SSTRAN Power Supply

Hi All,

The SSTRAN AMT3000 wall wart is simply a transformer that supplies 18VAC RMS and the load is about 200mA. The on-board bridge rectifier converts the AC to DC before feeding the 15V regulator. There is a 470uf cap across the bridge output for pre-filtering. The 15V regulator requires a minimum of 17VDC at trough of the pre-filtered DC. The trough of the filtered bridge output is 25VDC.

So the allowed wire resistance will be:
(25V-17V) / .200A = 40 ohms

There is plenty of margin here for long power runs from the wall wart to the transmitter. A 40 ohm drop equates to the following lengths for some common wire gauges:

Sorry about the truncation due to the part15.us software.
(fixed - scwis)

Here is an important CORRECTION to the length table above. The lengths should be reduced by half. There are two conductors in the power feed circuit! My mistake.

Thanks for formatting the table Scwis!

Phil,

Nice post about wiring. Do you have any suggestions about lightning protection for wiring running outside of a house?

Neil

Phil,

Nice post about wiring. Do you have any suggestions about lightning protection for wiring running outside of a house?

Neil

Not really. Lightning is too unpredictable!

We have a radio "dog fence" surrounding the perimiter of our property. It's #18 gauge wire, about 1000ft long, buried 2" underground (seems like a great ground setup). A couple years ago, a tree next to the house was hit. The dog wire vaporized near the tree, and strangely, it also opened in one spot about 200ft away. It took out the dog fence transmitter and left some scorches in the house where the wires passed next to grounded conductors. We also lost various electronic devices in the house, but I don't think that was due to the dog fence wire. No fire, thankfully.

My judgement is that as long as the wires leading from your house to the antenna are relatively small, they will fuse (vaporize) before any serious damage can occur inside your house. This is just my somewhat educated opinion. Results may vary!

Phil,

Your experience is similar to mine. I assume your dog didn't vaporize. I have thought that buried wires would probably shunt a strike to ground through the insulation but this doesn't seem too scientific.

Here, all wires are grounded at the point of entry to the electrical ground stake. I had a hit to a tree 10 feet from the house which took out all my phones, some audio stuff, two garage door openers, and half of the tree, yet my ham radio and part 15 stuff survived. I can't say it was the grounding which save it but it sure didn't hurt. (As an aside, this was the second time in my life that I have seen plasma lightning...my neighor saw it also so she will witness to those who don't believe this).

Do you think it would be a reasonable idea to at least ground one of the power and one of the audio leads for an outdoor transmitter to the electrical stake ground?

Neil

After reading these posts, I'm feeling guilty. My original SSTran wall wart has been quietly & reliably running for over 2 years. It's feeding the transmitter via 30' of underground landscape lighting cable. This stuff has thick insulation and is designed to live under the dirt.

1610AM Copperhead Radio,
Lucama NC

Do you think it would be a reasonable idea to at least ground one of the power and one of the audio leads for an outdoor transmitter to the electrical stake ground?

Yes, that sounds like an excellent idea to me. You could ground the audio shield and one wire of the 18VAC feed to a ground rod outside before the wires enter the house. This would help to divert the lightning current to ground before it enters the house. One or both of the grounded cunductors will likely "vaporize", but at least the path won't extend into your house.

BTW, the dog is fine and had no ill effects. But I have since made a practice of removing the collar from our dog during lightning storms because I wonder if the huge electric field in the area during a local strike might trigger the collar receiver into the zap mode.

Phil,

When I read your post with your reply to my question it got me thinking. Since the power supplied to the SSTRAN units is AC and feeds a full wave bridge, neither of the wall wart secondary AC lines can be grounded to the circuit ground as would happen if the audio ground and one 18VAC line were tied together at the electrical stake since the circuit ground is on the output side of the bridge. Each half cycle, each 18 VAC line will be above gnd. potential. So, it appears that we should NOT do this.

I was thinking of a DC feed and should have realized this is not the situation with the SSTRAN unit. Do you a agree?

