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Author Topic: 250W Dry Dummy Load Issue  (Read 489 times)

K1KIM

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Re: 250W Dry Dummy Load Issue
« Reply #15 on: July 24, 2022, 09:48:36 AM »

Thanks Glenn and Dale for the informative responses.

10-4 Good Buddies......Hi Hi Hi Hi
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So Many Toys.......So Little Time!

WD8SBB

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Re: 250W Dry Dummy Load Issue
« Reply #16 on: August 30, 2022, 01:44:22 PM »

Quote
What does peak my curiosity is why the oil filled Cantenna with the large coil resistor does not display these results on the higher frequencies.

The Cantenna is actually a long resistor.  As I recall,  a hollow ceramic core and outside resistance material coating.  The resistor is then mounted inside a cylinder of aluminum forming a section of feedline.  The center of the feedline, the resistor, happens to attenuate the RF energy very well vs transfer it.   That is why the Cantenna does so well at higher frequencies.
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N7EKU

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Re: 250W Dry Dummy Load Issue
« Reply #17 on: October 24, 2022, 07:29:41 AM »

Thanks Glenn and Dale for the informative responses.

10-4 Good Buddies......Hi Hi Hi Hi

Hi,

It's easy to forget about the importance of lead lengths.  Normally it's OK but when one goes to the bands above HF it's a big jump.

How did you make the connection to the resistor?  Best might be to use a teflon insulated coax with the center conductor and braid soldered right to the tabs and as short as possible.  Likely on the datasheet for the resistor, there is a PCB layout designed for minimizing the reactance all the way up to the GHz range, so one could copy that.

73

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Mark -- N7EKU/VE3

WA3SKN

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Re: 250W Dry Dummy Load Issue
« Reply #18 on: October 24, 2022, 10:33:34 AM »

The resistor does not "attenuate" the RF energy... it simply converts it to heat.  This heats the oil.  The aluminum creates a "chimney" and the heated oil rises, circulating the oil.  The can provides the shielding and keeps any RF inside.  The oil does expand with heating... plan for it!

-Mike.
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KD6VXI

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Re: 250W Dry Dummy Load Issue
« Reply #19 on: October 25, 2022, 04:53:48 AM »

The resistor does not "attenuate" the RF energy... it simply converts it to heat.  This heats the oil.  The aluminum creates a "chimney" and the heated oil rises, circulating the oil.  The can provides the shielding and keeps any RF inside.  The oil does expand with heating... plan for it!

-Mike.

I dunno about 'keeps any RF inside"...  The cantenna will radiate nicely throughout a neighborhood.

People have also made contacts on dummy loads, including cantennas.

In this regard, he is right.  It simply attenuated the signal.

--Shane
WP2ASS / ex KD6VXI
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