Transcript Possible Impact of VDSL on Stations Operating in the

Possible Impact of VDSL on
Stations Operating in the
Amateur Radio Service
Ed Hare, W1RFI
ARRL Laboratory Manager
225 Main St
Newington,CT 06111
[email protected]
860-594-0318
Part 15
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Absolute Maximum Limits
Unintentional Emitters
Non-interference
Manufacturer responsible for FCC
authorization and maximum limits
• Operator responsible for harmful interference
• Both are important to mitigate possible
harmful interference
Unintentional Emitter
Emissions
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Radiated emissions above 30 MHz
Conducted emissions below 30 MHz
Good engineering practice
Carrier-current devices must meet
intentional emissions limits – 3
installations
• Meeting the intentional emissions limits
on HF is good engineering practice
Intentional Radiator Radiated
Emissions Limits - HF
• Sec 15.209
• 1.705-30.0 MHz – 30 uV/m at 30 meters
• This should protect users of the spectrum
against interference, yes?
No!
• If the absolute emissions limits were set to offer
unconditional protection to all radio services, the
permitted levels would be unworkably low
• Amateur Radio Service, by design, uses very
sensitive equipment and weak signals
• The “legal limit” will result in a strong signal to
nearby Amateur HF installations
• On 3.5 MHz, a half-wave dipole placed in a 30
uV/m field will receive a –86.4 dBW signal (338
microvolts across 50 ohms)
• To hams, this is S9+16 dB – clearly harmful
interference to typical amateur communications!
• Harmful interference at even greater distances
than the compliance distance is likely
• The absolute limits are not enough to prevent
interference to nearby receivers
Harmful Interference
• The repeated disruption of radio
communications
• Merely hearing a signal is NOT harmful
interference
• 30 uV/m at 30 m works somewhat well for
discrete signals
• If from broadband device, however, will
interfere with entire band(s)!
• 30 uV/m works somewhat well for isolated
sources
• If from VDSL, interference potential exists for
occur for entire length of wiring in areas where
VDSL is deployed!
A Case History – Wireless
Modem Jacks
• Carrier-current devices that use residential electrical
wiring to couple modem signals between a computer
and a remote telephone connection
• Phonex model PX-421 designed to operate on 3.53 MHz
• These were purchased in volume by TCI Cable and
installed in conjuction with their digital cable systems
• Widespread S9++ levels signals and harmful
interference
• Phonex responded promptly, redesigned product
• TCI, now AT&T still in midst of system-wide recall!
• Costs?
What Can Be Expected from
VDSL?
• Better scenario than power lines and
electrical wiring
• Phone system reasonably well
balanced at audio
• At HF? 20 dB to 30 dB balance
typical?
Amateur HF stations
• Bands at 1.8, 3.5, 7.0, 10.1, 14.0, 18.1,
21.0, 24.8 and 28.0 MHz
• Receiver sensitivity –135 dBm
• Ambient noise levels –125 dBm
• Antenna gain 2.14 dBi (F.S) on 3.5 Mhz
• Antenna gain 7.5 dBi (F.S) on 14-30 MHz
Balance
• EZNEC 3.1 used to model 50 feet of simple
phone wiring (uses NEC-4, written by
Lawrence Livermore National Laboratories)
• Terminated in 100 ohms – j0
• Fed with two sources, one on each wire, 180
degrees out of phase, with 20, 25 and 30 dB of
balance
• Showed “gain” of –16 dBi to –26.4 dBi
• Real-world installations – bigger radiators, but
more loads on line
• Correctable defects
Balance
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20 dB = -16.8 dBi
25 dB = -21.8 dBi
30 dB = -26.4 dBi
Will use –21.8 dBi for following
calculations
Frequency = 3.5 MHz
Receiver bandwidth = 2500 Hz
Transmit power in 1 Hz = -50 dBm/Hz
Transmit power in 2500 Hz = -16.0 dBm
Telephone-wiring antenna gain = -21.8 dBi
Receive antenna gain = 2.14 dBi
Distance to receiver = 0.03 km
Free-space pathloss = -12.9 db
E-field estimate in 30 kHz = 140.8 uV/m peak
Receive Noise Figure = 24 dB (includes external noise)
Calculated receive system sensitivity = -116.0 dBm
Received noise in receiver bandwidth = -48.6 dBm peak
Received noise in receiver bandwidth = S9 + 24.4 dB
Receive system noise floor increase in dB = 67.4 dB
Frequency = 14 MHz
Receiver bandwidth = 2500 Hz
Transmit power in 1 Hz = -50 dBm/Hz
Transmit power in 2500 Hz = -16.0 dBm
Telephone-wiring antenna gain = -21.8 dBi
Receive antenna gain = 7.5 dBi
Distance to receiver = 0.03 km
Free-space pathloss = -24.9 dB
E-field estimate in 30 kHz = 140.8 uV/m peak
Receive Noise Figure = 24 dB (includes external noise)
Calculated receive system sensitivity = -116.0 dBm
Received noise in receiver bandwidth = -55.2 dBm peak
Received noise in receiver bandwidth = S9 + 17.8 dB
Receive system noise floor increase in dB = 60.8 dB
Phoenix VDSL testing
Conclusions
• Pre-standard system, but approximately –50
dBm/Hz
• Underground wiring, relatively new homes
• No VDSL signals detected except near one
neighborhood hub – just audible
• Other noises
• In areas of underground wiring, notching not
needed
• However, this should NOT be extrapolated to
determine that notching is not needed under other
circumstances!
HPNA
HPNA
HomePlug – Final Specification
40
40
45
50
POWER DB M / HZ
55
60
65
MASK
y
70
75
80
85
90
95
100 100
0
0
2
4
6
8
10
12
14
16
y mhz
FREQUENCY MHZ
18
20
22
24
26
28
30
30
Industry Measurements of
Interference Potential?
• In general, industry has not made measurements of
interference to other services
• Such measurements, made by Amateur Radio in
other, similar disciplines show interference
potential
• In all cases where industry groups have conducted
joint studies with ARRL, they have chosen to
include spectral masks in their industry standards
or specifications
• To date, no widespread interference from
protected products
What is Needed?
• Based on modeling and calculations, -50
dBm/Hz will probably result in harmful
interference with overhead wiring and older
homes
• Amateur Radio vs other services?
• These models not exact, but demonstrate
clearly the need for further study
• ARRL wants to participate in field studies,
especially any near New England, but I will
travel!
What Does ARRL Want to Accomplish?
• Participate in field studies
• Protection to –~80 dBm/Hz in ham bands
• Such notches will exist naturally in residential telephone
wiring, so product must be robust enough to function with
small segments of frequency band attenuated
• Advisory language in standard about harmful interference,
the need to use notches when needed and the need for
manufacturers to include such advisory information in their
product literature
• Not necessary to use filtering – HPNA standard achieves this
level of protection by not using OFDM carriers in the ham
bands.
• This will take care of MOST cases of harmful interference.
Remainder are “correctable defects” or can be addressed on
a case-by-case basis
• If frequencies not used, additional filtering can be added
• Why waste a good notch? Other services?
More Information
Ed Hare, W1RFI
ARRL Laboratory Manager
225 Main St
Newington,CT 06111
[email protected]
860-594-0318
• http://www.arrl.org/~ehare/rfi/vdsl/vdsl.html
• http://www.arrl.org/tis/info/part15.html