[600MRG] OFF Topic - Need info for toroid to choke RF on phoneline

[Tom W8JI]

Only using a bead *might* work if the line and load have a low enough 
shunt impedance or you don't have much to clean up. The advantage is, of 
course, it is very simple and non-invasive. You would want the highest 
impedance bead possible at 1.3MHz, which is getting into 78, 73, 77, 75, 
or 76 Fair-rite corporation materials.  31 or 33 mixes would be high on 
the list. See the attached list I keep in the shop.

Multiple passes through a bead are much better than adding beads, 
provided you do not saturate the core from too much current.

A bead on each active conductor helps get rid of both common mode and 
differential mode, a bead over the bundle will not attenuate 
differential RFI. A bead over the bundle only attenuates common mode RFI.

Throwing a bead at it often works and is simple, but there are a number 
of operational flaws in the "throw a bead at it" solution. Usually it is 
far more effective to filter rather than just throw a bead at a problem. 
In my contesting barn in the days of DSL I made a dead bug filter on a 
small unetched copper circuit board. We could run multiple 1.5kW 
transmitters at the same time and never drop the DSL signal. Beads alone 
would not do that.   I no longer have copper telco lines so if you want 
some official ATT filters I probably have them. But it is easy to build 
you own and Mouser would have the parts. A filter is dozens to hundreds 
of times more effective than a bead...depending on the situation.



73 Tom



On 8/5/2023 1:13 AM, Andy - KU4XR via 600MRG wrote:

> Hello Gentlemen:
>
> I am needing a toroid that will choke off 2.5 KW on 1390 KHz
> on a phoneline in the TX building connected to a dial up
> remote control unit.
>
> What material is good for this , and sources to obtain it.
>
> Thanks for suggestions: 73
>
> Andy - KU4XR
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