high SWR at radio only when amplifier turned on

[Shockwave]

You can yell that the earth is flat but it doesn't make it so. Neither is that BS about the input impedance not determining what an SWR meter reads, only what comes after it.
- 'Doc

You can assume adjusting a load control will change the SWR but it doesn't make it so. Don't call it BS until you've twisted the load control right off your amp trying to change the SWR. You can't make the source impedance change the SWR, I can't make it happen and no one else can either. Put this to the test yourself or shut up and stop trying to confuse others. Will you take 60 seconds to test your theory or will you continue to be the great fountain of misinformation?

Since Doc probably won't prove himself wrong, I'm sure there are 10 other people out here that can adjust a load control, recalibrate the SWR for the loss in power transfer and confirm to the forum this does not cause the SWR to rise. Adjusting the load control on any tube amp will shift its output impedance and quickly put Doc's misconceptions to rest or at least allow others to see why they can ignore him on this topic. Can we get anyone else willing to try this?

 

[W5LZ]

You've got part of it right, but unfortunately you don't seem to understand how it doesn't apply to the BS about an SWR meter's reading only depending on the impedance after the meter and not before the meter. Of course the antenna system's impedance isn't changed by the 'load' control on an amplifier. But that's not what this is about. This is about the "no tune" circuit at the output of an amplifier commonly being at fault if there's a difference between the antenna system's apparent change in SWR when an amplifier is placed in line.
- 'Doc

 

[Shockwave]

You've got part of it right, but unfortunately you don't seem to understand how it doesn't apply to the BS about an SWR meter's reading only depending on the impedance after the meter and not before the meter. Of course the antenna system's impedance isn't changed by the 'load' control on an amplifier. But that's not what this is about. This is about the "no tune" circuit at the output of an amplifier commonly being at fault if there's a difference between the antenna system's apparent change in SWR when an amplifier is placed in line.
- 'Doc

Wrong, the point is source impedance has nothing to do with SWR. Changing the source impedance on a tube amp by adjusting its load control would quickly educate you on this topic. But at least you claim to know the antennas impedance will not be affected by adjusting the load control. Now if you could just put two and two together and realize that also means you will not see a change in SWR, you'd be on track.

The problem with these solid state CB amps is not that they are no tune broadband circuits. It's that 90% of them are designed and built by people who don't have a clue about proper RF design and layout. When was the last time you seen a FCC type accepted solid state amp oscillate and cause a spike in reflected power? Now ask the same question about Texas Star or all the new MOSFET crap on the market.

This quote says it all "Of course the antenna system's impedance isn't changed by the 'load' control on an amplifier." Will you now argue that changing the load capacitance doesn't alter the source impedance??? You'll need to study Pi and Pi-L circuits some more if you think that. One thing is for sure, if changing the output impedance on any amp causes reflected power to spike upwards, you got an unstable amp. One of the first things we do when testing a prototype amp is to make sure it runs stable over a wide range of output tuning.

 

[W5LZ]

"Will you now argue that changing the load capacitance doesn't alter the source impedance???"
No, I won't. And why do you change the source's output impedance? What are you trying to make that output impedance? Now is the 'light' dawning for you even a little bit?
- 'Doc

 

[Shockwave]

"Will you now argue that changing the load capacitance doesn't alter the source impedance???"
No, I won't. And why do you change the source's output impedance? What are you trying to make that output impedance? Now is the 'light' dawning for you even a little bit?
- 'Doc

The problem is not with my light dawning. What you said there is done to achieve the best power transfer between the source and the load. The mistake is you still think the transmitter has to match the 50 ohm cable and load in order to see a good SWR, or have you changed your mind on this yet?

You're measuring reflected power with SWR. Where is that power reflected from? The load of course and nothing to do with the source. Forward power on the other hand has a lot to do with the source impedance matching the load.

Here is a question for you Doc, you claim if the impedance in front of the SWR meter is anything other than 50 ohms, we get a high SWR. If you move your antenna tuner in front of the SWR meter, can you adjust your SWR? The tuner can transform the output impedance of the transmitter to a value other than 50 ohms but the only result you will see is a drop in forward power when the source impedance does not match the load. That actually does the exact opposite thing you claim and lowers reflected power too.

