Hum in the transmitted signals of Part 15 transmitters is an eternal subject that we will always have as long as there is a part15.us.
I just re-read the whole thread, and in particular noticed PhilB's mention that perticular electric appliances can contribute noise and this is all too true.
I have an LED lightbulb that puts so much noise from 600 kHz on down to 100 kHz that it looks like a Geiger Counter during a nuclear event (on my spectrum analyzer). Yet two other similar bulbs work fine.
There is a CFL (compact-flouriscent-light) bulb which puts hum on some AC wiring but not all, and the same with a toaster oven.
The heaviest hum attack I ever experienced was when the Big Talker Shortwave Transmitter was in test mode with a 17-foot dipole strung through the house. All indoor radios picked up loud buzz, but it wasn't heard outdoors on 13.560 MHz. I also picked up shortwave transmissions on my wireless mic receiver on 184.3 MHz, but this was solved with a toroid filter added to the power wire of the wireless receiver.
I'm very late on this thread, but the PS is where I'd go first to eliminate that possibility. PS' are infamous for producing hum. There's really no such thing as perfect isolation, nor, for that matter, a perfect ground, but a top-notch isolating transformer has solved many a hum ptoblem. Also I'd make sure the audio production gear and the TX are on the same circuit. If they're plugged into different recepticles, the difference can produce a potential voltage across the chassis'.
One other thing....check the frequency of the hum. You can sweep with an equalizer with Q peak narrowing to find it. If it's 60 Hz, you probably have a ground loop. If it's not, then it could be a proximity induction from a transformer, or some other piece of gear, tho' it looks like you've dealt with most of that.
Ken you are late to the dance. He tested the transmitter on battery power.
Something to note: The power supply for the talking house is a source of grounding for the device. That power supply has a third conductor in it (it even says that it is a special power supply on the PS label)
In the Part15.US Library I found a hum-related thread with many useful links on the ground-trouble subject...
http://part15.us/content/why-does-my-transmitter-hum-0
Why does it hurt when I pee?
I suppose it depends upon what you are doing at the time. If trying to improve your ground conductivity perhaps you need turn off the transmitter first.
Just a follow up on the hum problems.
The “hum” as I called it consists of a buzzing noise and also some lower frequency hum type noise. The buzz part is like that created from a light dimmer but I made sure all of those were off, and all florescent lights were off.
The noise and hum vary in level around the house and will depend on what radio receiver I use and if it’s portable or plug in but all radios will have the noise or hum depending on how the antenna in the radio is orientated to the transmitting antenna.
I have three different antenna installations and three AM transmitters which can be connected to those antennas.
I did extensive trial and error “fixes” which all had results.
To start, I had one transmitter running at 1510 KHz and I was successful at clearing most of the hum on that transmitter/antenna combination by going around in the basement and running grounding straps across the hot and cold water pipes at two different locations. (I tested several locations, some made no difference some made a big difference)
I really don’t know why running ground straps across the pipes changed the hum level as the transmitters are grounded to a solid ground. I can only assume that it had something to do with the reducing the circulating currents of possible concentration of the transmitter radiated signal or the asorbution of the power line radiation. The pipes are copper and the main cold water pipe is a solid ground but apparently there is potential difference between pipes (grounds) and between different locations. I realize this is a common known factor when grounding.
After getting the 1510 system cleaned up, I thought I had had the problem taken care of. Then I turned on the 1680 kHz transmitter and its corresponding antenna. This system was always relatively quiet in regards to hum and noise but now after making the grounding changes to the 1510 system, the 1680 frequency (different transmitter and antenna) was full of noise and buzz. It was apparent that making the grounding changes for 1510 kHz system, now the grounding on 1680 kHz was messed up.
These changes only affected using the inside antennas.
I do have an outside antenna located outside my home but relatively close to the house. This antenna does give better hum and noise qualities but it’s not when the transmitters are fed from the AC outlets in the house. The best combination is outside antenna and battery power. (Or turning off the AC at the main breaker so the house has no power!) Then all hum and noise is gone.
