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Author Topic: QUESTIONS REGARDING A SCREWDRIVER INSTALLATION ON A CARGO TRAILER  (Read 850 times)
KB8RSA
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Posts: 1




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« on: March 31, 2013, 07:42:31 PM »

I am in the process of installing a Scorpion SA-680S screwdriver antenna on the roof of my cargo trailer www.werv2.comham shack. 
The antenna is mounted to a mechanism that will raise the antenna from a horizontal position (stored for traveling) to a vertical position for stationary operating purposes. The mechanism is powered by a linear actuator that has internal limit switches which limit the maximum throw of the actuator shaft/plunger. I do not believe they are adjustable as I have no data on the SuperJack II+.
I am unsure just what to call this equipment due to not knowing the proper names for the components or the total package. Here are some photos to give you an idea of what I am dealing with in this installation.

Try this one first:
http://tinyurl.com/cqch758


Or this one....
http://i9.photobucket.com/albums/a98/Escaper/SCORPION%20ANTENNA%20INSTALLATION/IMG_1403_zpsebf26fb3.jpg

It appears that I do not have adequate adjustability to have the articulator move the antenna from an appropriate (slightly above horizontal) horizontal position to a proper vertical position without putting a limit switch in the control line. I would like the antenna to be inclined a little from the horizontal to avoid rain from running down the antenna and in and under the top section and into the coils. I could use some ideas on what switch to use and how to wire it. It seems that a diode is needed to make the system work and I have no idea at this point what the current requirement of the diode would be needed.
I am running the control wiring about 30-35 feet from the station to the antenna. I am concerned about voltage drop and what size wire to use in this 12 volt run.
I do not have any specifications on the SuperJack II+ HQ linear actuator and hope someone has those specs.
The wire size for the sensor inside the antenna is very small, maybe 22 ga or so.  I wonder about the wire size and voltage drop on this item too.
I will appreciate any and all suggestions or advise anyone may offer.
Regards,
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G7DMQ
Member

Posts: 40




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« Reply #1 on: April 01, 2013, 10:11:41 AM »

The limit switches on jacks normally work by the switch being normally closed with a diode across the terminals and the two limit switches connected in series with the motor.  When the jack reaches the end of its travel, the switch opens such that the diode is now connected in series with the motor.

The diode is polarised such that it stops current flow in that direction.  However, if you reverse the current, it flows through the diode running the motor in the opposite direction (until it reaches the other limit switch).

Thus, all you need to control it is a switch which reverses the power to the motor.

If you need a limit switch which operates before the built in limit, just fix a microswitch in an appropriate position such that the contacts open when the jack reaches the desired location.  Connect a diode (rated for the motor current) across the normally closed contacts and connect the NC contacts in series with the motor (or with the wire going in to the jack).  If it does not work, reverse the polarity of the diode.

Si
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K0JEG
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Posts: 646




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« Reply #2 on: April 02, 2013, 02:20:49 PM »

A google search for Superjack and following a few links led me to this site:
http://www.geo-orbit.org/sizepgs/tuningp3.html#anchor485744

The Superjack is a linear actuator arm used for positioning a C band satellite dish. Looks like it was modified to raise or lower the antenna in a very interesting way. I'd have to see the inside, but according to this (http://www.satelliteguys.us/threads/150256-Connecting-a-SuperJack-QARL-3024-actuator) page, that limit switch is actually a turns counter to send feedback to a satellite receiver to help position the antenna.
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WN2C
Member

Posts: 438




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« Reply #3 on: April 03, 2013, 09:32:09 AM »

Have you talked to Ron about whether rain will get in to the coil?  This may be an exercise in futility if you are doing this for just keeping out rain from the coil.  Nice install by the way.  How high is the Antenna element (at top) when say on 40 meters or 75? Just wondering how high the antenna is mounted on the trailer and what your max height is.  Do you use the 6 ft element or an 8 ft element?  Why the install on the cargo trailer?  Unless you are pulling it, that is the only time you can HF mobil?  Why not put it on the tow vehicle so you can go mobil all the time?

Rick  wn2c
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