[TowerTalk] Alpa SPID RAK motor noise

Thu Oct 11 15:58:15 EDT 2018

Gary,

Checking the GH specs, "In most cases, adds PWM speed control" and since 
the Spid uses a DC motor, the GH is likely using PWM for ramp up/down.

So my thoughts of what should be done - to start, it isn't clear if this 
is brush noise or PWM noise

0. run the rotator on pure DC from a linear power supply - no noise = 
pwm problems; noise = maybe both, your waterfall might help decide how 
much of either

1. either problem, insure you have a good 6m feedline choke right at the 
feedpoint plus a choke at the entrance panel plus a choke at the base of 
the tower -

2. either problem, use shielded twisted pairs for the rotator motor and 
position leads -   ground shields only at tower base

3. if PWM noise

     choke the motor cable at the GH output for 6m to further knock down 
any common mode PWM hash,  two, maybe three turns in a big clamp on.

     ground the GH, maybe try 0.01uf to ground on both GH motor leads 
and see if it tolerates them.  Try larger if it does.

     if this isn't enough it gets complicated, use a controller without 
PWM,  add a common mode choke on the motor leads although finding a 
commercial one for 50MHz and several amps is challenging, make a low 
pass filter, muck around inside the GH with its PWM switching risetimes, 
etc.

4. If motor noise - I've seen bifilar windings on rod ferrites plus 
ceramic caps right at the brushes (better inside the motor) do a go job 
of suppressing hash. At 50Mhz you need SMD length cap leads - i.e. none. 
Rods and caps work on the K0XG 180vdc 1/2hp motors on my rings.  Also 
this is what K7NV does on his prop pitch motors and I hear only a very 
slight whine on mine, 80m and no PWM noise from the GH internal amp.   I 
don't have design details, perhaps others can provide advice, but the 
Spid motors are small in comparison.

I've been battling PWM amplifier noise for a couple of years with 
limited success, seven GH + remote commercial PWM amps for K0XG rings.  
Got it mostly tamed 20m and up, still struggling on 40m. I have a bucket 
full of filters I made that didn't work.  And I've added  bucket of big 
clamp-ons on everything.   Wish I had used shielded wire from amps to 
ring motors.  The reasons this is so hard are commercial PWM amps have 
all sorts of self protection stuff which don't like what would surely 
work as a low pass filter.  They also want the biggest HP rating in the 
smallest size so design for wicked fast rise times on the output IGBT.  
And the design does not at all have a balanced output or any filtering.

Grant KZ1W

On 10/11/2018 8:25 AM, Gary Smith wrote:
> There are four wires to the rotator; two
> for DC and two for control. There are
> small disc caps attached to each of the
> control lines with a common wire to ground
> which is screwed to the protective cover.
> There are no caps I can see related to the
> power side. There's a resistor in series
> with the + line but that's not going to
> help in this regard.
>
> http://doctorgary.net/spid-caps.jpg
>
> The black wire hanging down terminates in
> a brass eye terminal that is screwed down
> to the cover, this anchors to the metal
> case providing the ground.
>
> Gary
> KA1J
>
>> Inside all of my TIC Ring rotators are filters connected to the wiper
>> motors. Perhaps a filter can be added at the Alpha SPID RAK motor to
>> reduce the hash.
>>
>> John KK9A
>>
>>
>> From:	"Gary Smith"<Gary at ka1j.com>
>> Date:	Thu, 11 Oct 2018 01:39:41 -0400
>>
>>
>> I have motor noise when I rotate the new
>> SPID RAK & I've held off asking here till
>> I completed properly grounding the house,
>> coax & rotor lines. Unfortunately it
>> hasn't helped the issue I'm having with
>> the rotor and maybe someone has a
>> suggestion of something I can try.
>>
>> The antenna is a 6M7JHV, it is on a tripod
>> mounted in the center of the house. There
>> is a #4 Gauge wire attached to the tripod
>> which goes to an 8' ground rod. This
>> ground rod is connected with #4 solid
>> copper to the breaker box and the ground
>> rod with the Polyphasers which goes to the
>> shack, the ground to the shack attaches to
>> this last ground rod. There are 3
>> additional ground rods attached to the #4
>> wire.
>>
>> When I turn the antenna it obliterates the
>> waterfall and raises the meter 7 S units.
>> As soon as the motor stops all is well.
>> The controller is a GH RT-21D. The
>> tailtwister it replaced never left any
>> indication it was turning other than the
>> meter.
>>
>> It was suggested it is because it is a DC
>> motor in the SPID and the noise is likely
>> coming from the brushes. Also that the #4
>> to ground is not a RF ground and if it
>> were attached to a tower instead of a
>> tripod I likely wouldn't have this issue.
>> The possibility was raised of the brushes
>> having an issue or perhaps the two caps
>> attached to the control lines to ground
>> may be a problem.
>>
>> Here is a photo of the SVGA output from
>> the K3.
>> http://doctorgary.net/spid.jpg
>>
>> I started at 180 deg and rotated clockwise
>> to 179 deg. The dark red is at 240-290
>> degrees, the two strips of blue where
>> there is no interference happens around
>> 340 and 80 degrees respectively.
>>
>> I've never read of anyone having this
>> problem before, guess I'm the lucky guy.
>>
>> Any suggestions I might try?
>>
>> Thanks & 73,
>>
>> Gary
>> KA1J
>>
>> _______________________________________________
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