Subject: [NEXTEL-1] Re: Is BPL an interference threat to radio communications?]

From: [email-masked]
Date: Wed, 20 Aug 2003 17:33:41 -0400

-------- Original Message --------
From: Simon Parsons <[email-masked]>
Subject: Re: Is BPL an interference threat to radio communications?

On Wednesday 20 August 2003 10:52 am, BobC wrote:
> I see BPL as a neat concept but not feasible yet.
>
I work over in the UK as the Spectrum Manager for the UK Fuel & Power 
Industry's PMR systems and got involved in PowerLine Telecommunications (as 
it's called over here) in the early days of Nor.Web (an offshoot of what was 
called the North Western Electricity Board, NORWEB) who started the whole 
sorry mess.

The two guys involved were both radio hams, by the way.  Not that it has much 
to do with the end effect on HF communications - they were doing it to see if 
it could be done and if it was possible to perhaps make a go of doing remote 
consumer  meter reading or (pie-in-the-sky) delivering a fast internet 
service using the technique.  By modern standards it's not very fast - they 
were looking at 1 or 2MBit/s maximum with a contention rate of however many 
subscribers were on the circuit - say 20-50 households.  That's about what 
you get using ADSL over here. 

> I cannot see a consumer benefit from a system like this. Perhaps I
> can't think "outside the box" on this.
>
There is no consumer benefit - unless the consumers live away from a telephone 
exchange that's got ADSL.  They still need to be close to the electricity 
substation, so it's still an urban-ish service.  The benefits are mainly to 
small towns and not bigger towns and cities, although the technique works 
best in high-density housing areas which probably have an ADSL-enabled 
exchange!  That narrows down the possibilities a bit.  The sales-droids gloss 
that bit over....

> Although the transmission medium is mostly in place, the remainder of
> the system will still be costly to purchase and incorporate. Will
> this new infrastructure require spreading the start-up costs amongst
> all power users? Even those who don't need or use BPL?

You need to install equipment in the local transformer station and I'm sure 
the costs will be spread across the customers as it will no-doubt be added to 
your bill in some way.  There's no sense in buying venture capital if you can 
offload the costs onto your customers :-) 
As I understand it, the signal won't even travel through an electricity meter, 
so every subscriber needs a box to tap the signal off before it.  in other 
words, the only electricity company asset being used is the cable between the 
substation and the meter. in other words, yes, it's probably just as 
expensive as using real radio - and probably more restrictive too.  Another 
thing the salesmen don't like to mention.

>
> If I understand correctly, BPL is more a last mile system than
> anything else. I understand the range of the sysytem is less than a
> mile and requires repeaters back to the data backbone. Off the top of
> my head I ask would it not be a similar (or lesser) expense to
> install a "run of the mill" wireless network as is customary in rural
> areas now?
>
Last mile, definitely. I don't see (at least here in the UK) BPL being used in 
rural areas - it's more of an urban system as the cost of backhauling the 
data for several miles cross-country back from an 11kV poletop transformer 
just outside a village would be prohibitive. Nor.Web always assumed the 
backhaul would be from a local urban substation with an existing fibre or 
microwave link back to an exchange somewhere.

> What I can see is a tremendous problem looming on the horizon in the
> way of interference to anything from AM broadcast to aprox the 80 mhz
> region. (if this high a frequency is allowed or used) This might even
> find its way into FM broadcast or worse, the vhf aircraft band
> through harmonics and/or mixing. I'm sure the active HF band Ham
> users will see yet more noise from power line interferences. I'm sure
> mother nature will provide a suitable transport mechanism to ensure
> whatever signals radiate in one part of the country will find their
> way to another part and add to that noise floor.

Oh, it's bad, but not QUITE that bad.  It's been shown in various experiments 
to radiate in the lower HF bands - they have to offset cable losses by using 
a low frequency - 5MHz works better than 25MHz, for instance.   You shouldn't 
have real problems outside that band unless you're real close, i.e. you have 
the service on your power circuit!  I don't know of anyone actually detecting 
BPL emissions from any existing trials, but I haven't kept too close an eye 
on the trials recently. In a way, when people start detecting the hash from 
these systems it will already be too late to do anything about it.

>
> As I see it, the only folks that will readily benefit from a BPL
> system is the power company itself. Their internal telemetry and
> control systems might be enhanced. Perhaps their own voice/data
> communications infrastructure will benefit through MDT's and VoIP. If
> the day ever comes when they have sufficient subscriber numbers that
> provide a ROI, this would be a nice sideline enterprise.
>
Nor.Web found it was too expensive.  They didn't even consider putting fiters 
in street lamps to stop them becoming radiators, which would have made it 
even more expensive if a little less noisy.  Electricity supply companies 
over here use GSM data for their comms, or MPT1411 scanning telemetry or even 
Short Data on their MPT1327 trunked PMR systems.  National Grid Transco uses 
PowerLine Carrier for long-haul comms over the High Voltage Pylon network and 
have been doing so for years - about 200-450kHz.  The supply companies don't 
yet require comms for the last mile, so BPL is of no use to them unless they 
can make use of the extra backhaul capacity that may need to be installed.

>
> In a pro BPL statement I read a particularly distressing paragraph in
> which the power companies expressed a "screw you" attitude towards
> anyone possibly ill effected by a BPL system.
>
The problem is Power Engineers are not Comms Engineers and the Electrcity 
company Managers pushing this technology are being advised by IT people who 
have a sad history of misunderstanding radio and what you can do with it and 
just how badly you can screw up if you don't know what you're doing!
This is likely to become a VERY big mess indeed.

Simon

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