"The top 25% of most antennas does very little at all in comparison to the mid and base sections."
It makes the antenna usable I would of thought (VSWR), that is pretty important ; )
@222DBFL
Well it is a curious thing... I have a Sirio HP4000 mag mount antenna and I have made a few European DX contacts with it on 15Watts radio power to the tune of about 1,000 miles into I think if I recall Slovakia or Czech Republic maybe... the details escape me, anyway it was about 1,000 miles. Other than that I have not faired particularly well. It certainly does not hear any where near as good as a silver rod on a pole. Not even close. And we are talking multiple S points, not dB's. I would educated guess
3-4 S-points in practice on the RX side coupled with the pole clearance from earth. That is clearly audible in RX noise floor alone. It simply picks up more of everything... it is a vastly superior antenna
system for the RX side.
I hear a few people saying they can work 10,000 miles using a mag mount. I have no doubt that has happened.
So we can say if you have exceptional conditions you can work the work using a mobile mag mount.
I do not currently have a "through hole" capability and as I gather this means you are kind of limited to around 100W before the capacitive coupling becomes less effective with associated problems. So there is 1 immediate limitation.
You see when I go out there are 2 set ups I use.
No compromise (full day) performance omni station using Gain Master at 7.5 meters height and around 150-250M ASL and about 170W PEP
And the Silver Rod "quick set up" at around 4.5M height. This is a perfectly quick and easy set up with the same power.
Given you can work the entire planet DX wise on a 1/4 wave whip or less on the top of a car why does anyone bother with any other antenna ?
My own personal reasoning is because conditions are mainly far from optimal right now, we are on the down stroke from the 11 year cycle. By using the Gain Master IMO the best vertical mono pole DX antenna out there (
for my specific set up situation) I stack the odds in my favour of filling in the log book in only moderate conditions or even weak conditions.
That is the reason. I also believe if you wish to give an S1-S3 13,300 miles away which I did long path to NZ recently that you need that very low radiation angle that such an antenna provides. (and I am not on a GM is the only and best antenna crusade, clearly other antennas and the system (ground conditions, radials, height, pole, coax, grounding, local geography etc.) they are employed can be equally as good.
Now we know chance is part of the game on 10-11m. I want to make sure that when luck is on my side that I am in with the absolute best chance possible.
Maybe I could have spoke to NZ with a Silver Rod, maybe I would not have been heard. Maybe my lobe at a 4 degree take off got through and the SR or a mobile antenna would not have output sufficient energy at that angle to get through.
Or maybe not !
It is about hedging bets. I read again and again and again the GM is the best vertical DX antenna. I am glad I did not ignore it because by and large and without guarantee or detailed evidence from a lab I would have to concur.
Once you have spoke around the entire world on an omni on 10/11m (the long way) there is not much left to do. Of course there is.... if you wish but for myself that is one major goal achieved as I now have solid evidence I can talk anywhere the conditions will allow me to. You can hear that from others but till you experience it it is not a reality/ a tangible experience.
Now of course the guy at the other end had a beam and this is a very significant factor, but I have no more control over that than the conditions of the F2 layer themselves.
I can choose how to operate my end and stack odds in my favour.
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Salt water is like radio turbo juice. I have understood this in theory and in practice as a station not far from me hears greatly more than I using an IMAX. He could use a silver rod and it would probably be similar. Salt water is the exception and not the rule that applies to most operators.
I did not think that being on a hill helped with DXing until I read about the affect of being on a hill on your lowest lobe.
In simple terms (best for me !) the first reflected wave from the earths surface does not have such a negative influence on your low angle performance as being on flat earth (of similar quality). It seems being on a hill reduces the negative effect of out of phase destructive recombining of waves.
So the reflected wave from a sloping surface leave the lowest angle rays of radiation in tact more so than a reflected wave from flat land.
In effect it means your lowest angle ray is likely to be emitted at a lower angle than that of a "flat land" station on similar ground quality. (let's say "good")
This effect depends on the steepness of the slope, electrical qualities/skin resistance etc. of ground around you and is not easy to calculate as most hills are not exact uniform gradient slopes on either side and vary considerably.
I am going to guess something here. The geography of my location means there is water in most directions within 30-40miles... if I am at 170-250M I would hazard a guess that this is advantageous. I can hit close to a +30 signal 30 or so miles away at the coast, from there the signal has no obstacles (no hills in the way). That has to be a good thing as it means unimpeded RF energy is getting to the sea at 3 poles of the compass.
Now I think the edge of my understanding is reached as I think for salt water to have a positive effect on RX and TX signals it is in the first 100 wavelengths distance or so that is critical to keep the Pseudo Brewster Angle below 1 degree which means ALL reflected energy is in phase with your direct wave. This is why it is like magic for radio waves, greatly increasing both TX and RX signals.
The beauty of radio is the technical scientific aspect and the in practice results and integration of what is happening in ones mind given the sky we can see and understanding of the atmospheric layers above us. I think the aspect of visualizing what is happening has helped me make better operational decisions even if they were not scientific on my behalf. (Though they clearly were for those at Sirio designing the Gain Master)
It is immensely fascinating.
