RF Power Resistors from Caddock
 

Hi All,

In regard to other postings originally inquiring into the utility of
network terminations as dummy loads, the thread drifted into more
serious power levels with the Caddock MP9100 being suggested.

I have been in correspondence with their engineers who have kindly
supplied me with these details:

We have test data for the similarly constructed, smaller scale model MP930,
that indicates pretty good frequency performance up to about 300 MHz or so.
We have verbal reports that the MP9100 looks pretty good up to similar
frequencies, but of course ³pretty good² depends on expectations and actual
requirements. I seriously doubt that it will be useful at 3 GHz, or
anywhere near that frequency. I have attached a drawing of an impedance
model derived for the TO220 sized parts. The inductance for the MP9100
should be about 10 nH, and freestanding capacitance should be about 1.5 pF.

The impedance data is from testing we did using an HP 4291A Impedance
Analyzer. Because the resistance film pattern is the same for all MP930
resistance values (MP9100 uses the same pattern * scaled larger), and
measurements performed on low ( 1 Ohm) and high ( 1 kOhm) resistor samples
confirm it, the model is valid for all resistance values. Referring to the
impedance model depicted in the attachment, inductance (l1) in nH and
capacitance (Cm) in pF is:

Isolated One lead common
Freestanding On heatsink to heatsink
Model nH pF nH pF pF
=================== ============ =======
MP930 7.60 0.75 8.00 1.75 3.65

==

We measured these resistances and phase shifts with 50 Ohm nominal value
resistors:

===================================
Phase
Shift
F, MHz Ohms degrees
====== ===== =======
MP930 (freestanding)
100 50.2 5.1
250 51.6 12.2
500 56.5 23.2

MP930 (isolated, on heatsink)
100 50.1 2.9
250 50.3 7.4
500 51.6 15.0

MP930 (one lead common to heatsink)
100 49.7 -1.80
250 48.5 -4.50
500 43.8 -9.70


73's
Richard Clark, KB7QHC

RF Power Resistors from Caddock
 

What would this cost and from where do we buy them?

Buck





On Tue, 22 Jan 2008 09:19:45 -0800, Richard Clark
wrote:

Hi All,

In regard to other postings originally inquiring into the utility of
network terminations as dummy loads, the thread drifted into more
serious power levels with the Caddock MP9100 being suggested.

I have been in correspondence with their engineers who have kindly
supplied me with these details:

We have test data for the similarly constructed, smaller scale model MP930,
that indicates pretty good frequency performance up to about 300 MHz or so.
We have verbal reports that the MP9100 looks pretty good up to similar
frequencies, but of course ³pretty good² depends on expectations and actual
requirements. I seriously doubt that it will be useful at 3 GHz, or
anywhere near that frequency. I have attached a drawing of an impedance
model derived for the TO220 sized parts. The inductance for the MP9100
should be about 10 nH, and freestanding capacitance should be about 1.5 pF.

The impedance data is from testing we did using an HP 4291A Impedance
Analyzer. Because the resistance film pattern is the same for all MP930
resistance values (MP9100 uses the same pattern * scaled larger), and
measurements performed on low ( 1 Ohm) and high ( 1 kOhm) resistor samples
confirm it, the model is valid for all resistance values. Referring to the
impedance model depicted in the attachment, inductance (l1) in nH and
capacitance (Cm) in pF is:

Isolated One lead common
Freestanding On heatsink to heatsink
Model nH pF nH pF pF
=================== ============ =======
MP930 7.60 0.75 8.00 1.75 3.65

==

We measured these resistances and phase shifts with 50 Ohm nominal value
resistors:

===================================
Phase
Shift
F, MHz Ohms degrees
====== ===== =======
MP930 (freestanding)
100 50.2 5.1
250 51.6 12.2
500 56.5 23.2

MP930 (isolated, on heatsink)
100 50.1 2.9
250 50.3 7.4
500 51.6 15.0

MP930 (one lead common to heatsink)
100 49.7 -1.80
250 48.5 -4.50
500 43.8 -9.70


73's
Richard Clark, KB7QHC

--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."

RF Power Resistors from Caddock
 

On Tue, 12 Feb 2008 20:14:51 -0500, Buck
wrote:


What would this cost and from where do we buy them?

Hi Buck,

I think Digikey for about $8 - $10 apiece.

73's
Richard Clark, KB7QHC

RF Power Resistors from Caddock
 

Richard Clark wrote:
On Tue, 12 Feb 2008 20:14:51 -0500, Buck wrote:


What would this cost and from where do we buy them?

Hi Buck,

I think Digikey for about $8 - $10 apiece.

73's
Richard Clark, KB7QHC

Mouser (http://www.mouser.com/) and Allied (http://www.alliedelec.com/) also
stock Caddock. If you need only one or two, you won't get stung $5 for a
less-than $25 order. Their prices are only a tad higher.

For higher power capability, you can go with series-parallel combinations of
such devices (on a heatsink). For even higher power, there are devices up
to ~800W in a flange-mount. The RF Cafe (http://www.rfcafe.com/) has a list
of vendors.

vy 73,
Bryan WA7PRC