[TenTec] Front End Protection

[Steve Ellington]

I believe we can all see how putting a 100k resistance across the feed line
of a 50 ohm system would have virtually no effect on the transmitted signal.
The real question is how the 100k resistor could dissapate static fast
enough to protect the front-end of a radio. Looking at the schematic for the
Omni V, I count no less than 9 coils connected between the RF input and
ground before the first RF amplifier. These should offer considerable
protection to the front end however, there are numerous switching diodes
along the way which could be damaged by ESD.

My concern is whether the static charge can dissapate quickly enough through
the 100k resistor  to protect anything. And  the obvious question is; Why
don't manufactures put the 100k resistor in their radios? The possible
reasons are:

1. The resistor cost too much. Doubtfull since, if it worked, lots of
warranty work would be prevented.

2. Manufactures don't know any better. Unlikely since engineers have been
dealing with ESD for decades.

3. It wouldn't help.

Here is what I think is a good precaution against atmospheric ESD.

Use an antenna system that stays at dc ground potential. Loops qualify as do
beams with matching coils, verticals with ununs quads etc. If in doubt,
measure across your antenna with an ohmmeter. If it reads
infinite....beware!

The most dangerous antenna is the simple dipole fed with coax directly into
the rig. The only path static will find to discharge will be INSIDE your
radio. A voltage type balun such as the W2AU will provide the dc path you
need.
Open wire fed dipoles, zepps or whatever are only safe if the EXTERNAL
antenna tuner somehow provides a dc path to ground. Some designs do and some
don't. Check your schematic or use the ohmmeter to find out. The G5RV
connected directly to the rig is again asking for trouble even though the
rig may have an internal tuner the static charge may have it's own little
field day jumping around inside your rig.

Unhooking the radio from the antenna when not in use is a good idea but ESD
can still zap it during a qso. Just a dry breeze across the wires of a
dipole can build up 100's of volts!

Unhooking the antenna from everything may not be such a good idea. The
antenna systems needs to be at dc ground potential at all times. Believe it
or not, a grounded antenna is less likely to be struck by lightning than one
that is floating above ground potential.

Just some thoughts. Hope they help. 73

Steve Ellington
Amateur Radio Operator N4LQ




> Last week there was a posting regarding using a coax T connector with a
100K
>1 watt resistor between the center and the sleeve to dissipate static
buildup
>on the antenna.  How can this arrangement be "transparent" to a 100 watt
>output at these values and still dissipate a static charge?  I fully admit
my
>lack of understanding.  Any elucidation will be greatly appreciated.
Thanks.



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