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That whole coax length thing...
- Thread starter The Jerk
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The E1/2 wavelength or multiple of coax works every time and gives you room to move around while tuning plus eliminates the risk of breaking an antenna jack on your meter. In all reallity a short jumper six inches to a foot or so long is more than adequate and will not introduce much error at all.The problem is getting the meter within a foot or so of the feedpoint on a base install.
I use 468 as my calculation number for a 1/2 wave length, as stated on page 313-315. Of ( Lou Franklin's )
Understanding & Repairing CB Radios For The Professional Technician
I must say it works for me!
Oh by the way, C W Morse, I'm waiting on hearing you reply to captain Kilowatt question on post #56 that was directed toward you?
Understanding & Repairing CB Radios For The Professional Technician
I must say it works for me!
Oh by the way, C W Morse, I'm waiting on hearing you reply to captain Kilowatt question on post #56 that was directed toward you?
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Me too. Just so he does not have to search for it here it is:
http://www.worldwidedx.com/general-...825-whole-coax-length-thing-6.html#post200967
B
BOOTY MONSTER
Guest
captian kilo , in a previous post you told me you were mistaken when you told me on another forum that 468 was the right number in the formula to calculate the length of an electrical quarter wave length of coax ...... that 492 was the correct number .
http://www.worldwidedx.com/cb-antennas/30479-10k-tunes-1-3____102-3-0-a.html
see post #5 .
that several inch difference per quarter wavelength may not be critical , but if someone is gonna go to the trouble to do the calculation and cut the length it seems to me using the most accurate number to get the optimum length and getting as close to perfect as possible is their intent .
anyhow ..... is the correct number 468 or 492 ? and if its 468 what have you learned to cause you to change your mind from correcting your 468 to 492 comment in the older thread ?
http://www.worldwidedx.com/cb-antennas/30479-10k-tunes-1-3____102-3-0-a.html
see post #5 .
that several inch difference per quarter wavelength may not be critical , but if someone is gonna go to the trouble to do the calculation and cut the length it seems to me using the most accurate number to get the optimum length and getting as close to perfect as possible is their intent .
anyhow ..... is the correct number 468 or 492 ? and if its 468 what have you learned to cause you to change your mind from correcting your 468 to 492 comment in the older thread ?
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BM, the base number 492 relative to frequency has scientific value and is used to calculate, in free space, the approximate length of a 1/2 wavelength in feet---for antennas and coax, not a 1/4 wave.
The number 468 has no scientific relevance, except that it happens to be an adjusted value of 492. 468 results in an average 1/2 wavelength(') for a resonant radiating antenna element below 30 mhz, which accounts for the element's length/diameter ratio ie., "k" factor.
When the number 468 is used, it will be used to get a closer length(') for a 1/2 wavelength radiator. With this said, the element may also need to be further trimmed due to, among other things, construction, end effect with insulators, and stray capacitance around the antenna when mounted.
In the "K" factor chart, the average ratio in the range of K values is .95, which is about in the middle of the range from a very thick diameter to very thin. K-FACTOR Table & Chart by dxzone.com
edit:
I find the chart for the "K" factor chart is hard to get to. From the link above click on Theory, then scroll down to Alphabetical and click on page 2. Again, go down to Alphabetical and near the top of the list you will see K-Factor Table & Chart
Real world length(') = 492 x K / f (mhz) = 492 x .95 / 27 = 17.31'
Free space length(') = 492 / 27 = 18.22'
Real world length(') = 468 / 27 = 17.33'
The stuff above is not relevant to coax. Coax has its own factor called Velocity Factor (VF) and again 492 is the base number to use if you need to calculate a tuned resonant length of coax.
This distinction is often missed when looking at pictures and not reading the words that describe the pictures. This is likely what happened to the chap that claims to have read Lou Franklin's book. Lou discusses these same distinctions, but again you have to read his words, and not just look at the pictures.
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B
BOOTY MONSTER
Guest
B
BOOTY MONSTER
Guest
purenrg , since you apparently have lou's book and know where to go to find the info could you possibly scan the page and post it here as an attachment ?
thanks
thanks
BM I'm sorry, I do not have a scanner only his book, maybe someone else could help me back up what I am trying to quote. All that I can do is re-write what Lou stated/published. This is a great book I highly recommend this to everyone in this forum it has really helped me out, I have no connections to Lou what so ever just hate when someone talks down to others/me like that without quoting what was published! I will not wast my time with BS!
eddie,
lou does not get everything correct in his books,
this was talked about on another forum, i have seen at least one error about coax electrical length,
when calculating phasing harnesses other than 1/2waves you must also have resonant antennas with the same characteristic impedance as the coax,
terminating coax with a pure resistance other than its own characteristic impedance causes reflections and those reflections cause an interference pattern of current and voltage between forward and reflected wave
( remember the double slit experiment )
current will lag or lead voltage as you move along the line dependant on the pure resistive termination been higher or lower than coax characteristic impedance and inverting at 1/4wave points,
if the load also has reactance it causes further phase shift,
as far as i am aware ( always trying to learn ) the only time current or voltage delay is proportional to the calculated electrical length is when the line is terminated by a pure resistance of its own characteristic impedance or when the line is an electrical 1/2wave.
another instance i can think of where coax length has an effect is when the coaxial outer braid common mode impedance causes line radiation screwing up your radiation pattern,
is coaxial length important?, that depends on what you expect the coax to do.
