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5/8 Wave groundplane 1.5:1 SWR all over the band

Discussion in 'CB Antennas' started by mattsowders1989, Dec 4, 2019.

  1. Blackcat630

    Blackcat630 Sr. Member

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    All this talk about cb and tv antennas had me reminiscing about my childhood. Got a midland "emergency handheld" as a Christmas gift from parents. I already had a scanner and that sparked my interest in radio but I needed something I could transmit on! The handheld had a magmout that you would scew the rubber duck into for mobile use. I jammed a piece of sheet medal under my 2nd story window sill for this. It plugged into the top of the radio with a male rca connector. Of course as a 10-11 yr old I didn't know anything about impedance so it made perfect sense to run to Radio Shack and buy a rca male to f type tv female adaptor. I immediately connected my handheld to the big winegard tv arial at 40 ft. Boy did I hear alot more than my little mag mount duck outside the window... dont think I made any contacts though..

    This is a pic of the exact model I had (courtesy of google). My first transmitter, that I of course had to take apart after I acquired a couple hand me down mobiles.. it never worked again lol.

    MIDLAND-Emergency-Radio-Model-77-912.jpg



    Sorry to further derail this thread BUT I bet my swr was WAY over 1.5 :LOL:
     

  2. AudioShockwav

    AudioShockwav Extraterrestrial Admin
    Staff Member

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    Ummm
    I unhooked it from the TV.
    I could tell you a story about living in a Apartment complex and loading up the Cable Tv 75 ohm coax with a home made Balun and a tuner.
    Feeding RF into the connection caused a huge amount of TVI to a lot of TV's.
    So much in fact that Comcast was out in force a few days later.
    But the connection had been unhooked by that time and they could not find any interference.
    And I took my Devil horns off and put them back in the closet.
    Oh
    I mean my friend did, I would never do anything like that.

    73
    Jeff
     
  3. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Haha, your friend is a funny guy! haha
     
    AudioShockwav likes this.
  4. SIX-SHOOTER

    SIX-SHOOTER Sr. Member

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    I don’t remember the radio but I had an old tube type radio as a teen that the manual mentioned using an outside TV antenna as a base antenna.I had so many radios that I am unsure of which radio it was but when I read some of the replies here it brought back memories of that owners manual.I seems that it had an adjustment on the back of the radio to adjust the SWR or something but again it’s been a very long time since then.

    SIX-SHOOTER
     
  5. Woody-202

    Woody-202 Sr. Member

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    This thread sure did get my memory going...My Dad, while not having any radio/electronics "likes" (or dislikes) himself, encouraged me during my embryonic years. He bought me a shortwave radio kit which required a lot of soldering (It was a Lafayette or Allied kit and I think it had 2, maybe 3 tubes). Memories can be deceptive, which explains why I recall the soldering iron as being as large (or larger) than my forearm :LOL:. Nonetheless, it was a great learning experience plus, my neighbor (the Bald Eagle) came blasting thru the speaker, which increased my interest in 2-way radio...:D
     
  6. 357

    357 Walkin' the dog

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    I heard they use junk for hardware. If its not stainless nuts bolts and washers, thats why.
    corrosion
     
  7. sp5it

    sp5it Master of puppets

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    That SWR obsession....
    The question is: where is resonance?
    Mike
     
  8. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Matt, I have the same question as Jay. What confuses me is your words I highlighted in red.

    Do you have a close up picture of what you are describing as the feed point on your SP 500?

    Are you telling us this is a modification you did to the antenna?
     
    #38 Marconi, Dec 7, 2019
    Last edited: Dec 7, 2019
  9. mattsowders1989

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    It's not that I don't understand SWR or reflect or impedance, I'm just a perfectionist I guess. I like to see an antenna as close to perfect as i can (and coax). Maybe it just eases my mind to see a 1:1 match. Thanks for all your guys input.

    direct fed at the match: coax is directly soldered to the antenna, then shrink tubed and black taped to help keep water out.

    like i said though, it was a bad jumper.
     
  10. RT431

    RT431 In the swamp

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    Some pictures would make us better understand how the coax is directly fed to the antenna.
     
  11. Road Squawker

    Road Squawker Sr. Member

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    If that were really correct, you wouldn't be worrying about a "1:1 match".

    Hint: see post $37
     
  12. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    I risk the wrath of some here in this thread getting "triggered" with my comments, but I have an opinion about what might be going here.

    I see Matt possibly having in mind his ideas about coax, connectors, and what I call the JoGunn approach with coax connections. If you check his posts history, you'll see that he does the "direct connect" idea on radios too. See PDF file below.

    IMO, this idea has been promoted by JoGunn followers for years. Among other things...the coax pig tail connection idea is the only way to go. This thread is more about egos, big radios, big signals, big power, big amps, and a big sound ie., Super Audio or Audio Gain.

    What I don't get is this idea by some Ham Operators suggesting that SWR results are futile and worthless bits of meaningless information...and in particular when chastising CB operators from on High. :D
     

    Attached Files:

    #42 Marconi, Dec 11, 2019
    Last edited: Dec 12, 2019
  13. Jay Mojave

    Jay Mojave Well-Known Member

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    Hello All: The SWR controversy goes on no dought. Antennas will perform quit well with a high SWR on some frequencies and not so well on other frequencies.

    Measuring two identical 800 MHz 1/4 wavelength ground plane antennas about 10 feet apart, well into the far field. With a network analyzer I saw the two ground plane antennas in S21 measuring the loss from one antenna to the other, I saw were the dead nutz SWR frequency was, and that wasn't the least amount of loss measured. The best loss measurement was slightly above the lowest SWR frequency.

    Rechecking the network analyzer calibration several times the S21 loss measurement was always the same. Changing the antennas around to different locations and swapping the coaxes around, again the same loss measurement results.

    Point is again some antennas will work quit well with a high SWR on some frequencies, and not very well on other frequencies. Measuring the field strength of antennas isn't easy as its the easiest thing to screw up a electromagnetic measurement and get it all wrong. Hope this helps a little.

    Remember the antennas SWR is also that of the coax loss that will make the antennas SWR look lower and have a wider bandwidth. But it is a valid SWR at the end of the coax as this is what the transmitter sees.

    Jay in the Great Mojave Desert
     
  14. 2NC995

    2NC995 DAN

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    Regardless of what one considers a “good” SWR...I would be checking things out if mine showed a significant change as the OPs did.
     
    Marconi likes this.
  15. The DB

    The DB Sr. Member

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    If I may. SWR, in and of itself, does not affect an antenna's performance. I have set up and operated antennas well in excess of anything discussed here, many of which have outperformed the "resonant" antennas that had a much lower SWR (fan dipoles and the like) they replaced at the same heights.

    Why do some antennas seem to work well even with sky high SWR, while others seem to work like crap? The reason is not the antenna, its the feed line. The fewer overall losses in the feed line the better the antenna with a higher SWR will function, this is why ham's tend to use window line or ladder line when operating this way. At the SWR ranges some of us operate at comparing ladder line to LMR-400 is like comparing LMR-400 to RG-58.

    I understand why those who operate on a single set of frequencies like the CB band don't often get the chance to experience this. With a single band system a "Z0" (that is the letter Z and the number 0) match, which is just the technical term for keeping everything the same impedance, is much easier to set up and maintain (and can have other benefits depending on the situation). Sometimes one is the better way to set up an antenna system, and sometimes the other is.


    The DB
     

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