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Thread: Feedline radiation question

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  1. #11

    Default

    Quote Originally Posted by W6OGC View Post

    How does one build a current meter?
    http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

    http://vk1od.net/measurement/icm/index.htm

    http://www.w8ji.com/building_a_current_meter.htm


    If you follow the link in the first paragraph, there is a link to VK1OD's article on building a current meter. W8JI has a similar article on his website.

    Did you actually look at my link?

    Have you ever used Google?

    G3TXQ - I said in my write-up that common mode is a standing wave and not a universal indicator - however high common mode current measured anywhere it isn't supposed to be indicates a problem. I also mentioned it is responsible for receiving as well as radiating. I also referenced your table on chokes and impedance.

    G3GQK - ignorance is not bliss. It is just ignorance, and particularly annoying to those people looking for and sharing understanding.
    Charley K1DNR

  2. #12

    Default

    Quote Originally Posted by K1DNR View Post
    G3TXQ - I said in my write-up that common mode is a standing wave and not a universal indicator - however high common mode current measured anywhere it isn't supposed to be indicates a problem. I also mentioned it is responsible for receiving as well as radiating. I also referenced your table on chokes and impedance.
    Charley,

    I wasn't being critical of your write-up - simply trying to re-inforce those points for the benefit of members who read forum posts but don't read the linked articles

    73,
    Steve G3TXQ

  3. #13

    Default

    Quote Originally Posted by K1DNR View Post
    If you follow the link in the first paragraph, there is a link to VK1OD's article on building a current meter. W8JI has a similar article on his website.
    Here's another way to go: http://www.mfjenterprises.com/Produc...ductid=MFJ-853
    73, Cecil, www.w5dxp.com
    Can CO2 emissions save us from the coming ice age?

  4. #14

    Default

    Quote Originally Posted by W6OGC View Post
    What approach is most satisfactory?
    You could just ignore the fact that coax will radiate – physics of the beast.
    I would not ignore it or bother to measure it – it will be there!
    I prefer KISS approach – choke “balun” - unless you are using RG8 and than you have to do something about the weigh of the choke. Not a problem when the feed line is supported.
    Ferrites are my second choice, but the weight may also be a challenge.
    73 Vaclav

  5. #15
    Join Date
    Mar 2009
    Location
    Texas hill country
    Posts
    1,565

    Default

    Quote Originally Posted by K1DNR View Post
    http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

    http://vk1od.net/measurement/icm/index.htm

    http://www.w8ji.com/building_a_current_meter.htm


    If you follow the link in the first paragraph, there is a link to VK1OD's article on building a current meter. W8JI has a similar article on his website.

    Did you actually look at my link?

    Have you ever used Google?

    G3TXQ - I said in my write-up that common mode is a standing wave and not a universal indicator - however high common mode current measured anywhere it isn't supposed to be indicates a problem. I also mentioned it is responsible for receiving as well as radiating. I also referenced your table on chokes and impedance.

    G3GQK - ignorance is not bliss. It is just ignorance, and particularly annoying to those people looking for and sharing understanding.
    IOW,



    Some of us who are less technically proficient need more basic explanations, I'm afraid.
    73 de W6OGC

  6. #16
    Join Date
    Jan 2000
    Location
    Commerce MI (Detroit area)
    Posts
    8,024

    Default RF in shack?

    If you have high levels of RF in shack, getting loud noises in computer speakers, little RF burns off metal equipment housing, mic, key etc, I would start by placing the Ferrite beads or UnUn or BalUn on your coax at the feedpoint of the antenna and not inside the shack beteen tuner and rig etc.
    73.....JD, FISTS #3853,cc 455,SKCC # 1395,tribune #12,
    Official US Taxpayer

  7. #17
    Join Date
    Jan 2011
    Location
    Houston Texas
    Posts
    4,859

    Default

    You can do a lot with a field strength meter.

    You can check stuff that is in conduit without needing to direct couple to the wire.

    How to fix a problem, may be harder than finding a problem.
    "Theory only works perfect in a vacuum." KA9JLM Don

  8. #18

    Default

    The OP "What approach is most satisfactory?"

    And your answer is.....


    Quote Originally Posted by K8JD View Post
    start by placing the Ferrite beads or UnUn or BalUn ...
    Just curious - did you watch the video ?

    Nothing personnal, but this is why US does not have people interested in engineering.
    It is easier to BS than to be factual.
    Last edited by AA7EJ; 04-10-2012 at 06:15 PM.

  9. #19
    Join Date
    Feb 2002
    Location
    Right here
    Posts
    12,995

    Default

    As an AH4 owner, user, and experimenter I can tell you that the only situations that ever gave me any significant common mode on the feed line was a. not having an adequate RF ground, and b. using an end fed antenna that was very close to a half wavelength.

    If you have a good RF ground at the tuner and that means a very short run to a good RF ground, you should never have any significant RF on the coax or the control line. This only applies to end fed wires and verticals.

    For loops and dipoles (balanced antennas), unless you are close to one half wavelength at the frequency of operation or, the antenna is not balanced (like a dipole with one side shorter than the other or hanging over a metal roof) common mode RF current should be insignificant. I like Eric's suggestion of measuring the return current on the coaxial shield, it may not be enough to worry about.
    I'm sorry you don't have the experience or understanding to realize that others possess a skill set that you seem to dismiss as fantastical.

  10. #20

    Default

    Quote Originally Posted by W6OGC View Post
    IOW,



    Some of us who are less technically proficient need more basic explanations, I'm afraid.
    I don't consider myself technically proficient. I was trained as a musician, who went into computer support in my 30's, and then got a masters degree in management. There is little about me that is formally technical.

    I have spent some time over the past year trying to understand fundamental ham radio theory concepts, like basic AC theory.

    What part don't you understand? I see you are a lawyer and have done a lot of volunteer work, etc - so clearly you are up to task from an intellectual standpoint.

    You also have an Advanced ticket, which means at some time you learned basic concepts like reactance and resistance = impedance.

    All I presented to you were:

    1 - a suggestion to make a rather simple device to measure the current
    2 - a little bit of info on chokes, and how to measure their effect.

    There is another approach which is to throw ferrite at stuff until the problem goes away.

    I think it is more fun to measure, and know exactly what works, where, and just a little bit about why.

    No equations have been presented. No trig or calculus.

    I don't follow the reference to the admittedly funny video, even If I do consider it a bit insulting.
    Charley K1DNR

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