lou does not get everything correct in his books,
this was talked about on another forum, i have seen at least one error about coax electrical length,
when calculating phasing harnesses other than 1/2waves you must also have resonant antennas with the same characteristic impedance as the coax,
terminating coax with a pure resistance other than its own characteristic impedance causes reflections and those reflections cause an interference pattern of current and voltage between forward and reflected wave
( remember the double slit experiment )
current will lag or lead voltage as you move along the line dependant on the pure resistive termination been higher or lower than coax characteristic impedance and inverting at 1/4wave points,
if the load also has reactance it causes further phase shift,
as far as i am aware ( always trying to learn ) the only time current or voltage delay is proportional to the calculated electrical length is when the line is terminated by a pure resistance of its own characteristic impedance or when the line is an electrical 1/2wave.
another instance i can think of where coax length has an effect is when the coaxial outer braid common mode impedance causes line radiation screwing up your radiation pattern,
is coaxial length important?, that depends on what you expect the coax to do.
Notice that 468 is 95% of 492 and that is the difference between a half wave in free space and one in the real world. Also since the post you reference was made in 2008 I suggest that the reason I switched formulas is because of CRS commonly known as Can't Remember $hit.
Since I tend to live in the real world and not the imaginary free space world I use 468. It has worked for me and that's all I can say. I REALLY think the difference is being WAY over estimated and debated. If you needed to steer a deep null in a certain direction to protect a co-channel station like in broadcasting it makes a difference but in the hobby world it does not matter. So what if it results in an SWR of 1.01:1 instead of 1:1 and that is about all the difference it will make.If phasing two antenna on a mobile setup, it won't matter at all because there are other factors that will skew the pattern such as differences in groundplane.
Agreed.
I have read about all of Lou`s Books and find valuable info in them, but he makes mistakes as we all do.
Years Of Experince is sometime`s as valuable as written word.
And Hello Marconi, I did not get the hint on the other post, I have been doing well, and Glen And Jeremy Are doing fine, Jer and the Grand Kids Live In Sadila Mo Now.
Hope you are doing well.
Please tell "Old Grampa" Hello for me...I do miss hearing him on 36 LSB....the Driver is Missed
73
Jeff
Purenrg, I don't have Lou's book, but I have seen a list of his calculations I think, and he makes this whole issue of coax measurements vs. antenna measurements clear, and that is what keyed me to your remark about making a 1/2 wave---whatever was on your mind at the time. I don't know if you were talking about coax or and antenna.
The topic of this thread originally was about coax length in a mobile, and IMO the topic got side-tracked a little. The issues between the use of 468 as a base number for calculating the length of a near resonant antenna and 492 as a base number to calculate the length of a tuned jumper or multiples of a tuned feed line seemed to me to be confusing. This thread was all over the place.
In your original post noted below you asked CW Morse to answer the question that CK asked him and that question was about coax length. In the beginning of Ck's post #56, he was talking about trimming an antenna
and toward the end of his post, including his question to CW, he was talking about coax length. This is where you commented below and where I thought you were talking about coax length:
So, I figured again that you were talking about using 468 to make a 1/2 wave tuned jumper or feed line, and thus my remarks about Lou's book. If so, then I think you were technically wrong. However, if you were talking about making an antenna or cutting a resonant 1/2 wave antenna---then I owe you an apology. But, if you were talking about coax instead, you will have to prove me wrong by posting something that Lou writes on this issue.
Personally I might make an argument that this little difference probably is
not really important, but if we want to be right and understand the issue then we should use the right formulas and measurements to make a tune length of coax or measure close when making an antenna so we don't have to trim and test so much. In any case we can successfully use both numbers to our advantage if applied correctly.
If I'm wrong here, I will tell you I'm wrong.
Hello Jeff, you're just not use to seeing me posting with so few words, right? I'm doing better, but I'm still not up to par.
I notice that you and Bob85 are giving me the caution about Lou's book. You are going to force me to go back and look at what I said in that regard. I didn't mean to leave an impression, one way of the other, about the veracity of his books. I just recall seeing a list of formulas and calculations that spoke to the problem I saw in this discussion, and I think he authored the list. The web address where I think it was is not working any more. I think all of his stuff is not a product of www.Google.com/books.
I completely disagree with his ideas on mobile co-phasing for example, and with all that the man has written---he has to have made mistakes like we all do---plus he has to deal with opinions too.
I have to give any man that started his radio experience with two #303 Libby's tomato juice cans, two buttons, and some kit string, credit for paying his dues for experience in two-way communications.
I notice that you and Bob85 are giving me the caution about Lou's book. You are going to force me to go back and look at what I said in that regard. I didn't mean to leave an impression, one way of the other, about the veracity of his books. I just recall seeing a list of formulas and calculations that spoke to the problem I saw in this discussion, and I think he authored the list. The web address where I think it was is not working any more. I think all of his stuff is not a product of www.Google.com/books.
I completely disagree with his ideas on mobile co-phasing for example, and with all that the man has written---he has to have made mistakes like we all do---plus he has to deal with opinions too.
I have to give any man that started his radio experience with two #303 Libby's tomato juice cans, two buttons, and some kit string, credit for paying his dues for experience in two-way communications.
Haha... not at all my "old Friend", I was in fact, Agreeing with you. I have read much of Lou`s stuff, and have gleaned a lot of knowledge from his Writings, but over the years I have learned to not take everything I read as Gospel...as they say.
You and Guys like Bob have earned my respect by the many hours you have put into trying things outside of the box and taking the time to share that with all of the guys here.....
73
Jeff
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