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Thread: Lamp cord for twinlead????????

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  1. #21
    Join Date
    Mar 2006
    Location
    Newcastle, NSW, Australia
    Posts
    2,845

    Default

    There are several ways to measure the characteristic impedance of a line; all require some kind of RF instrument and/or generator.

    A DVM is not included in that instrument category, I'm afraid.

  2. #22
    Join Date
    Oct 2001
    Location
    "Downeast" Maine
    Posts
    893

    Default

    Found a coupla pix...





    JW
    [CENTER][FONT="Times New Roman"][SIZE="4"][B]It's not the [I]"class of license"[/I] that an amateur holds..
    It's the [I]"class of the amateur"[/I] that holds the license.[/B][/SIZE][/FONT][/CENTER]

    [CENTER][URL="http://www.geocachingmaine.org"][IMG]http://www.geocachingmaine.org/logos/GM-large.gif[/IMG][/URL][/CENTER]

  3. #23
    Join Date
    Jan 2000
    Location
    Indiana
    Posts
    4,970

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    Those of use who, years ago used Zip cord as feed line, had no clue what SWR was, didn't even care. We made contacts ... THAT was what counted. We used toggle switches as antenna changeover relays (who could afford a relay)..! Our cords had rubber insulation. Never heard of plastic for that use at the time..!

    Used to be that whenever you had a lamp repaired, the cord at the plug was tied in the UL knot. Same for many new lamps and corded devices we used to purchase. Not any more, the things are molded together and hopefully they made the connections to the plug ... have see a few that were not. Dead open from wire to plug tip.

    There was a time when a cord went bad that you took it to a Radio repair shop ... and they fixed things. Amazing technology..!!

    Bill, W0LPQ

  4. #24
    Join Date
    Feb 2003
    Location
    **** Rest in peace sweet Caylee *****
    Posts
    9,031

    Default

    But what kind of impedance bump will that UL knot present? I think a flattop and twinlead one-piece combination would be better with a cable tie at the top to hold the feeder from pulling apart. No impedance bump.

    Hey, I've use toggle switches as antenna T/R switches. Worked just fine. Of course I'd had my General a while before I ever ventured above 40M . . .

    I suspect I'll be experimenting with zip cord as a feedline here in the house. I'll let everyone know how it turns out.

  5. #25
    Join Date
    Jan 2000
    Location
    Indiana
    Posts
    4,970

    Default

    Chris, no one that I knew in southern Idaho as a kid used a UL knot to tie off an antenna. We used standard insulators (either brown or ivory color) for the center and ends. Usually we begged or borrowed these from others who had more than they needed. We used copious amounts of the old electrical tape (before plastic) to help hold these things up. Usually the zip cord terminated in the old Heath Balun and then coax to the rig.

    Fun days and we did not realize what we did not know that never hurt us ..!

    SK's: My uncle, W7HTR; Robbie, W7NTQ, and others I can no longer remember were instrumental in educating many of us .. including at least 3 hams from the TV station I worked at in 1957 (KMVT).

    Bill, W0LPQ

  6. #26

    Default

    Quote Originally Posted by [b
    Quote[/b] (WA2ZDY @ Sep. 16 2006,08:19)]Hey, I've use toggle switches as antenna T/R switches. #Worked just fine. #Of course I'd had my General a while before I ever ventured above 40M . . .
    I still some times use toggle switch
    for antenna change over

    the hb glow bug transmitters
    don't care

    heck still sometimes do not bother
    to check or use swr bridge

    last night fired up the GRC-109 transmitter
    ( big 15 watts )
    ran 6 ft of telephone wire to knife switch
    that is hooked to the 600 ohm feed line

    ( no swr bridge, no antenna tuner,
    two diffrent impedances in feed line )

    loaded up fb on 80 cw

    did not bother with antenna change over
    hooked R-390 A receiver to the 60 ft long
    receive antenna

    had a fb rag chew with station in NYC
    received a 599 signal report

    real radios still glow in the dark

    Mac

  7. #27

    Default

    Quote Originally Posted by [b
    Quote[/b] (N1MLF @ Sep. 16 2006,01:02)]Found a coupla pix...





