On 7/16/2012 7:06 PM, Dan Hearn wrote:
> Rob, you do not seem to be getting any help so I will give you some
> suggestions.
Gee, he only posted a few hours ago -- we're not exactly ignoring him.
:) But you've given great advice.
Yes, the Fair-Rite #61 material, or equivalent by another mfr, is the
material of choice for those frequencies, and you'll want multiple cores
in series on the coax. Cylinders are less expensive for the same RF
performance, but clamp-ons go on with the connector in place. Impedance
is approximately proportional to the length of the core. The natural
resonance of #61 is already lower than you want it, so you do NOT want
to wind multiple turns.
As to the total impedance required -- that will depend on what you're
trying to accomplish and how much imbalance there is in the system. In
general, the greater the imbalance the more impedance you need, both to
kill noise and for power handling.
Finally -- don't expect a lot of suppression on 23 cm -- even the
highest frequency ferrite materials are starting to "run out of gas"
when you get much past 800 MHz.
73, Jim K9YC
> 1. Get the Fair Rite catalog at
> http://www.fair-rite.com/cgibin/catalog.pgm#select:freq1
> 2. Select suppression, then cables, then round cables.
> 3. At the top select 200-1000mhz, type 61.
> When you select a core size and click on its type number you will get a
> page which shows a graph with R , Z, and X versus frequency. You need
> several thousand ohms resistance for legal limit power. You can series
> enough cores to get this value. You can get split cores if you wish or
> solid ones. This should get you started to designing the chokes you need.
> Mouser and others sell Fair Rite cores.
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