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 Post subject: Success With Talking House Hum
PostPosted: Jan Wed 07, 2015 6:14 pm 
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Joined: Nov Wed 12, 2014 9:35 pm
Posts: 1034
Location: Ann Arbor, Michigan 48108
I bought a couple Talking House units on Ebay. I wanted to be able to rebroadcast a couple Internet streaming programs and be able to listen on my AM vintage radios.

They seem to work great. The range was easily throughout my house. I stream the programs through a couple old cellphones connected to the TuneIn radio internet app through WiFi in the house. The drive the LINE INPUT audio on the Talking House units. I keep the cellphones powered by USB wallwarts.

Audio bandwidth is adequate for me, but the programs are all talk radio. I don't need bass to make music sound good. It is all news and talk.

Once up and running, I did noticed the annoying 60 cycle hum on both signal. It wasn't a deal breaker, but it was annoying. From reading the posts on here on ARF about Talking House, I was sure that it has to be the power supplies that come with the units. So I constructed a battery power pack using two 9v batteries in series to get 18V, and then those in parallel to give me a little more current capacity.

It made NO difference. The hum on the signals was the same.

My solution came by experimenting with two things: (1) Selection of the AM frequency and location of the Talking House units in my house. I found a place for each where now the hum has almost completely disappeared! Also, by moving down from the 1500-1700 part of the AM band to more around 700-900, that made an additional huge difference.

My only conclusion is that I found the right combination of location and frequency, and the hum is almost unnoticeble. I lucked out! Secondly, driving the LINE INPUT with as high a volume as possible from the cell phones helps too. I think it is unavoidable to pick up some hum from all the electrical activity in the house and the power lines running in the walls. It seems I was able to minimize it however.

Mark K8KZ


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 Post subject: Re: Success With Talking House Hum
PostPosted: Jun Wed 07, 2017 5:47 pm 
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Joined: Apr Mon 18, 2011 3:52 pm
Posts: 42
Location: United States
Mark- That hum can be maddening, I'm glad you were able to alleviate it. I can't explain it but I'd found that if I pressed on the audio input miniplug with my finger, the hum would go away- only to return when I let go and walked away. I thought if might have been a bad ground but it's not. Besides, the audio source is floating with relation to ground anyway. Grrr...

What were the characteristics of the spaces you found within your house to minimize the hum? Did you place it away from walls with power lines, or outside walls? A certain way you deployed the antenna? What was the magic combination in your case?

Thanks!


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 Post subject: Re: Success With Talking House Hum
PostPosted: Jun Sun 11, 2017 12:01 am 
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Joined: Dec Mon 20, 2010 5:14 pm
Posts: 583
Location: Central Pennsylvania
I don't have a talking house but I had the same problem at work measuring phase noise of 100 MHz crystal oscillators. The phase noise measurements were strongly contaminated with 60Hz and higher harmonics.

Battery power supplies had no effect but small changes in equipment location and cable length had huge effects. How can changing from a 12inch long bnc cable to a 20 inch long bnc cable affect 60 Hz noise?

It turns out what was happening in my phase noise measurement set-up and what i feel sure is happening in all these talking house and other AM broadcaster hum problems is the radio frequency energy from the transmitter is getting onto the house power 60 Hz electrical lines. If that is all that happens, then no problem. But if a substantial amout of RF gets into a line powered electronic device having an internal rectifier to create a DC supply from an AC input current, the rectifier diodes driving into and out of conduction at a 60 Hz rate will amplitude modulate the stray RF thereby creating 60 Hz ( and higher harmonic) sidebands. This 60 Hz modulated signal is then re-radiated to be received as 60 Hz hum.

Notice the 60 Hz hum is not created by the transmitter so battery and voltage regulated power supplies and sheilding and isolation transformers between the transmitter and the audio source have no effect.

Moving the transmitter location changes the amount of RF coupled to the AC line as well as its distribution.

Every line powered device in the house is a potential hum generator.

A RF de-coupling capacitor across the rectifier kills the hum. RF chokes in line cords - whihc can be implemented by wrapping excess line cord length over a high mu ferrite or iron core rod or toroid might work as well.

I suggest getting a 120vac line cord plug, connecting a rf bypass capacitor of suitable value with sufficient voltage rating across the plug terminals and then plugging in this in various ac house outlets. You might also try connecting the bypass cap from line and from neutral to ground however you must not use excessively large capacitance values as to prevent overly large leakage currents.

Installing by-pass capacitors in the house utility breaker box might be useful but I have no idea how local electrical codes deal with that. Years ago I had a bad hum problem with a radio shack 49 MHz cordless phone and the breaker box bypass caps almost completely fixed that problem.

So good luck.

Don't fool with the house wireling if you are unable to do it safely.

bruce


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 Post subject: Re: Success With Talking House Hum
PostPosted: Sep Fri 22, 2017 5:52 am 
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Joined: Jul Sat 23, 2011 9:33 pm
Posts: 789
Location: Long Beach Ms. USA 39560
Several years or decades ago I saw a report of someone trying this plug-in bypassing.
"If .01 microfarad is good then 20 microfarad must be a lot better."
The explosion hurt him.
(This is being posted for someone just discovering electronics).

_________________
Pat W5THT
Unhappy tubes blush while unhappy power FETs scatter plastic


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