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

[Brian Clarke]

Hello all,

Let's be very clear,

The Heath Cantenna uses a carbon resistor (good) in a parallel sided tube 
(very bad). What this means is that as a dummy load, the main dummy is the 
user. In a word, the Heath Cantenna is, in this format, only good for DC. 
The air-surrounded MFJ jobbie is just as useless. For a proper dummy load 
look for a Bird Termaline.

If you have a friend with a very good lathe, get a negative exponential cone 
turned up to house the carbon resistor - then it will have performance flat 
beyond at least 1 GHz. I have designed such a cone, used one surrounding 
that self same carbon resistor and achieved the performance I specified at 
least up to 500 W.

If you are worried about the possibility of PCBs, visit your local 
electricity supply authority and ask for a gallon of the latest synthetic 
transformer oil - they will also probably dispose of the suspicious oil you 
have.

73 de Brian, VK2GCE
B Eng, PhD, CPEng, Fellow IEAust

On Saturday, August 25, 2012 8:33 PM, Rob said:


>I disagree.  PCB oil is only a problem if it leaks out and you come
> into contact with it.  The fear about PCB is similar to the fear about
> lead paint and asbestos.  All only bad if you rub yourself with it or
> ingest it.  There are still PCB caps in use in industry--they just put
> warning stickers on the fronts of the cabinets saying that oil caps
> inside have PCBs, and drive on.  Besides, it is not certain the oil
> has PCBs.  If the oil in the cantenna is clear and clean you may as
> well use it and add some mineral oil to it if the resistor is not
> submerged.  Then you don't have the hassle of disposal.  As a
> precaution against the can leaking, go to a supermarket and get a
> cheap disposable aluminum turkey pan and set the Cantenna in it.
>
> Now, having written all that, let me also add that for AM the Cantenna
> is inadequate in my opinion, except for brief test transmissions.
> That sucker will get hot if you dump a carrier into it for more than a
> minute or two, especially over 300 watts.  Use it, but keep looking
> for something better.
>
> 73
> Rob
> K5UJ