Neil

A telephone line provides an interesting study in lightning protection schemes. Our old style phone line enters the basement and goes directly to a Western Electric termination block 239 with 3-wire binding posts, a pipe-ground in the middle. Each side of the balanced line has a screw-in cap which holds little cylinder-like devices that look like tiny fuses (JOSLYN H3 71565), but all I know is they're not resistors or capacitors (guessing), one of them appears to have a dangling end suggesting it was damaged.

If anyone knows what's taking place in this case it would be applicable to balanced audio wiring in general.

I can't find a description of these standard items on any web searches.

Thank you MRAM for the interesting info about lightning protection on phone line.

A new twist I just learned about is "longitudinal imbalance," in which for some reason the phone line is out of balance, and often carrying "induced voltage," which is found by measuring each side of the line to ground for AC content. My green wire is carrying 100 VAC! The red wire has 6 VAC. This goes to explain why I sometimes hear crackling on the telephone and the DSL is completely erratic. I'm guessing that the 100 volts may have blown the "carbon plug."

Any further thoughts about this situation?

Thank you MRAM for the interesting info about lightning protection on phone line.

A new twist I just learned about is "longitudinal imbalance," in which for some reason the phone line is out of balance, and often carrying "induced voltage," which is found by measuring each side of the line to ground for AC content. My green wire is carrying 100 VAC! The red wire has 6 VAC. This goes to explain why I sometimes hear crackling on the telephone and the DSL is completely erratic. I'm guessing that the 100 volts may have blown the "carbon plug."

Any further thoughts about this situation?

The two wires of your phone line are called the "tip" and "ring" which comes from the old cord style switch board. The plug the operator plugged into the jack had a "tip" and the hole it went into was the "ring". Looked very much like the 1/4" audio plug.

When your phone is hung-up (on-hook) the phone company equipment grounds the "tip" side of your phone line. They know you hung up as the circuit becomes a high impedance or open.

When called, the "ring" side of the line will carry the 108 Vac to ring your phone. Old phone systems actually used the ground connection for the return path to ring the phone but over the years, since tip is grounded anyway, they quit using ground and the return path is now the tip.

When on-hook your phone line is unbalanced since the tip is grounded and you will measure AC noise on the ring side of the line. There will also be about 48 Vdc, called battery, between tip (or ground) and ring. Since the tip is grounded at the phone company you won't see much voltage if any between tip and ground.

As soon as your phone goes off-hook the phone company equipment senses the low impedance between tip and ring as dc current begins to flow. The equipment ungrounds the tip and the line is now a balanced line. The dc voltage drops to about 6 to 12 Vdc as the dc current is limited by the phone company.

Now days they don't worry so much about which is the tip or ring. If you want to figure out which one is the ring, measure for dc voltage on each wire to ground. The ring will show the battery voltage.

If you'd like to know why they use a balanced phone line, connect your phone between ring and ground. You may hear the dial tone when you go off hook but oooooooh boy will there be a lot of AC hum.

P.S. wired correctly, the green wire is supposed to be the "tip", red to be the "ring".

Thanks again MRAM.

Yes I knew about the DC "loop current" and AC "ringer voltage, as well as the terms "tip" and "ring."

Also I should mention my measurements were made with all of my equipment removed from the line so I was measuring only the phone line.

When there is no ring signal present, I don't believe there should be 100 VAC on one side of the line. I hope you will revisit the subject once more to comment on this.

By "ring signal" I am talking about the ringer voltage, and not the "Ring" as compared to Tip."

Thanks more.

Something that I learned many years ago: red, right, ring. The red wire should be on the right (looking at the jack) and it is the "ring".

Yes indeed, you may measure 100 Vac to ground into an open circuit when using a high impedance meter. It could be RF but most likely 60 Hz from the power lines. If it wasn't just noise, your bells would never stop ringing.

Try measuring it with a cheapie VOM which has a much lower impedance and you'll most likely find that voltage drops quite a bit. One of those inexpensive ($10) automotive test meters usually has a pretty low ohms/volt impedance.

With regard to which wire is the "ring", the DC battery voltage will be minus (-) on the ring and plus (+) on the tip.

Some phone companies offer Voicemail Message Waiting signals. That shows up as a series of short duration 108 Vac pulses which make a neon lamp flash. The duty cycle of the pulses is to short to cause the ringer to sound but will flash the neon lamp.