To sum things up:
From my experiences, inside antennas for transmitting especially if the antenna is around house wiring in the attic may give you a lot of mixing of RF with power line radiation, and result in hum and buzz. I found in some cases makes the transmission useless. (Maybe if all the wiring was in conduit this would not be a problem)
I have also found that there are times without even changing anything in regards to grounding, the noise and hum will be at low levels and at times it is a total mess. This all depends on the time of day it may happen to be. I assume circuit loads on the power in the house and even on the power mains are a contributing factor. And as we all know the noise level and type of noise may change as to what appliance is on or even just plugged in, to some degree.
I spent a few days trying to get rid of the noise and had some success but found that with all the variables due to hourly and daily conditions it’s almost impossible to eliminate.
There are better alternatives to get rid of the noise. If you lower the power out of the antenna you have a much better chance to get a clean signal around the house, as during my testing, I have found the stronger the signal is the more it gets mixed up with the 60 HZ power line radaditon. Reducing the signal level is not something any of us would care to do but if anyone has this problem of hash and hum and buzz, and all you want is to get your program to your radio in the house, you may want to consider dropping the RF level with either an attuneuator or just detuning the loading coil.
This next solution is obvious but the best thing you can do is get the antenna as far as away from power lines and the building structure as possible.
After a few days spent working on this problem, I know now in my own case, which grounding straps to connect and disconnect in the house to get a better signal. (If the moon and stars line up right and all other factors are in my favor at that particular moment so all aspects of the physics involved are just right.)
I do want to thank all of you for providing your input, all was helpful and appreciated.
Radio Joe
Despite managing to get a hum-free system with two transmitters on two frequencies plus other transmitters acting as STLs (Studio-Transmitter-Links), I don't have a hum free system.
What did I just say?
Here's the stinger in this deal. It gets detailed but radio life is not always simple...
All the programming churning from my playlist gets sent to two main transmitters, AM3000 connected by hardwire to the computer, and AMT5000 receiving its audio from a Wi-Fi MCM device (no longer available).
In the Upper Management Lounge (kitchen) a Panasonic radio is my monitor for the many times when I'm in there messing with drinks and snacks, but the signal from the AM5000 overloads the radio, so I depend on the signal from the farther away AMT3000, but the RADIO hums! Why?
Because the power supply for the near-by Wi-Fi receiver puts a buzz on the very local wiring which gets right up to the radio. I've tried toroid filtering on the audio-line, the DC wire and the AC wire, but the hum doesn't care.
This to me is a project... get that hum, even if it costs everything.
The offending power supply is of course sealed up and not user servicable, but I want to surgerize and get inside where I can plan improvements.
Reverse engineering is a fundamental right.
I've been testing a Talking House II for three days now. The first day, the hum was unbearable, even outside. Yesterday and today I've noticed that if the music I play is at the right level, it drowns out the hum for the most part until there's a couple of seconds between songs or during my liners/ID's/live reads. Don't worry, that hum will be completely gone as soon as I get my hands on a Behringer HD400 so I can patch it between the laptop and the THII. Is there anything else I can do in the meantime to drown out the hum besides having high enough music levels?
A couple things:
1) I have read that if your home has aluminum wiring those homes are notorious for inducing hum. Many homes built in the 70s have such wiring.
2) A couple years ago a friend who was mentoring me on the subject of restoring antique radios recommended this device to prevent any and all noise ingressing from the power line. He was very knowledgeable, a true "rocket scientist" with a PhD in engineering and retired from a career at NASA so I have tremendous respect for him. He recommended this:
Now that said, if your hum is ingressing wirelessly, this won't help with that. However, I run both my Procaster and the PC that serves my content on this box.
I don't have a the Spitfire AM transmitter anymore, got rid of it quite a while ago when I realized I wasn't going to go AM in the forseeable future and didn't know at the time that a transmitter just "meeting the rules" couldn't be used here(Canada) and don't have the facilities for a proper install.
But the humming problem....It's the a/c wiring and 60hz electromagnetic field surrounding you in the house and picked up by the 10 ft antenna and the transmitter so it's getting modulated on the carrier. This doesn't happen with FM.
Mark
Druid Hills said: "Why does it hurt when I pee?"
Stop peeing on the electric fence!