I remember having to replace the coax inside a number of amps back then. One
end of the braid would overheat to discoloration and melt the dielectric
which of course shorted the coax. *IF* I remember correctly this was the
lead that went to the transfer relay and was a common problem with that
particular amp. I've even forgotten the model now, but I sure fixed a bunch
of them.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com
>> I think W8JI posted on this one a while back, and if my
> memory serves me
>> correctly, the reason braid is inferior is that as it
> corrodes it increases
>> resistance.
>
> Skin effect forces current to the outside surface. Since the
> outside weaves into the inside, current has to flow through
> the hundreds and hundreds of pressure connections. The
> connections are bad enough when the braid is fresh and shiny
> and has pressure forcing the strands together. They are
> terrible when the braid becomes tarnished or the pressure
> lightens up.
>
> As a matter of fact this is one of the main reasons coaxial
> cable goes "bad" and has high loss after moisture gets
> inside.
>
> When testing HF amplifiers in the 70's or 80's we found the
> braid removed from RG8 coax had more loss than number 14 or
> 16 wire in ten meter tank circuit leads. Despite being
> larger (meaning it would dissipate more heat) the braid
> overheated to the point of discoloration while #16 wire with
> much smaller surface area remained shiny.
>
> 73 Tom
>
>
>
>
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
> any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|