    JW
    hey
    is zipper coard lesser of a loss than using coax as a feed line?
    say for a 100 ft run.
    We do not stop playing because we grow old;
    we grow old Because We Stop Playing.
    Never Be The First To Get Old

    Any System Is Only As Good As Its Weakest Component.
    .................................................................
    Web Link:
    [URL]http://groups.yahoo.com/group/K4EEZ/[/URL]

  8. #28
    Join Date
    Jun 2005
    Location
    Tucson, AZ
    Posts
    3,810

    Default

    Too often, we give the impression that unlkess you have the ne-plus-ultra feedline, antenna, rig, etc. ad-nauseum that you cannot have an effective amateur station. We lead newcomers to the expectation that they must always have armchair copy and that hams aren't hams unless they spend thousands of dollars on the newest and the latest feedline, antenna, rig...

    A perfectly adequate antenna feed can be made with 18-2 lamp cord or with a chunk of catagory 6,5,4,3 or 2 telecommunications wire. With the price of copper these days, an adequate feed can be made of electric fence wire and plastic spreaders. Connectors do not need to be gold plated, (however there are good reasons to use silver plated connectors), rigs do not need DSP or spectrum scopes, Mics don't need to be made by Heil or keys by bencher (They must be made by Vibroplex, however ).

    In our blind rush toward the newest and latest, we forget that a straight key can be made from a couple of pieces of springy metal or out of a micro-switch. A crystal, FET and a few other pieces and parts can make a perfectly decent QRP transmitter. Build your transmitter withj a tube and a home-wound tank coil and chances are, you can feed that oddball zip-cord fed dipole directly from the transmitter without an external transmatch.

    73 DE KAGKT/7

    --Steve
    73 DE KAGKT/7

    --Steve

  9. #29

    Default

    I determine Zo by attaching a small variable resistor to the far end of the cable under test. Send a narrow pulse down the line and monitor the reflections with a scope. Adjust the pot for min reflections, disconnect and measure pot and this is very close to the Zo. I tested every two conductor piece of wire I could find laying around including the zip cord and agree with results given above-close to 70 or 80 ohms.

  10. #30
    Join Date
    Sep 2004
    Location
    Wise, Virginia
    Posts
    4,309

    Default

    Quote Originally Posted by [b
    Quote[/b] (ka0gkt @ Sep. 16 2006,14:41)]Too often, we give the impression that unlkess you have the ne-plus-ultra feedline, antenna, rig, etc. ad-nauseum that you cannot have an effective amateur station. We lead newcomers to the expectation that they must always have armchair copy and that hams aren't hams unless they spend thousands of dollars on the newest and the latest feedline, antenna, rig...

    A perfectly adequate antenna feed can be made with 18-2 lamp cord or with a chunk of catagory 6,5,4,3 or 2 telecommunications wire. With the price of copper these days, an adequate feed can be made of electric fence wire and plastic spreaders. Connectors do not need to be gold plated, (however there are good reasons to use silver plated connectors), rigs do not need DSP or spectrum scopes, Mics don't need to be made by Heil or keys by bencher (They must be made by Vibroplex, however ).

    In our blind rush toward the newest and latest, we forget that a straight key can be made from a couple of pieces of springy metal or out of a micro-switch. A crystal, FET and a few other pieces and parts can make a perfectly decent QRP transmitter. Build your transmitter withj a tube and a home-wound tank coil and chances are, you can feed that oddball zip-cord fed dipole directly from the transmitter without an external transmatch.

    73 DE KAGKT/7

    --Steve
    Amen!
    Experiment, build and recycle. If you want to know if something works, try it as long as it's not TOO dangerous.
    I don't have a Vibroplex key, though. I made my own. It's no work of art, but it works.
    Audie
    SKCC #927
    Virginia Fone Net #72

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