Re: RF Chokes + Bypass caps = resonant rise?
From: David Sharpe[SMTP:sccr4us-at-erols-dot-com]
Reply To: sccr4us-at-erols-dot-com
Sent: Saturday, November 22, 1997 9:55 AM
To: Tesla List
Subject: Re: RF Chokes + Bypass caps = resonant rise?
Tesla List wrote:
> From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
> Sent: Friday, November 21, 1997 6:40 PM
> To: Tesla List
> Subject: Re: RF Chokes + Bypass caps = resonant rise?
> Hi Adam,
> > From: Adam[SMTP:absmith-at-tiac-dot-net]
> > Sent: Thursday, November 20, 1997 1:10 AM
> > To: tesla list
> > Subject: RF Chokes + Bypass caps = resonant rise?
> > I just thought of something kind of disturbing. It occured to me that
> > the 2mH RF chokes I borrowed from my small coil setup, in combination
> > with my 500pF bypass caps, should have a cutoff freq. of 160kHz. Now, my
> > current larger coil with it's big toroid operates at almost exactly
> > 160kHz, so this is really bad- especially dangerous with no damping DC
> > resistance. I suspect that these small chokes are actually working
> > against me in this new setup! I am removing the chokes, and I will
> > probably try to replace them with 10mH values or bigger, so that any kick
> > back from the tank is dropped across the choke, not across the bypass
> > caps!
> > Any thoughts? Am I correct to do this?
> > -Adam
> Yes - go bigger and usethe smallest wire you can get away with for
> max choke current (contributes to killing their Q).
Adam, Malcolm, ALL
It just dawned on me that in vacuum tube days, d-Q'ing networks were
placed on vacuum tubes to prevent UHF / VHF "birdies". They were
usually 20-50ohm 5-20W carbon comp. resistors with close wound
insulated wire (20-32 AWG) around the body of the resistor. A more
modern equivalent might be a tapped inductor with HV capable high value
resistors across the taps to d-Q the entire assembly. FWIW.
DAVE SHARPE, TCBOR