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THROUGH THE GLASS ANTENNAS

Discussion in 'CB Antennas' started by TonyV225, Nov 1, 2010.

  1. TonyV225

    TonyV225 Supporting Member

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    How do these things work?? Is it a mist for the outside whip or antenna seeings how theres actually no connection between the 2 antenna parts?I actually bought a box of odds and ends and there was a brandnew through the glass but the stinger or outside mini whip is missing

    I thought about using this when doing a trip if someone doesnt have a radio or antenna I can put a portable setup together for them with this antenna and if need be will have to mak a new outside stinger. I already know they are not the best way to go but for a portable for someone with nothing it will be fine for a few hundred feet of communicating or monitoring / emergency.


     
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  2. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    i'm not sure of your question.

    are you asking how (why) they work?
    or
    are you asking how (well) they work?

    @VHF & above, i have run 100 wats thru one with no problems.

    as far as "why" they work, think of the 2 sides as the primary and the secondary of a transformer
     
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  3. SIX-SHOOTER

    SIX-SHOOTER Active Member

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    Thru glass!

    Most that I have seen have ONLY 50 watt or so power ratings so that could be an issue with some of todays rigs with higher output on 2 meters & 440 mhz.I have NEVER heard ANYONE bragging about how GREAT their THRU THE GLASS antenna was either! The connection is ALL RF thru the glass so that may be the issue with output power? :unsure:

    SIX-SHOOTER
     
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  4. W5LZ

    W5LZ Crotchety Old Bastard

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    Those 'thru-glass' antennas work because the two parts act like the two plates of a capacitor. RF is AC and AC can 'pass' through a capacitor rather easily. The 'size' of those two plates, along with what separates them, determine the value of the capacitor.
    Never having 'played' with them to determine the required size of those plates, or the dielectic insulation between those plate, I won't even guess as it. I can tell you that the frequency is also important in all that because 'higher' frequencies require 'less' capacitance than 'lower' frequencies.
    Power ratings for the things? I don't know, but I certainly wouldn't expect as much capability as with a "real-live" antenna. That automotive glass insulated capacitor just isn't going to have a huge power rating.
    Do I like the 'thru-glass' antennas? No, and I wouldn't have one unless absolutely necessary. Do they work? Yes, they do. Very well? No. They are adequate at VHF/UHF and higher, but forget it for HF. Just want one, or have to have one for some reason? Fine, do it. You can have the one reserved for me, tell'em I said so.
    - 'Doc
     
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  5. packrat

    packrat Active Member

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    Wouldn't be any good for "portable" use, as they are glued in place, and kinda difficult to move around. Also, I hear they are pretty picky when it comes to exact alignment of the plates.
     
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  6. TonyV225

    TonyV225 Supporting Member

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    I was actually thinking about making a scanner antenna out the one I have. I was thinking about that today and found replacement outside whips and plates with the adhesive but I am wondering if this would work at all. I have the main part but never got the outside plate and antenna so I found these replacements but there for cell phone I believe.
     
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  7. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Doc is correct about the basic principle of operation being like a capacitor. I have used one on 2m and it was not bad. I actually made one several years ago when one of the radio station's clients wanted to play our audio thru their PA system but could not pick us up inside the mall,too much concrete and steel. It was also nearly impossible to run coax cable thru the brick wall but a sealed window was nearby.Myself and the other engineer at the time made up two pieces of copper clad PC board with the center of the coax cable connected to each plate, one inside the window the other outside, and the shields connected to the window frame on each side. The inside piece went to the receiver and the outside piece went to an FM antenna mounted on the roof. It worked like a charm with no continuity between the two pieces.
     
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  8. W5LZ

    W5LZ Crotchety Old Bastard

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    :)
    I've also seen pictures of such a 'thru-glass' system, home made, for use on the HF bands, which did work adequately. It definitely was not small, was not simple, and while the cost wasn't discussed, I'll bet it wasn't cheap either! Was too large for a mobile unless you drove something with windows the size on a Grey Hound bus. So impossible, nope. Unlikely, very much so!
    - 'Doc
     
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  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    I am envisioning a no holes glass mount antenna for 80m mobile. :whistle:
     
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  10. TonyV225

    TonyV225 Supporting Member

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    A peice of diamond plate over the back window LMAO!
     
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