An alternate approach is to keep the RF energy outside in the antenna
field where it belongs.
Jim Brown K9YC in his RFI tutorial shows the use of quite effective
common mode chokes. 4 or 5 type 31 stacked ferrite toroid cores with 5
or 6 turns of coax wound through the stack. Use of one of those at the
antenna feedpoint, and another where the feedline enters the shack will
kill most all of the RF being brought into the shack on the outside of
the coax shield.
If you can keep that RF out of the shack by attacking it at its source
and keeping it in the antenna field where it properly belongs, you may
have little or no need for additional ferrite RFI suppression inside the
shack.
If you do need to use ferrite clamp-on cores on your in-shack cables,
use ones with a large enough center that you can wind several turns
through the core rather than adding more ferrite cores along the length
of the cable - it is much more effective - you are building an inductor
to choke off the common mode currents.
73,
Don W3FPR
On 11/5/2014 5:33 PM, Mike K2MK wrote:
Hi Mike,
I think multiple ferrites will help but you might be surprised to find that
it works best when applied to a cable you haven't yet tried. Take off all of
the clamp-ons and get things set up to reliably cause RFI. Then put 4 or 5
clamp-ons on one cable at a time. Try this on every cable in and out of your
equipment. Such as the DC cable from your power supply to the K3. Then move
onto the various PC cables.
One of those cables is bound to show a reduction in RFI. When that happens
just keep loading on the ferrites. For serious RFI one or two ferrites on a
cable is never enough.
73,
Mike K2MK
mike wrote
When using KPA500 my external monitor (and the P3 display) often freezes,
sometimes up to 5 seconds, after I transmit. With the external display
disabled, the P3 does not freeze (and incidentally it refreshes much
faster without the ext monitor enabled.) I also notice a slight flickering
of the monitor screen while transmitting. I take this to be a RFI problem.
I have added four snap on ferrite beads on each end of the VGA cable. The
monitor is as far away from the amp and feedlines as I can get it and all
equipment K3, P3, KPA500, KAT500 are bonded to a ground bus. This is not
unique to this monitor as it happened with a different smaller monitor I
used before.
This has always been a problem, and I would like to eliminate it as it is
very disruptive to is usefulness in finding a clear spot to break through
a pileup. Not sure what else to do. Has anyone else had this issue?
..mike AI6II
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