“Ham stick” dipole again.

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N3JPB, Mar 18, 2012.

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  1. N3JPB

    N3JPB Ham Member QRZ Page

    Hello all,

    I understand that it is now “antenna season” in the northern hemisphere. Time to put up the outside antennas.

    Some background: Last fall I put together a “hamstick” dipole (actually each side of the dipole is a Hustler RM-40-S resonator at the end of a Hustler 54 inch aluminum “mast” section – I was told that the further apart I could get the resonators, the better the performance would be. I used the appropriate center bracket that includes a nylon washer to separate the two “ends of the dipole electrically. This horizontal dipole is mounted in my attic and oriented in a north-south direction (the “long” axis of the attic). I tuned each “leg” of the dipole for 40 meter phone using an MFJ 259B antenna analyzer. I am using a MFJ 915 RF Isolator at the junction of the dipole and connecting the feed line to that. For the amount of effort expended on this antenna I am amazed at the overall performance (especially in light of the many “you will be disappointed” comments I have heard). I have been able to consistently get into the Caribbean several times a week from Pittsburgh (remember this antenna points north-south???) and have made many UK contacts and countless North America contacts. I wondered (in this forum) what would happen if , come spring, I assembled an outdoor vertical dipole of similar construction and it was explained to me that it would be difficult to “come off” the antenna with the feed line at a 90 degrees angle, and at best the result wouldn’t be worth the effort anyway.

    So, I have had some time to digest all of this and now I have another thought that I would be like to present for discussion on this forum. WHAT IF (there are those two little words yet again) I were to move the two legs (resonator and 54 inch mast”) of my “Hamstick” dipole outside the two ends of the attic leaving the center bracket, feed line and isolator right where they are (inside the center of the attic) and turn each (now outside) “leg” to a vertical orientation (both pointing up). Then connect each of the “legs” to the original center bracket using equal lengths of good quality, high velocity, coaxial cable and retuning each “leg” of the dipole for 40 meter phone using an MFJ 259B antenna analyzer at the connection to the center bracket? I would still have a dipole, and the two (now vertical) “legs would be 28 feet apart, 35 feet off the ground and they would be outside and NOT projecting off my property. Should I expect to see an increase in performance? Any thoughts?

    Thank you for sharing your expertise.

    Regards, John (N3JPB)
     
  2. KC7YRA

    KC7YRA Ham Member Volunteer Moderator QRZ Page

    Wouldn't be a dipole anymore. You would essentially be trying to phase 2 verticals. Each would require ground radials and you would have to build the matching network properly. It could work, but not quite as simply as you plan.

    Brad
     
  3. N3JPB

    N3JPB Ham Member QRZ Page

    Thank you very much for your reply but it raises another question. Why would it NOT be a dipole any more?

    The feed line center conductor and the braid will each still have independent paths to only one of the resonators - electrically isolated. The antenna fundamentally will not change from its existing (fairly successful) design, only real difference is that the resonators will be further apart, moved outside and turned from horizontal orientation to vertical orientation. I understand that each of a pair of phased vertical antennas would be a completely independent antenna with its own counterpoise. I think what I am proposing is more like an "un-inverted" "V" in concept. Sort of like this:

    http://www.cometantenna.com/pro_images/H-422_V.jpg

    .....but with the bottoms of the resonating elements moved 28 feet apart and "straightened-up" to a vertical orientation. In fact, if what I am proposing would work, I could mount three resonators at the top of each vertical - DX Engineering makes longer (and more robust) masts to use with Hustler resonators) and use the antenna for several ham bands(?). The Hustler bracket for three resonators is here:

    http://www.new-tronics.com/main/html/mobile_accessories_page_1.html

    I DO understand that I am "giving away" the ability to rotate the dipole for directional operation but it seems like my idea (if it is in any way valid) might be a next step in improving what I now have at a minimal additional expense.

    Any other thoughts folks?

    John (N3JPB)
     
  4. KC7YRA

    KC7YRA Ham Member Volunteer Moderator QRZ Page

    I guess I didn't understand your idea. But I still don't think it would work.

    If you use coax to go from the "T" to the antennas and only use the center conductor on 1 and he braid on the other, it seems like the coax would not longer be coax. You would essentially have dipole starting at the center "T" and the coax on each side would be part of the radiating element. The Hustler antennas at the end would just be like end loading a dipole.

    Here is an image from a W5GI antenna. You can see the idea behind it's construction. They are using a piece of coax as part of the radiating element. Once you take away the balance between shield and center, it no longer acts like coax.

    w5gi_ant_open_end-300x201.jpg

    Brad
     
  5. W5DXP

    W5DXP Ham Member QRZ Page

    In general in its two favored directions, a horizontal dipole over ground has ~6dB gain over a vertical dipole.
     
  6. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Getting the antenna outside is a good idea. Seperating them by 28 feet and splitting the coax to feed them is not such a good idea. As has been mentioned the coax is now part of the radiating system. There will be some difficulty in matching that kind of setup. You might try using a coax feed to both antennas and with a good radial field on each Ham Stick you can then experiment with the feed to the antennas. There is a lot of information in the ARRL Antenna Book on what different spacings and phasings of the antennas will do to your signal.
    The operation you have with the Ham Sticks in the hortizontal position is probably the best configuration for that type of antenna.
    You can use the multi-band adaptor to obtain other bands you wish to operate. However seperating the antennas in the manner you have specified will have some very confusing results.
    There are better antennas to experiment with and you can make these yourself.
    73
    Gary
     
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