Sloper - what to do w/ Counterpoise?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W8WJW, Apr 10, 2019.

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  1. W8WJW

    W8WJW Ham Member QRZ Page

    Hi, a VHF/UHF guy forever, but trying my hand at HF now.
    Sloper, sorta an 80/40 up 25' on chimney slopes down to 8' off of the ground (black rope to a metal post), and commercial antenna has two inline coils (I think it was an old Alpha-Delta antenna?). I ran RG8X mini coax to it (at chimney feed), center conductor to the sloper wire, and a 50 foot 'zip cord' (actually black low voltage lighting wire pair) to the shield at the antenna connection. This zip cord hanging down perpendicular is intended to be the 'counterpoise'. When the zip cord gets 6' from the ground, I split it in two, one wire east, one wire north, both on the ground. No connections to those wires. 'Splitting' the zip cord provided much better coverage on BCB, 160m, 80m, but zippo on 40m, rather than leaving it parallel and on the ground.
    Questions:
    1: Leave the 'counterpoises' as two separate routes?
    2: Ground one of the counterpoises?
    3: Ground both of the counterpoises?
    4: I made a 'choke' with an 1-1/2" PVC pipe and wrapping the coax around it 20 times before it goes into the house. Good idea, or not so good?
    5: Anything else I need to keep RF off of the coax?
    6: Is it my older Kenwood HF rig having problems on 40m and higher frequencies, or is it my antenna?

    Using an old MFJ antenna tuner, can match enough to hear half a dozen stations on 160m, hear a dozen on 80/75m, hear little 2 or 3 on 40,, hear nothing on 20 meters.
    I have not tried transmitting yet as I assume that the Kenwood TS-140S will 'foldback' if the SWR is above a certain match??

    Elmer help appreciated,
    73, John, W8WJW
     
  2. NH7RO

    NH7RO Ham Member QRZ Page

    25' sloping to 8' above ground presents a miserable outcome for 40/80m; why not try a vertical for those bands instead? Definitely a much better way to go!
     
    WB5YUZ, KC8VWM, KP4SX and 1 other person like this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    Think of it this way: an 80m dipole is ~135ft long. An 80m vertical is 67ft long plus several 66ft radials...
     
    KC8VWM likes this.
  4. AI3V

    AI3V Ham Member QRZ Page

    When Heinrich Hertz invented radio he used a center fed half wavelength dipole and a full wavelength loop for antennas.

    You should endeavour to make your antenna look like his.

    Rege
     
  5. N5CM

    N5CM Ham Member QRZ Page

    Give it a try as is. At very low power, use the tuner to get minimum SWR as indicated on the SWR meter on your TS-140. Gradually increase power on the TS-140 and watch SWR on rig. Tweak tuner as needed. See what it does. Report back.
     
  6. K4SAV

    K4SAV Ham Member QRZ Page

    This will be a learning experience for you. Nothing wrong with trial and error experimenting as long as you learn from the experiment. A little research on how half slopers work will help alleviate some of the head scratching you are going to have.

    Half slopers can work well when installed on a very tall tower. The wire is only half of the antenna. The other half is the tower and for best performance that other half should be above the feedpoint. In your case, the other half of the antenna is that counterpoise and part of it is lying on the ground. Look for a lot of ground loss and very low antenna gain, especially on low bands. The other half of the antenna is much too short on the low bands and it forms a very acute angle with the first part of the antenna (not good).

    Normally half slopers do not use baluns or chokes at the feedpoint because there is no way to prevent feedine radiation when it is right next to a radiating tower. Normally a choke for a half sloper will be needed on the feedline where it exits the base of the tower, unless the tower has a lot of radials, or the tower is very tall and the bottom part of the tower looks like a high impedance at the operating frequency. In your case, it's very likely the feedline will have lots of common mode currents on it because your "counterpoise" will not look like a low impedance on all bands. That helps for hearing stuff from inside the house like the router, computer, wall warts, etc. It also means you will likely cause RFI to things inside the house when transmitting. Your home brew choke for the feedline is a good idea, but you may find that it is insufficient, especially on low bands.

    That's just a few things to look for. Then you have to figure out how to solve some of these problems. Should be fun.

    Jerry, K4SAV
     
    WB5YUZ likes this.
  7. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    This is my own take. It's different from Jerry's, but his is very good.

    This is about learning curve. The antenna system you have now, frankly, is a mess and will have a steep learning curve.

