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poor mans gainmaster

bob85 said:
we don't know what the red coax is, its 5mm same as rg58, you have standing waves on the section of coax above the stub, 500w into rg58 with high vswr is pushing it hard.
Click to expand...

I suspect that teflon dielectric is used throughout the Gainmaster but when I try my hand at home-building one I want to use RG-213 for it's power handling characteristics, but the capacitance is a little higher than RG-303 and RG-393 so it might not tune correctly, depending on the importance of that spec on the lower half of the main element, not the matching sections.
I definitely have a couple questions about the reason for the 16 turns and how interesting it is that it is close to an electrical half wave, depending on the velocity factor.
 
eddie, i don't know how much putting the antenna inside a fiberglass radome will detune it, i will start by taping it to the outside to experiment,

the top-one we cobbled together had 90" radials from the old style vector so it would not tune on 11mtrs, its stripped down in the garrage, the new top-one does not intrigue me like the astroplane does.

a new 8mtr pole cost my buddy £24 delivered, he uses them for other antennas like portable dipoles xbeam ect,
i hope to use an old fiberglass pole used by the electric board if the bottom section turns up, its hiding from me at the moment.

m42duster
for the electrical side of it we are using parts we already have, none are the same as sirio use, its just an experiment, listening to this bird made me try,
ECE3300 Lecture 13b-1 Impedance Matching Intro - YouTube
 
Needle Bender said:
I suspect that teflon dielectric is used throughout the Gainmaster but when I try my hand at home-building one I want to use RG-213 for it's power handling characteristics, but the capacitance is a little higher than RG-303 and RG-393 so it might not tune correctly, depending on the importance of that spec on the lower half of the main element, not the matching sections.
I definitely have a couple questions about the reason for the 16 turns and how interesting it is that it is close to an electrical half wave, depending on the velocity factor.
Click to expand...



i have had the same thoughts about the red coax, between the stub and the feedpoint you have standing waves, the antennas power rating seems high for rg58 size coax with standing waves,
i aim to find out if there is anything special about the red coax, 213 is on the list to try.
 
Well a bottom fed 5/8 is about 100-150 ohms without a matching circuit, so I'm wondering if a center fed would be about the same. If it is, then some sort of matching device will need to be employed aside from the phasing sections.
Interestingly, If you add the 16t of the 2.8" coil to the 134" above it plus the 4 inches below it to the connector you get 278.75" divided by a .85 velocity factor (like LMR400) = 328" which just happens to be a 3/4 wave at 27mhz.
An electrical 1/4 or 3/4 wave piece of 75 ohm can be used as an impedance matching transformer for a 100 ohm load, a 90 ohm 1/4 or 3/4 for a 150 ohm load. :blink:
 
just to let you know, the new pole i had delivered was £24.70 inclusive, and it is 10 mtr,we aim to loose the top 2 sections which gives us 8 mtr and the o/d is 16 mm at the tip,also we aim to add glassfibre at the mounting point where needed !
 
simonradioman said:
Check Shackpix.com there is a Portuguese home made Gainmaster there and also some excellent videos on youtube how it works

Rx Gain of three different antenas Sirio Gain Master, Sirio 857 Cubical Quad 5 Elem Vert Polar - YouTube

rx test v 5 element and a sirio 827^can not stand it^
Click to expand...

Simon, I notice this station is testing RX in sideband mode and according to most of my critics...this makes all results invalid. I don't have any problem seeing and understanding the differences I see on his radio, even if I don't see such differences using my GM compared to some other antennas I have.
For the last year I've had the GM up to compare against my Starduster that is about 8' feet lower to the tip, and they do me about the same...with first one then the other typically showing an insignificant difference in signal.

Do you have any idea about how the height of his GMx vs. the 827 compared in this test?

Thanks for the post and good luck.
 
Marconi said:
Simon, I notice this station is testing RX in sideband mode and according to most of my critics...this makes all results invalid. I don't have any problem seeing and understanding the differences I see on his radio, even if I don't see such differences using my GM compared to some other antennas I have.
For the last year I've had the GM up to compare against my Starduster that is about 8' feet lower to the tip, and they do me about the same...with first one then the other typically showing an insignificant difference in signal.

Do you have any idea about how the height of his GMx vs. the 827 compared in this test?

Thanks for the post and good luck.
Click to expand...

Hey Eddie,

Much to my chagrin, a local guy Jack (625) erected a new Gainmaster in place of his Imax2000 on a 36' push-up mast in his field and with non-metallic guy line and has seen no difference in performance.

Perhaps there are bad heights for the balanced design of the Gainmaster? Or perhaps he lives in a relative hole where he does not benefit from the lower TOA?

It sure was a disappointment to those of us who expected improvement, which he does have considering the superior strength of construction of the Gainmaster, and lack of bending to a 90 degree Imax angle in the wind!

Interesting the differences in comparative performance relative to each Gainmaster installation.
 
Without stating what would seem to be the obvious unless I'm missing something, a 5/8 wavelength antenna would show no more advantage over a similar antenna when the TOA is the only thing of issue with each one. As I understand it, the maximum advantage would be in the far field contacts of many miles out, and/or for DX, and we know DX is a fickle mistress where testing is concerned.
For consistently measurable nearer contacts even a 1/4 wavelength antenna has long been at the advantage locally due to its higher TOA. One should not be surprised if a drop in meter readings was reported locally when a longer antenna with lower TOA is put up. . .
I think being able to consistently report measurable advantages of one over the other beyond modeling differences will never happen. All of the reasons we use longer wavelength antennas are because of our quest for greater gain to the horizon that gives us better contacts (hopefully) into distances where conditions are simply uncontrollable: between us and the distances we are aiming at with very low TOA are too many variables to think of.
It's been said before better than I just did . . .
Nevertheless, I am awaiting the results of this poor man's GM anxiously.
 
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