SWR

[Cj1]

ok, so i have a Galaxy 959,a 2 pill amp and a wilson 2000 trucker on a trunk lid mount... my swr is a 1.2 bare foot, then when i kick the amp on (high,med.or low) it jumps to 1.6
i tried everything, adjusting antenna, changing jumpers.... can't get it any lower... i think it could be some amplifier mis-match..

any tips?
it's like that all across 40 channels..


Thank in advance..

[231]

ok, so i have a Galaxy 959,a 2 pill amp and a wilson 2000 trucker on a trunk lid mount... my swr is a 1.2 bare foot, then when i kick the amp on (high,med.or low) it jumps to 1.6
i tried everything, adjusting antenna, changing jumpers.... can't get it any lower... i think it could be some amplifier mis-match..

any tips?
it's like that all across 40 channels..


Thank in advance..

Cj1,
Set your standing wave up without the amp in line. Once that is done, it's done. Afterward and assuming for a moment you are using an external SWR meter, the meter should be placed between the amp and antenna...not between the radio and amp. If you are using the SWR meter in the radio, it's seeing the input circuitry of the amp, which is common that it would be a tad higher. But the amp itself is still seeing the good standing wave.

Now, if your external SWR meter is between the amp and antenna and still high, are you recalibrating the meter to accommodate for the higher power? If not, you must do that.

In essence, the standing wave shouldn't change hardly at all because you added an amp. That is assuming the coax and feed point's aren't having a problem. And with the little bit of change you've mentioned I'd say they are just fine.

Hope that helps clarify things some.

[Cj1]

i have the meter between the amp and antenna, its jumping that high.. i know it shouldn't. that's why i'm thinking its a prob with the amp..
i mean, amp gets out fine.. nice wattage on all 3 stages. but i know it shouldnt jump up THAT much , even on high(80 watts DK)

['Doc]

A 1.6:1 SWR isn't high at all. In fact, it's not bad.
- 'Doc

[Red Warrior]

Another consideration is your amp could be driven too hard and is generating out of band spurs. Since these spurs are outside the band the antenna is tuned for, and power outside the band will be reflected by the antenna, and an SWR meter measures power that is not frequency specific (broadbanded), the SWR (reflected power) reading will be higher. Only way to tell is to reduce the deadkey into the amp and see if the SWR drops. If it does, you are driving it too hard.

[Cj1]

i'm driving it with 2 or 3 watts.... i'll lower it though.. i know 1.6 isn't bad.. but to me its not good. and it shouldnt jump up that high from barefoot to amp

[Red Warrior]

i'm driving it with 2 or 3 watts.... i'll lower it though.. i know 1.6 isn't bad.. but to me its not good. and it shouldnt jump up that high from barefoot to amp

Let us know what you find.

['Doc]

That 'jump' from barefoot to amplifier just says that the output impedance of that amplifier is not the same as the output impedance of that radio. Considering how most (if not all) amplifiers commonly found are not tunable (input/output), that impedance difference is about as normal as you can get, and since it isn't that much of a difference, it ain't bad!
- 'Doc

[bama7474]

I have pretty much the same setup...So what your saying Doc, is that the additional coax used by adding the amp would cause a slightly higher DK coming off the amp? This is what I figured was going on with my setup...I'm content with my 1.5:1 ratio reading between the amp and antenna, it's only what, 3% loss.

['Doc]

No, that's not what I'm saying. I'm basically saying that the "no tune" circuit in amplifiers is almost always -one- of the things that will determine the SWR seen by a meter. The biggy is the antenna's input impedance, naturally, and if that impedance is the same as the feed line's impedance, then the only other place there can be a 'difference' is the impedance of the output of the amplifier. There are only three places that can change the SWR when it's measured between the amplifier and the antenna. The input impedance of the antenna, the characteristic impedance of the feed line, and the output impedance of the amplifier. If the antenna is right, and the feed line is right, what does that leave you with? That "no tune" circuit not being right is very common.
- 'Doc

[bama7474]

No, that's not what I'm saying. I'm basically saying that the "no tune" circuit in amplifiers is almost always -one- of the things that will determine the SWR seen by a meter. The biggy is the antenna's input impedance, naturally, and if that impedance is the same as the feed line's impedance, then the only other place there can be a 'difference' is the impedance of the output of the amplifier. There are only three places that can change the SWR when it's measured between the amplifier and the antenna. The input impedance of the antenna, the characteristic impedance of the feed line, and the output impedance of the amplifier. If the antenna is right, and the feed line is right, what does that leave you with? That "no tune" circuit not being right is very common.
- 'Doc

Thanks for setting me straight...I was way off the chart!

