Our job is to recommend for Jim Henry, who is building an AMT5000 Radio Transmission site 150' from his studio, a best method for transmitting 12 VAC by wire from studio out to transmitter.
I'll put my recommendations here, inviting comment on accepting or improving what I suggest.
The wall-wart supplied with the AMT5000, at least in the case of my own transmitter and assuming Jim Henry has the same, is:
TRIAD CLASS 2 Power Supply
Model: WAU12-200; Input: 120 VAC 60 Hz 4 W; Output: 12VAC @ 200 mA
In previous instructions for building an audio line we described a home-built project box containing the parts for a simple audio mixer: stereo to mono and connecting lines from computer audio out to 150' audio transmission line.
In the same project box we suggest mounting a terminal block for voltage wire connections.
With the TRIAD Power Supply located where it can be plugged into the same AC Power Strip as the station computer, extend the existing AC output wire to the project box and cut the wire so as to neatly reach the terminal block for screw connection. Strip and tin the wires accordingly.
The corresponding screw terminals of the terminal block will be used to attach 150' of appropriate voltage transmission wire.
Jim, you have previously listed a stock of wire already on hand... please list that information here so readers can select and recommend the wire type they find best for the job;
At the transmitter end you can run the 12 VAC voltage line into the AMT5000 and connect to J5 Terminal block, next to where the audio line is connected.
The Terminal Block J5 is labeled [+ 12V -] because the AMT5000 can also be modified to accept DC voltage, but we are using the original AC supply, so connect the wires without concern of polarity.
If a shield exists on the wires, depending on what is recommended by others, connect it to the GND terminal;
Thoughts: For best AC line transmission twisted wire should be used. True or false?
With twisted pair wire no shield is needed. True or false?
System ground between computer and transmitter is supplied through the audio line shield. True. Any comments about this?
I strongly recommend against running 120 VAC home electric out to the transmitter. Any other comments or opinions?
There is no power off/on switch designed into the AMT5000, so you can add one by building an approprate on/off toggle switch into the project box. The TRIAD Supply will still be ON in such case, only the 12 VAC low power will be switched.
Turning off the power strip will turn off the TRIAD Power Supply.
What other ideas might anyone have?
I recommend supplying the transmitter with 12 Volt (or whatever DC voltage the AMT-5000 requires) filtered DC, not AC. Doing this eliminates crosstalk between the power and audio lines which would cause hum.
It can be done to run AC but most likely the audio line needs to be balanced on both ends with ground loop isolation.
Neil
Neil's suggestion to employ DC rather than AC is good advice, but here's the situation:
The AMT5000 comes with an 12 VAC Power Supply.... the conversion to DC is done within the transmitter.
Because this is an extremely professional transmitter design it can accept a DC Power Supply with only a few jumper changes (2 I think... I'll look it up later).
We'd need to set aside the AC Power Supply and replace it with a an appropriate DC Power Supply at the computer end of the 150' .
It's an easy change to accomplish and that is now the NEW plan.
"How To" details will be posted by me tomorrow unless someone does it sooner.
I agree with Neil on the DC recommendation.
When my AMT-3000 was in my backyard about
75 feet from the house - - I used a little bench supply.
I trusted that more than a wall wart. The supply came
from a friend's junk pile. It was fused and could deliver
between zero and 35 volts. I set the DC for 20 volts - which -
if I remember correctly - - is what the AMT-3000 wants to see. The voltage
was varied with a pot. After it was set for 20 volts - I put a big piece of
duct tape on it so the setting could not be chsnged.
The supply had voltage and current meters on the front. The highest current
amount the supply could deliver was 500 mA. That was the highest marking
on the front panel current meter. I watched the meters all the time - that's just me.
The supply was an unknown - - in any case - - I didn't run the supply and transmitter when I was asleep.
Brooce, Part 15, Hartford
My AMT5000 is outdoor on approx 35 metres of cat 5e cable.
IIRC when one pair was used for the supply, the cable dropped approx 1.5 volts
I then used 2 pairs in parallel, for good measure.
I also use a dc unregulated supply at 17v.
Also the earlier version of the AMT5000 had a very small flat regulator heat sink, a later revision version used an improved heat sink, for good measure i upgraded the earier version with a larger heat sink.
Paul.
Carl, Thanks so much for your help. I wish I had read this sooner. I spent much of today running a 120vac line from the house to the transmitter/antenna location! It is all strand mounted and ready to go.
Jim Henry reports: "I spent much of today running a 120vac line from the house to the transmitter/antenna location!"
Wow, you've really got the pedal to the metal!
I'll continue commenting on the building of a 12VDC line so you have the information in the event you decide to put an OFF switch on the AC Power Line.
Not a bad idea to have multiple ways of doing things.
The AMT5000 Manual Page 27 Power Supply...
Discusses only using the supplied 12 VAC Power Supply and (in my version of the manual) does not discuss a way of inputting a VDC power source...
WITH THE EXCEPTION of using a DC Battery...
Page 22 PC Jumper Options...
shows that Jumpers S16 and S17 should be DISABLED for powering with a 12 VDC battery, but it does NOT mention using another kind of DC power supply.
For copyright reasons I cannot show any of the manual text nor schematic, so I will bow out of the discussion on building a DC power supply for safe connection to the AMT5000.
If I happen upon new information I will bring it here.
Well, yesterday I was looking at the Harbor Freight solar system with deep cycle battery. I could do that for about $200 and would use a cooler (ice chest) for a battery box. AC just seemed so much easier and cheaper though.
Carl, it lookd like I still have a couple hundred feet of STP Cat 5, plus a couple thousand feet of UTP C.AT4
Carl,
Jumpers s16 and s17 should be enabled to 12v dc operation !
These jumpers bypass 2 diodes so connecting the supply input direct to the 12v regulator, the reason for this is to remove the 2 diodes voltage drops, that would happen when using a dc supply to it.
For ac input, the diodes rectify the input, so supplying unregulated dc supply to the regulator.
As the 12v regulator requires a slightly higher input voltage to regulate properly, as well as some voltage drop on the cat 5 run, the dc supply would ideally need to be more that 12v, say 15v to allow for this.
The 12v ac rms supply if used, and when this gets rectified by the internal rectifier and smoothing cap, produces 16v dc to the 12v regulator.
So strapping the diodes for external dc operation, i would use 14v to 15v at the input of the amt5000.
Paul.
BOARDMAKERS comments sound right, the main thing about trying whatever we try is to protect the AMT5000 from damage.
One huge factor is polarity!
Make darn sure + connects to + and - to -.
About Jim's wire inventory...
I am not up on types of cable, but other members will know exactly.
ALSO...
Jim, you can try AC without harm, the main thing to watch for is hum being induced over to the audio line, which very well might not happen.
If using ac mode, as long as the ac supply is isolated from ground, so fully floating, and the audio is the same, i see no problem, as there is then no ground loop issue.
So connecting unbalanced domestic audio gear to the transmitter would cause problems.
Paul.
BOARDMAKER has contributed good information to this discussion, and I refer back to his first post when he said:
"IIRC when one pair was used for the supply, the cable dropped approx 1.5 volts
I then used 2 pairs in parallel, for good measure."
That brings out an important point...
Sending low voltage over long wires will experience some loss in the resistance of all that wire.
This power loss must be taken into account when evaluating the performance.
Well that was unfortunate "Kooking Back".
I hope everyone knows I was trying to say "Looking Back".
It's this keyboard.
Damn thing can't spell worth a bime.