Sirio GM-ground level question

Shockwave said:

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.

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I agree SW.

I was surprised with the patterns too. The 6" raised model suggest to me that Penn's idea for DX might work just as he notes, even though the gain looks to suffer badly. With that said, I've made some very good long distance contacts with very low watts out, and when conditions were working for me. DX is just unpredictable and depends a lot on how the antenna propagates...with waves combining somehow or not.

If the ground mounted model is even close to accurate, it would appear like the bottom lobe is out of phase with the top, but far worse than a regular 5/8 wave ground plane. IMO this might account for the very low gain we see reported by Eznec. SW, wouldn't that too be sorta' predictable also?

BOOTY MONSTER said:

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 .

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Perhaps not optimum, I agree with that, but it depends on the design of the antenna. Typically when verticals are ground mounted it's out of necessity, my case included. I keep mine low and incognito to avoid having neighbor issues and to preserve the curb-appeal of my home. I live in an anal neighborhood.

so the gainmaster is a perfect antenna to mount right on the ground if you live in a canyon or at the bottom of a steep mountain range and need to talk over it

BOOTY MONSTER said:

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 .

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I agree Booty, but I mentioned earlier that Penn did not give us any real details, so we really don't know the height he was talking about. When we hear discussions about ground mounting, I think most are referring to lower HF antennas, a really good ground radial system, and situations similar to what Eagle is suggesting. SW might agree or not on that.

gamegetter said:

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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gamegetter, admittedly I was not as close to the ground as my model here, but I showed you what my GM did at 11'. If you'll look at the SWR bandwidth curve again...the SWR hardly changed. If you do look again, this time look at what happened compared to when I used the analyzer.

The only difference I can recall from operations of my GM at 11' feet back then, was that I noticed the antenna responses were very attenuated. This is why I have recommend to set your GM well in the clear, and at or above 20' feet.

eagle1911 said:

Perhaps not optimum, I agree with that, but it depends on the design of the antenna. Typically when verticals are ground mounted it's out of necessity, my case included. I keep mine low and incognito to avoid having neighbor issues and to preserve the curb-appeal of my home. I live in an anal neighborhood.

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marconis right. i think youd be better off with a imax or i10k mounting it that low

Needle Bender said:

marconis right. i think youd be better off with a imax or i10k mounting it that low

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An IMAX is what I use. The OP was interested in the GM.

Well, I can only say what I've heard for myself.

It seems that every station that I have talked to that ran that GainMaster (including Marconi) had an outstanding signal.

Most were running them around 30 ft or more.

The evidence is anecdotal; but consistent . . .

yeah i dont understand these guys who badmouth the gainmaster. its a 5/8 so like other 5/8 it should have a good amount of gain but since its driven in the middle and is all in phaze it can only be better when its high in the sky

Robb said:

Well, I can only say what I've heard for myself.

It seems that every station that I have talked to that ran that GainMaster (including Marconi) had an outstanding signal.

Most were running them around 30 ft or more.

The evidence is anecdotal; but consistent . . .

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Hey Robb, my GM is at about 39' feet. No radio since June for me. With the heat and no rain for months, everything including signals was dying. Several of my regular buddies, on 39, live in the brush fire areas we've been having in Texas. For them it has been touch and go. We've even had smoke problems here in the big city.

Just last week, conditions were improving, but still no rain to speak of. It's time for some antenna changing, don't you think?

Robb said:

Well, I can only say what I've heard for myself.

It seems that every station that I have talked to that ran that GainMaster (including Marconi) had an outstanding signal.

Most were running them around 30 ft or more.

The evidence is anecdotal; but consistent . . .

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That consistency with good performance is not what we typically see in any other fiberglass stick. The Antron 99 and Imax 2000 can have widely varying results especially with DX from one installation to another. It comes down to them radiating off the mast and coax. This causes many different problems but the most interesting one is in the secondary lobe of the radiation pattern.

The effects different lengths of coax and mast radiation has on secondary lobe in the A-99 and Imax 2000 can cause DX performance to range from relatively good, to completely crippled. Thankfully the balanced design of the GM eliminates these issues. The first clue that the GM is different is the notable absence of any RFI radiating from the coax.

Shockwave said:

That consistency with good performance is not what we typically see in any other fiberglass stick. The Antron 99 and Imax 2000 can have widely varying results especially with DX from one installation to another. It comes down to them radiating off the mast and coax. This causes many different problems but the most interesting one is in the secondary lobe of the radiation pattern.

The effects different lengths of coax and mast radiation has on secondary lobe in the A-99 and Imax 2000 can cause DX performance to range from relatively good, to completely crippled. Thankfully the balanced design of the GM eliminates these issues. The first clue that the GM is different is the notable absence of any RFI radiating from the coax.

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SW, I agree. Very good point, and I think you're right. Good idea to remember, and one that I never though about before. I think this sorta' proves Bob85's long standing claim in this regard, and he should love this idea.

Good to see you out here. Have you talked to Bob lately?

Thanks!