Your transient measurement is a very good clue. It appears to me the 12V
drop represents the power supply voltge regulator response time to the
current surge due to the antenna tuning. For very long cables, I would think
that the current pulse (and voltage transient) could be higher.
That kind of transient on the supply line could very easily confuse the
From: K4SAV [mailto:RadioIR@charter.net]
Sent: Sunday, June 17, 2007 10:03 PM
Subject: Re: [TowerTalk] SteppIR problem-update from the front lines
Doing engineering analysis from where I am sitting is very difficult,
and you are down to that point. The part substitution method hasn't
worked and there is only one part left that hasn't been substituted.
(And I doubt that will solve the problem either.) Plus you didn't give
us many details of your measurements other than you made them and they
were OK. So everyone is just taking wild guesses. (I thought the water
in the cable guess was pretty good.) Here are some questions. The
answers to these would help a lot.
1. When you ohmed the lines to the motors what were the readings? Were
they all very close to the same?
2. Did you check every line for resistance between each line and every
other line and ground? Were they all open except for the mate for the
one being tested?
3. Is the DC ground for the power supply tied to station ground? Did
you measure it?
Note: This can be a difficult to measure, because there may be some
small voltage on it.
(This DC ground should not be connected to the tower ground at the
If it is connected, remove the serial cable to the computer and
re-measure it. If it is still connected, this may be a problem.
4. Are there any other devices connected to this cable such as
transient suppressors or a tuning relay?
I have a 4 element SteppIR with 250 feet of cable. I just looked at the
output of my power supply with a scope to see if I could learn
anything. Seems this is the only way since SteppIR doesn't publish
their schematics. I was a bit surprised at what I saw. The supply
output was close to the nominal 33 volts, but when the antenna was tuned
there was a 12 volt negative going spike on the DC power supply line.
It then ramped back up the nominal voltage in 30 ms. This did not
continue as the antenna was tuning, but occurred only once at the start
of tuning. It also occurred each time the antenna was moved one
frequency step. I also measured the current spike that was causing this
voltage spike. It was 6 amps.
If the cable to the antenna is disconnected, this 12 volt spike is still
present on the power supply, but it only takes 1 ms to recover to
The cause of this spike or its effect is unknown since I don't have a
schematic, but it doesn't look like something that is very good, and it
is sure going to complicate the problem of keeping the controller from
shutting down when heavily loaded. I could take a guess at the cause of
this, but I won't because it would only be a guess. This kind of
engineering stuff belongs back at the factory.
I also tested the supply by itself to see if it had good regulation. I
did transient load tests up to 2 amps which is the rated current for the
supply. The output showed no sign of dropping voltage. I did not test
to see what it would do with a 6 amp transient.
The resolution of this problem, is it is a problem, belongs at the
factory. A beefier power supply might hold the voltage up better,
however since the controller can cause this spike without the cable
connected, the source of the problem is probably in the controller.
I hope FM reads this message because I would like to suggest that they
set up a test fixture and measure the acceptable limit of cable. Having
someone report that they have one working that has 500 feet of cable
hardly qualifies as engineering data. The max limit should be measured
and the reason for failure above that limit should be determined. If
they haven't done the system analysis for the cable system, that should
be done also.
Bill Carnett wrote:
>Ok, Friday I received a new 440 foot control cable
>from Mike at SteppIR. In addition he prepared a 6
>volt DC battery pack to piggy-back on the 33 volt
>power supply for the controller.
>Neither worked. Unit comes on, then shuts off with
>band selection. Even tried going into set-up mode to
>individually select elements, same problem. Make the
>selection, and the entire unit shuts down. With a
>short control cable, i.e. 80 foot at the base of the
>tower, the unit works fine...full functioning.
>So, anybody have other suggestions? The problem seems
>to be related to the cable length. Increasing the
>controller voltage to the maximum 38 doesn't help.
>The SteppIR folks, Jerry, Jim, and Mike have been
>great, but we still can't figure out the problem.
>This is pretty frustrating. I want to give this
>antenna a good opportunity to get functional, but I'm
>not sure it will in my application, i.e. 500 feet from
>controller to antenna. It might be time to start
>looking for an alternative antenna?
>Again, thanks to all and any suggestions appreciated.
>Moody friends. Drama queens. Your life? Nope! - their life, your story.
Play Sims Stories at Yahoo! Games.
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