omni ground elements effecting a beam below them

[Sickpuppy22]

Henry much appreciation for clearing this up, from what I've read I still had a small doubt that a vertical with radials stacked over a beam would'nt have any ill effects on take of angle and lobe strength, you know when you get a "that just does not seem right" moment but you can't quite figure which direction seems more feasible .

When the day comes I'll post a thread with the new setup and with and what the final tuning was with the mfj, and it may help out other in the future that want to use a similar setup.

 

[Marconi]

Some years ago, I mounted a Starduster above my 4 element horizontal, which I felt worked very well for me. I was surprised that I did not have to re-tune my beam after mounting the SD'r so close.

Due to the design of the Starduster, it needs a mast that is at least 10' feet long so the radials can be clear at the bottom. These radials hang down about 8' feet below the hub were the mast is attached. This allows for a foot or two of clearance. The way I mounted the antenna, the 10' mast also lost a foot of length in mounting, so the SD'r radials ended up very close to the elements on the beam. Initally I was concerned that this setup would affect the beam's match, performance, and maybe even the bandwidth, but I noticed none in operations with both and the SWR bandwidth remained the same. This was before analyzers were reasonably available, so I was not able to compare at that level.

When I modeled the setup I posted above based on BM's question, I was again surprised to see there was so little difference. I admit I did not attempt to make my models anywhere near to specs...by any means. I just put the two antennas together, and like I said earlier I used the beam model provided with my Eznec 5 software listed as: "11m5elyagi.ez"

Henry, you no doubt have more experience with beams, and for sure you have more experience with modeling, so, unless you are talking about the minor issues seen in my model posted above, could you post here the wires view, PM, or Email me a model that supports your claim posted above, where such a setup would have issues?

The model I posted earlier, pretty well confirms what I think I saw in my real world experience, and I would like to see what it is that you are considering in your claim that such a setup with resonant radials would really mess things up.

 

[HomerBB]

Marconi, I can not do more than speculate, but with respect to radials on a GP that are resonant length having some kind of pattern altering effect it would seem reasonable to expect so when you think of the changes in patterns that occur when two identical/similar Yagis are co-phased. Coupling is desirable in co-phasing setups, and this effect depends on resonant lengths of the two (or more) antennas in such cases, does it not, and if so, why would we not expect pattern shifts from similar length antennas near each other?

It makes sense to me that 18' long radials sitting above a horizontal Yagi would couple and alter the RF pattern. Properly co-phasing antennas for a desirably effective pattern begins at about a 1/2 wavelength apart, or for a compromised mobile setup, 1/4 wave apart, as I understand it, so an inefficient distorted pattern might be expected when co-resonant length antennas mount nearer to each other than 1/2 wavelength.

I will say that I had to retune the Yagi when I mounted the short radial 5/8 above it, and then retune when the radials came off. I did not retune when the Qv4k went up over it.

Just my thoughts, and certainly not meant to dispute anyone's experience. I do enjoy the tidiness of experience and science reflecting each other.

 

[BOOTY MONSTER]

just a guess on my part .........

if your beam was horizontal i wouldn't expect the sharply sloping down ground elements on the starduster to have much operator detectable effect . similar to how a beam that has both H and V elements can have its polarity switched . i think detectable interaction can be expected when a omni with near full 1/4 wave length horizontal ground elements is on the mast as a flat side beam below . but the stardusters elements are 70ish degrees out of phase in that example/guess .

i do look forward to a definitive answer to see if im on the right track or not though .

 

[Marconi]

You both might be right about the SD'r, which is the only real world example I have, but the model didn't have slanted down radials.

I believed the same thing when I first put the SD'r up there, but I was wrong, I saw little difference that I could tell. That is why I did horizontals above my Eznec5 model. I also expected to see what Henry claims happens, whatever that is. But I was wrong again, I got that weird feeling, "what tha' heck just happened."

I would and have suggested, in fact, that it is a bad idea with horizontal radials above a beam. After I had my experience I started advising folks to try their idea anyway, and keep us posted. That, is why I was surprised when I saw the Eznec5 model looking so very similar to my personal experience with a somewhat similar setup. That is also why I asked Henry for his help in understanding, requesting him to sending me his model that shows us exactly what happens and as he describes.

