On Wed, 03 Feb 1999 15:55:14 EST Mark S Graalman <wb8jkr@juno.com>
writes:
>
> Well, I have two cantennas and have run both of
>them at 2KW without any problems with SWR shift BUT
>I've never left it key down more than about 1 minute continuous.
>Both use transformer oil. I did build the "super dummy" project
>in the handbook and it handles the higher power levels much
>better but still gets VERY HOT after about 5-8 minutes at 2 KW.
And that uses two 1 gallon cans in series.
If you were to take it a step further and mount that load in a 5 gallon
can with several fairly large size holes for circulation the power
handling would increase.
The internal can will act as a heat sink to some degree but for pushing
the limit I would guess that a circulating pump would help.
It is also not something for continuous use and abuse since once heated
it takes quite a while for the oil to cool. IOW, this is not a load for
production line testing.
BUT, we are getting away from the basic simplicity of the Cantenna when
we go into water cooling and other complexity.
Suffice it to say that my earlier suggestion does work well for the
purpose of amp testing at the legal power limit far exceeding the basic
Cantenna and it does have its limits.
73 Carl KM1H
.
>
>Mark WB8JKR
>
>
>
>On Wed, 3 Feb 1999 14:02:05 -0500 "Gilmer, Mike" <mgilmer@gnlp.com>
>writes:
>>
>>Not knowing the innards of the Cantenna, may I suggest a quick test
>>for
>>the usefulness of simply a bigger can of oil. The test would be to
>>see
>>if the sides of the existing Cantenna are warm after the "10 or 20
>>seconds" at 2KW claimed to be the maximum before VSWR change. If the
>>outside of the can isn't warmer than before the test started, then a
>>bigger can filled with more liquid will not help. It would seem
>that
>>one would have to get the oil circulating around the resistor better
>
>>to
>>justify a larger reservoir. My guess is the can surface will NOT be
>
>>any
>>warmer.
>>
>>Is it true that the Cantenna's VSWR changes appreciably after 10 to
>20
>>seconds of 2KW?
>>
>>Mike N2MG
>>
>>> >> The Cantenna dummy loads just can't take 1.5 Kw for
>>> >>very long. ........
>>>
>>> >You can use a 5 Gallon can which are usually throw aways from
>auto
>>> body
>>> >shops.
>>> >With some creative work with tin shears, drill, and a propane
>torch
>>> you
>>> >can adapt the Cantenna as a unit.
>>> >Thoroughly wash out the solvents in the can first!
>>> >
>>> >With 5 gallons of xfmr oil you can run 2KW for at least 20
>minutes
>>> and
>>> >still maintain the Cantenna frequency response.
>>>
>>>
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