Michael,
It is not the coil intercepting the magnetic field, but the core, whose
effective permeability is being modulated. I had a similar problem some
decades ago with a Ten Tec Triton II; when I drove over rebar in the
paving, or over steel beams, etc., the PTO would hiccup momentarily as
the local magnetic field changed, and the VFO would QSY perhaps 50 Hz
even when I turned a corner.
For those with a severe problem , a 'hum-bucker" might help; in this
case, a smaller transformer located on the desktop, whose position and
orientation could be changed to null the sizeable field coming from the
linear's more distant power supply. More permenant solutions suggest
themseves; an iron shield around L30, making L30 air core, or perhaps
even adding a regulated core bias current at L30 to swamp the external
field. (Like hiring a bagpiper to drown out a neighborhood garage band,
but....)
Cortland
KA5S
K1'ing since 30 October
<
[hidden email]> wrote:
> <>What I don't understand is this: I figure L30 has perhaps 14 turns,
> and 2.3 ohms winding resistance. I figure that the effective aperture
> is 1 cm squared. I figure that the winding resistance of T5 is 0.05
> ohms, so a 1 gauss vertical 60 Hz field will induce 37 micro volts on
> T5. That should cause 0.3 Hz FM modulation on 80 meters. No one should
> notice that? BTW, I calculated 2.3 ohms from the Q, sensitivity at T5
> goes way up if L30 has less resistance.
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