Re: [amsat-bb] BPL - Rant2

[Emily Clarke <w0eec@xxxxxxxxx>]

At 09:23 AM 6/25/2004 -0500, you wrote:
>Hi Emily
>
>Please comment on how Amateur Radio Spread Spectrum ( SS ) , SSTV and
>BPL.

I'm not sure how SSTV factors into it since its normally a SSB or FM 
signal.  I'm also not sure what comments you expect about ARSS.

>I note the FCC is expanding Amateur SS frequency authorization.

Expanding it yes, but I don't think to the extent it will be a 
problem.  It's secondary to other amateur emission types, so in the 
interference race  the SS station loses.  However, while I believe it will 
be easy for a SS station to "listen before transmitting" I don't think the 
reverse will be true.  If a conventional station is receiving interference 
from SS signal I'm not sure they would have a means of identifying it.

I think that those who have experimented with SS in the amateur bands to 
date have demonstrated that it hasn't caused harmful interference. Thus 
far. This is probably because of two things.  Because of the requirement 
for automatic power control, emissions were kept under a tight control. For 
simplex and in-band duplex transmissions using SS this is probably an 
easily thing to accomplish because the same antenna (or likely pair of 
antennas) with matched gain are used.

The second reason is that today's amateurs probably wouldn't immediately 
identify a SS signal.  I don't know how many would have a spectrum analyzer 
that could store a SS signal and recognized what it was.

>Why was FFH chosen over sequential .

It is less susceptible to jamming and has higher noise immunity - ie, in 
this case from other services.

>Are there some numbers that will better guide the measurement of noise
>floor reference.

I'm not sure what you are asking, but if you are asking what numbers are 
acceptable in a pre-BPL world in absolute db, it will be whatever it is for 
your specific location today.  I live in a dense suburban environment - we 
have Part 15 noise all over the place.  So my noise floor is quite a bit 
higher than someone living in a small town, someone living on a farm.  What 
you really want to measure is a delta, and you should do it in a scientific 
way (multiple readings at different times of day, on different frequencies, 
etc) and work as a team to make sure the work is reviewed and witnessed.

>How does pointing a high gain antenna ( a mono seven elements on ten
>meters with a RF switched preamp at the driven dipole) at the power line
>impact noise floor measurement.

Although interesting, I'm not sure this is not a good way to make a 
measurement.  But since you are trying to record a delta in a pre-BPL world 
I would take measurements at angles that correspond to the half-power beam 
width of your antenna.  This is not scientific, but it will help detect 
problems in the future if the noise floor is raised.

>More information is needed on the ability of the BPL system to control
>their use of  a part of the spectrum .

I'm not sure what you mean - if you mean to control and mitigate 
interference, my understanding is that they are using frequency agile 
techniques that can be programmed away from specific frequency 
bands.  However I agree that more specific technical information is needed. 
However, with several competitive vendors I'm not sure they will make 
public their intellectual property (if it is intellectual.)

>Whether this is an adaptive of manual system of spectrum use control .

I presume it must be adaptive.  If it were manual this would be bad.

- EMily

---------------------------------
W0EEC - CM87tm
AMSAT Area Coordinator - San Francisco Bay Area
http://www.projectoscar.net    http://www.PlanetEmily.com 
http://www.experthams.net/ao7

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