I will do some more work with the Eznec model I posted above. First I'll look closely at the match and see what differences I can see there. That could account for why Homer had to re-tune his beam.

Then I'll try removing just the vertical section of the previous model, the part what was supposed to be an end fed 1/2 wave, and see how the beam is affected just by radials up there. Maybe that will show us something different and what we might expect.

I will also model just a 1/4 wave ground plane with horizontal radials above the original beam model. That will require some matching at the feed point too, but not near as much as an EF 1/2 wave, and it should work. I'll post whatever results it shows. I'm not afraid to discover my own errors, and then show that I was wrong about something, the light of truth is always good enough for me.

 

[jazzsinger]

Back in the 80's i ran a 3 element beam about 6 feet below an A/S mighty magnum 3, like Eddie i noticed no interaction whatsoever, neither antenna needed retuning and both worked superbly well. thats not to say someone in a different location/setting with similar antennas wouldn't have problems.

Only problem i ever had was the faggoty pink coil cover on the magnum letting in water, to the point where it froze one night and cracked the coil cover, everytime it rained the swr went up to about 2.5:1, but even at that it still blew away nearly every other twig in the city, even dare i say it a couple of avanti sigma 4's that didn't have as good a location as i had with respect to height asl. in saying that tvi/rfi was olympic standard (not that i gave a fuck at the time, i was 15 and working the world, when others were struggling to get across our city), although i think with hindsight that was more down to me overdriving the shit (my power mad days,before i learned how power actually works) out of the ham int la120 linear with my mk2 cobra 148 gtl-dx and the fact i was still using AM a fair bit back in those days.

i learned the hard way one night at about 2am whilst working auroral into iceland when the then post office interference service and half the local cuntstabulary (yes i'm still f@cking bitter) knocked my door and alleviated me of my beloved cobra and dragged my sorry ass into court.

what works fine for some can be major bad news for others.

 

[Henry HPSD]

Hello Eddy!

Attached a word document with a example where it can go wrong.
(3el yagi with only two radials above it).

And just to be clear to all readers..in most cases it will not go wrong or cause issues.
but escpecially with "full wave" radials with the same polarisation.
Thats just a asking for issues.

Im more than happy to share that file towards you Eddie, my appologize i have seem to lost your email adres.

ps..dont take advantege of my new yagi lol.

Kind regards,

Henry
All about antennas

 

[Marconi]

Henry, don't bother exposing your model to the Internet or the email system. The file you posted is good enough.

I am, however, surprised that these models are so different in the feed point resistance values shown.

I also did a step by step, as I removed the elements that I added earlier. I can't explain why our models are so different, but again I saw similar results with little differences to pattern, match, gain, and maximum angle.

 

[walterb]

BM,
I have tried and tested an A99 for receive and transmit at 36' to the bottom with and without ground plan radials and found that the radials changed the standing wave some an it was not as flat over the range of frequencies this antenna can cover without using a tuner. In AZ the soil is not good for good reflection for antenna radiation, like if it were on SF bay on a boat over water (Best) setup. A dipoles does good in this environment. I do have two inverted Vee antennas under my A99 and it does not seem to improve or detract for any or the three antennas to any degree, space is somewhat of a problem for me, but can load all antennas to 1000 watts but my 20-40-75 meter inverted Vee I built will still load to a 1000 watts but do have CMC that come back to the shack but still loads 1000 watts. Have a friend that has a beam antenna under his IMAX-2000 for use on 11 meters and it works up to 200 watts OK but above that there big SWR problems and thing break down quick because of to much antenna interaction. At my location I have never found a ground plan antenna that works better than the A99 at 36' to the bottom, the A99 handles the wind way better than most antenna I have tried, and does a good job with SKIP, Ground wave and does the bottom part of 10 all of 11 an 12 an 15 meters with the use on a tuner using 100' of RG9913U coax....................Oldtimer

 

[MeatMan]

I tried this very setup:

I found the Yagi had no problems with the vertical w/short GPS about 5 feet above, but the short GPs made for inferior performance compared to what I'd experienced with full length radials on my 5/8 wave antennas.

