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Author Topic: Powering an SGC Autotuner  (Read 2498 times)
KD4ALY
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Posts: 9




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« on: January 19, 2013, 11:48:38 AM »

I have several questions on the topic of installing/powering an SGC SC-230 autotuner.  The autotuner will be used with a 175’ wire loop antenna I have running inside the perimeter of my attic, so additional weatherproofing of the autotuner will not be an issue.  (RF may be an issue, but not weatherproofing.)  I didn’t invest in the optional SmartLock, although it sounds like it is an important status indicator that could be standard equipment. 

If I’m incorrect in any of my assumptions or statements below, please let me know.

I’ve purchased 2 MFJ 4117 Bias Tee Injectors to supply power to the autotuner through the coax.  I also have purchased 2 DC plugs.  I know one Bias Tee should be located in my shack and one is located at the autotuner.  To get power to Bias Tee #1 in the shack, it appears I need to solder two wires to one of the DC plugs, insert the plug into the Bias Tee, and connect the two wires to my power supply. Since the SGC manual specifically said to obtain power from the same power supply that powers the rig to help prevent ground loops, I assume it’s ok to run connect this set of wires to the positive and negative terminals of that power supply and not use a second dedicated power supply?  A short coax jumper from my rig will connect to one SO-239 on this same Bias Tee, and then a 40 foot run of coax to the Bias Tee’s other SO-239 (this coax which will go to the attic). 

In the attic I’ll connect the other PL-259 of the 40’ run of coax to the Bias Tee #2.  I assume I’ll need to solder the red and black wires of the 9’ cable supplied on the autotuner to the second DC plug, and plug that into this Bias Tee.  I’ll also connect the 9’ coax from the autotuner to the remaining S0-239 on the Bias Tee.  Finally, I’ll connect one side of the loop to the “antenna” post on the autotuner and the other side of the loop to the “ground” post.   

I apologize for asking these questions and for going into such seemingly insignificant details.  I’m frustrated after reading the autotuner’s manual, which doesn’t go into details of powering the rig other than using their 9’ cable.  I’m surprised they don’t address using using a longer length of cable since many, if not most, installations will need a longer length of coax and power/control cable.  I question why SGC even supplies 9 feet of coax to begin with?  Why not instead have an SO-239 and a plug for the DC on the autotuner itself?

Again, I apologize for posting such simplistic questions, and thanks in advance for any assistance and advice. 

Tommy
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WD4ELG
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Posts: 877




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« Reply #1 on: January 19, 2013, 04:06:31 PM »

Your description is perfect, that's exactly how I did it for my autotuner (although mine is outside).

Not sure why they provided the cable they did.  Maybe the 9 feet is from the tuner to the antenna, assuming you will be using coax from the tuner to the feedpoint?  Maybe check on the Yahoo groups under SGC Smarttuners.
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AA4PB
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« Reply #2 on: January 19, 2013, 04:29:11 PM »

It looks like you have the connections correct. Make sure you tape up the other unused control wires so they don't short to anything.

If you used the smartlock you wouldn't be able to control it via the coax. You'd have to run a separate control cable down to the operating position. The only thing useful on the smartlock for a fixed installation is the tuned LED. If you look at the smartlock schematic you can see how to wire a simple LED to act as the tuned indicator. The problem is it still requires a separate wire to operate the LED.

The lock feature on the smartlock prevents the tuner from automatically re-tuning due to a high SWR. That's only a problem if you have an antenna that blows around in the wind causing the impedance to change while you are operating. If your antenna impedance is stable then you are better off having the tuner unlocked so that it automatically re-tunes if you move to a new frequency.

You might want to add a power switch between the power supply and the bias-T so that you can turn the tuner off from the shack. Cycling power is how you reset it to bypass mode (all tuning elements out of the circuit). Bypass is useful for receiving on a new band or outside the ham bands without having to apply an RF signal to tune it. Bypass often provides better receive signal strength than having a tuner in line that is tuned for the wrong band.

Oh, I think SGC used the cable (rather than a connector on the tuner) because it is easier to waterproof the connections. In my case the SGC is outside and the cable lets me make the connections inside of a waterproof enclosure.
« Last Edit: January 19, 2013, 04:31:50 PM by AA4PB » Logged
WN2C
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Posts: 479




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« Reply #3 on: January 19, 2013, 06:34:22 PM »

SGC sells the coax with the wire in it for $2.00 p/foot.  I think this is why they only supply 9 feet. 
I too have an SGC tuner, a 237 but I am already puting power down the coax for an Ameritron RCS 4 and am at a loss as to how to power the SGC.  Would still like to use the switch for switching between antennas.  Huh?

Any suggestions anyone Huh

Rick  wn2c
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KD4ALY
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Posts: 9




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« Reply #4 on: January 19, 2013, 07:12:22 PM »

Thanks for the replies.  I wanted to make sure I was on the right track, and had enough doubt to start the thread.

Interestingly, this MFJ Bias Tee has a power switch so I can bypass or cycle power.

Again, thanks.

Tommy
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N6AJR
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Posts: 9921




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« Reply #5 on: January 20, 2013, 11:25:18 AM »

on my 236 I did not have the cable, so I took a fifty foot coax and zip tied 50 feet of speaker wire to it to power the box.
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AA4PB
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Posts: 12981




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« Reply #6 on: January 20, 2013, 11:35:16 AM »

I just ran some unshielded 6 conductor cable along side the coax. I parallel connect two wires for 12V and two wires for ground (to lessen the voltage drop over the long 100-foot run and maximum 1A current). The remaining two wires are the control wires (I only use the tuned LED wire but the lock wire is there is I ever need it).

There is no way that you can provide tuner power and antenna switch control voltages over the same coax. Control cable is not very expensive.
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N4CR
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Posts: 1692




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« Reply #7 on: January 20, 2013, 08:39:47 PM »

There is no way that you can provide tuner power and antenna switch control voltages over the same coax. Control cable is not very expensive.

Sure you can. It would require using a pair of diodes on the output of the bias T. Negative pulses could toggle the latching relay, positive power would power the tuner.

This assumes you don't need to tune either antenna while you are switching between them.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
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