I have made some progress on solving the TV interference problem referenced
below, but I can use some more help.
A colleague at work gave me five split cores with an inside diameter of 0.5
in. Some are type 25 material the others are unknown material. I was able to
wrap 3 turns of the AC line on a core. Four of these cores stopped the TVI
with all other cables disconnected from the TV.
I wrapped two turns of the TV cable on the one core I had left and
reattached it to the TV. The TVI is back. Obviously, I need more impedance
on the TV cable.
Replies to my previous post indicated that type 31 material is the optimal
choice to make the RF chokes I need. This is what I have been able to find
for sale:
DX Engineering
Split beads, Type 31,
for up to 0.275 inch Cable, Pack of 10 for $23.25 for up to 0.525 inch
Cable, Pack of 5 for $22.25 for up to 0.750 inch Cable, Pack of 5 for $25.8
>From Amidon
Type 31 non-split beads
OD 0.485in ID 0.20in Length 1 in. $0.80 each OD 0.562in ID 0.25in Length 1
in. $1.50 each
With the split beads I can put one to three turns of a pre-made cable on a
bead depending on its size. The non-slit beads will need to be put on before
the connector is attached to the cable. I will need to use the bigger size
beads unless I can find a 75 ohm cable that is smaller than 0.20in in
diameter.
What is the most cost effective bead to purchase for this application?
-----Original Message-----
From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On
Behalf Of jeff_list@burnshome.org
Sent: Monday, December 13, 2004 22:47 PM
To: rfi@contesting.com
Subject: [RFI] Core for common-mode choke?
I am trying to eliminate RFI problems with my TV. Even with all the inputs
disconnected and terminated I still get moderate blanking of the screen when
I key my rig at 100w. Hopefully, adding a common-mode choke to the AC line
will solve the problem. Since I will probably need chokes on several other
lines once I start reconnecting the various cables I want to find the most
cost effective source for the chokes.
Amidon lists FT-240-77 toroids for $9 each. Is there a cheaper source for
these? MFJ-701 RFI Choke Kits are only $15 for four. Are these effective
enough on the AC line?
If I find that I need a choke on the component video cable from my DVD
player what should I use? It may be too big to wrap on an FT-240-77 toroid.
Jeff Burns
AD9T
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