Topband: 160 Meter BALUNS

[i4jmy at iol.it]

RG8X is a fancy name chosen for commercial reasons and is not an official code for a qualified cable like other RGs. 
All foam cables without a rigid shield and a rigid jacket are infact very questionable cables in a number of transmitting applications, and as long term devices. Their best use is with UHF TV/satellite reception, when placed in boundles. 
Mechanical troubles of foam cables like RG8X is more evident in peculiar applications, expecially where the cable geometry has to be mantained. 
Foam is not a good choice material in power chokes made of coax cable, not only because it mechanically squeezes, already it does winding on a core, but because it might melt, already at moderate heat. If some heat is developed on the inner conductor and the flexible foam cable is subdue to mechanical forces, i.e. when wounded, a short can be developed.
Note that the above really happened, it's not only a theorical thought.
One word about teflon. 
Although some individual believe is not, teflon dielectric is quite lossy at VHF and UHF, worse than PE. Anyway Teflon is a good material because of its mechanical characteristics, i.e. it doesn't contaminate, and because it withstands a lot of heat, just the opposite of foamed PE. Teflon cables are quite expensive ones anyway, and there’s really no reason to use them instead of cables with PE below 7 MHz.

73 & season greetings

Mauri, I4JMY



> 
> Some may ask if RG58 is OK for a solenoid balun. Sure it is but for lower 
> power than RG8X. Since it is slightly smaller in diameter, 50 feet have a 
> slightly higher impedance. Since the power handling ability of coax goes 
> down as frequency increases, it maybe safer to use Teflon (RTM) type coax 
> such as RG303 if you are running high power, especially at 80 meters and 
> above. ."
> 
> Happy holidays and best of DX in 2004.
> 
> 73,
> 
> Joe, W1JR
>