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Re: [TowerTalk] SteppIR problem-update from the front lines

To: "" <>
Subject: Re: [TowerTalk] SteppIR problem-update from the front lines
From: "Jim Brown" <>
Date: Mon, 18 Jun 2007 09:22:08 -0700
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On Mon, 18 Jun 2007 06:23:02 -0700 (PDT), Bill Carnett wrote:

>The station
>ground is an 8 foot rod approximately 5 feet from the
>unit. Connection is via a 4 ga solid wire and 2 inch
>ribbon to a SPG bulkhead plate.  The house ground is
>via the AC circut, approximately 15 feet from shack
>and utlizes 2 - 8 foot ground rods approximately 8
>feet apart.  BTW, building inspector told us we didn't
>need any of that lightening stuff "we don't require it
>any more."  go figure?

I haven't been following this thread up to now, but I'm beginning 
to see a possible clue to your problems. All I know about StepIR's 
that they are mostly made of non-conductive structure, and use 
motors to tune the elements. I don't know a thing about the motor 
controllers or their wiring. So please take my comments in that 

The word "ground" can be VERY confusing when used in the context 
of transmitting signals from one point to another. Also, the use 
of the EARTH as a signal conductor is a really bad idea. 

1) In the context of your motor controllers, what they are calling 
"ground" should really be called "common."  If they have done it 
right, it probably has no relationship to the EARTH at all. These 
motor control wires should have no connection to anything that is 
connected to the earth, except possibly at the controller (up to 
the designer of the controller). I'd bet that they are not 
connected to any conductive frame or mast at the antenna, but that 
might be an interesting thing to probe with a DC meter. 

2) Your tower ground rods should definitely be BONDED to your 
building ground and your station ground. In this context, the word 
BOND means a connection that is PHYSICALLY ROBUST and has the 
LOWEST PRACTICAL IMPEDANCE over the widest range of frequencies. 

3) Your mains power ground should be bonded to your station 
ground, and BOND means the same thing here that it does in #2. In 
other words, ALL of your EARTH connections should be bonded 

As I see it, there are two or three possible causes of your 

4) A connection (including a capacitive connection) between the 
control wiring and the earth is VERY likely to introduce noise 
into the control wiring. 

5) Excessive capacitance in the cable connecting the antenna 
motors to the controller. 

6) Excessive resistance in the cable connecting the antenna motors 
to the controller. 

7) Noise pickup on the cable itself (most likely power-related, 
but possibly from electrically noisy equipment). Noise pickup on 
the cable is greately reduced if each motor runs on its own 
twisted pair. Shielding of these pairs does not matter. BUT, it is 
quite important that neither conductor of the pair have any 
connection to EARTH. 

8) At very low frequencies (power and power harmonics), current 
will follow the lowest RESISTANCE path. At high audio frequencies 
and above, currents will follow the lowest IMPEDANCE path. If the 
circuit is connected by a transmission line (for example, a 
twisted pair cable), that will be the lowest impedance path. 

As others have noted, this is a matter for StepIR's engineers to 
unravel. But it's important that we not screw up their system by 
miswiring it, or miswiring stuff around it. 


Jim Brown K9YC


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