FM Transmitter FCC Rules & Regualations

[wftxlites]

One of the things I noticed this year is that it seems like my ss mega tree interfered with my radio transmitter. The range this year was significantly less and if the tree was running and the fm transmitter was not, I got a low frequency hum on the station I was using - 89.9 FM.

My range was still more than 4 houses in any direction...

RM

I also had this problem. Does anyone have a suggestion to eliminate the HUMM? Seemed to be coming from maybe the power supply or maybe it is data transmission thing? I'm not sure which.

Thanks,

Greg

[rrowan]

Did you try to lower the volume on your computer? That is normally the first cause of hum with a transmitter being over driven by the sound card.

Rick R.

[rm357]

My hum was only when the fm transmitter was off.

To combat hums and buzzes in any sound related system:
- try to keep all items connected to the same power phase. Same power strip is even better.
- use good quality cables
- try to make sure none of the volume settings are too low or too high. Noise is usually introduced at a constant level at every stage in any system. If the volume setting is too low at any point in the chain, that provides an opportunity for the signal to noise ratio to lean more towards the noise - which will be amplified in later gain stages. Also, Most amps get noisy if pushed past 80%.

RM

[wftxlites]

Did you try to lower the volume on your computer? That is normally the first cause of hum with a transmitter being over driven by the sound card.

Rick R.

Yes, also my radio xmtr has a incoming volume control. I have tried all kinds of things: power on the same strip and off. I even used shield audio cable and grounding. I never could get rid of the humming. I guess I will do more experimenting this year. If it turns out that it is the computer  then I will use an optical isolator. If it is coming from the smart string hub then I'll try putting it in a all metal enclosure, etc etc etc...

I was just hoping someone else saw this and had an easy solution.

Thanks, as always.

Greg

[Timon]

Hum normally comes from two main sources. One is a bad power supply and the other is ground loops. If it's a power supply the hum will stick around even with you disconnect the source. If it's a ground loop the simple fix is to run balanced connections or transformer couple unbalanced ones between the source and the transmitter. There can be other reasons but this is a good place to start.

In college I worked the radio station. We rewired the entire studio with all sources having balanced inputs and outputs. When done the hum was so far down that you had to really crank up the gain to hear just a faint hum.

BTW, my plan for my transmitter will be to place it in a water proof enclosure and have it either in the Mega Tree or on the side of the house. That way if an issue came up I could just tell the FCC inspector well there it is and that way I never have to worry about them wanting to come in. Also by having it very close to the street I don't need much power to get the job done. My other issue is that I have to protect my Amateur Radio license so I have to make sure that any unlicensed transmitter will pass FCC muster. If that means I need a field strength meter to stay legal then I have to get one.