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Sirio GM-ground level question

Discussion in 'CB Antennas' started by gamegetter, Sep 29, 2011.

  1. gamegetter

    gamegetter Well-Known Member

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    "Please note that if you are going to use your Sirio Gain Master for DX purposes then it should be as mounted as close to the ground as possible for optimum results. On the other hand, if you are only use the antenna for ground wave purposes, i.e. talking to your mate 5, 10, 20 miles away then it must be mounted as high as possible and away from obstructions"

    I borrowed this from this gentlemans web site Sirio Gain-Master Hi-Tech Fibreglass Base Station Antenna for CB & 10m Band - Tetraplegicliving.com and was wondering if anyone had tried the gm at ground level? If so what kind of swr were you getting and how were your dx results?



    If no one has tried it perhaps a discussion could be had on the theory behind it. Thanks in advance.
     

  2. Robb

    Robb Yup

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    I think that like any 5/8 wave antenna, that it best optimized by having a clear 'line-of-sight' with the horizon. Since that is the nature of the polarization for a true 5/8 wave.

    Doesn't a 5/8 wave a 5/8 wave possess the same characteristics - no matter who makes it?

    So, ground mounting it or any 5/8 wave could be done; but I suspect that mounting it high enough off the ground for a clear LOS with the horizon might be necessary. High enough above buildings may not be necessary; but might be the best way.

    Interesting discussion to follow . . .


    5/8 wave antenna compared to a 1/2 wave antenna's propagation:
     

    Attached Files:

  3. Needle Bender

    Needle Bender ...he thinks it's funny that I stepped in it

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    i think he doesnt understand the gainmaster design. that antenna is a balanced antenna and fed in the middle so by placing it close to the ground you will cause it to have screwed up unbalanced performance. even sirio tells you to have it no closer to 6 meters above other things. its not a typical end-fed 5/8
     
  4. just because a ham said it , or just because its on the WWW doesn't mean it's true .
     
  5. cbradiomagazine.com

    cbradiomagazine.com 2008 - 2014 / Pau Hana

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    I didn't test DX with it low to the ground but I can say that it performed better at 25' than it did at 10' locally.

    If you have a choice to mount it at 10' or 36' I'd suggest going higher.
     
  6. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    I agree completely with NB's remarks on this one.

    Robb, in this case a 5/8 wave ground plane is not exactly the same as the GM 5/8 wave simply based on the way they are fed. The GM is a center fed design, where the whole radiator length radiates all in phase just like gamegetter's link suggested and NB mentioned. On the other hand, the 5/8 GP shows cancellation in the lower 1/8 wave, and that is due to its being out of phase with the upper 1/2 wave part of the radiator. That might make some noticeable difference...if both antennas were installed at the same height to their mounts.

    I don't typically compare my antennas during DX conditions, so I can't speak to the issue of mounting the GM as close to the ground as possible for the best DX, as noted on Penn's site. However, my local results were nearly identical to what CBMag reported. I also didn't hear any discussion about antenna heights in either video. The issue of height was a concluding remark in Penn's presentation, and he did not explain further with specifics.

    I've posted plenty of report info and videos where I compared my GM to other antennas, and compared signals with it standing alone. I don't think my opinions about this one has changed one bit on hearing these other viewpoints, but I don't totally disagree either with what Penn said or reported.

    I'm confident that the GM design, with its very well balanced matching and decoupling systems, is what also makes the GM very effective and sensitive to its surroundings. Therefore I recommend it be installed well into the clear and no less than 20' feet high above the Earth up to the mount. Or, like NB suggested...Sirio recommends no less than 6 meters above ground. I don't think Sirio said that for nothing. This idea has also been suggested when installing the GM above a beam that is high above the Earth, and I'm not sure yet how that might work out.
     
