...or how to hide it when you don't need it .
I don't have access to my cad here but I'll try to explain .
With RF transparent telescoping tube (fiberglass in this case) what you do is get the largest diameter you can and work your way down .
http://www.mgs4u.com/fiberglass-tube-rod.htm#pricelist
In this case 2 1/2" . Then refer to the "sample kits"
http://www.mgs4u.com/fiberglass-guide.htm
The next size down is 2 1/4" . Cut several rings of the 2 1/4" for bushings and seal support . It works like this . At the top of the 2 1/2" section insert three rings of 2 1/4" leaving enough room between them for a commercial square "O" ring . Do a bit of sluthing on
http://www.mcmaster.com/#o-rings/=13s4y4u
or
http://www.mcmaster.com/#o-rings/=13s4yta
I found the "X" profile to work best with irregular surfaces and the 1/32" inch interference to provide a good seal without a great amount of friction/stiction.
Now you have two internal "O" rings and a bushing at the top of the 2 1/2" base section . Repeat this at the base of the 2" second section making three more rings from the 2 1/4" and gluing them to the 2" section leaving room for the same size "O" ring you used on the top of the 2 1/2" section !
Repeat the process as far as you can and you have a radome that can contain anything you can stuff inside . You can easily get to 40' plus in 6 sections .
Modify a small piston compressor to apply pressure . Turn it around to apply vacuum . Store vacuum as well as pressure in small tanks . This has the added benefit of a vacuum source for de-soldering as well as air pressure for blowing the crud everywhere .
The hybrid . With a non-conductive base and metal follow on sections you can make a tuned vertical at any of the common magic lengths . The same practice applies . Skip one size on the way down for bushing and seal support all the way to 1/4" if you think you can get it to work . I found that 3/4" is the practical lower limit . Some sort of electrical continuity will have to be maintained section to section. A simple replaceable brass or copper , sprung , feeler strip is probably okay for all but kilowatt operation .
As far as tuning a 31' or 43' vertical ? SG-230 , manual , rotary switched loading or tuner of your choice . As far as stuffing the radome goes , you are a resourceful experimenter with some imagination or you wouldn't have read this far .
I posted this as an answer to a thread but it may need it's own as the membership offers suggestion, criticism and improvement. (please have a say !)
Hope it helps some one .
73
I don't have access to my cad here but I'll try to explain .
With RF transparent telescoping tube (fiberglass in this case) what you do is get the largest diameter you can and work your way down .
http://www.mgs4u.com/fiberglass-tube-rod.htm#pricelist
In this case 2 1/2" . Then refer to the "sample kits"
http://www.mgs4u.com/fiberglass-guide.htm
The next size down is 2 1/4" . Cut several rings of the 2 1/4" for bushings and seal support . It works like this . At the top of the 2 1/2" section insert three rings of 2 1/4" leaving enough room between them for a commercial square "O" ring . Do a bit of sluthing on
http://www.mcmaster.com/#o-rings/=13s4y4u
or
http://www.mcmaster.com/#o-rings/=13s4yta
I found the "X" profile to work best with irregular surfaces and the 1/32" inch interference to provide a good seal without a great amount of friction/stiction.
Now you have two internal "O" rings and a bushing at the top of the 2 1/2" base section . Repeat this at the base of the 2" second section making three more rings from the 2 1/4" and gluing them to the 2" section leaving room for the same size "O" ring you used on the top of the 2 1/2" section !
Repeat the process as far as you can and you have a radome that can contain anything you can stuff inside . You can easily get to 40' plus in 6 sections .
Modify a small piston compressor to apply pressure . Turn it around to apply vacuum . Store vacuum as well as pressure in small tanks . This has the added benefit of a vacuum source for de-soldering as well as air pressure for blowing the crud everywhere .
The hybrid . With a non-conductive base and metal follow on sections you can make a tuned vertical at any of the common magic lengths . The same practice applies . Skip one size on the way down for bushing and seal support all the way to 1/4" if you think you can get it to work . I found that 3/4" is the practical lower limit . Some sort of electrical continuity will have to be maintained section to section. A simple replaceable brass or copper , sprung , feeler strip is probably okay for all but kilowatt operation .
As far as tuning a 31' or 43' vertical ? SG-230 , manual , rotary switched loading or tuner of your choice . As far as stuffing the radome goes , you are a resourceful experimenter with some imagination or you wouldn't have read this far .
I posted this as an answer to a thread but it may need it's own as the membership offers suggestion, criticism and improvement. (please have a say !)
Hope it helps some one .
73