Advice needed: persistent audio hum

[mndflmr]

Hi all,
I have a problem with audio hum in a satellite TV system that I have
installed at my parent's house. It sounds like 60 cycle hum to me.
Recently I had similar troubles at my own house when I tried to
transfer some cartoons from my laptop to a DVD burner. I managed to
eliminate the hum by plugging my laptop into a three-prong adapter,
thereby eliminating the ground. I have attempted a similar fix at my
folk's place and it didn't help. Here is a rundown of the setup (I
apologize this is so long; I don't want to miss something important):

The setup is basically two separate systems, one at each end of the
house. At one end there are two DBS dishes (receiving our local
channels requires the 2nd dish), a 2:1 switch, an amplified off-air
antenna, a 2:1 splitter, a satellite receiver, a VCR, and a 900 MHz
A/V transmitter.

At the other end of the house there is a 900 MHz receiver, a UHF RF
modulator, and a Ward Signature 25" color TV. This television has a
nice picture, but it has no RCA inputs and it is unable to tune in
channels 2 thru 6, due to an issue with the tuner. This is why I used
the UHF modulator, which I had laying around.

The signal comes into the house, through the receiver, the VCR, the
900 MHz xmitter, the 900 MHz rcvr, the UHF modulator, out to the RF
input on the television. This setup allows my parents to view the
satellite, off-air signals, the VCR, and allows recording of satellite
and off-air programming.

Also important to note: This is a rural property, and the house power
is supplied by a generator.

In my attempts to eliminate the hum I have tried the following:
I have bypassed the house ground by plugging the power strips at both
ends of the house into three-pronged adapters. No luck.

I have disconnected the coax input to the satellite receiver. The
receiver then defaults to an ACQUIRING SIGNAL message. The hum is
still present.

I have tried tuning the UHF modulator to different channels. No luck.

I am at a loss. It seems to me that I have eliminated the possibility
of a ground loop (by bypassing the house ground at both ends). I also
eliminated the possibility of hum induced on the coax (unplugging the
coax input to the receiver).

Please offer advice. Any help would be most welcome!

Joe

 

[Jerry G.]

The only thing I can think of, is one of the units in line has a defective
power supply, or there is a phase difference between the power from one end
of the house to the other, which is very possible.

When you use the AC power to the devices, the outlets in one end of the
house may be on the opposite side of the buss in the power distribution box
where the breakers are. Many homes use a split input from a tapped
transformer that is outside of the house.This is a 3 phase type of power
feed. If you are in North America, and have 220 Volt heating and a 220 Volt
stove, they get this type of voltage by using the opposite sides of the
power buss in relation to each other. They split this to get the 110 ~ 120
Volts to run the standard appliances.

You can do a test for this by running in a long extension cord from one end
of the house to the other, and make sure that all the devices being used are
from the same power source. If this works, then my information here is
correct for your case.

 

[ezwizzard]

The only thing I can think of, is one of the units in line has a defective
power supply, or there is a phase difference between the power from one end
of the house to the other, which is very possible.

When you use the AC power to the devices, the outlets in one end of the
house may be on the opposite side of the buss in the power distribution box
where the breakers are. Many homes use a split input from a tapped
transformer that is outside of the house.This is a 3 phase type of power
feed. If you are in North America, and have 220 Volt heating and a 220 Volt
stove, they get this type of voltage by using the opposite sides of the
power buss in relation to each other. They split this to get the 110 ~ 120
Volts to run the standard appliances.

You can do a test for this by running in a long extension cord from one end
of the house to the other, and make sure that all the devices being used are
from the same power source. If this works, then my information here is
correct for your case.

Hi, it sounds like the noise is being generated by the generator,so
you need a EMI filter, you can get this at any hardware store. This
same thing happens when people install a CB radio in the car,they get
the same effect from the altenator.

 

[Glenn Gundlach]

The only thing I can think of, is one of the units in line has a defective
power supply, or there is a phase difference between the power from one end
of the house to the other, which is very possible.

When you use the AC power to the devices, the outlets in one end of the
house may be on the opposite side of the buss in the power distribution box
where the breakers are. Many homes use a split input from a tapped
transformer that is outside of the house.This is a 3 phase type of power
feed. If you are in North America, and have 220 Volt heating and a 220 Volt
stove, they get this type of voltage by using the opposite sides of the
power buss in relation to each other. They split this to get the 110 ~ 120
Volts to run the standard appliances.

You can do a test for this by running in a long extension cord from one end
of the house to the other, and make sure that all the devices being used are
from the same power source. If this works, then my information here is
correct for your case.

I'll buy everything you say except the 3 phase power. I believe you're
referring to 'split phase' which is a center tapped 240 volt feed with
the center being the neutral. This gives you the 120 volt feeds with
some being on the opposite half of the transformer. The 240 units use
the 2 hot feeds. Ihave never run into an average residence using true
3 phase power. 3 phase is used for large loads, usually commercial
establishments.

Your neighbors house MIGHT be on a different pair of phases such that
house one is 120 degrees different from house two. Running connections
betweeen the two buildings would very likely have hum issues.

gg

 

[mndflmr]

You all have given me food for thought. I will try the extension cord
first, then the filter if this doesn't work. It make be a week or two
before I get back up to the property, but I am looking forward to
trying these things. Thanks guys.
Joe