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Jaws792
New member
Username: Jaws792
Post Number: 6
Registered: 5-2007
| | Posted on Tuesday, June 19, 2007 - 9:43 pm: | 
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Correct me if I'm wrong but I am still wondering why people would use the ground plane kit if according to statements made here quote "A .64 wavelength radiator is much more efficient and will have a much lower angle of radiation (keep the signal down on the horizon instead if wasting it up in the sky) with a proper counterpoise system. Adding the GPK-1 to the Imax 2000 (according to my math and previous .64 wavelength test range plots) will result in a 0.3 dB gain improvement. This will bring the Imax 2000's actual gain up to 3.2 dBi (or 1.1 dBd). ". Based on further reading that I have done, you need at least a full 3 dB gain in order for the other person you are talking with to even notice a change in your signal. That being said, the 0.3 dB gain would amount to almost nothing. So why would anybody waste the time or $ installing this unless they have TVI issues to contend with??? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2560
Registered: 9-2004
| | Posted on Thursday, June 21, 2007 - 12:59 am: |
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its not about DB gain.
its about take off angle.
picture this:
draw a vertical line on a piece of paper to indicate your antenna.
draw a horizontal line below the vertical line to indicate the ground level.
it should look like an upsidedown T.
now, starting at the base of the vertical line, draw a line at a 45* angle, coming up from the horizontal line.
lets say that the vertical line is a 1/2 wave antenna like the A99.
this angled line is your take off angle.
now draw another line at a 30* angle.
this would represent the take off angle of a 5/8 wave antenna like the IMAX 2000.
now draw another line at about 25*.
this would be the take off angle of the IMAX using the groundplane kit.
now, why is having the lowest possible take off angle important?
because the lower the take off angle, the more your signal "hugs" the curvature of the earth, thereby getting you further out into DX land.
remember that we are dealing with physics here.
to further illustrate this point; draw a horizontal line across the paper about 2" above the top of the vertical line.
this will represent the ionosphere, which your signal bounces off of, sending your signal out into DX land. this is why its called "skip".
now, extend that 45* line out to where it meets with the "ionosohere" line.
draw a line at 45* showing the signal bouncing off of the ionosphere.
now do the same with the 30* line, and again with the 25* line.
you will no doubt see that the 25* line has extended further on the paper than the 45* line did.
that is why take off angle is so important to good DXing.
hope this makes sense and clears some things up.
later,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Jaws792
New member
Username: Jaws792
Post Number: 7
Registered: 5-2007
| | Posted on Thursday, June 21, 2007 - 9:52 am: |
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thank you for the simple easy to follow diagram. I do however understand take off angle and I'm not challanging that law of physics or your explanation. But still, is it correct, that you need at least a full 3dB gain in the signal for the other person to even notice you as well as a full 3dB gain on the receive end to here any change in their signal. That was the point that I'm making because adding the GPK, as stated by tech 833 only gives you a .03dB gain on transmit and receive and this would include the change in take off angle I'm presuming.
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2561
Registered: 9-2004
| | Posted on Thursday, June 21, 2007 - 10:39 pm: |
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im not an RF engineer or anything even close, so what i think i know is just from my own reading and studying.
from what i understand, the take off angle of the antenna is not the determining factor in figuring the DB gain.
a 3db gain is equivilent to a doubling of power.
a 6db gain is equivilent to a 4X power increase.
you need to increase output power by 4X to gain 1 S-unit on someones receiver.
the lower angle of radiation will bounce back to earth at a further distance than higher angles of radiation.
how that relates to db gain, i dont know.
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Marconi
Advanced Member
Username: Marconi
Post Number: 734
Registered: 11-2001
| | Posted on Friday, June 22, 2007 - 2:23 am: |
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I'm not a pro either, but I think we really need to understand what some of the conditions for modeling are before making a judgment as to how good a TOA really is when presented a graphic of an antenna pattern we might see on the Internet or in print. For sure those used in advertising, even if not a lie, are often show to be the best patterns, but are taken under misleading circumstances.