The truth is unless you use FM or CW, 90% of your transmission is being done with a transmitter output impedance higher than 50 ohms. Maximum power transfer occurs when the source matches the load. What do you think happens on AM or SSB during average speech?

The transmitter is only at maximum power during the positive audio peaks in these modes. That is also the only time it matches the 50 ohm line. In order to produce anything less than full rated power, the source impedance must rise above 50 ohms so that it can drop to 50 ohms under full load to reproduce those positive peaks.

 

[bob85]

doc cannot find any article to back up his technobull, they don't exist outside of his fictional physics,

he never did any test ( we know the result if he did )

here is another article in agreement with arrl walt maxwell + many more and what can be proven by simple tests.

VSWR and displacement

-------------------------------------------------------------------------
Determinants of VSWR

The VSWR at any point on a uniform transmission line is determined entirely by:

• the load impedance;
• the line's characteristic impedance, velocity factor and attenuation;
• and distance of the point from the load.

Apart from a very special case that hams are unlikely to encounter, the VSWR on a transmission line decreases smoothly from the load end to the source end as a result of line attenuation.
The decrease is predictable from line loss. Alternatively, line attenuation can be determined from the decreased VSWR.
VSWR is not in any way dependent on the equivalent source impedance of the generator.
-------------------------------------------------------------------------

what does w5lz keep telling people?

this^^^ proves a complete lack of any idea how amplifiers or feed-lines work,

so w5lz are all these guys wrong and only you are right?

where are all the people that agree with you and where are their links to articles? books to read?

why when anybody else tests your theory do they see what all the smart folk tell us we should see and never what you claim?

 

[Shockwave]

Next Doc will telling us the moon is closer than the other side of the world....because you can see the moon.

 

[jazzsinger]

Link no worky.

probably got it on your ignore list{Cry_river}

 

[W5LZ]

Actually, the next thing I'm going to tell you is that I'm through with this.
- 'Doc

 

[Shockwave]

Hopefully this means you'll stop telling people that their SWR is high because their transmitters aren't at 50 ohms too. That would have saved a few pages. No matter how much time is taken to explain this, you seem to rehash the same myth at least once a year.

 

[jazzsinger]

Next Doc will telling us the moon is closer than the other side of the world....because you can see the moon.

PMSL, In Doc's universe anything is possible, he has a deal wae mother nature to reinvent physics. He makes Nikola Tesla appear dense.:headbang:headbang

 

[jazzsinger]

you seem to rehash the same myth at least once a year.

a very conservative estimate Donald if you don't mind me saying.

Doc is highly stuck in his beliefs,

i appreciate its not easy to admit your wrong, especially with the evidence presented against you being from such credible sources, but its much better to admit it than persevere under accumulating evidence to the point you lose all credibility.we all get shit wrong from time to time,its no biggie.

 

[Shockwave]

a very conservative estimate Donald if you don't mind me saying.

Doc is highly stuck in his beliefs,

i appreciate its not easy to admit your wrong, especially with the evidence presented against you being from such credible sources, but its much better to admit it than persevere under accumulating evidence to the point you lose all credibility.we all get shit wrong from time to time,its no biggie.

While it may be hard for some to admit they are wrong, it's fairly easy for most to avoid being wrong on the same topic multiple times here.

 

[jazzsinger]

While it may be hard for some to admit they are wrong, it's fairly easy for most to avoid being wrong on the same topic multiple times here.

i believe that's called openmindedness and is best practised by not only learning from your own mistakes but also from those around you

i find you learn more when you have the mouth shut and ears and eyes wide open as well as the possibility always in your mind you could be wrong and there IS ALWAYS someone smarter than you,

i believe cristopher columbus poved that beyond all reasonable doubt,everything else is in my opinion questionable, todays fact soon becomes tomorrows myth.yesterdays myths are boring,especially if they revolve around groundhog day.

i learn new shit everyday.

 

[towerdog]

after reading a bunch of CB publications and manuals I learned VSWR > 2 is kind of normal due to all the crap and harmonics they try to put out. I decided to just roll with it for now, not much crap is going to make it past the antenna, and what does, well, be glad TV has gone digital