-----Original Message-----
From: rfi-bounces On Behalf Of Mike Martin
Tom,
I think what you mean is If I'm not going to agree with the common
assumptions I shouldn't tell people about my experience. I think people
shouldn't ask questions if they are only going to agree with the answer
they want to hear. Some people talk to themselves so they get the answer
they want. ---snip---
------------------------------------
Mike,
I think you're a pretty nice fellow having met you in person, but I feel
it is a bit arrogant to say that your readings are "real" experience
while those of all other are just assumptions.
The fellas from Rockwell-Collins, mostly RF engineers, took real
measurements in Cedar Rapids, IA, just as we did here in Omaha last
week. No assumptions were made. Just real measurements.
I don't know which vendor's equipment you evaluated, but you should be
aware that "experience" can be easily manipulated when you're testing
something like BPL which is a mixture of I.T. networks and RF. If we
had not demanded that we do a "real world" test by having a computer on
the system downloading files, we would've gotten the same impression
about our BPL test that you apparently did at yours. Their claim that
they had 60% loading when in fact it was only 2% would've gone
unchallenged.
Direct Sequence Spread Spectrum, which Main.net uses, has a very "thin"
power density in idle mode--i.e. no active users on the system. We
"experienced" and measured very little interference under those
conditions (2% loading or less). There were noise pulses there that
were about 40-60db above the noise floor, but they were very thin across
the band so they didn't cause much interference.
Once we had a user's computer actively downloading data, the 40-60db of
thin noise pulses began to thicken up a bit, or in technical terms, the
power density increased (perhaps tenfold). However, the amplitude
remain unchanged.
The tenfold increase in power density at 300kbps was enough to cause
harmful interference under Part 15. This was at only 20% loading for a
T1, and was caused by a single user on the system. Multiple users will
only cause the power density to increase even more.
The 18db notches they tried here were both too narrow (they thought the
notches were like band stop filters) and not on the correct frequencies.
But with 40-60db of noise, a thin 18 db notch wouldn't have much effect
anyway.
BPL uses several different spread spectrum technologies depending on the
vendor. All of them have complex RF signals that are very different
from the broadbanded emissions of simple sparking and arcing normally
found on power lines. I respect your knowledge and experience in the
field of tracking power line sparking noise. I'm no expert in Spread
Spectrum so I doubt you are either. If you don't have much experience
or knowledge in the digital spread spectrum field, perhaps you should
look into this aspect of "radio" before making statements that stand
alone as aberrant.
73,
de ed -K0iL
<p class=MsoNormal><span style='font-size:8.5pt'>This e-mail contains Omaha
Public Power District's confidential and proprietary information and is for use
only by the intended recipient. Unless explicitly stated otherwise, this
e-mail is not a contract offer, amendment, nor acceptance. If you are not the
intended recipient you are notified that disclosing, copying, distributing or
taking any action in reliance on the contents of this information is strictly
prohibited.</p>
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|