[observer_1]

No, that's not what I'm saying. I'm basically saying that the "no tune" circuit in amplifiers is almost always -one- of the things that will determine the SWR seen by a meter. The biggy is the antenna's input impedance, naturally, and if that impedance is the same as the feed line's impedance, then the only other place there can be a 'difference' is the impedance of the output of the amplifier. There are only three places that can change the SWR when it's measured between the amplifier and the antenna. The input impedance of the antenna, the characteristic impedance of the feed line, and the output impedance of the amplifier. If the antenna is right, and the feed line is right, what does that leave you with? That "no tune" circuit not being right is very common. - 'Doc

utter nonesense, transmitter output impedance does NOT effect vswr, no tune amps are never the reason vswr rises when the amplifier is turned on,
this has been explained to you more than once along with simple tests to prove it yet you still spread the bs to people that want to learn about radio

['Doc]

observer_1,
So tell me which part I've got wrong.
SWR is a ratio of forward power produced by some source, transmitter, amplifier, whatever, and the reverse power coming back from the stuff on the antenna side of the measuring SWR meter (yes, I know it's actually voltage that the meter is measuring, but that corresponds directly with power and impedance in this sort of instance). So if that SWR meter is comparing what it sees on one side of it with what it sees on the other side of it, how does the source, transmitter or amplifier, NOT play a part in that comparison? If the SWR meter shows that there is some differences between the front side and back side things it's comparing, then what says that 'difference' has to be on the back side of it and not the front side of it?
If there are three things making up a system, source, feed line, and load. And the meter is located between the source and feed line, then it is comparing the source with the 'rest of' the system' which is composed of feed line and load. If the source is 50 ohms, the feed line is 50 ohms, and the antenna is 50 ohms, that meter will show an SWR of 1:1. If it shows other than that then it means that either the source's impedance isn't the same as what it sees on the other side of it. If the feed line and load is really 50 ohms impedance, then where does that 'difference' HAVE to be?
So, show me the mistake in that logic.
- 'Doc

That SWR meter is like a balance scale. It compares the 'weight' placed on one side of it with the 'weight' placed on the other side of it. It has no idea what makes up the 'weight' on each side of it, it can only tell you when they are the same or not.

So, how can you not think that the 'source' (transmitter or amplifier) can't affect the outcome?

[observer_1]

doc,
what you have wrong is how vswr meters AND amplifiers work,
vswr meters do not compare weigh measure sniff or otherwise the transmitter output impedance to the impedance connected to its antenna port, it was explaind by the guys in the other thread two causes of elevated vswr with increased power on an antenna system with a very low vswr,
amplifier instability ( large increases )
detector diode none linearity ( small increases )

somebody posted a link confirming
" VSWR is not in any way dependent on the equivalent source impedance of the generator"
[Please login or register to view this link]

where did you get the idea that vswr meters compare the output impedance of the transmitter to the impedance of the load?
where do you get the idea that no tune amplifiers are the cause of the elevated vswr on an otherwise near flat line?

do some actual testing, you will get a shock

['Doc]

Those two things, "amplifier instability ( large increases )", and "detector diode none linearity ( small increases )" are -possibilities-, not common probabilities, and never the only causes.
An SWR meter works by comparing forward and reverse voltages or currents. Those voltages or currents are a product of impedance differences between a source and load, which also includes the path between the two, the feed line. Change the impedance of any of those three things and you will see a change in the voltages or currents which produces that SWR reading. Simple as that. that tells me that the source, the transmitter, is one of the determining factors of that SWR reading.
If you and Mr. Duffy would like to test that, you certainly have my permission! Your results should be interesting.
I have something like 40 years of that sort of stuff. Both 'hands on' and theoretical. You have shown me no reason why I shouldn't think that I have the right idea. Good luck, and may the force (and reactances) be with you!
- 'Doc

[observer_1]

'Doc wrote:Those two things, "amplifier instability ( large increases )",

you don't have much experience with cb amplifiers,

"and detector diode none linearity ( small increases )" are -possibilities-,"

diodes are none linear devices, its more noticeable when changing power level on longer runs of feedline with low vswr

w2du says
Of course, for practical reasons there may be small, or even large errors in the actual results from obtained by SWR measurements for one example, diode non-linearity at various power levels

"and never the only causes."

agreed

"An SWR meter works by comparing forward and reverse voltages or currents."

agreed, you leared something since the other day

"Those voltages or currents are a product of impedance differences between a source and load,"

no, between a feedline and its termination, matching transmitter to feedline input impedance does not remove standing waves from the line if they exist nor cause them if they don't,


w2du says
The SWR on the transmission line between the antenna and a matching network at the input to the line is determined only by the mismatch conditions at the load, and is not changed or “brought down” by the matching network. “Low SWR” obtained by using the device indicates only the mismatch remaining between the input impedance of the network and the impedance of the line from the transmitter.


"which also includes the path between the two, the feed line."

agreed

"Change the impedance of any of those three things and you will see a change in the voltages or currents which produces that SWR reading. Simple as that.
that tells me that the source, the transmitter, is one of the determining factors of that SWR reading.

im pleased you find reflections simple, i don't but im slowly learning
does your vswr go up when you mistune your amplifier into a 50ohm line terminated with a 50 ohm dummyload?

"If you and Mr. Duffy would like to test that, you certainly have my permission! Your results should be interesting."

thanks, if i bump into duffy whoever he is, i will tell him he has your permission!

"I have something like 40 years of that sort of stuff. Both 'hands on' and theoretical."

you still have time to learn, i don't believe you can't teach an old dog new tricks

"You have shown me no reason why I shouldn't think that I have the right idea"

are you from jefferson?

"Good luck, and may the force (and reactances) be with you!"

i reflect that none dissipative remark

- 'Doc