Properly sealed, fiberglass makes a good insulator, but a couple words of
warning. Cutting fiberglass on a lathe creates a hazardous dust that gets
into just about anything. It takes a good vacuum/dust collector and dust
mask (One that seals to your face, not the inexpensive fiber ones) to make
working with with the stuff safe. It's also abrasive and very hard on tools
so it needs to be kept off all moving parts of the lathe. It'll even rapidly
wear down carbide tipped cutting tools. It also gets into your clothes and
on your shoes to be tracked into the house where kids and pets will be
exposed.
Exposed fiberglass, like the surface you get from turning it down is easily
attacked by water and needs to be sealed as well as protected from UV.
Look at the insulator designs in the two links that were given earlier.
http://www.comteksystems.com/tower-insulators.html
http://www.arraysolutions.com/Products/commercialtowerinsulators.htm
I prefer the insulator design in the second link made from Delrin but the
same shape could be applied to fiberglass. It's much stronger than the other
design, but needs to be made longer to keep the capacitance between the
mounting plates to a minimum. I'd definatley use the cover which could be
made from the bottom of plastic pop bottles of the proper size and shape.
BTW, Delrin is much safer to work with than is fiberglass. OTOH you'd want
the insulators to be 3" to 4" in diameter. Just purchase a Delrin rod of the
proper diameter, cut to length, add tapered groves for added electrical
length, make flat plate to tube (tower leg) adaptors, drill and tap the
Delrin insulator and bolt between the adaptor plates.
There are some alignments that are important, but "with access to the proper
tools" these could probably be built for $100 or less. Delrin this size
isn't cheap! <:-))
73
Roger (K8RI)
> I know K4SSU has turn down the fibeglass and make insulators for Rohn 25.
> Ron K4WZ
>
> ----- Original Message -----
> From: "Mark Robinson" <markrob@mindspring.com>
> To: "jeremy-ca" <km1h@jeremy.mv.com>; "James Bloomfield"
> <rn23crna@windstream.net>; <towertalk@contesting.com>
> Sent: Tuesday, June 19, 2007 5:47 PM
> Subject: Re: [TowerTalk] Tower Insulators
>
>
>>A friend of mine made Rohn 25 insulators for his 80m 4 square by turning
>> down fiberglass rods
>>
>> Mark N1UK G3ZZM
>>
>> ----- Original Message -----
>> From: "jeremy-ca" <km1h@jeremy.mv.com>
>> To: "James Bloomfield" <rn23crna@windstream.net>;
>> <towertalk@contesting.com>
>> Sent: Tuesday, 19 June, 2007 5:42 PM
>> Subject: Re: [TowerTalk] Tower Insulators
>>
>>
>>> The ones mentioned are $400 and $1145! Ouch!
>>>
>>> Consider feeding the tower as a folded unipole, all you need is some
>>> copper
>>> wire. Ham literature shows a single drop wire; commercial AMers use 3 to
>>> 6
>>> and report improved bandwidth when the electrical length is 110-115
>>> degrees..
>>>
>>> Carl
>>> KM1H
>>>
>>>
>>>
>>> ----- Original Message -----
>>> From: "James Bloomfield" <rn23crna@windstream.net>
>>> To: <towertalk@contesting.com>
>>> Sent: Tuesday, June 19, 2007 2:52 PM
>>> Subject: [TowerTalk] Tower Insulators
>>>
>>>
>>>>
>>>>
>>>> I plan to install a 90 ft. vertical Rohn 25 that is fed with two 'L'
>>>> networks for 160 and 80 meters.
>>>>
>>>>
>>>>
>>>> This is described in Low-Band DXing by John Devoldere ON4UN.
>>>>
>>>>
>>>>
>>>> I think I can do everything necessary except I have not been able to
>>>> find insulators for the base of the tower. There was one commercial
>>>> source
>>>> but they wanted $300.00.
>>>>
>>>>
>>>>
>>>> This is a 'budget' project. The towers were acquired by taking down
>>>> "TV" towers that were no longer in use. The Coax is commercial
>>>> hardline
>>>> purchased for $30.00 (260 ft!)
>>>>
>>>>
>>>>
>>>> The only 'plan' that I have is to build 6 metal disc welded to rods
>>>> that
>>>> fit inside the tower legs. They would be insulated with Lexan and
>>>> bolted
>>>> together in such a way that the bolts would also be insulated. I have
>>>> some
>>>> 1/2 inch lexan - from a flee market.
>>>>
>>>>
>>>>
>>>> I am aware that Rohn made insulators for the tower legs but they are
>>>> no
>>>> longer available.
>>>>
>>>>
>>>>
>>>> Ideas and opinions are needed and welcome.
>>>>
>>>>
>>>>
>>>> KV4FE
>>>>
>>>> Jim Bloomfield
>>>>
>>>> On the Suwannee River
>>>>
>>>> Fl.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> TowerTalk mailing list
>>>> TowerTalk@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>>
>>>
>>> _______________________________________________
>>>
>>>
>>>
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>>
>> _______________________________________________
>>
>>
>>
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>>
>>
>
> _______________________________________________
>
>
>
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