Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

EVERYONE SHOULD READ THIS SITE!!!!!!!


You got to admit though, that there Star Gun shore is a purty antenner.

I think DJBoutit needs 4 of those on his bread box on wheels.
 
I may be off on this one but I'll put it out there anyway. I have a problem with The author's myth #8. The writer makes the statement that a particular coax length can not change the SWR of the line . He is very correct in that The coax length has nothing to do with the antenna or feedline impedence. However, SWR by definition only measures the stanging wave at a single point in the line. If the SWR bridge happens to be at the point in the line where the reflected wave is the right fraction of the resonant frequency, then the swr at that point is what ever it is (which can be 1:1). Changing the feedline length does not "fool" the meter. The meter is doing what it is supposed to do and measuring the reflected wave compared with the forward wave at that place in the line. The author makes this statement:

"To get a Standing Wave Ration of "1 : 1" both the antenna and the coax must have an impedance of 50 ohms."

This is simply untrue if the point of measurement happens to be at a null voltage point in the line (usually multiples of 1/2 wave). There is no "line" SWR, only point of measurment SWR.

Of course none of this means that the antenna and feed line should not be matched for best power radiation. However a mismatched feed line/antenna will perform it's particular best, when the coax is is of a length which allows for a 50 ohm feed from the radio. When this is acheived, the radio can put out it's maximum power rating, which will help a poorly matched feed line/antenna combo perform better than it would with a higher SWR.

Like I said at the outset, I may be wrong here but this is how I see it.
 
I think you are seeing it right. So, another way of saying that the meter is 'fooled' would be the meter and/or the operator is being 'fooled' into thinking that the whole antenna system is 'right' and wouldn't benefit from being re-tuned the really 'right' way. The transmitter might be 'fooled' into producing max output, but because there's still an imbalance in the system, -all- of that output isn't getting to the antenna to be radiated.
Something/someone is still being 'fooled' into thinking things are 'right' when they're not. (Personally, I'd rather think that the silly meter is being 'fooled' rather than I am, you know?) What it amounts to is that you/I are depending on the ability of a meter that just doesn't have the ability to tell you what you really need to know to make things right.
- 'Doc


(You ready for this? "Percussive ausculation"(sp) can tell you a lot of the things that an x-ray can tell you. I think I'd rather rely on that x-ray than someone's 'pa' abilities, you know? Sort of?)
 
Nursecosmo said:
"To get a Standing Wave Ration of "1 : 1" both the antenna and the coax must have an impedance of 50 ohms."

This is simply untrue if the point of measurement happens to be at a null voltage point in the line (usually multiples of 1/2 wave). There is no "line" SWR, only point of measurment SWR.
Click to expand...

I think you may be referring to VSWR.
There are fairly sharp null points of voltage standing on a poorly matched transmission line.
But the current standing at the same point is opposite: it peaks at the voltage null point.

Maybe its better not to think of antenna/coax mismatch that way.
I think it better to think of it in the context of return loss, which is specified in dB.
For example: an SWR of 3 is same as a 6dB return loss, meaning that the power reflected back to transmitter is 6dB down from the transmitter "forward" output power. Another swr, such as 1.2 is a 20dB return loss.
Return loss does not change depending on coax length, except for the coax insertion loss which is small for CB frequencies.

PS: an SWR of 1 is actually physically impossible. nothing in this world is perfect.
 
dudmuck said:
I think you may be referring to VSWR.
There are fairly sharp null points of voltage standing on a poorly matched transmission line.
But the current standing at the same point is opposite: it peaks at the voltage null point.

Maybe its better not to think of antenna/coax mismatch that way.
I think it better to think of it in the context of return loss, which is specified in dB.
For example: an SWR of 3 is same as a 6dB return loss, meaning that the power reflected back to transmitter is 6dB down from the transmitter "forward" output power. Another swr, such as 1.2 is a 20dB return loss.
Return loss does not change depending on coax length, except for the coax insertion loss which is small for CB frequencies.

PS: an SWR of 1 is actually physically impossible. nothing in this world is perfect.
Click to expand...

Yes, both the author and myself are referring to VSWR, being that the cheap SWR meters we are discussing don't directly measure ISWR or PSWR.

My beef with the article is not that his reasoning isn't sound regarding misconceptions about antenna/feed line matching, But rather with the fact that he is himself perpetuating misinformation about what a SWR meter actually does, and what SWR (in its various incarnations) actually is.

PS#2: A SWR of 1:1 is absolutely possible(as near as can be measured with known equipment and methods). It is a perfect radiator which is impossible. A good dummy load is capable of returning 0% of the wave form back to the source. A very long feed line which does not even terminate in an antenna will also provide a perfect load.
 
4) To get out you need lots of swing in your AM signal.​
Wrong. An AM signal is fully modulated when the "swing" doubles the carrier. That is to reach 100% modulation a 4 watt key should swing no more than 8 watts. Anything more than that is distortion to your voice. The AM carrier is necessary for the receiver to properly demodulate the audio from the signal. If you add excessive swing it will distort your audio. It will not help you get out better.







Pity the site owner doesn't understand AM swing though,for 100% modulation you will see 6 watts forward swing,not 8 watts on an average reading meter and just under 16w pep on a peak reading meter.


The carrier's voltage amplitude will be doubled,not the power.
​
 
well now, if everything can/could be fooled,whats the use???????????

just throw up an antenna,hook up some coax,and talk

heh heh heh
 

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom
      Back