dgsvetan at rockwellcollins.com dgsvetan at rockwellcollins.com
Tue Oct 6 09:16:58 PDT 2009


A quick list of possible RFI would include static (same as P-static on 
aircraft), but I would think that can be handled by static dissipaters, 
also as done on aircraft.  From articles I've read, it does appears that 
at least two different technologies are involved with the electrical power 
generation:  AC alternator directly driven by the blades, but resulting in 
non-constant frequency; DC generator driven by the blades and feeding a 
combination of storage batteries and large inverters to produce 60 Hz. 
Since the grid demands 60 Hz, I presume that the alternator systems use an 
inverter to provide isolation and create the constant 60 Hz output from 
those systems.  Either way, I do not recall seeing very many posts on this 
reflector from persons living near wind farms.  Having worked on the 
design of medium large (30 kW or so) inverters years ago, I can vouch for 
their potential to create havoc on power lines.  On the other hand, when 
running at a fixed frequency and a reasonably constant load, the circuit 
components can be optimized to provide a lot of noise attenuation and yet 
still have a high efficiency system.

One other possible form of interference to consider:  are you a fan of the 
higher bands, like 6m and up?  If so, those big blades act like "choppers" 
and I have read reports from VHF and UHF ops who have tried to copy weak 
signals thru the blades of windmills and suffered the problem of signal 
chopping at  rate controlled by RPM of the blades.  There might be some 
effect from blades on HF signals, but that would depend upon band you are 
using, angle of arrival of those signals to your antenna, direction, and 
so forth. 

As for noise, we have some large wind farms in NW Iowa (I live in eastern 
Iowa), and I have stopped to take photos when passing by those farms near 
sunset.  I have stood within 100 feet of the base of operating wind 
turbines and can tell you that there are two sounds, neither of which is 
loud or objectionable to me:  a low level whine sound from the gear box up 
at the turbine itself; a low level "hum" of sorts from the blades.  The 
speed of rotation is not fast enough to create loud "swooshes" or 
whistling from the blades.  Perhaps others have heard different sounds, 
but that's what I have experienced in the two times I did photography 
among the turbines.  I spent about 30 minutes to an hour each time, and 
all of that time quite close to a number of the machines (on a public 

This trial system sounds small scale.  The 40 foot pole is quite a bit 
shorter than used in the major wind farms (which I believe those support 
towers to be in the 170 foot class, at least).  Also, if the blades are 
less than 7 feet in length, I think the only bands that might suffer 
chopping effects will be VHF and UHF.  The blades on the systems I 
photographed were on the order of 75 feet in length, or more.   Take a lot 
of data if you can, but bear in mind that with respect to output power, 
the output from this trial system is a fraction of what major units can 

73, Dale


rbaker <rbaker at cloudnet.com> 
Sent by: rfi-bounces at contesting.com
10/05/2009 07:19 PM

rfi at contesting.com


Hello all--- Does anyone have any information concerning possible RFI 
being produced from a Wind Energy Conversion System ?? There is a 
proposal to put one in our residential area.It will be up on a 40' 
monopole,with a maximum rotor ( blades ??) diameter of 6'8",producing 
1000/1400w/48volts,depending on wind speed.This is a test case, as our 
city has no regulations concerning wind generators--towers yes--but not 
a WECS!!My concern is the possible production of static charges from the 
blades,sound, RFI from the generator,attenuation of my signal by the 
rotating blades to the SW.eg.the S. Pacific.
                  Have fun with this one, people!!
                 de    Bob   W0ROB
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