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mfj /wil 5k?

D

dxing440

Active Member
Apr 10, 2011
161
10
28
Just curious, Im running a Wilson 5k (thru the roof mount), 11.75ft of coax (1/2wl of rg58a/u), using a mfj 259b antenna anylizer'
Ch 1=1.2swr,46ohms,and 0 react, ch 20=1.1swr, 43ohms, and 2 react ch40=1.3swr, 39ohm, and 8 react. I've never been able to achieve 50ohm reading on any antenna, mobile or base! But usually Swr are good.
ANYONE ever been able to achieve 50ohm, with an antenna, using thru the roof?

Would some of you guys post some readings of your antenna using 1/2wl of whatever coax you are using? So every one can compare
 

dxing440 said:
Just curious, Im running a Wilson 5k (thru the roof mount), 11.75ft of coax (1/2wl of rg58a/u), using a mfj 259b antenna anylizer'
Ch 1=1.2swr,46ohms,and 0 react, ch 20=1.1swr, 43ohms, and 2 react ch40=1.3swr, 39ohm, and 8 react. I've never been able to achieve 50ohm reading on any antenna, mobile or base! But usually Swr are good.
ANYONE ever been able to achieve 50ohm, with an antenna, using thru the roof?

Would some of you guys post some readings of your antenna using 1/2wl of whatever coax you are using? So every one can compare
Click to expand...

On a mobile installation you should never be able to achieve 50 Ohms where the antenna is resonant (X=0). Neither is a quarter wave vertical 50 Ohms in a base installation nor a dipole which is 48 Ohms. In fact the only thing you'll ever come across that is 50 ohms is a dummy load.

SWR is never 1:1 where X=0 unless you're using a really crappy antenna with a lot of loss. The fact you have 46 Ohms and a SWR of 1.2:1 where X=0 is a good thing.

X=0 is where your antenna is actually tuned, not where the lowest SWR is. I'd leave it alone, it appears to be installed quite well and its not worth tweaking any more. A drop to 1.2:1 at the top end will not be noticeable performance wise.
 
To the best of my knowledge I have never seen any antenna measure out to a 50R x 0J. In most cases the 'R' isn't that big a deal, but the 'J' is. If the SWR works out to something less than 2:1 and the 'J' is as low as it's possible to get (single digits), then the antenna is as tuned as it can possibly be without using an impedance matching device of some kind.
Antenna tuning always involves two parts, resonance and impedance matching. Most people only do that impedance matching thingy, which is at the expense of resonance. The 'bad' part about tuning is that it can not be done with only an SWR meter.
- 'Doc
 
I've not had any issues, I very pleased with the Wilson, don't regret at all drilling a hole in the roof. Just wondering if any one ever got 2 or 3 outta 3 Swr,ohms,react.
 
I've seen pictures of perfect 50 ohm readings for various antennas on various forums, so it is possible, but really your chasing irrelevance.

Your using that analyzer to get a perfect SWR match, however, the perfect SWR match is rarely the best performance setup for an antenna. As a matter of fact, SWR by itself tells you nothing about antenna performance. On the plus side, you are looking at the right place, namely the X and R values that are shown, unfortunately you are using them for the wrong purpose and in the wrong way.

To put SWR into perspective, SWR tells you exactly one thing, and that is how well the signal at the radio (or amp or whatever) end of the coax will match up to the 50 ohm device it is being plugged in to. When it comes to antenna performance you need to look at the other variables that you are already looking at and learn about them.

X you likely already have an idea about. It shows reactance, well kindof. Well enough for most people in the CB/Ham worlds anyway. Here you are balancing the two types of reactance, and when they are equal you have resonance, or X=0.

When it comes to R many people, especially new users of antenna analyzers who came from using SWR meters before hand, are still thinking in terms of SWR, so for to many R=50 is as good as it gets. That is fine, but R is more than just a number to get close to 50, and in some cases getting it closer to 50 will actually hurt antenna performance. In reality, for best performance, you want R to be as low as you can get it while X=0 and still maintaining a reasonable SWR (2:1 or less). This is because R is representing two things added together, the radiated power and the lost power due to things like ground losses and loading losses ect. As you lower losses the radiated part of R takes up more and more of the whole, meaning a stronger signal is transmitted. This loss is entirely different than the losses caused by SWR which, due to re-reflection is rarely anywhere near as bad as people make it out to be.

This is easily confirmable by using a field strength meter along with your antenna analyzer. If you used a field strength meter with just an SWR meter before getting an antenna analyzer you would already have been aware that the strongest radiating tune on the antenna is not always the lowest SWR point...


The DB
 
The DB :To put SWR into perspective, SWR tells you exactly one thing, and that is how well the signal at the radio (or amp or whatever) end of the coax will match up to the 50 ohm device it is being plugged in to. When it comes to antenna performance you need to look at the other variables that you are already looking at and learn about them.
The DB : That is fine, but R is more than just a number to get close to 50, and in some cases getting it closer to 50 will actually hurt antenna performance.
The DB : the strongest radiating tune on the antenna is not always the lowest SWR point...


Very Well Explained! Sometime swr goes up (say 1.6) but Ohms go down, and react goes down as well, : Hince: power difference from ch1 to ch20 to ch 40. Different swr,react, and ohms at all 3 channels,But the person on the receiving end never notices.

Thanks for everyones input
 
The part often forgotten about transmitted signals and which is completely misunderstood in the CB fraternity is it takes more than a doubling of the radiated signal to have a noticable difference at the other end whether that be local or DX.

Changing from a 50W amp to a 100W amp won't gain you much. You'll notice going from 4W to 50W though because its a twelvefold increase worth a good few S points on the meter.
 

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