[cma-l] Singing posters and talking shirts stealing from your FM signal...

Thu Mar 9 13:30:55 GMT 2017

They don't seem to be talking about inserting additional RDS data Ian, or
indeed interfering with the RDS subcarrier in any way. If they only wanted
data they point out they could use Bluetooth BLE, but this can't carry
audio. Their focus is on creating audio streams, and the option for data is
simply to use the audio channels they are creating to carry FSK encoded data
(ie a modem method). They needed massive error correction to achieve good
data at a range of more than 2 metres, so the real throughput is reduced
greatly.

One of the three schemes they describe is 'overlay backscatter' in which
they "overlay arbitrary audio on ambient FM signals to create a composite
audio signal that can be heard using any FM receiver". They propose
generating this in the first or second adjacent channel (eg a few hundred
kHz away from the host signal) because broadcast planning means that is
almost always guaranteed to be empty

Band II FM transmitters of 50nW or less don't require a licence in the UK,
so maybe they could get by with this for the audio version. However, they
say they can achieve a range of up to 60 feet, which would usually need more
like a microwatt of effective power.

For using potentially white space in the multiplex spectrum they have Stereo
backscatter which applies to stations that are essentially mono audio but do
broadcast a stereo multiplex (eg news/talk stations). They backscatter data
and audio on these to achieve what they say is "a low interference
communication link." Note not 'interference free'!

They also have a subsidiary technique to trick FM receivers receiving mono
FM signals by inserting the stereo pilot signal and inserting their own
audio interference free as the stereo subcarrier - effectively locally
turning the mono station into a stereo one (that doesn't seem a very novel
or complex idea, and easily workable, but how many powerful FM stations
operate in mono mode nowadays?). 

Their third scheme requires two or more smartphones to cooperate to set up a
sort of MIMO wireless scheme to null out the main FM transmission and give
them cleaner reception of the intermodulated parasitic signal.

NB any unlicensed use of RDS for non programme-related data ("private data")
is prohibited at the moment. The coming of RDS2 might make it a lot harder
for them to make used of 'unused portions of the stereo signal" since RDS2
fills in a lot more of the 'white space' in the current multiplex spectrum.

But there's still the question of legal provisions on unauthorized use of
somebody else's electricity (which have somewhat dubiously been used to
prosecute hackers!), and of unauthorized interference with radio broadcasts.

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: 09 March 2017 12:31
To: The Community Media Association Discussion List
<cma-l at mailman.commedia.org.uk>
Subject: Re: [cma-l] Singing posters and talking shirts stealing from your
FM signal...

I think it's intimating that it can add on data in unused parts of the RDS
section of a multiplex signal - eminently feasible - but I'd like to see how
that propose achieving that.
And it would also requires licensing as a standalone transmitter.

Ian Hickling

Partner

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From:  <mailto:cma-l-bounces at mailman.commedia.org.uk>
cma-l-bounces at mailman.commedia.org.uk <
<mailto:cma-l-bounces at mailman.commedia.org.uk>
cma-l-bounces at mailman.commedia.org.uk> on behalf of Associated Broadcast
Consultants < <mailto:info at a-bc.co.uk> info at a-bc.co.uk>
Sent: 09 March 2017 11:56:23
To: The Community Media Association Discussion List
Subject: Re: [cma-l] Singing posters and talking shirts stealing from your
FM signal... 

Alternatively you could say the original transmission IS indeed unchanged.
It is the identical signal broadcast from a big mast miles away and there is
no way this system can change that.

What it's changing is the reflection environment from what I understand.
Maybe a bit analagous to sonar or radar.

But maybe I understand wrongly!

Glyn

On 9 March 2017 at 11:42, Alex Gray, Two Lochs Radio <tlr at gairloch.co.uk
<mailto:tlr at gairloch.co.uk> > wrote:

Exactly Ian -    I guess he means ".without significantly affecting the
original transmissions." or perhaps he's found some new laws of physics. 

Interesting technique though if you read the full details. Reminds me of the
cunning Russian passively bugged 'friendship' emblem that sat in the US
Embassy in Moscow for some time. Also the (apocryphal I think) tale of the
farmer prosecuted for lighting his house using power tapped off the near
field of the Droitwich log wave transmitter.

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 Ian Hickling
Sent: 08 March 2017 22:37
To: The Community Media Association Discussion List <
<mailto:cma-l at mailman.commedia.org.uk> cma-l at mailman.commedia.org.uk>
Subject: Re: [cma-l] Singing posters and talking shirts stealing from your
FM signal...

".......we developed a new way of communication where we send information by
reflecting ambient FM radio signals that are already in the air, which
consumes close to zero power." The UW team has - for the first time -
demonstrated how to apply a technique called "backscattering" to outdoor FM
radio signals. The new system transmits messages by reflecting and encoding
audio and data in these signals that are ubiquitous in urban environments,
without affecting the original radio transmissions......"
Oh yeah? 

Ian Hickling

Partner

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