I haven't been around for a few years. A while back, I sold my SSTRAN transmitter that I had outside with a homemade base-loaded antenna. I used to get about one mile with that.
Now that I am in a new place, I got out my second SSTRAN transmitter, which I kept. Initially, I want to just use it indoors, for my own listening enjoyment. For now, I'm using the wire antenna/ground included with the SSTRAN.
The problem is, I have hum on the receiver end. The hum is definitely being transmitted, as it goes away with the transmitter off. Also, the hum is present when listening on a vehicle radio.
To eliminate potential sources of hum, I removed the audio input cable. The hum is still there. I next powered the SSTRAN from batteries (24 VDC). That didn't help either.
Then I started turning off circuit breakers. The hum diminished when the bedroom went dark. It seems that my cell phone charger is generating quite a bit of hum.
With that source eliminated, I still had a fair bit of hum. Turning off other circuits didn't improve things. One thing that did decrease the remaining hum was turning on the dining room light. Some hum is still there, however.
I'm at a loss as to what to try next. The dining room light thing is baffling. Any suggestions (other than taking the transmitter outdoors)?
Joe
Please describe how you have the antenna and ground arranged... for example, is the white antenna wire vertical?
Is it near a wall?
Perhaps there is an AC wire inside the wall near the antenna, in which case the antenna would pick up AC noise from that wire-in-the-wall. Try moving a few feet in a different direction.
Is the black wire attached to a ground, or perhaps laid horizontal along the baseboard?
If the black ground wire is laid horizontal along the baseboard it creates an "out-of-balance" situation and may be contributing to the hum.
Add a second ground wire that can be laid horizontal along the baseboard in the opossite direction, make both black ground wires the same length. That will give you a ground plane and might help the hum situation.
Adding toroid RF chokes on the wires connected to the cell-phone charger might keep that from putting hum into the AC wiring. Those toroids are inexpensive from Radio Shack.
Also make sure your setup is not close to any light dimmers. They emit a lot of electro magnetic interference.
Andre
Can you describe the hum in a bit more detail? In other words is it a soft tone or a harsh buzz? This might give us a clue. Also, can you tell if it is 60 Hz or 120 Hz? With practice I learned to tell this frequency and it helps determine the source. 120 Hz hum is most likely produced by the internal electronics of the transmitter or receiver.
The SSTRAN AMT-3000 has internal inductors which can be set to isolate the power and circuit ground from RF coming in the lines. Check the jumper settings according to the manual and try the transmitter with the inductors in and out of the circuit. NOTE that these are not the inductors which are selected with switches and are used for antenna tuning.
Some brands of light dimmers emit RF hum even when turned off. Your idea of turning off the breakers is a good process to find this. Turning the breakers off one at a time may not eliminate these as a source if there is more than one dimmer and they are on different circuits.
In general you need to find if the hum is coming from the transmitter itself or from some other electrical/electronic source nearby. Since the hum is still there when operating with a battery it seems the power supply and transmitter are not at fault. But the hum could be coming from the audio source. Try this again with the audio disconnected. If there is still hum then it is coming from something other than the transmitter and audio source.
About the only thing left would be to change the location of the transmitter and the antenna.
Neil
Let me offer a ray of hope by telling you that the AMT3000 (and 5000) is able to perform perfectly without any hum at all, and so do not give up hope and keep experimenting based on the suggestions that have been given.
I have one of each of the SSTran transmitters running indoors and they are perfectly hum free.
As a matter of fact I just tracked down and solved a hum problem with one of them when I added a new piece of audio equipment in the chain. The solution was to wrap the audio cable several turns through a square toroid assembly from Radio Shack.
The worst case of hum I ever had was while running our member-designed shortwave transmitter with an indoor dipole antenna. But the situation was not the same as with the AMT3000, but my point is that hum can happen with any transmitter/antenna, including the large licensed facilities.
I found the culprit(s). The reason turning off circuit breakers didn't get rid of all the hum is because I had multiple sources. When I flipped the main breaker off, I had no hum at all. As to why turning lights on/off changed the hum level, I don't know.
The guilty parties were the cellphone charger, Roku supply, laptop charger and the AC adapter supplied with the SSTRAN. The AC adapter makes no sense, as I've used it before (elsewhere) with no hum.
Due to some other electrical issues, I'm thinking that there is a problem with the wiring in this house that is making my hum problem worse than it should be.
Powering the SSTRAN from another supply is no problem. The laptop is another issue. I'll see if I can find another Dell supply that doesn't cause hum. Alternately, I could remove the laptop battery and power the laptop from a clean DC supply.
I did try wrapping the various power cords through ferrites (I have several snap on types). This had no effect on the hum.
Joe
Install an isolation transformer between your computer and the Xmtr. Could be a ground loop thing..
I also tried powering the SSTRAN from batteries, as mentioned earlier. I also disconnected the audio lines at one point. These steps would eliminate any ground loops.
The hum I'm getting is definitely being induced into the audio section of the SSTRAN and being transmitted out.
I'm going to ask an electrician to take a look at the electrical service panel to see if anything is amiss there. I'm also going to try a "good" surge strip, like an APC brand that has real filter components in it. This may keep the junk from the power supply from getting back into the AC wiring.
I'll report any progress.
mojoe,
What you have already found is interesting. Things have become very complex and unpredictable in regards to RF interference in the past few years with the advent of all the electronics and their switching power systems.
By all means, report back when you finally solve the problem so we all can learn from your experience.
Neil
I just tried plugging the laptop adapter (the worst offender) into a Tripp Lite Isobar. This Isobar has four pairs of outlets. Each pair has an LC filter and the filters are additive. So, pair #4 has the most filtering.
With the laptop adapter plugged into pair #4, the hum that the SSTRAN is picking up is reduced, but not gone. Moving the adapter to pair #1 increases the hum. This proves to me that the hum is being injected into the AC wiring and the wiring is acting like an antenna, which is causing the unshielded SSTRAN to pick it up and re-transmit it on frequency.
All this makes sense, but I am still not convinced that there isn't something wrong with the wiring in this house. Perhaps a bad ground connection? I have never had this type of hum problem elsewhere, using many different types of power adapters and other equipment.
The electrician is supposed to come by this weekend. Hopefully he will find the problem.
Joe
I was using a D.C./D.C. converter (12 to 18.5 volt) to operate my projection TV system and it wiped out everything! I tried filtering, shielding, anything to help but.. I ended up engineering another analog supply..
Don't discount the computer. I do 2-way radio and we find subcarriers on our service monitors made by computers. Flat monitors make junk too..