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

[Chris Waldrup]

Hi Andy,

I used to help people who lived adjacent to my 5 kW's on 1360 and 920.  

I ended up buying 1 mH molded Fastron chokes from Mouser and added as many as needed in series in each pair of the phone line. Sometimes I would add one too many and picking up the phone would no longer bring up the dial tone so I would back off one choke. 

Chris
KD4PBJ

> On Aug 5, 2023, at 3:38 PM, Tom W8JI <w8ji at w8ji.com> wrote:
> 
> 
> 
> 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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