[Lf] A coil to bleed static to ground

[Andre Kesteloot]

Talbot Andrew wrote:
> 
> But much better still a bleed choke, making sure the inductance is high
> enough not to affect the matching.  A good choke would be made from a
> ferrite core and as it is not carrying any power a smaller core can be used
> than would be the case for a matching transformer.  Make sure there are
> enough turns to not saturate the ferrite with the highest RF voltage
> present.  Saturation was almost certainly the case in an earlier posting
> where a choke 'got hot'.
> 
> Use the formula    Vrms = 4.44.F.N.A.B   to calculate the Minimum turns
> needed on any given core, using a B of around 0.1 Tesla for a good safety
> margin.   All non-gapped ferrites designed for SMPSU transformers will have
> more than enough inductance - up in the tens to hundreds of milli-henries -
> when wound with enough turns to satisfy this equation.
> 
> Andy  G4JNT
> 
> > -----Original Message-----
> > From: Tom Boucher [mailto:tom at telemetry.demon.co.uk]
> > Sent: 2001-06-20 08:40
> > To: rsgb_lf_group at blacksheep.org
> > Subject: Re: LF: Re: Static effects
> >
> >
> >
> > Dave G3YMC wrote:
> > >
> > >If you feed your antenna, as many do, via a matching
> > transformer (3C85 core)
> > >then the
> > >antenna and the line to the tx/rx will be automatically
> > grounded.  Another
> > >advantage
> > >of this method of feeding antennas.
> >
> > Well I do Dave but I have rather an odd T/R relay arrangement based on
> > single pole on/off relays which I had available. This means
> > that when Tx
> > supply is switched off, the antenna is connected to neither
> > transmitter
> > nor receiver.
> >
> > I didn't fit a bleed resistor as Andy suggests because I figured it
> > would have to dissipate a fair bit of power unless it was a
> > high value,
> > however even a high value will be adequate to discharge any
> > build up of
> > static, I guess.
> >
> > 73, Tom
> >
> 
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