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Tuning 102" Whip?
- Thread starter buickid
- Start date
BTW Bob, you might be right that M.W. Maxwell states the theory best. However, I figure the link Booty Monster posted and starting with the 3rd paragraph beginning with: "If your antenna is truly 1:1 it doesn't matter........is an important consideration too. We can't just choose to ignore this part. So, I think this part supports my contention: that we are no better off using a tuned length vs. a random length line whether the match is good or bad.
I have the book, and I've highlighted many points, but I can't find the particular part where it says something to the effect...that this rather common 1/2 wave idea is dubious in its use at best. I thought maybe since you suggested Reflections as a resource...you could go right to it.
"I" claim about the same as Walter I think. So if the theory is true, then a random line will get you to a good tune just as easily as a 1/2 wave tuned line will...assuming your match is really bad to start with. And as the match gets closer, what is the problem that a little tweaking won't help solve using either line length.
If you use the line for a monitor hoping to keep a handle on a good match, then goto "I" where both such lines should produce the same matching results at both ends, and at every other part of the line when the load is perfect or just close to pefect.
This does not even consider what we've talked about recently regarding a grounded antenna with a tuned 1/2 wave multiple feed line length, and concerning common mode current issues.
What can I say 850? I have never been able to detect a difference with bonding ideas used by a couple of my buddies on their mobiles either. It makes sense that it does make some difference, but I and others were never able to detect it. Kind of goes with the tech reports that it makes a difference, but when you check the difference is very small. So, when it gets into the CB thinking all these differences suddenly become inflated.
I have an Eznec model of a mobile P/U truck, and I can add wires and remove wires. I see removing wire improving the characteristics I think. So I figure all metal mobiles probably tend to have too much ground plane rather than too little. So, when I talk about the ground plane in mobiles, I refer to it as being suitable or not. IMO this model supports the fact that I see the resonance go lower in frequency as I add more wires to the model and visa versa. The only other thing I can say about my mobile models are they do not show very good gain and angle results, in fact the mobile model typically doesn't show any gain at all. So any difference, even a small difference, could be of an advantage or a disavantage, but I just have not seen a difference. So, maybe my comment below in my signature is close to right. How say you?
I can only assume this might relate to real world mobiles however. On the other hand bonding seems like it would make sense, but I do not know how this all works out, and nobody seems to ever talk about anything except how successful they were after going to all that trouble. So I remain cornfused.
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I won't feed anymore into the personal comments here. You know I was just giving back a little of what I got. Like I told #6, I don't bite.
You're right on all your comments above concerning my questioning my own ideas and my ability or lack of getting my points across. Guilty on all counts. When I write stuff down it usually makes sense at the time, and sometimes I go back and I find some errors or disconnects.
When I write I use a lot of words, and I know that probably pisses most members off sometimes, but I'm usually trying to tell a descriptive story of my thinking. I could just cast comments, like a lot of folks do, and some are good enough to make reading even those a joy to read and respond to.
My whole point here was based on a post that 'Doc made in this thread sometime back. I responded, but that is likely long forgotten by most members that followed this thread. I should have just held my piece at his comments and not brought the subject up. This is not the first time I've attempted to talk about this as the chances came up. This idea of the tuned 1/2 wave line is a complex topic, that everyone else tends to make a matter of fact. I just see it differently, and that makes it hard to explain when rejection of any other idea is brought up. Like I said above, I have my own problems in saying what I mean, so it is no body's fault except my own.
Thanks for talking with me about it anyway.
I'll do the same as you CK suggest, and call this a failure to communicate and stop. I'm probably talking to myself anyway.
Before I drop this subject, I know this is not the theory in full, but here I have something to consider from Maxwell's Reflections II. <gotproof>
Even though only Bob gave and answer to my question, here is one of the portions in Reflections II, on the subject of 1/2 wave lines I was looking for.
Answer the last question #28, in full. The answer to all these T/F questions are True.
View attachment Reflections II.pdf
Even though only Bob gave and answer to my question, here is one of the portions in Reflections II, on the subject of 1/2 wave lines I was looking for.
Answer the last question #28, in full. The answer to all these T/F questions are True.
View attachment Reflections II.pdf
eddie,
the perfect 1:1 has nothing to do with 1/2waves and 1/2wave multiples have nothing to do with vswr on a matched or mismatched line,
you don't need a majic 1/2wave line in order to measure what the vswr is at the feed-point,
that's the part of the link i don't agree with,
all you need to know to calculate vswr at the antenna is vswr at the point of measurement, distance to antenna and line loss per mtr/foot etc,
vswr reduces smoothly the further away you move from the antenna due to coax loss,
changes in vswr with small changes in line length above what could be caused by any change in line loss indicate other issues such as common mode current changing the load impedance,
impedance looking into a mismatched line changes with line length, vswr ignoring line loss does not,
i think what you are getting at is how the complex rs and x readings change with line length on a mismatched line and how resonance measures at a different frequency as you change line length,
you are likely wondering if booty's majic 1/2wave feeder is leading him astray since he's measuring resonance at a frequency other than where his majic feeder is cut for or is he wasting his time with 1/2waves,
some software for vna's can do the maths/spin the smith chart for you and tell you the conditions at the feed-point or any other point on the line by calculating out the coax effects as somebody else pointed out in a different thread,
an example of how this works, look at the scans around 146.5mhz, impedance changes, resonant frequency changes but vswr stays about the same when he calculates the coax out of the readings,
Constructing a 2m colinear Part 2 « waynemerry
you beat me to it it is what you are getting at
the perfect 1:1 has nothing to do with 1/2waves and 1/2wave multiples have nothing to do with vswr on a matched or mismatched line,
you don't need a majic 1/2wave line in order to measure what the vswr is at the feed-point,
that's the part of the link i don't agree with,
all you need to know to calculate vswr at the antenna is vswr at the point of measurement, distance to antenna and line loss per mtr/foot etc,
vswr reduces smoothly the further away you move from the antenna due to coax loss,
changes in vswr with small changes in line length above what could be caused by any change in line loss indicate other issues such as common mode current changing the load impedance,
impedance looking into a mismatched line changes with line length, vswr ignoring line loss does not,
i think what you are getting at is how the complex rs and x readings change with line length on a mismatched line and how resonance measures at a different frequency as you change line length,
you are likely wondering if booty's majic 1/2wave feeder is leading him astray since he's measuring resonance at a frequency other than where his majic feeder is cut for or is he wasting his time with 1/2waves,
some software for vna's can do the maths/spin the smith chart for you and tell you the conditions at the feed-point or any other point on the line by calculating out the coax effects as somebody else pointed out in a different thread,
an example of how this works, look at the scans around 146.5mhz, impedance changes, resonant frequency changes but vswr stays about the same when he calculates the coax out of the readings,
Constructing a 2m colinear Part 2 « waynemerry
you beat me to it it is what you are getting at
Thanks Bob, I don't fully understand all the issues you note above, and I'm sure Booty Monster would have to get on some oxygen fast if he had to explain or understand this. I'm not really counting on him to test a little as we talked about earlier, I haven't heard a word from him in months. My discussion with him was the last time I considered this idea and after all those words back then, I have no idea what or how he was doing anything.
I asked him to check with me if and when he put his Vector up. If it had a bad match like it did before, then I wanted him to check a bit and see what he saw with a bad match. He of course would only have an SWR meter, and I wasn't sure if the idea of a changing SWR with a change in feed line length would reveal anything on his SWR meter or not. I don't think he would see a good SWR at the radio end, and I doubt seriously he would be able to test his SWR at the antenna.
I'm a bit confused at this point, but I think I've always thought the SWR at the antenna might not change due to change in the feed line unless the antenna changed physically, but beyond that you are probably right the SWR does not change with match at the feed point.
Again, I may be wrong, but I don't consider all this high tech talk valuable to the average Joe, like myself, that just wants to try and know more about what guys are doing when they talk about ideas like the 1/2 wave tuned line.
To tell you the truth, sometimes when I'm working with this stuff and I think I have to go right, just for the hell of it I go left, and more times that not...that is the right direction. I don't have all this stuff in my mind's eye like you do, but I do get some value with my experiences.