As Jaws792 suggests, I too understand the example noted above, but this might also suggest to some that the A99, at 45 degrees, will not be able to communicate with stations that exists at angles below and within the lower (30 degree) angle range represented by the Imax w/o GPK simply because it has a higher TOA. Say nothing about the even lower (25 degree) range for the Imax w/GPK suggested. I might even go so far as to state that I have seen a 1/4 wave ground plane antenna produce a better signal at some far field station when comparing it to a higher gain radiator. I cannot prove this to you, but I have seen it happen a few times. I have also seen a 1/2 wave make better signals to some stations than a higher gain antenna that typically out performs the 1/2 wave. So something else is going on at times and can best be seen when comparing two antennas at the same height and at the same point in time using a good switch box.
The TOA is only one angle measured at a point in a pattern where the strongest RF is measured as produced for that particular radiator under the conditions that exist for the model. Even with the differences noted in the graphics we see representing these antennas and the amount of power they produce at the peaks, all of these antennas radiate at very low angles towards the horizon and into very similar areas of patterns.
I believe you will find that most graphics depicting what we might call perfect patterns are nowhere near what the patterns are for the antennas in our back yards. But, even if the patterns were the same showing the insignificant peak difference in power (Db), it is typically so small as not to be noticed in operations. Yet we have seen RX signal differences between different antennas under certain circumstances, right?
So why do we make claims about how much multiplication it takes to make a gain of an S-unit (3-6 db) on a RX meter somewhere in one discussion, and then turn around and argue that the little differences we see in the peaks of the patterns discussed in this topic show us to be significant in gain.
The big factors controlling a well designed, constructed, and installed antenna is the soil conditions below the antenna in the near field, the soil, atmospheric, and environmental conditions in the path of the signal in the medium and far field. The height of the antenna might also encourage phasing of ground reflected and direct signals emitted that could be said to be cumulative (increasing by addition) at some receiver in the distance. And then on the other hand when the same setup discourages the combining affects note above by the signals being out of phase when reaching a far field receiver. We sometimes see this when we make a DX contact with two neighbors a distance apart, where the signal for one seems very strong compared to other station nearby. Sure it could be power, but I find it sometimes is probably not power. The right mix of angles is in your favor with one station and you have a solid contact. This can happen just as well with a 1/4 wave or 3/4 wave vertical antenna.
Sorry to be so long. Wish I could say this with fewer words. I like Jaws spunk in questioning this business about GPK's for the Imax. I know that some people have had real good sucess with a GPK, but I have just never seen a difference other than in the bandwidth changes noted. |
Jaws792
New member
Username: Jaws792
Post Number: 8
Registered: 5-2007
| | Posted on Friday, June 22, 2007 - 5:30 pm: |
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Thanks for all the feedback everybody.It shure is true what all of you have said, there are just so many variables that come in to play when it comes to this hobby. By the sound of the replies I'm getting from all of you, even though you say your not experts, you sure know a lot more than me and I find it very helpful listening.
I am new to this hobby but I'm having lots of fun with it. I really can't believe how much DX I have been able to accomplish in such a short period of time. I never thought it would be this consistent.I can't even imagine what it is going to be like when the next 11 year sunspot cycle rolls in. Research says, it is going to be 30% to 50% more intense than the last!! Is it going to be just a huge pile up out here? I have never experianced one.
I wonder if that guy with the clean signal, got that washing machine at a C.B. store? Do they have a front loading model available? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2563
Registered: 9-2004
| | Posted on Saturday, June 23, 2007 - 11:13 pm: |
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LOL, i found the washing machine pic online.
i do know who the guy is that built it, and it really worked. not just for show.
i really should change that avatar. i only meant that one to be there for a little while.
yes jaws, it is going to be very crowded when the sunspots get heavy in a couple of years.
thats why we all spend so much time tweaking our setups during the lull; so we can be #1 on the channel when the skip is rolling.LOL
marconi, i only meant that "diagram" to be an illustration of what take off angle means.
it is way too simplistic to explain any of the variables going on.
i like to use the 4X power thing, as it brings people back to reality when wondering if they should replace their 4 pill with a 6 pill, etc...
if i had to worry what might be inferred by a statement i make on here, i probably wouldnt post it. i just put the info out there and let the chips fall where they may. LOL
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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