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:[email protected]]
Sent: 2001-06-20 08:40
To: [email protected]
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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