I also noted another T/F question #23, at 2-5 in Reflections that speaks about the invalid results using a 1/2 wave line if the results change significantly along the line. To me that idea is suggesting we have a mismatched load when that happens, and then I wonder what these guys do with the information their analyzer shows them at that point that helps them tune better than just using any old feed line.
But Bob, all this stuff so far is what other folks say, even with Maxwell, so I just try and line my experiences up with these ideas, and see if I can make any sense out of the process. I have seen good results through a tuned 1/2 wave length line before looking at a good load that is very close, but that same line has never helped me tune any better than a random length if the match was bad. My eye sight and lack of stamina is so bad these days, I can't even test in the shack anymore. My old meter is also getting raggedy and now with a weak battery is about off by 10 ohms with a 49 ohm resistor testing across the leads, so I don't even see a resonant load with less than 10 ohms of reactance.
So, I can still stand corrected. It is late and I'll probably check this tomorrow, and find all kinds of error and disconnects. Forgive me.
Thanks.
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No Eddie you are not talking to yourself. I look at all threads/post as part my admin duties. I comment when and where I feel like it.
I know I said I would comment no further but since you are still having a problem understanding something I will add just this one last time.
THERE WAS NOTHING GIVEN THUS NOTHING TO GIVE BACK OR BITE ON! I WAS NOT SHITTING ON, YOU JUST TRYING TO (1) UNDERSTAND WHAT YOU WERE TRYING TO SAY AND (2) POINT OUT WHERE I THOUGHT YOU WERE MISSING SOMETHING. :bdh:
Now feel free to continue with the discussion in any way you see fit. I will NOT interject any more. At all. Period. Nope. Not unless it requires admin action or there are any more posts directed specifically at me. Carry on with the discussion free of any encumbrances from me. Have at boys.
Somehow I missed everything on that page after my post... So this is a somewhat late response...
You won't get any heat from me over this. The way most CB radios are tuned out of the box you could typically get away with a 5:1 SWR and even higher with no real problems, and depending on the antenna system, likely no real negative effects either. The problems come in when someone pushes the radio/amplifier well beyond the chip specifications.
I merely mentioned the 2:1 SWR figure as that is when either SWR lights or SWR protection circuits in modern radios typically kick in.
SWR as a whole is highly misunderstood today, and has been for quite some time. When SWR was first discovered those who discovered it didn't notice any difference between a high SWR and a low SWR on the far end. That lack of any difference in the real world has not changed, so long as you have minimal losses in your feedline.
The DB
I don't know what da fuk your problem is, do you take medicine? or perhaps drink a lot?
it's an old JOKE,..........
the "alternative" is not getting any older,.............. Gomer.:angry:
just because you repeat the same incorrect concepts over and over and over again will not change accepted FACTUAL information...... as you were told by others in this thread.
oh, by the way,.................
YES
eddie,
this topic keeps cropping up over and over, at one point not so long ago i thought we were all singing from the same hymn sheet almost, now i don't think we are,
the only solution i can think of for you is to buy a decent vna software & some decent quality loads ( hot ham crap in a paint tin ) and do some testing of your theory,
if you can't do that as you just told us then its a choice,
do you believe maxwell, mfj and a myriad of others that vswr does not change along a line anymore than that cause by line loss even when the line is mismatched,
or you can believe majic 1/2wave guys misinterpretation of what they are measuring,
im with walt and the other guys until it can be explained and demonstrated as incorrect
this topic keeps cropping up over and over, at one point not so long ago i thought we were all singing from the same hymn sheet almost, now i don't think we are,
the only solution i can think of for you is to buy a decent vna software & some decent quality loads ( hot ham crap in a paint tin ) and do some testing of your theory,
if you can't do that as you just told us then its a choice,
do you believe maxwell, mfj and a myriad of others that vswr does not change along a line anymore than that cause by line loss even when the line is mismatched,
or you can believe majic 1/2wave guys misinterpretation of what they are measuring,
im with walt and the other guys until it can be explained and demonstrated as incorrect
