One other thing might check out, is the Salt Water Dummy Loads
(on several web sites). One mearly uses (can, Jar with lid),
and with metal plates attached to coax connector, filled
with salt water - Fill with water, then with ohm meter , add
Salt until the brine hits 50 ohms! Tho, don't know how high
frequency it is reliable to, should work to at least 50 MHz.
Jim NN7K


John Passaneau wrote:
JIMMIE wrote:
On Jan 1, 8:34 pm, "Bob Campbell" wrote:
"JIMMIE" wrote in message

...


Nothing wrong with PoCo oil. They havent used PCBs in years. We use
the same stuff at work made by Shell . Its just mineral oil with a few
additives.
That's good to know.

I have a 200 watt air cooled dummy load made of 2 watt resistors. I
was curious as to how much power it could safley disipate if placed in
a gallon container of mineral oil. It seems to handle 200 watts
continuously with just a muffin fan on it.

Jimmie

Not an easy question to answer. allot depends on how the thing is made.
How much power it can handle is controlled by how fast the heat can be
moved away. It doesn't matter if it's oil or air. In oil the speed is
set by how obstructed the path the hot oil would need to travel to get
away from the part thats making the heat. I think the resistor in a
cantenna in free air is only good for about 50 watts but it designed for
the smooth passage of the oil around the resistor. I don't think that
your mass of 2 watt resistors will allow the oil to pass freely enough
to get to a KW for vary long. If you used a pump to move the oil it
would work better in the same way that a fan works.

John Passaneau

"Jim-NN7K" . wrote in message
...
One other thing might check out, is the Salt Water Dummy Loads
(on several web sites). One mearly uses (can, Jar with lid),
and with metal plates attached to coax connector, filled
with salt water - Fill with water, then with ohm meter , add
Salt until the brine hits 50 ohms! Tho, don't know how high
frequency it is reliable to, should work to at least 50 MHz.
Jim NN7K


Back in the mid-1960's there was an article in QST where they did this.
The load will definitely be frequency dependent as demonstrated by
experimental results. Also the salt used will effect the results. From a
theoretical standpoint, the mobility of ions is dependent on the size of
the ion. The bigger the ion, the slower it will move. This conveniently
explains much of what is seen in ground losses and is why electrolytic
capacitors are essentially useless above 1 MHz. The ions cannot move fast
enough in the small times seen per cycle, so the current falls off. Ion
mobility also decreases as the temperature drops which explains why
electrolytic capacitors also do poorly at low temperatures.

I have done as Jim suggested when testing a kilowatt amplifier on 80
Meters. The load is useless if the water boils!

73, Dr. Barry L. Ornitz WA4VZQ

On Fri, 16 Jan 2009 16:59:29 -0500, "NoSPAM"
wrote:

I have done as Jim suggested when testing a kilowatt amplifier on 80
Meters. The load is useless if the water boils!

Is this the dawn of another debate over power in standing waves?

73's
Richard Clark, KB7QHC

"Jim-NN7K" . wrote in message
...
One other thing might check out, is the Salt Water Dummy Loads
(on several web sites). One mearly uses (can, Jar with lid),
and with metal plates attached to coax connector, filled
with salt water - Fill with water, then with ohm meter , add
Salt until the brine hits 50 ohms! Tho, don't know how high
frequency it is reliable to, should work to at least 50 MHz.
Jim NN7K

Generator tests (60 or 400 Hz, multi-KW) are routinely performed with a
trailer-mounted device called a load bank, where plates are immersed into a
tank of salt water. The depth of the plates determines the load resistance.