AC hum in transmitted signal

[KC8TCQ]

Ok I got a problem and I've about out of ideas.

I have used a longwire (150 ft) at my house for HF since I upgraded, never had any issues with any hum or noise on my signal. I took the antennas down last spring while the house was being remodeled, and never got around to putting them back up until recently. I purchased a "G5RV Lite" by Radiowavz at the Fort Wayne hamfest last month, I am limited to a shortened dipole inless I do a lot of bending of the wire.

I installed the antenna and it tunes great, recieves great. but I was talking to some of my friends on 80 and they all said I had what sounded like an AC hum on my signal. I have no flourescent lights, I checked all connections and they were tight. I even changed power supplies, and no change in condition. I brought my rig and tuner to the office and connected to the HF antenna here (Gap Titan DX) and has no noise issues.

Any thoughts?

[KC2UGV]

Do you have a solid electrical ground? Sounds like a bad ground somewhere.

[ad4mg]

I'd be suspicious of the power supply running the rig ... unlikely that an antenna change would create a hum on the transmitted signal. Sounds like a filtering issue in the PS, and the timing of the two events is likely a coincidence.

[KC8TCQ]

I tried a different power supply and still had the noise, and as for the grounding, I have the exact same setup I had before, just a different antenna. Maybe my other power supply has isses as well, it is about 12 years old. I'll grab one of the spare astrons from the EOC to lug home to compare.

[HUGH]

Assuming you can check your PSUs with a scope if it's on CW then a grounding problem, not necesssarily an equipment fault, otherwise it could be getting into the microphone.

[KC8TCQ]

Solved the problem, it was RF getting back into the shack, a home brew choke balun solved the problem. The antenna is working great.

[KC2UGV]

Solved the problem, it was RF getting back into the shack, a home brew choke balun solved the problem. The antenna is working great.

Excellent! I learned something here :)

[Currahee]

20 odd years ago I had an old 8 Amp Radio Shack power supply that powered a 20 watt 2M fm rig just fine. I got a 50 watt yeasu and everybody told me I had a bad hum on my signal. I could power it down to 15 watts and the hum went away. I think when I pushed the PS near its limit, the filter capacitor wasn't adequate to take it. I complained so much some one gave me a better (BIGGER) power supply! I still got the old one, although I use switching power supplies on everything now.

73,

Don

[kb2vxa]

More likely it had an active filter/regulator. When overloaded the supply voltage drops and as it approaches the output voltage the ripple is no longer absorbed by the pass transistor(s).

[w8nsi]

I'd be suspicious of the power supply running the rig ... unlikely that an antenna change would create a hum on the transmitted signal. Sounds like a filtering issue in the PS, and the timing of the two events is likely a coincidence.

Another possibility is a ground loop. Good grounding is a must. Radio, amp, tuner, any auxiliary gear such as an adapter between computer and rig for psk31, etc. Clip on ferrites are handy for all long leads between equipment too.