In article , rickman
wrote:

What is wrong with pacemakers that they can't make one that functions
around radios and microwaves?


They can and do, for most situations. But an end-fed antenna will have
common mode currents and I'd just as soon not have such flowing in my
pacemaker wiring.

My pacemaker is located just to the right of, and below, my left
shoulder. There are two wires leading out of it which go to my right
atrium and right ventricle. These wires bring signals up from the heart
to the pacemaker telling the pacemaker when the heart is beating, and,
when necessary, take much stronger signals down from the pacemaker to
the heart to get it to behave correctly if it is not doing so. There
must in effect also be a "ground" connection with the metallic pacemaker
case embedded in tissue in front of my ribs. Common mode current from an
unbalanced antenna sysem flowing in my body might do the pacemaker no
good. I'd just as soon not find that out 10 miles from a trailhead. So I
use balanced antennas, balanced feedline, and a good 1:1 current balun
at the bottom of the feedline. The tuner inside my KX3 then makes the
KX3 final amplifier happy.

I have also used a coax-fed balanced antenna with balun at the antenna
feedpoint, but a doublet with open-wire feedline and balun at the bottom
is a better multi-band solution.

Magnetic fields are also bad for pacemakers. When my cardiologist tests
things he brings a magnet close to my chest while monitoring the
pacemaker performance. This is done in a controlled way with observation
of the effect. I have been warned that high intensity magnetic fields
are very dangerous. At airports I present a card indicating I have a
pacemaker, and I get gone over by hand instead of magnetically. I
definiely don't put my iPod earbuds in my shirt pocket! The iPod itself
is often placed there when I use it while walking or hiking. I have been
warned that I must never have an MRI done on me.

There is no reason to believe that the very low power cordless phones
used with our landline telephone, or cell phones, pose a problem. The
magents in them are up by my ear, not near the pacemaker, and aren't all
that strong. The electromagnetic fields aren't all that strong either.
But consider how much RF current flows, especially in a low-resistance
high-reactance short unbalanced antenna, even at QRP levels. That's why
I want what comes out of my KX3 to be radiated and do some good, not
generate common mode current that may make my pacemaker, and then me,
unhappy.

Maybe I'm being too cautious. But better safe than sorry. And anyway, I
suspect my balanced doublet fed with open wire is a lot more efficient
than the typical random length end-fed wire connected to a transmitter
through a possibly very lossy Unun. It does require two trees, unless
erected as an inverted V, whereas an end-fed wire gets by with one.
Doing it the safer way is correct from an engineering standpoint too. It
would be a shame if one had to choose between efficiency and safety.

David, VE7EZM and AF7BZ

--
David Ryeburn

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