[RFI] Help on speed drive motor controller RFI

Juan EA5RS ea5rs at ono.com
Mon Jan 29 17:00:54 EST 2007

Thank you very much for all responses, both direct and thru the reflector.
It was very enlightning to hear your opinions.

When I said the speed controller did not have any RFI filters fitted, I
meant it was not using the separate, optional RFI and "dV/dt" filters
offered as options by the manufacturer. I actually don't know if the
controller has any type of RFI filtering inside. 

I have to agree that even performing to EMC standards, and I am sure this
one is not, the RFI from this controller is absolutely unacceptable for weak
signal reception.  Just from the beginning I anticipated this would be a
very tough RFI problem to deal with due to proximity and tremendous QRM

That is why, to be practical, it seems to me that the only feasible total
cure is to avoid the speed controllers all together, and this is going to be
my goal. According to an Hydraulic Engineer I have been consulting with, the
pressure controlled system and specifically the pump motor does not demand a
variable speed drive at all, and a simple relay "on-off" controller could do
the job and this would completely eliminate the problem. Now I need to be
persuasive with the contractor and my neighbours.

Still, the doubt remains why this controller generates so much QRM while
those others I am sure also exist near my antennas (i.e. elevator motor
controllers) are apparently QRM free. I also would like to know if the fact
the controllers supply currents near square wave is a real requirement for
motor control or it is just the way it is being done. I have a hard time
believing slightly rounding the waveform could impair motor performance.

Juan EA5RS

-----Mensaje original-----
De: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] En nombre
de Tom Rauch
Enviado el: lunes, 29 de enero de 2007 11:37
Para: Ian White GM3SEK; rfi at contesting.com
Asunto: Re: [RFI] Help on speed drive motor controller RFI

> Please read what was actually written, Tom.

The EA5's post must have choked in a spam filter, but  my 
points are twofold.

1.) even when the supply meets or exceeds FCC and CE specs, 
it can cause bad RFI problems.

2.) even if we don't see an obvious filter it may have one

I certainly agree a unit that fails CE and is labeled CE in 
theory gives a complainer great power, but I can tell 
everyone from first hand experience units that meet or 
exceed CE can cause slight problems a mile way and can be 
devastating within a few hundred meters.

There is a chicken farm about two miles from that has a 
controlled made in the Netherlands that does pass CE and FCC 
but still has birdies several dB out of my noise on 160 

I worked on good three phase controllers at another location 
that were several hundred feet from the receiving antenna 
and caused bad problems in a moderate background noise 

It is virtually impossible for most people to test for CE or 
FCC compliance or to know if there are really filters in the 
unit (if they are necessary to pass). The bottom line is if 
it bothers the radio... and a device that passes certainly 
can be a problem. In such cases, and they are common, 
filters from the manufacturer often are useless.

73 Tom 

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