Long wire antenna HELP PLEASE!

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N4CLY, Nov 19, 2009.

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  1. N4CLY

    N4CLY XML Subscriber QRZ Page

    I have installed a long wire Antenna 1024 feet installed. I do not have a counterpoise yet so I have not use the antenna. I need options for the counterpoise. I read losts of stuff but still confused. I understand that the best counter pose would be another 1024 feet of wire buried like 1 inch deep.
    If this is true can it be buried in any configuration ie back and forth in the yard, around the house several times, or should it be under the antenna like a radial? Are there other counterpoise options that are not as big a project that will work just as well? Please give me some options so I don't blow up my rig.
     
  2. R3BU

    R3BU Ham Member QRZ Page

    There are two options of counerposes: first rezonant, 0.25wl at some height. Second is artificial ground with 20-100 wires(non rezonant) ~0.1-0.3 wl buried in the ground, lying on the ground etc...with center under the feeding point. With high impedance of your 1000 feet wire it is possible to use only several instead of 20-100....The first will radiate/receive. To exclude radiate/receive we need two 0.25wl rezonant in oposite direction of each other. What for that too long antenna ? At low heights it will give a good directivity and good s/n ratio for DX. The transmition efficiency is a question of the height of the wire. The ground will absorb a big portion of transmitted power.
     
    Last edited: Nov 19, 2009
  3. N4CLY

    N4CLY XML Subscriber QRZ Page

    I chose that length after reading online for several days. The S/n ratio was the big reason for receive. As to the height off the ground, at the lowest point it is 10 feet at the heighest it is around 25 feet where the field slopes downward. If the antenna is no good for transmitt I will simply use it for receive and find another option for transmitt. I am currently using a G5RV-Max which preforms very well. However I would like to have the gain provided by the antenna as I have limited tx power. I read somewhere that I should bury the same length of wire about 1/2 inches deep that I put in the air is that a good counterpoise option?
     
  4. R3BU

    R3BU Ham Member QRZ Page

    No !! 0.25wl is maximum lenth for conterpose. It is possible to use shorter counterpose, not buried, 5-10feet . In this case the feeding point will have bigger impedance and be fed throgh HF transformer or balun from 1:5 to 1:20 to be connected to 50 ohm coax. Better to make electric connection inside the balun via magnetic field. This option is so called or similar to FUCHS ANTENNA.
    ( just to see, how short counerpose could be done) May be someone of local HAMs would give You better explanation. I do not poses all the "bolts and nuts" of my English :)
     
    Last edited: Nov 19, 2009
  5. K4SAV

    K4SAV Ham Member QRZ Page

    If you have that antenna pointed in a direction where there are lots of stations (like Europe) you may like it, even though the ground losses will be very high. If it's pointed in a direction where there are few stations, you will be very disappointed at both the receive and transmit performance.

    It will be a DX only antenna. High angle gain will be very low, and your G5RV will blow it away for local stations and any stations not within the beamwidth of the longwire. The lobe bandwidth will be very narrow especially on the higher bands. Lobe width on 20 meters should be about 23 degrees. That won't cover all of Europe, even when centered, but it may be good enough. Lobe width becomes about 17 degrees on 15 meters. It won't be very good on 160, but it will get you on the band. Where is it pointed?

    Input impedance of this antenna should be fairly high on most bands. I would recommend using low loss coax and an 8 to 1 un-un at the antenna. That should keep the SWR under 2 to 1 on most bands except for 160 and parts of 80 meters. I would also add a choke on the feedline to prevent coax common mode currents from messing up the antenna pattern, and prevent noise coupled onto the coax shield from getting into the antenna.

    For a radial system I would install a buried radial system at the feedpoint with about 25-30 radials, maybe about 100 ft in length. Ground loss is going to be high because of that low horizontal wire but it is going to be difficult to do anything about that. Antenna gain will make up for some of that loss but the beamwidth will be narrow. A radial wire buried under that long horizontal wire may help but I have no way of evaluating by how much.

    If you don't want to transmit and want to only use this for receive, loss is not an issue and the radial system can be very small, maybe even just a ground rod, and then I would use RG6 for the feedline and a 5 or 6 to 1 un-un.

    You will need some way to protect against induced voltage due to lightning strikes. The sparks will be impressive. Short it to ground when not in use.

    Jerry, K4SAV

    edit:
    NOTE: My recommended radial system is based only on a guess and not on any scientific calculations.
     
    Last edited: Nov 19, 2009
  6. K7NNO

    K7NNO Moderator QRZ Page

    If you want to use it only on one band, feed it a quarter wave from one end with a 4:1 balun and coax.

    If you want to use it multi band feed it in the middle (best) with open wire or at the end. (I wouldnt recommend this)

    Trying to use coax for multi band use using a balun is bad practice since baluns dont work well when the reactance is high.

    You dont need any radials or a counterpoise (consult an antenna book to know the difference)

    Sounds like a great antenna. Good luck.
     
  7. KI4WCA

    KI4WCA Ham Member QRZ Page

    Care and feeding of long wires

    The counterpoise I used was composed of ground rods and radials.My tuner was a L tuner that was grounded to a very wide copper sheet that ran from the window the antenna wire came into to ground.Radials of copper tubing went 10 feet to the first ground rods, then 20 feet to the next rods.I used 5 main runs, each of which was 60 feet long in total.At the point where they were tied together, there was a ground rod as well.This ground field was for lightning protection with a nod to passable counterpoise use.The very effective ground eliminated most of the rf in the shack that was conducted, even so the antenna wire is right at the window and it is hot with rf.An antenna as low as the one you have will be lossy, but it will be quite directional in the direction the wire runs.My wire was only 300 feet long....I imagine you will have some fun with your wire, especially on the higher bands.

    There is no need for a wire the same length as the antenna in the counterpoise.The more area your counterpoise covers, the better it will work.Use a very wide copper strap to bring the ground inside the station to minimize inductance and a ground that is high impedance on the higher bands.
    Good luck!
     
  8. WB4RHQ

    WB4RHQ Platinum Subscriber Platinum Subscriber QRZ Page

    I use a 170' long wire that is 90' above a retention pond for all bands with a tuner. At the feed point I have a DX Engineering 4:1 balun and lightning arrestor. All of this is coax fed from the tuner. For a counterpoise I have a single radial run just under the surface of the ground out to the pond then across the pond under the water. The length of the counterpoise is roughly the same as the elevated wire and roughly under it. Reception is great and have worked all around the world with it. The wire is nothing more than #14 single conductor copper building wire.
     
  9. R3BU

    R3BU Ham Member QRZ Page

    This is how to feed LW with short counterpose under the ground.
    The advantage- NO QRM from home electronics and AC wires.
     
  10. KB9MZ

    KB9MZ Ham Member QRZ Page

    I would make a ladder line out of it and join wires at the far end .
    Keep the wires 1/2" or less apart to keep the impedance down.
    Feed it with 50 or 75 ohm coax. Note you are joining balanced and unbalanced sections so you will need a balun to stop the coax radiating.
     
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