Re: [TowerTalk] RFI Beads & Sleeves

[Joe Giacobello <k2xx@swva.net>]

Tom, do you want the impedance to be largely resistive so that it's not 
so frequency dependent and the ferrite is effective over a wider 
frequency range?

Just curious, because I just bought a bag of inexpensive ferrites on 
Ebay, and they didn't start showing a resistive component until about 7 
MHz.  Name brand ferrites specified for amateur applications (e.g., 
Fair-Rite) show a resistive component at 2 MHz and below and have a 
higher reactive component until about 11.5 MHz, where the cheap ones 
become more reactive.  However, their resistive component was still 
substantially below the Fair-Rite.

I posted the data on the TenTec forum, but the tabulation was verkecht.  
If you're interested, I can send it to you privately.

73, Joe

Tom Rauch wrote:

> > I am going to order some used components from Surplus
> >    
> Sales of Nebraska. I
>  
>
> > thought I might order some beads to use to help me with
> >    
> some RFI problems I
>  
>
> > am experiencing. For example, the A/D for in computer
> >    
> assisted rotator
>  
>
> > controller has some RFI problems on the higher HF bands.
> >    
>
> Bypassing and grounding is generally much more effective
> than throwing a bead at a problem.
>
>  
>
> > Can someone recommend which type of beads I should have
> >    
> handy to assist with
>  
>
> > RFI problems as they arise.
> >    
>
> You generally want the highest possible **resistance** and a
> core that allows multiple turns. Impedance goes up nearly by
> the SQUARE of the turns increase. Two turns through one bead
> is generally about twice the impedance of one turn through
> two of the same beads.
>
>
> Look carefully at the impedance vs frequency, and IGNORE the
> "frequency range" in descriptions. Pick the highest
> impedance in the operating frequency range where you have
> the problem. Once again, bypassing with capacitors is often
> much more effective than slapping a bead on the problem
> (unless the equipment already has good bypasses). A bead is
> useless when the common mode impedance is significantly
> higher than the bead impedance.
>
>  
>
> > Here is the URL to the web page with the information on
> >    
> the beads and
>  
>
> > sleeves that Surplus Sales of Nebraska sells.
> > http://www.surplussales.com/FerBeaSle/FerBeaSle-1.html
> >    
>
> Why not go to a regular suppression core vendor? At least be
> sure you look at the real data for the cores. You generally
> want hundreds or more ohms of impedance, and you want that
> impedance to be largely resistive. That precludes using 43
> and similar materials in suppression applications. You want
> something with a well-defined broad peak at HF for HF
> suppression, not a material who's impedance keeps climbing
> with frequency well up into VHF.
>
> 73 Tom
>
> _______________________________________________
>
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>  
_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk