Homebrew Spiderbeam, not using the commercial kit...

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AE7F, Jan 4, 2012.

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  1. AE7F

    AE7F Ham Member QRZ Page

    The antenna is partially raised.

    The standpipe is sitting on the launcher shelf, which is about 7ft off the ground. The antenna is strapped to the mast. The next step is to hoist the antenna assembly up, drop it into the rotator, and bolt the standpipe into the clamp. Unfortunately, this is the most difficult step. Even more unfortunate is that despite the 60f temp tomorrow, winds are expected to increase to 20mph.... So... I may or may not get the antenna on the mast. Best chance is early AM or late PM due to wind.

    Tuning is acceptable on all bands except 17m, which seems to be touchy. Right now it resonates too high. I need to unfold some more wire or let it go as is but if the antenna raises frequencies 100khz when it is at height, 17m will be off quite a bit.. Meh.... might just use the tuner on this band.....

    Will post details on tuning specifics a bit later....
  2. AK5B

    AK5B Ham Member QRZ Page

    Dunno, Ben, might want to unfold some more wire on the 17m elements before you get that up higher. Sounds like it'd be a hassle to bring it back down to tune it and if elevating increases the frequency of resonance...

    Good luck with the wind tomorrow and we'll keep our fingers crossed for you all the same.

    73, Jeff
  3. G3TXQ

    G3TXQ Ham Member QRZ Page

    It's worth remembering that if a beam is "off frequency" because of ground effects or wire characteristics, ideally you need to adjust all elements - Driver, Director, Reflector - by the same percentage in order to re-tune and retain the performance characteristics; it's not sufficient to simply adjust the Driver, even if that shifts SWRmin to the required frequency. What gives the beam its performance is the right relationship between the self-resonant frequency of each element - if you change one, you should change them all.

    Similarly, even though you may be able to reduce the SWR of an "off-frequency" beam using a tuner, that's no indication that it will have much gain or F/B "off-frequency".

    My advice to folk tuning the hexbeam is to always adjust Driver and Reflector together, in order to keep their self-resonant frequencies in the correct relationship. One SWR sweep with the beam at its final height followed by one adjustment should be sufficient, using the formula:

    Required length = Old length x Old frequency / Required frequency

    I would expect the same applies to the Spiderbeam.

    Steve G3TXQ
  4. AE7F

    AE7F Ham Member QRZ Page

    Got it Steve. Makes sense and thanks for that information. That will help.
  5. AE7F

    AE7F Ham Member QRZ Page

    Too much wind. Sigh...

    Well, since the beam is pointed west/southwest, I should figure out the best time to try to work that direction.... :)
  6. AE7F

    AE7F Ham Member QRZ Page

    Preliminary results at about 12ft off the ground:

    10m - 28 - 29.6 = ~2.0 SWR
    12m - 24.89 - 25 = ~1.8 SWR
    15m - 21 - 21.45 = ~2.5 SWR
    17m - 18.068 - 18.168 = ~1.8 SWR
    20m - 14 - 14.34 = ~1.5 SWE

    15 is my only concern so far. On the SB, the 15m dipole lays out right along the spreader and has no feedline.

    Haven't been able to raise or rotate the beam but I have made a few contacts with it:
    VP2MOM, LU2FE, JJ1NDP, V31YK, etc. I heard A35YZ but was not able to make contact. My beam is pointed away from them and I am running barefoot as well.
  7. AE7F

    AE7F Ham Member QRZ Page

    Finally, the wind calmed down to around 10mph or so and I was able to lift the standpipe up another 6ft or so and drop it into the rotator clamp. The standpipe is guyed at the thrust bearing.

    I still have quite a bit to do. I now need to loosen all of the guy cables and ropes and raise the launcher to its fully extended position, where it locks into place. Then I can simply begin to crank the mast up, which will tighten the guys. When it is at full height (probably around 35') and along the way, I will have to do the best I can to keep everything level. We have some wind headed our way this weekend so I will see how it does in the wind.

    I also need to obtain some more rotator cable so I can operate the rotator from the shack. Whether I raise the antenna to full height now or later, I will plan to test the rotator and then I will be able to see if there is any f/b ratio and gain.

    SWR looks pretty good on the bands and I will post pics later.
  8. AK5B

    AK5B Ham Member QRZ Page

    Your news sounds pretty good, Ben. We're looking forward to further developments and photos when you can.

    I'm at a standstill with my cobweb as we've been having so many rainy days that it is futile to try to adjust the elements now. I'm also fairly busy packing and preparing to move next month so I don't know when I'll really finish it, either.

    At least your SB project is about to bear the fruits of your labor, Ben and it'll be great to hear how well it performs. We'll stay tuned!

    73, Jeff
  9. AE7F

    AE7F Ham Member QRZ Page

    Thanks Jeff.

    Last night I obtained some 7-strand sprinkler wire to use as rotator cable: $35 bucks for 100ft. Now I can turn the antenna from inside the shack.

    Got this put together after dark last night and there wasn't a lot going on on 20 meters but there was enough activity for me to experiment. When I would hear a QSO, sometimes I wouldn't hear the 2nd party. So I turned the beam and sure enough, I could pull the other party out of the mud. I did this on several US stations and then did it on some Japanese and Australian stations as well.

    I didn't try to transmit and I didn't test the other bands yet but the antenna does appear to be directional. As time and weather permit, I will do more tests, especially more transmitting and testing of the other bands.

    One big problem this weekend is that we have a high wind watch in effect for the weekend. NWS is predicting gusts up to 55mph but for my area, I tack on another 10mph as a baseline, so I expect the wind will be roaring like a jet engine this weekend. So while I have met most of my goals in building a homebrew spiderbeam and modifying it to work with my mast, etc., the big questionmark is whether or not my gear will survive the next couple of days. It's already guyed as well as I can guy it but I will double-check everything again.

    I was telling the YL last night that even if the project doesn't survive very long, I have proven the homebrew spiderbeam concept. It can be done; it can be done for half the cost of the commercial kit; it does appear to work; yes some PVC can be used; yes crappie poles can be used; MaxGain fiberglass is incredible stuff; etc. etc.... In other words, if my project doesn't last, I'll just build another and make it stronger and better.

    Anyway, I'll get back to work on it after I see what the winds do.
  10. AE7F

    AE7F Ham Member QRZ Page

    Snagged the following DX today:

    Having the ability to turn a beam onto a station is a wonderful thing compared to trying to work DX on an inverted V G5RV.... Makes me not want to use the V anymore. However, I will be back to dipoles quick if my project doesn't survive the winds tomorrow. We'll see....
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