[Elecraft] Contact your Representatives (BPL)
John A. Magliacane
[email protected]
Tue Sep 30 13:34:00 2003
--- "Guy Olinger, K2AV" <[email protected]> wrote:
> 5 watts in band on the antenna of a spread spectrum receiver will
> certainly swamp it. Spread spectrum overcomes that kind of
> interference when it's at the SAME power level as it's desired receive
> signal.
Hmmm... I'm not fully convinced that's true. Remember, these are
digital signals, presumably sent with enough redundancy to tolerate
certain errors. If the transmission system is adaptive, then perhaps
it could even compensate for interference of this sort.
I do agree that 5-watts into the front-ends of MOST receivers would
overload them to the point of being pretty useless. But coupling
5-watts of RF into a power line ain't easy!
5-watts is only about 26 dB below the 1500-watt FCC Part 97 power limit.
Assuming a frequency of 30 MHz, we could induce 5-watts of RF into a
RESONANT antenna from a 1500-watt transmitter at a distance of about
60 feet. (Reference: Isolation vs. Antenna Separation -
http://www.guerrilla.net/reference/quick_ref/dplx_ant_sep.html)
Lower frequencies could achieve this at larger distances. If the
distance is halved, the amount of coupling increases by 3 dB.
But the point is that these figures assume a RESONANT receiving
antenna. For the majority of situations, a power line is anything
BUT a resonant receiving antenna. Therefore, it would take a LOT
closer spacing between power line and antenna to achieve this amount
of coupling -- so much so that it would probably throw your antenna
out of resonance.
I don't believe many amateur stations fall into this situation.
73, de John, KD2BD
=====
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