I removed the GPs as suggested and lowered the 5/8 within a foot of the Yagi. The severe storm system we experienced came through and I removed the 5/8 without an opportunity to compare the setup in this way. I had been redoing the Qv4k in the meantime and put it up in the air above the Yagi instead right above the Yagi. Both still perform very well:

Hey Homer,

Sorry to rejuvenate such an old thread, but I have a 2016 as well which is less than 1 year old and I would love to add a beam to my set-up but I have nowhere else to mount it as my 2016 is taking up my only location available. I don't want to remove it since it's still new and shiny, and works very well. Did your set-up seem to work ok for you with minimal re-tuning? I'd like a beam for better DX'ing and working 10 meter once I get my Tech license later this year, but is there any advantage to utilizing both (at separate times of course) or should I just switch to a beam? I only have a 10' mast mounted to the gable eave of my house so I'd have to keep the beam fairly close to the roofline and put the Sirio as high on the mast as possible to maximize the distance between the two. Am I wasting my time, or do you think I should be able to make it work. I mostly use 11 meter, but I'd like to work 10 as well once I get my license. I DO plan on getting an ATU to help, but am I going overboard here? Should I just take the 2016 down and put it away in the attic or garage for a day when my beam gets taken out by a tree limb or bad storm? I've never used a beam so I'm not sure what functionality I'll lose if I ditch the Sirio.

Thanks for everyone who commented on this thread, it's been helpful.

73 from 106 Central Massachusetts, I'm back in my corner...

 

[undertaker]

I had a 3 element beam with an A 99 above it and it worked perfectly!!

 

[MeatMan]

I had a 3 element beam with an A 99 above it and it worked perfectly!!

Did it have the GP kit? My 2016 has a GP with shorter radials like the top picture.. Those are what I'm worried about.

 

[undertaker]

No sir no ground plane kit..

 

[Alabama Buckeye]

on 27 MHz , are the short ground elements on a omni antenna like a sirio 2016 mounted a few feet above a flat side beam long enough to effect the beams performance enough to be detected by the typical user ?

and ...... how much do full size ground elements effect a horizontal beam below them ? does it help or minimize the effect if the omnis ground elements are 45 degrees parallel to the beams elements ? like a X over an H . HXH

Very glad you asked the question.

A monopole above a yagi? 2 of 3 of my previous inquiries were negative. I'd thrown the idea out. I'm now gonna go with it.

I'd surmised the Beam, elements are grounded to it, would serve as an effective GP. Imax 2000 over Sirio SY-3. But, my concern was the impact of monopole element disrupting the Yagi functions. Particularly because the monopole would be 3" from directly over the Yagi Driven element.

And there it is, Henry said it best:

"Conclusion:
A beam with the elements grounded to the boom will provide a good groundplane system. Infact it can be better than most commercial vertical antennas with a radial system underneath it. It is in such a case a good option to drop the original radials.
A vertical with the original radials attached can (doesnt need to) provide serious problems when placed above a beam."

Aside, the original GPK (kit) was a 4x 6' radials were not believed to be effective.
The 72" radial elements were swapped out for 4x 103" SS whips. Noticeably greater reception. Can attribute SWR drop by .2 units with swap; now, 1.05:1.

 

[MeatMan]

Very glad you asked the question.

A monopole above a yagi? 2 of 3 of my previous inquiries were negative. I'd thrown the idea out. I'm now gonna go with it.

I'd surmised the Beam, elements are grounded to it, would serve as an effective GP. Imax 2000 over Sirio SY-3. But, my concern was the impact of monopole element disrupting the Yagi functions. Particularly because the monopole would be 3" from directly over the Yagi Driven element.

And there it is, Henry said it best:

"Conclusion:
A beam with the elements grounded to the boom will provide a good groundplane system. Infact it can be better than most commercial vertical antennas with a radial system underneath it. It is in such a case a good option to drop the original radials.
A vertical with the original radials attached can (doesnt need to) provide serious problems when placed above a beam."

Aside, the original GPK (kit) was a 4x 6' radials were not believed to be effective.
The 72" radial elements were swapped out for 4x 103" SS whips. Noticeably greater reception. Can attribute SWR drop by .2 units with swap; now, 1.05:1.

So...the 2016 radials are much shorter (30"?) and more of them to make up the area difference for a ground plane. Being as they're not extending out as far, they "shouldn't" cause as much of a disruption to the pattern of the beam as they're extended much less off the central point, at the mount. With the 72" and 102" radials those would extend much further into the pattern of the beam thus causing more issues yes? Also the father away I keep them (height wise), the less they should interfere?