hey HomerBB ...............

[BOOTY MONSTER]

could you post some pics of your gamma on your home brewed sigma ? or if they're already posted in a thread here can you link to the page in the thread that has them ? could you also describe the materials and construction of your gamma ?

thanks

if anyone else would like to share info on home brewing gammas and/or provide pics of theirs id appreciate it also

 

[bob85]

i posted the vector gamma dimentions here for homerbb,
http://www.worldwidedx.com/cb-antennas/31799-avanti-sigma4-alternative-view-point-26.html

its just a rod and tube with a very loose fitting plastic tube between them for insulation..

 

[BOOTY MONSTER]

thanks bob . so there is no continuity between the rod and the tube in the gamma ... the plastic tubing insulates them from each other %100 ?
correct ???

 

[bob85]

yes

 

[jazzsinger]

yes

i just love it when bob gives these highly technically detailed answers.

 

[mackmobile43]

i just love it when bob gives these highly technically detailed answers.

He has a way with words and does not discriminate between those technically minded or me.

Booty the gamma is a large air space capacitor.

 

[HomerBB]

BM,
As I recall I used Bob's dimensions to make my gamma. the exception would be that I used electrical tape along the rod inside the sleeve at various places instead of the plastic tube. I did not have a hose/tube that would go around my rod and also fit in the tube.

Here is the link to that info:Bob's Post http://www.worldwidedx.com/cb-antennas/31799-avanti-sigma4-alternative-view-point-27.html#post226120

Here's the only photos of the gamma I posted (not so good): Homer's Post http://www.worldwidedx.com/cb-antennas/31799-avanti-sigma4-alternative-view-point-28.html#post226365

And many thanks to Bob for that info. So many helpful suggestions came from that thread I can't imagine ever having gotten a working model together without them. The gamma was the feather in the hat to making the match I sought.

 

[bob85]

lol

 

[BOOTY MONSTER]

the stock 7/8 vector gamma use

tube
.512" x
.049" x
14-3/8" ( not including the 1-1/4" fold )

rod
.236" x
34"

maximum capacitance ) is 50pf

is there a little room for error in these measurements ?
is the .512 tube the inside or outside diameter ?
could i use 1/4 inch rod and 1/2 inch inside diameter tube ............. ?
............ with about 1/8 inch of insulating material between them ?
at what height from the base of the vertical does the bracket for the top of the gamma connect to the vertical ?
how far out from the vertical is the bottom of the gamma ?
how far out from the vertical is the top bracket of the gama ?
im assuming the antenna tuned by adjusting the rod length in the gamma tube tube .
is the top gamma bracket used in the tuning also ? or is it a set position ?


a 31 ft vertical seems to get the most performance from the sigma styles . if using much larger diameter tubing (six 6 ft sections from 1 inch on top to 1 3/4 at the bottom) will there need to be any length compensating for the increased surface area/diameter ?

thanks

 

[HomerBB]

is there a little room for error in these measurements ?

My experience is this antenna is more sensitive to its dimensions and settings than any other I've done. There may be forgiveness in it, but, if so, it is close.

is the .512 tube the inside or outside diameter ?

I used 1/2 ID tube

could i use 1/4 inch rod and 1/2 inch inside diameter tube ............. ?

yes

............ with about 1/8 inch of insulating material between them ?

yes

at what height from the base of the vertical does the bracket for the top of the gamma connect to the vertical ?

varies with tune

how far out from the vertical is the bottom of the gamma ?

about the same as the radials

how far out from the vertical is the top bracket of the gama ?

I don't recall anyone discussing this. i just went with what i always have on a yagi. 4"

im assuming the antenna tuned by adjusting the rod length in the gamma tube tube .

yes, partly

is the top gamma bracket used in the tuning also ?

yes, this, too

or is it a set position ?

Only after the match is found

a 31 ft vertical seems to get the most performance from the sigma styles . if using much larger diameter tubing (six 6 ft sections from 1 inch on top to 1 3/4 at the bottom) will there need to be any length compensating for the increased surface area/diameter ?

Someone else will have to give you an answer for this but I would think it would affect the antenna length some.

thanks

Sure.
Now that I've put my answers in here maybe someone smarter can improve upon them.

 

[BOOTY MONSTER]

thanks homer . very encouraging
what did you use for insulating the gamma sections ? i was thinking about heat shrink wrap or electrical tape with enough layers to keep the rod snug in the tube . maybe if im very lucky lowes or home depot may carry some tubing thats ..... close enough to a perfect fit . i know lowes (and home depot too i think) carries 3 ft sections of aluminium rods and tubing in different diameters . if they have them in the needed diameters it would make things pretty easy....... if i get brave enough to try to make one .

 

[HomerBB]

I used wraps of electrical tape to make the fit. Yes, you can get your aluminum rod from either of those stores. I did.

 

[BOOTY MONSTER]

sweet . thank you sir

if i made this gamma is there any reason it would work for tuning a half wave dipole ... like the driver on a beam or the sirio 27 dipole ?
and..... if....if it works on that will it work on a sigma style/copy ?

 

[BOOTY MONSTER]

if.... if i wanted to try to make a sigma style antenna this spring would my base plate that im currently using be too big ? or rather big enough to cause problems ?

its about 12 inches square (30ish cm) . if i can make a working gamma attaching it , the vertical and 4 ground elements going up to the hoop would be very very easy . its a very strong platform to build on .

 

[bob85]

you could make a direct fed open sleeve with that baseplate and isolator,

if you want a sigma/vector i would make it look like a sigma/vector complete with gamma