Hi Mark,
Interesting! I checked out the spec sheet for the resistors you mentioned.
The inductance for 2-8KW is <3 uH and 5-16KW is <5 uH. Would be interesting
to see some practical tests on HF.
73 Bert, VE3OBU
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Mark Marsden
Sent: Wednesday, May 25, 2005 8:47 AM
To: amps@contesting.com
Subject: Re: [Amps] Dummy Load
Hi Stefan & Will
That's very interesting to me. I'm looking at a possible 50R 40dB attenuator
based on the new thick-film-on-steel planar resistors by
TT-electronics/Welwyn. They aimed at the automotive dynamic braking &
welding industry, with a very low £/kW ratio.
Farnell part numbers are
465-9569 50R 2-8kW £13.93
465-9600 50R 5-16kW £23.52
It'll be interesting to see if the meander-line construction can be matched
to give a good return loss across the HF spectrum.
Best 73 Mark G4AXX
*********** REPLY SEPARATOR *********** Stefan,
One way I've seen them built the way your wanting to do it is use 4 narrow
PC boards with an etched line down eachs middle. The resistors solder across
this line where it made two long copper pads. Each 4 was done this way
mounting resistors on each in parallel. The 4 boards were then connected
together in a box shape during hookup. Then, the top of each board went to
the ground of a RF connector, and it center pin went down through the middle
of the boards thus connecting at the bottom. These were built in 1 gallon
paint cans to be oil cooled. if I recall, the builder took a piece of
aluminum tubing and slid it over the board assembley and left it open at the
top and bottom by brackets. That way the oil could circulate through the
center easily. I'm not sure how well they worked, I just happened to see one
built that way.
Best,
Will
*********** REPLY SEPARATOR ***********
On 5/23/05 at 5:22 PM Stefan wrote:
>Dear friends
>
>I am trying to build a Dummy load made out of many parallel resistors
>(200x 10k/2W), and I am thinking of which would be the best
>configuration. I have seen (and even used myself) a bus capacitor
>circuit with 10uF MKT caps (power capacitor) which to enhance
>capacitive behaviour made a very clever layout in which current flew in
>each device in the opposite direction to cancel thier magnetic fields
>(and therefore reduce their stray inductance).
>You can place caps on the top and the bottom and if current flows in
>the opposite direction on each one at its sides and beneath it the
>parasitic inductnace is reduced.
>
>I have thought of using this idea also for the dummy load. Using to
>very wide tracks on both layers and placing components on TOP and BOT
>layers, where current flows in the opposit direction on each one. But
>which is the minimum distance (clearance) I have to maintain between
>pins of opposite voltages (for Po=400W, R=50 => V=141V). Would 5mm do it?
Or even less?
>
>I hope somebody could share his expertise with me.
>
>Thanks in advance,
>
>Stefan
>EA5FY
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