[Boatanchors] Should dummy load oil ever need to be changed?

[Bill Cromwell]

On Sat, 2012-08-25 at 22:43 +1000, Brian Clarke wrote:
> Hello Charles,
> 
> Look up any good reference on transmission lines and there you will learn that cylindrical tubes are like a coaxial cable. Even the ARRL Antenna Handbook shows a design of a tapered cone style of dummy load which comes close to the negative exponential paragon, but does not explain the theory of why a parallel-sided tube is useless.
> 
> If the load at both ends of the cable is the same as the impedance of the cable, there will be no SWR problems. The problem with the Heath Craptenna and the MFJ similar is that one end of the cylindrical tube is shorted and the other is connected to your transmitter - so, there are SWR problems as soon as you drive any RF into it.
> 
> Just because 1,000,000 housewives poured their rubbish into London's River Thames, and killed all the fish for a generation, doesn't make it right. What I'm getting at is that you had no idea you had problems; science in general, and electronics in particular does not depend on democracy for correct explanations.
> 
> 73 de Brian, VK2GCE - who is polite enough to sign.
>   On Saturday, August 25, 2012 10:15 PM, Charles Ring said:
> 
> 
>   Without doubting the superiority of the Termaline, how are lesser dummy loads "useless"? We have been using them for decades with little trouble.


Thanks,

This going to save me a LOT of money. Useless 50 ohm dummy load, $75.
Cone shaped light bulb (maybe "useless" too) $0.50! The choice is so
clear now.

I don't work to 1 GHz so I can get by with a shoe string soaked in salt
water.

73,

Bill  KU8H