    In this case, if the chimney is the only support you have right now, an inverted "L" (or "Ls"), which are a type of vertical as recommend by Jeff above, could get you on 80, 40, and 20m, the three bands that account for about eighty-five percent of all amateur activity these days. You will need a radial field, but putting in a radial field isn't as much work as it may seem at first.

    An inverted "L" is a simple antenna and a known quantity; it is easy to make one work well; and they are known to be effective both for DX and local/regional work (although, of course, since there's no free lunch in physics, an inverted "L" does not work DX or local/regional stuff either one as well as an antenna that is specialized to do one or the other). An inverted "L" can have you on the air, making contacts, in the short term, while sorting out the antenna you have now will take a while.

    This assumes you can't get anything higher. If you can set up some kind of support to get to 35' or more, then you will definitely want a 20m dipole at that height.
     
    Last edited: Apr 11, 2019
    NH7RO likes this.
  8. W8WJW

    W8WJW Ham Member QRZ Page

    Thanks for the replies; I'm limited to the top of the chimney on height - the Ash Borer bug destroyed dozens of 36 year old Ash Trees, so no alternate using any trees.
    I'm sure that AT&T, cable and Edison wouldn't appreciate any amateur hardware attached to their wooden pole, not to mention the safety factor if one of the 3 phases dropped.

    So it sounds like one alternate might be to build my own 40m half wave dipole as an inverted 'V' (33' legs each way? NE/SE as an 80 m 1/2 dipole would be too long to fit in the backyard), but then put a 4:1 balun at the chimney and run the coax down, or does it have to be 450Ohm ladder line, or a specific length of ladder line to a 4:1balun? What determines if you need an 9:1? In this case, my "counterpoise" wire on the coax shield should just be grounded if I have a V dipole? Can you also have a 'parallel wire' for another band with a 'spacer'?

    As far as getting height, I hate to drill holes into my roof to mount some sort of a tripod, but I assume that tripod would then support a 10 foot pole to get me height? Putting a good ole NTSC Yagi antenna on the top of that 10' pole of any value, or is it just going to cause my TV to overload when the XYL is watching TV and I key-up?

    Keep the suggestions coming for when this monsoon weather (precip 5 of every 7 days) ever ends in the Great Lakes. Thanks.
     
  9. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    One of my buddies has had a "roof tower" (a tri-pod with four legs) on his roof for about thirty-five years, with a big heavy Tennadyne T-6 on it for most of the time, with no problems whatsoever (excepting only the fact that a composition roof only lasts about twenty years so he had to take it down and set it aside for a few days at some point and will have to do it again soon - you can see part of his roof from the street and it needs to be replaced, already).

    Steve, WB2WIK, has also had a roof tower up for some time. As far as I know, his has been trouble-free.

    The trick seems to be to do it right the first time.

    And yes, you can get useful height that way. You should be able to get to thirty-five feet or so easily with a roof tower/mast. A 20m dipole at that height will be a good antenna for you. A 40m dipole at that height will be kind of deaf to DX. You will still work DX with it, but there will be lots of times you will hear others working DX when the band sounds closed to your low (in terms of wavelength) 40m dipole. Thirty-five feet is a tolerable height for local/regional work on 40m.

    A 40/20m parallel-driven dipole, fed with one feedline at 35 ft. and pruned to resonance, is a good, simple antenna you can put up easily and will let you work the two bands that have about 3/4 of all amateur activity on them right now. But again, the included angle needs to be above ninety degrees or so.

    As far as an 80m dipole goes, you can bend the ends of it to fit available space, provided (1) safety is observed, and (2) the center part of the dipole is kept as high and straight as possible. An 80m antenna at that height can be lots of fun for local/regional work, but you will rarely hear DX on it (although there will be times). You should be able to drive it with the same feedline as the 20/40m elements with relative ease (when we add a fourth band to such a parallel driven dipole, or add a non-harmonically related band, the system can be harder to prune to resonance).

    You'll just have to try and see what happens with the teevee antenna...
     
    Last edited: Apr 12, 2019
    W8WJW and NH7RO like this.
  10. W8WJW

    W8WJW Ham Member QRZ Page

    WB5YUZ, so could I have a 20m/40m/80m half dipoles- all in parallel, per se with one feedline or multiple feedlines: ladder line, or 8xMini?
    Would you need a 4:1 balun on the 20/40m combo and another 4:1 (or is it 9:1) on the 80m, so two coax run to the shack? Run a ground line from the tripod tower down to earth ground? Thanks for your suggestions in my limited space.
    73
    JP
     

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