[cma-l] ever Community Radio Mast?
Alex Gray, Two Lochs Radio
tlr at gairloch.co.uk
Tue Mar 22 16:54:13 GMT 2016
Don't quite understand your point Ian - the encoding/decoding would be
needed for fibre or for air transmission, and in practice the figures are
similar. But either way those delays aren't significant - the codec delays
aren't anything like as long as you imagine.
A typical home computer will encode and transmit data in sub-millisecond
times. High quality wireless gear is also sub-millisecond, link-to-link
including all processing. For example a simple self-contained Motorola
PTP800 has a latency of 115us under maximum load. Specialist gear manages
sub-microsecond levels of latency - for example at higher frequencies the
Solectek SkyWayEB can put through 2.5Gbps with a basic latency of just 20ns!
Even their more basic links do 7us.
The underlying transit time for 240km from London to Brussels through the
air would be about 0.8ms, through a single-mode fibre (which is the sort
that would be used) would be about 1.2ms, so that difference could
conceivably make a difference to the punters as Glyn suggests.
On a 100km air path they will have to allow a pretty large fade margin for
heavy rain, but that would only have the effect of lowering the bandwidth,
it wouldn't affect the latency.
But more than the basic latency, I'd guess it's likely that greater jitter
and variable delays could occur through third-party network carriers, unless
'dark fibre' is rented, and internationally that is still super-expensive
compared to a wireless link. I should think the attraction of this system to
users is a consistent latency performance under their control (and also
avoiding the risks of someone else intentionally delaying the traffic?).
Of course, whether high-frequency trading should be allowed at all is a more
interesting and involved question, but not one for CMA!
Alex
From: cma-l-bounces at mailman.commedia.org.uk
[mailto:cma-l-bounces at mailman.commedia.org.uk] On Behalf Of Ian Hickling
Sent: 22 March 2016 14:44
To: The Community Media Association Discussion List
<cma-l at mailman.commedia.org.uk>
Subject: [cma-l] ever Community Radio Mast?
Nice idea - but encoding and decoding latency is way in excess of any
analogue/RF system!
Ian Hickling
Partner
<http://www.transplanuk.com/>
Office: 016 3557 8435 (07h to 22h GTS)
Car: 075 3098 0115 (only responds when driving)
6 Horn Street, Compton, NEWBURY, RG20 6QS
_____
Date: Tue, 22 Mar 2016 14:22:18 +0000
From: info at a-bc.co.uk
To: cma-l at mailman.commedia.org.uk
Subject: Re: [cma-l] Tallest ever Community Radio Mast?
I understand it's all about latency. Apparently the signals travel much
slower in fibre (approx 0.7 speed of light I'm told). So if microwave goes
close to speed of light, they gain themselves 3ms over 1000km ignoring
equipment latency which I guess would be in ns range.
All this so they can "cheat" and buy/sell knowing what the price will be in
a few milliseconds time. Still, at least it's creating something real (ie:
investment in a humongous mast). World's gone mad!
Glyn
On 22 March 2016 at 12:56, Alex Gray, Two Lochs Radio <
<mailto:tlr at gairloch.co.uk> tlr at gairloch.co.uk> wrote:
With a 100km+ path they would need masts of at least 250m at either side
purely to overcome the curvature of the earth.
They're using 2.4- 3.7m dishes at 6GHz with an 0.9 degree beamwidth, and at
maximum wind they put several tonne-metres of twist on the mast, so it will
certainly need to be pretty stable, but I guess they will have calculated
all that out.
NB the bigger dishes alone weigh in almost half a tonne each, and a max wind
load of about 2.5 tonnes each - and they're putting 4 on one side all above
280 metres - that's like putting the weight and wind area of several small
cars at the top!
With a 45dB gain and a beam crossing the channel lengthways towards Ostend
(about 110km), they'll probably manage a several Gbps link, but if they are
'high frequency traders' I imagine they are also as interested in getting a
link with the shortest and most stable possible latency, more than a huge
bandwidth.
I guess a direct fibre optic would outperform this, but maybe would be far
more expensive to lay (including all the legal consents and becoming a
telecoms operator etc).
Alex
From: <mailto:cma-l-bounces at mailman.commedia.org.uk>
cma-l-bounces at mailman.commedia.org.uk [mailto:
<mailto:cma-l-bounces at mailman.commedia.org.uk>
cma-l-bounces at mailman.commedia.org.uk] On Behalf Of Tony Bailey
Sent: 22 March 2016 12:03
To: <mailto:cma-l at mailman.commedia.org.uk> cma-l at mailman.commedia.org.uk
Subject: Re: [cma-l] Tallest ever Community Radio Mast?
Yes, Ian,
Why Richborough? it appears to have a mixed history, with a Roman site and a
coal fired power station, now proposed as a green energy site and Grid
interconnector to Belgium. I recall the problems with planning permission
when the IBA wanted to install the East Kent AM mast and this proposal looks
high enough for Long Wave!
Presumably the height is due to a need to do it in one hop, since repeaters
would slow it down and would probably not be faster than fibre cable (the
report indicates that data speed is the requirement). It would need to be a
guyed mast to avoid wind shifting the beam, are they sure that no-one is
installing wind turbines anywhere on the route? It will also need aircraft
warning lights so will be very visible at night.
Tony Bailey
On 22/03/16 09:17, Ian Hickling wrote:
I think a seasonal pinch of salt might be wise.
I wonder if they have any idea how much these things cost - and how they can
be used in a real-life situation?
I would have thought we have adequate ways of sending material across the
Channel very cheaply already.
Ian Hickling
Partner
<http://www.transplanuk.com/> Office: 016 3557 8435 (07h to 22h GTS)
<http://www.transplanuk.com/> Car: 075 3098 0115 (only responds when
driving)
<http://www.transplanuk.com/> 6 Horn Street, Compton, NEWBURY, RG20 6QS
<http://www.transplanuk.com/>
<http://www.transplanuk.com/>
_____
<http://www.transplanuk.com/> Date: Sun, 20 Mar 2016 18:55:31 +0000
From: info at a-bc.co.uk
To: cma-l at mailman.commedia.org.uk
Subject: [cma-l] Tallest ever Community Radio Mast?
<http://www.transplanuk.com/> Interesting story from Alwyn on the MB21
discussion forum - don't think it's first of April yet...:
<http://www.transplanuk.com/> http//planning.dover.gov.uk
Application reference 16/00044
An application for a 320m high 3m face width mast at Richborough, which it
is proposed will host free of charge a community radio station for East
Kent.
The reason for such largesse? The mast will form part of a shortened
microwave path to mainland Europe for high frequency trading.
Believe it or not, a second application is on the way from a competitor in
this business for a 305m high mast, also at Richborough, also offering free
hosting of community radio:
http://www.kefmast.co.uk
http://www.theguardian.com/business/2016/mar/01/high-frequency-traders-turn-
rural-kent-into-telecoms-battleground
<http://www.transplanuk.com/> What a shame there's "no frequencies
available".
<http://www.transplanuk.com/>
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