Topband: Boradband noise on 160 meters tracked down to apartment complex

[Don Kirk]

Hi Jim,

Thanks, and I have shared a lot of documents with the folks that cover the
major points your section on variable speed drives covers, but found that I
still had to make a recommendations list for them (taking into account
simplicity of install, cost, and highest probability of success), while at
the same time telling them that I was not liable for anything they opted to
do.

Actually sounds like the technician is now trying to get approval to move
the drives up into the attic which would put them very close to the motors
(which are roof mount) and at the same time he would do a much better job
on the conduit run between the drives and the motors.  Currently the drives
are around 50 feet away from the motors with very questionable conduit runs
(and the current conduit runs are impossible to access).

Note : Previously one simple option I suggested was the use of common mode
cores on the output of the drives (similar to what George AA7JV suggested),
but the original technician that was working on the job did not contact me
for assistance and he installed the cores incorrectly which caused drive
faults, so they abandoned that approach (I'm giving them some time and
space before I bring up the common mode cores again).  I also want to
develop a better working relationship with the current technician (I have
offered to be onsite with him when he makes changes, but he has yet to take
me up on my offer).

I would like to make one comment about your section on VFDs.  It does not
mention shielded cable that is now available specifically for use on the
output side of variable speed drives, and these cables offer some major
advantages over the use of metal conduit (but at much greater expense).

73,
Don (wd8dsb)

On Wed, May 13, 2015 at 2:41 PM, Jim Brown <jim at audiosystemsgroup.com>
wrote:

> On Wed,5/13/2015 11:14 AM, Don Kirk wrote:
>
>> The local technician is now planning on additional changes since the input
>> line filters have not totally mitigated the problem (but they sure
>> helped),
>> and will provide an update when I have new information to share.
>>
>
> Hi Don,
>
> You might want to refer the people working on the problem to this Power
> Point for a tutorial workshop that I've taught to pro audio and video
> people. The principles are no different when the interference is at RF.
>
> http://k9yc.com/InfoComm-Grounding2012.pdf
>
> Henry Ott's excellent text on EMC includes a sub-chapter on these very
> nasty RFI sources. His book is widely used as an EE text, and considered
> "the EMC bible."
>
>
> http://www.amazon.com/Electromagnetic-Compatibility-Engineering-Henry-Ott/dp/0470189304
>
> 73, Jim K9YC
>
>
>
>
> _________________
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>