Coax question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WD8CSL, Jun 14, 2021.

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  1. WD8CSL

    WD8CSL Ham Member QRZ Page

    Living in an apt complex .. the antenna is of course the issue. Om here .. really old mam .. temp is 90 degrees outside. If you can help it will save some time in the heat and get you a big thank you.
    I have no other option the an antenna within 10 feet of shack window. No trees .. no roof access ..rules .. rules ..rules!!!
    It will be pee poor setup .. I know. A day without ham radio is much like a smoker without cigarettes.
    So just how short can I run a piece of coax and still get a low enough swr to operate. Yes, I could experiment.. cutting up the feed line .. but really don't want to ruin a good piece 20 ft or so. Cheap .. no .. retired ..yes and living on that income. This is just one ham asking for help from fellow hobbyists. Been a ham a long time and no I do not know it all. I remember when the hobby was full of brothers whose idea was to assist each other. I was hesitant to post this request as so many sites are full of disturbing replies. Used to be each of us were driven to get new blood involved .. especially young people. Never saw a license question referring being snobby or disrespectful. There are plenty of hobbies for that.
     
  2. W9IQ

    W9IQ Ham Member QRZ Page

    It takes a fair bit of coax loss to substantially improve the SWR. You do so at the expense of converting radiated and received power into heat.

    A better approach would be to use a short coax and an antenna tuner. While you will still lose some power to heat, it won't be as significant.

    Would that work in your situation? On which bands would you be operating?

    - Glenn W9IQ
     
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    Thomas,

    An "antenna" is either self contained (Hertz, dipole) or relies on a connection to "ground" (Marconi, vertical, random end-fed wire).

    Which of these are you trying to drive?
     
    AK5B likes this.
  4. WD8CSL

    WD8CSL Ham Member QRZ Page

    Wolf river coil
     
    KO4ESA likes this.
  5. WD8CSL

    WD8CSL Ham Member QRZ Page

    Have a ldg tuner . Band0s are 20 40 10 when open.
     
  6. WD8CSL

    WD8CSL Ham Member QRZ Page

    Woif river coil .
     
    KO4ESA likes this.
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    Wolf River coil implies you are trying to drive a shortened Marconi vertical. Question is, what are you driving it against? Marconi's need a large ground plane (at least as big as a car and ideally much bigger, approaching 0.5wlX0.5wl at the lowest frequency).
     
    Last edited: Jun 14, 2021
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  8. AK5B

    AK5B Ham Member QRZ Page

    Tom; That sounds like a tough situation to be in. What about a hamstick dipole for 20 meters? You could set it up on a painter's pole for temporary operation outside your window.

    Won't be a very good antenna but it would be cheap, easy and the biggest factor in the equation---better than no antenna at all.

    Best of luck to you, OM.

    73,

    Jeff
     
  9. W9IQ

    W9IQ Ham Member QRZ Page

    You should be able to use your tuner with a short piece of coax to the antenna if the SWR of the antenna is less than 10.

    As Mike noted, you may need a 'ground plane' or 'counterpoise'. That can consist of some longer wires laid out on the ground.

    You may also need a common mode choke on the short piece of coax but you can try it without. If you notice RF in the shack then you should add the common mode choke.

    - Glenn W9IQ
     
  10. W2SGM

    W2SGM XML Subscriber QRZ Page

    For an apartment, I feel it would be a waste of time and effort to build a ground plane large enough to make an indoor vertical effective. I have a wolf river coil and 9 foot ceilings; I can’t even fully extend the whip if I set it up indoors.

    If you don’t mind the expense, a tunable magnetic loop antenna will give you the best performance for its size, and you can easily swap polarization for groundwave HF. You wouldn’t need a rig tuner in that case.

    Barring that, a resonant dipole circling the crown of the room, but only if the room is large enough to accommodate your preferred band.

    You might also try an off-center fed dipole for multi-band use, but I have a feeling the poor performance and noise will make it unusable once you bend the legs to fit the room.

    Good luck!
     

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