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Paranoia or real effect?



 
 
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  #11  
Old March 11th 18, 09:49 PM posted to uk.tech.digital-tv
[email protected]
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Posts: 234
Default Paranoia or real effect?

On Sunday, 11 March 2018 16:44:04 UTC, wrote:
a real bugger with BI TV.


one of those "special interest" channels Bill?

Owain


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  #12  
Old March 12th 18, 08:23 PM posted to uk.tech.digital-tv
Vir Campestris
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Posts: 439
Default Paranoia or real effect?

On 11/03/2018 16:55, Jim Lesurf wrote:
I was wondering about the doppler from the plane's velocity. But you remind
me that the fan blades might also generate quite a lot of doppler on the
reflections. But I've not worked out the velocity needed to shift each
subcarrier by the difference in frequency between subcarriers.


IIRC the blade tips are high subsonic (300m/S) and of course further in
they are everything down from there... so about 1E-6 of C. the channel
is around 600MHz, so you'd potentially see a shift of 600Hz.

Surely I've got that wrong? I'm damn sure the blade tips aren't doing
Mach 10...

Andy
  #13  
Old March 12th 18, 09:52 PM posted to uk.tech.digital-tv
Java Jive[_2_]
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Posts: 1,774
Default Paranoia or real effect?

On 12/03/2018 21:23, Vir Campestris wrote:

On 11/03/2018 16:55, Jim Lesurf wrote:

I was wondering about the doppler from the plane's velocity. But you
remind
me that the fan blades might also generate quite a lot of doppler on the
reflections. But I've not worked out the velocity needed to shift each
subcarrier by the difference in frequency between subcarriers.


IIRC the blade tips are high subsonic (300m/S) and of course further in
they are everything down from there... so about 1E-6 of C. the channel
is around 600MHz, so you'd potentially see a shift of 600Hz.

Surely I've got that wrong? I'm damn sure the blade tips aren't doing
Mach 10...


No, the speed of sound is approx 340m/s, so, assuming your figures are
correct, they're doing just under Mach 1. However, as you seem to be
rather confused, let's check your figures:

https://www.google.com/search?q=dime...+turbine+rotor

People also ask ...

What is the rotor diameter of a wind turbine?
"As of 2015 the rotor diameters of onshore wind turbine blades are as
large as 130 meters, while the diameter of offshore turbines reach 170
meters."

So taking the 130m diameter, for the tips to be travelling at 300m/s,
they'd have to be spinning at 300 / pi*130 ~ 2/3 rev/s, which seems
reasonable - they don't spin very fast.

  #14  
Old March 13th 18, 12:44 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 2,448
Default Paranoia or real effect?

On 12/03/2018 22:52, Java Jive wrote:

What is the rotor diameter of a wind turbine?
"As of 2015 the rotor diameters of onshore wind turbine blades are as
large as 130 meters, while the diameter of offshore turbines reach 170
meters."

So taking the 130m diameter, for the tips to be travelling at 300m/s,
they'd have to be spinning at 300 / pi*130 ~ 2/3 rev/s, which seems
reasonable¬* -¬* they don't spin very fast.


The 'ordinary' on-shore ones have blades 45m long, so the diameter is
about 95m. The fastest speed is 18rpm. Above that they have to be braked
and stopped.

Bill
  #15  
Old March 13th 18, 02:06 PM posted to uk.tech.digital-tv
Indy Jess John
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Posts: 1,307
Default Paranoia or real effect?

On 13/03/2018 13:44, Bill Wright wrote:
On 12/03/2018 22:52, Java Jive wrote:

What is the rotor diameter of a wind turbine?
"As of 2015 the rotor diameters of onshore wind turbine blades are as
large as 130 meters, while the diameter of offshore turbines reach 170
meters."

So taking the 130m diameter, for the tips to be travelling at 300m/s,
they'd have to be spinning at 300 / pi*130 ~ 2/3 rev/s, which seems
reasonable - they don't spin very fast.


The 'ordinary' on-shore ones have blades 45m long, so the diameter is
about 95m. The fastest speed is 18rpm. Above that they have to be braked
and stopped.

Bill


This is what happens if they are not braked
https://www.youtube.com/watch?v=l3tqjuvy7i0

Jim

  #16  
Old March 14th 18, 08:52 PM posted to uk.tech.digital-tv
Vir Campestris
external usenet poster
 
Posts: 439
Default Paranoia or real effect?

On 12/03/2018 22:52, Java Jive wrote:
On 12/03/2018 21:23, Vir Campestris wrote:

On 11/03/2018 16:55, Jim Lesurf wrote:

I was wondering about the doppler from the plane's velocity. But you
remind
me that the fan blades might also generate quite a lot of doppler on the
reflections. But I've not worked out the velocity needed to shift each
subcarrier by the difference in frequency between subcarriers.


IIRC the blade tips are high subsonic (300m/S) and of course further
in they are everything down from there... so about 1E-6 of C. the
channel is around 600MHz, so you'd potentially see a shift of 600Hz.

Surely I've got that wrong? I'm damn sure the blade tips aren't doing
Mach 10...


No, the speed of sound is approx 340m/s, so, assuming your figures are
correct, they're doing just under Mach 1.¬* However, as you seem to be
rather confused, let's check your figures:

https://www.google.com/search?q=dime...+turbine+rotor

People also ask ...

What is the rotor diameter of a wind turbine?
"As of 2015 the rotor diameters of onshore wind turbine blades are as
large as 130 meters, while the diameter of offshore turbines reach 170
meters."

So taking the 130m diameter, for the tips to be travelling at 300m/s,
they'd have to be spinning at 300 / pi*130 ~ 2/3 rev/s, which seems
reasonable¬* -¬* they don't spin very fast.

The bit I wasn't sure about was the Doppler shift.

Andy


 




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