Hi,
I am totally unfamiliar with SteppIR stuff but one test I haven't seen
anyone mention
is checking the cable run with a megger.
A megger will produce a very high voltage at a small current that can
detect
ground faults and conductor shorts that a standard VOM won't see.
I used to work for the Railroad and we had to megger all terminals
periodically
to insure there were no high resistive ground/cross faults. Most Telco types
would have access to a megger or HI-POT tester.
Just an idea..
73's
RoD
KD0XX
A good friend will come and bail you out of jail,
A TRUE friend will be sitting next to you saying.....
"DAMN THAT WAS FUN"
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com]On Behalf Of Jim Brown
> Sent: Monday, June 18, 2007 12:22 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] SteppIR problem-update from the front lines
>
>
> 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
> context.
>
> 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.
> That
>
> 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
> together.
>
> As I see it, there are two or three possible causes of your
> problem.
>
> 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.
>
> 73,
>
> Jim Brown K9YC
>
>
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>
>
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