems to care...

The SWR meter - a question on the Ham test, they call it a Directional Wattmeter.

Ok?

So knowing that, then are we to ignore the wattage returning to the radio and simply tune for resonance - gosh darn the torpedoes or high wattage returns that can upset the radio and the operator - only to have the station go down in flames?

No, I think SWR has a right to be followed, used, or at least adhered to, many of todays MOSFET systems are not handling the issue of simple Resonance very well because of the SWR reflection wattage nodal or summed - however you look at it - is getting too high for many radios to tolerate.

We're losing Bipolar to warring factions that demand the magic smoke be released and after the first keyup - out it goes...not too many companies are reloading for another volley.

Sorry folks, SWR has it's place, and to ignore SWR for the sake of resonance means that if Resonance and SWR are NOT EQUAL in the impedance realm - then we have to accept the default of safety for the user and the radio and settle for the low-SWR even though the antenna might as well be an Isotropic.

If you don't want Isotropic, either find a better mounting location - or antenna - or both...

It may sound rough - harsh or even callous - but the truth is, SWR is a voltage measurement the maker looks, uses and tries to handle for the best trade of cost to performance and still offer an ability to transmit - it is frustrating to see that most people don't see the X=0 as not the only result they need to get at.

This is where having an Analyzer can be the best tool in the wrong hands - not that it is dangerous in itself - only that the search for X=0 they're forgetting the antenna, radio, coax and operator - all have to live with each other afterwards.

It's not always a happy ending.

I don't take sides here, I side with all of you, just how I look at the problem is thru "General>Problem>Symptom>Diagnosis>Investigation>Resolve>Repair>Adjust>SWR>Reinstate = 0 then True.

But SWR being the "Directional Wattmeter" - tends to be the go-to favorite for those that really just want the radio to live to see another day.

Analyzers, being more than just a novelty, can show even the antenna makers - a thing or two about why some complain and why some compliment and some swear by, while some swear at - their products.

If everything was the same, would we have advanced? Maybe - but it Shure (pun) would be awfully boring

 

[338_MtRushmore]

Hmm...

Ok, I'll throw this out there, because no one else seems to care...

The SWR meter - a question on the Ham test, they call it a Directional Wattmeter.

Ok?

So knowing that, then are we to ignore the wattage returning to the radio and simply tune for resonance - gosh darn the torpedoes or high wattage returns that can upset the radio and the operator - only to have the station go down in flames?

No, I think SWR has a right to be followed, used, or at least adhered to, many of todays MOSFET systems are not handling the issue of simple Resonance very well because of the SWR reflection wattage nodal or summed - however you look at it - is getting too high for many radios to tolerate.

We're losing Bipolar to warring factions that demand the magic smoke be released and after the first keyup - out it goes...not too many companies are reloading for another volley.

Sorry folks, SWR has it's place, and to ignore SWR for the sake of resonance means that if Resonance and SWR are NOT EQUAL in the impedance realm - then we have to accept the default of safety for the user and the radio and settle for the low-SWR even though the antenna might as well be an Isotropic.

If you don't want Isotropic, either find a better mounting location - or antenna - or both...

It may sound rough - harsh or even callous - but the truth is, SWR is a voltage measurement the maker looks, uses and tries to handle for the best trade of cost to performance and still offer an ability to transmit - it is frustrating to see that most people don't see the X=0 as not the only result they need to get at.

This is where having an Analyzer can be the best tool in the wrong hands - not that it is dangerous in itself - only that the search for X=0 they're forgetting the antenna, radio, coax and operator - all have to live with each other afterwards.

It's not always a happy ending.

I don't take sides here, I side with all of you, just how I look at the problem is thru "General>Problem>Symptom>Diagnosis>Investigation>Resolve>Repair>Adjust>SWR>Reinstate = 0 then True.

But SWR being the "Directional Wattmeter" - tends to be the go-to favorite for those that really just want the radio to live to see another day.

Analyzers, being more than just a novelty, can show even the antenna makers - a thing or two about why some complain and why some compliment and some swear by, while some swear at - their products.

If everything was the same, would we have advanced? Maybe - but it Shure (pun) would be awfully boring

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