  7. Shockwave

    Shockwave Sr. Member

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    While a ground plane may produce better DX results being mounted directly over conductive earth with buried radials in some cases, I don't think this is going to happen with the balanced GM. Some simple testing with EZNEC could easily confirm if this is the case since there is no reliable way to determine if it improved in DX over the air with varying conditions.
     
  8. Needle Bender

    Needle Bender ...he thinks it's funny that I stepped in it

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    now theres one for you marconi. try a gainmaster dead on the ground in enzec and lets see how screwed up the pattern looks. probably as bad ass my splelign
     
  9. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    I tend to agree with Shockwave, except I'm not sure what kind of test would be revealing in this case. I don't think that Eznec will allow me to mount radials directly on the ground unless maybe I set it to a free space model.

    I did set my simulated model of a GM directly on the ground and it did skew the pattern up around 46* degrees for a maximum gain of 2.27 dbi, but again I don't think I can put radials directly on the ground. Anyway, Penn did not suggest the GM be set directly on the ground, so I can mount them 6" high maybe.

    It will be easy to add radials and lower the height of my model. What do you want to see?
     
  10. Needle Bender

    Needle Bender ...he thinks it's funny that I stepped in it

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    im interested in what the skewed up model lokks like to have the gainmaster right on the gruond. no radials
     
  11. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    I'm not sure about these models or the ideas. In real world use I think the GM really needs to remain well decoupled at the bottom in order to remain balanced at the feed point at just about any height.

    I can't model the feed system or the choke, so that might make some really big-time difference if the modeled were fixed or as compared to a real GM setup low to the Earth.

    View attachment NB's idea for ground mount.pdf

    View attachment Shockwave's idea for radials.pdf

    Here are two GM work sheets showing what happens to the bandwidth curves at 11' and at 56' feet in my case. Notice that the SWR curves aren't much different however, and IMO that is what most guys will be seeing if they don't use an analyzer to do their BW curves.

    View attachment GM Work Sheets.pdf
     
  12. eagle1911

    eagle1911 Active Member

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    That is a fact, but it's well known even outside the ham community that ground-mounted verticals are excellent for DX work. I haven't modeled them in software, but I've seen simply awesome real-world results from antennas that are literally mounted on the ground, with the feedpoint at ground level. I use an IMAX 2000 mounted on a fencepost for the upper HF bands, with an antenna tuner of course. It's nice if the antenna has a clear view of the horizon all around, but it's not at all necessary for DXing and many verticals like being in close proximity to earth ground. It does depend a lot on the design of the antenna though.
     
  13. Shockwave

    Shockwave Sr. Member

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    One point of clarification is that my suggestion of adding long buried radials to improve the performance of a ground mounted vertical, only pertains to a ground plane antenna. Not the GM.

    Marconi, your EZNEC results are shocking! At first glance your ground mounted GM did exactly what I thought it would do. The pattern is horrible with a peak gain at 45 degrees. Too sharp of an angle for DX and useless for line of sight.

    I was stunned to see EZNEC report a significant change at only 6 inches above ground. The angle of radiation here at 17 degrees may be ideal for much DX work! From what I see here, the idea looks plausible. The one thing that concerns me is that it only takes 6 inches to make this difference in the model. It is such a small change that I suspect it will vary depending on soil conditions.
     
  14. it was said ......

    "Please note that if you are going to use your Sirio Gain Master for DX purposes then it should be as mounted as close to the ground as possible for optimum results.

    i don't think "as close to the ground as possible...." is going to provide "optimum results" for any antenna . it can still work , but i'll stick with higher is better for DX and local . mobile antennas are only a few feet off the ground and are much shorter antennas with higher TOA and they can work quite well ....... .
    i don't believe the gainmaster (or any other cb antenna) will have OPTIMUM RESULTS (the best results it can provide) with the feed-point on the ground rather than up in the air at even very modest height .
     
  15. gamegetter

    gamegetter Well-Known Member

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    the modeling is promising...only question i have is whether being so close to the ground, whether the swr would rise and make it inefficient.
     

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