In article ,
Rich wrote:

Hi all. Thanks for your replies. To give you more info, I'm only
capable of up to 100w. I'm thinking about adding a Bencher 1.8-30 MHz
Bandpass Filter to my set-up to minimize TV interference (even if I
use a dipole, ref. my other post, " Dipole/Balun? Commercially
Produced Alternative?"

This sort of bandpass filter may not help matters much if at all, for
several reasons:

- If you're using a commercially-built transceiver, it almost
certainly meets the FCC's harmonic-suppression filtering rules right
out of the box - it has the necessary low-pass filters built into
its output section. You _might_ get some additional, useful
suppression via an external filter, but I suspect that the benefit
will be rather minor.

- These days, it's more usual for RFI/TVI to be caused by
"fundamental overload". TV sets usually have wideband tuner
circuitry, and they can be overloaded by strong RF signals outside
of the frequency range to which they're currently tuned. The RF
drives their first stage into saturation, and can wipe out
reception of _all_ channels. This cannot be avoided or treated
with a low-pass filter on the transmitter - it requires a high-pass
filter at the TV set's antenna terminals (and, in some cases, a few
ferrites on the power and speaker wires, to keep RF from leaking
into the set through these paths).

- If you're using pipes/radiators/gutters as part of your antenna or
counterpoise, you have to worry to some extent about the
possibility of rectification at metal-to-metal junctions. This can
cause the generation of harmonics (including some in the TV band)
even if your transmitter's output is perfectly clean. Eliminating
this problem requires finding the corroded metal-to-metal junctions
which are acting as rectifying diodes, and correcting the problem
(either isolating the metals completely, or "bonding" them more
securely with rivets, wire, contact-surface cleaning and
preservation, etc.

The pipes/radiators throughout the building
would be the counterpoise to the hot-wire ... not at all intended as a
ground. I'm poised to do this rather quickly, minus the bandpass
filter, which I need to order from HRO or AES.

Well, it's probably worth a try, but I suspect that the risk of
problems is nontrivial.

So maybe I will try this out... Any last words about safety? Not
blowing up the furnace room and heating oil tank? ;-)

Keep your transmit power relatively low. Fundamental overload and
other RFI/TVI problems seem to be less common at transmitter outputs
below 20 watts.

Just remember that the RF voltages appearing at certain points on your
antenna and "counterpoise" can be quite high, even at moderate power
levels. You may be exposing people to a significant risk of shock or
RF burns. If somebody gets "bitten" when they touch a radiator,
they're likely to be really irate with you.

I'd encourage you to run through the FCC's RF-exposure calculations,
assuming an "uncontrolled" operating environment, and very small
working distances between people and the antenna/counterpoise.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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