Radio Scientists:
I have a question that some of you may have some experience with. I have a short horizontal antenna in my attic which I have loaded with a variable loading coil.
This antenna is feed by a RG 59 coax from the basement. The antenna tunes very well and I get very good range. The problem is the amount of hum I get on the radios in the house when listening.
The hum is also present but to a lesser degree some distance from the house, but it is still there if you turn up the volume, more than what I would like to see.
I have tried all sorts of polarizations of the long wire antenna including moving it to different parts of the attic and running it along the rafters up and down (semi vertical) and horizontal along the part where the rafters join together at the peak of the roof. I also tried running the antenna wire up and down in from the top of the roof to the ceiling joists and back up to get a vertical pattern. I was trying to get the least amount of coupling between the house wiring and the antenna
My loading coil at the coax end is grounded in the attic. I have also tried different ground routes which all connect to a copper pipe in the attic which connect to the cold water main pipe. I checked it out with an ohm meter to make sure the pipe is connected to a solid ground.
I use the standard Talking House power supply. I have also tried to isolate the hum by using a 12 volt battery and that made no difference so it’s not a power supply issue.
I have tried ground loop isolators on all sources and even made a dummy grounding plug which I used on the input of the TH5 Aux input, to make sure the hum was not originating from any attached gear.
Using the grounding plug on the input of the TH 5 AUX input made no difference the hum was still there on dead carrier.
I went up in the attic and tried all sorts of antenna variations and configurations.
Nothing really made a significant difference.
To test further I turned the transmitter on and used a 12 volt battery to power it, so I didn’t need to rely on AC power to power the transmitter and had no connection to the house wiring. I didn’t apply any audio to the transmitter because I wanted to test hum levels.
I then set up a battery powered portable radio near the circuit breaker box where I was going to turn breakers on and off. With the radio on and tuned to the TH5, I took one breaker at a time and switched off, I went through the entire panel till I got to the last breaker. As I went thought the process sometimes turning a breaker off made the hum less some time more.
The next test I did was pulled the main disconnect on the breaker box to turn everything off at once… ok finally no trace of hum in the carrier, so with all power disconnected to my house and no AC flowing in the wiring there was no hum, just a perfect carrier on the radio. I had to pull the main disconnect to get a clean carrier, with all breakers off, I still got some hum but pulling the main switch, all hum was gone.
Personally I feel since there is a lot of electrical wiring in the attic that the RF is mixing with the magnetic fields of the 110 volt power lines.
If this is true and anyone can explain to me how this happens I would appreciate it!
I think the only real answer is to this is an outside antenna mounted a distance from the house. I do have an outside antenna now on one of my AM transmitters and that is much more hum free, that transmitter I run off batteries when I use it but wanted this other transmitter for general purpose use, like I said everything is good but the darn hum.
My knees are worn out from moving around on the rafters, I tried every possible antenna configuration. The test with the breaker box confirms my beliefs that on this one there is not much of a way out but turn off all the power in my house I suppose if I want a pure signal! Bit of overkill but at least it was nice to hear that absolutely clear carrier. Any help anyone can come up with I would appreciate it!
Sad Radio Joe