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 Post subject: Transmitters, how do you fix hum and noise?
PostPosted: Sep Mon 24, 2018 4:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3903
Location: Cortez, Colorado
I have 6 transmitters: a SStran 3000 outside on a base loaded antenna, a 6888 inside, a pair of 6GY6s in one cabinet, a LM386 inside, and the ebay Japanese transmitter. All of the inside transmitters use a antenna matching network of a toroidal coil and a air variable capacitor, with about 10 feet of antenna wire. All of them tended to work well with radios near them; radios farther away would have hiss, buzz or hum. And all the inside transmitters used the ground at the outlet for the antenna ground.

I wanted them all have longer range and be quieter, so I dug up the house's ground rod and bought some 10 gauge wire to attach to the transmitters. I've always had a tough time getting the Japanese transmitter to tune, it seemed to get an oscillation in it, just when you thought it was tuned. When I attached the ground to it, it got a slight bit more range, but didn't sound any better just kinda noisy.

Next I got the 2 6GY6 transmitters and moved them to the other side of the house, near the ground and tried them out. They sounded awful, lots of hum and buzz. The hum was coming from a Magic jack USB adaptor. After removing that and unplugging everything else, one transmitter is slightly noisy, the other has a hum. Attaching the house ground did remove a tiny bit of hum. I swapped the 6GY6s and that didn't fix it. Of course the lights in the house are almost all LED and really effect the American radios. I tried installing a line filter, but it did nothing.

How do you get clean enough AC to run a transmitter?


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Mon 24, 2018 5:00 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 120
Try using a laptop adapter to power the transmitter. Bring the voltage down with 7812 regulator. Test it on one of your solid state transmitters. The laptop charger outputs 19V. Let me know if the hum disappears.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Mon 24, 2018 5:17 pm 
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Joined: Apr Thu 14, 2016 8:25 pm
Posts: 403
Location: pensacola fl
Do you have a lead acid battery of the kind used in battery backups? If so use the battery (12v) to run your sstran where it is and see what you get. If the hum stays up get a portable radio and recheck on it. Hum still there? If so go to your breaker panel and start turning off breakers and leave them off until either you run out of breakers or you find the one with the noise on it. You may have to go out to your meter outside as you may have some breakers out side with the main switch. Turn it off as well if it goes quiet with all breakers off then turn on main . If it gets noisy at this point then the noise is riding on the power line. Otherwise start each circuit and monitor until you fine the noisy circuit and then you can track it down from there.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Mon 24, 2018 7:15 pm 
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Location, location, location. Of the antenna, at least that's how I fixed mine.

You're likely bleeding RF into the house wiring, radio in turn receives it as 60 cycle modulated signal. Often somewhat dependant on AC load. The LM386 I have connected to cable box has the antenna placed somewhat haphazardly, hum can be noticed on dead carrier & low modulation levels. When wife uses dryer, hum approx doubles. I don't generally use this Tx more than once a week, maybe one day I'll be more concerned.

Main transmitter is in my garage, approx 100 ft behind house. At one time I had moderate hum if it rained, also if if lights were on in garage. Probably two years ago I ran a horizontal antenna pointed in direction of house, away from wiring, hum is 99% gone rain or shine. Transmitter of choice is my 9KC6(chassis standing on end on top my 2236 Tek scope), but I've tried the 6888 & 6GY6, none had hum using this antenna. .

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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Tue 25, 2018 1:38 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3903
Location: Cortez, Colorado
The Japanese transmitter is battery powered, I have 4-18650 lithium cells powering a 12 volt DC-DC convertor. The convertor is almost silent, but I get a lot of noise when it's charging from 12am to 3am. The 386 transmitter is near to (12 feet away from) a RCA 811K and they work great together. All other transmitters put hum on the 811K, and other radios farther way from the 386 get hum from the 386.

I can put both of the 6GK6s antennas horizontal under the deck and see how they work away from AC.

I was really surprised that the Magic Jack adaptor put out so much hum. On Saturday I used a 12 volt battery to power the Thai transmitter and it had so much hum I couldn't hear the audio. The Thai transmitter is number 7, but I don't use it, because when I tried to tune the antenna the frequency shifted, it's not crystal controlled.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Tue 25, 2018 2:43 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3903
Location: Cortez, Colorado
I just refound Mike Toon's Minimal Build AM Transmitter, Muntzed
I have most of the parts, except another oscillator. I did find another 5V oscillator at Arrow, a 1.544Mhz https://www.arrow.com/en/products/sg-53 ... cs-america


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Tue 25, 2018 3:10 am 
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Location: Beautiful Downtown Burbank CA
Tin Omen wrote:
I just refound Mike Toon's Minimal Build AM Transmitter, Muntzed
I have most of the parts, except another oscillator. I did find another 5V oscillator at Arrow, a 1.544Mhz https://www.arrow.com/en/products/sg-53 ... cs-america


It is dead quiet sitting atop a `58 Zenith console. I hit pause with the mp3 remote and I get dead silence.

Just tried it again to make sure!


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Tue 25, 2018 3:31 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3903
Location: Cortez, Colorado
Ima have to make a loop to go with it to cover the house.

I have 7 of the MP3 players, except with the display, and 4 of the LM386 amplifiers.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Tue 25, 2018 4:39 am 
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Posts: 13068
I have a supply of 1.54 osc, lemme kno...

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Tom


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Tue 25, 2018 5:44 am 
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Location: SoCal, 91387
35Z5 wrote:
Location, location, location. Of the antenna, at least that's how I fixed mine.


This, exactly.

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\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Thu 27, 2018 4:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3903
Location: Cortez, Colorado
I moved the antennas from a vertical mount on the side of the house to horizontal, under the deck, and that cleaned up almost all of the hum and buzz. 1.344Mhz still has a whine on it. 1.344Mhz is one of two identical 6GY6 transmitters, I swapped the oscillator and tubes at different times and found that the whine follows the frequency. I think I can plug in the 1.2288Mhz and see if that fixes it.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Thu 27, 2018 5:24 pm 
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Joined: Apr Thu 14, 2016 8:25 pm
Posts: 403
Location: pensacola fl
The whine is probably heterodyne from a carrier at 1350 which would be 6KHZ. The 1350 station doesn't have to be very strong at your location to produce this.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Fri 28, 2018 10:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3903
Location: Cortez, Colorado
I found that if I slightly detune the antenna, that it reduces the audible whine.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Fri 28, 2018 10:41 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2200
Location: Saskatoon
The only hum problem that I've ever had with my transmitters has been due to hum modulation from the RF getting into the house wiring. I added line bypass capacitors in the transmitter power supply and the problem completely disappeared. So you might want to consider that.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Sat 29, 2018 3:46 pm 
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Posts: 8187
Location: Beaver Falls, PA. USA
Your transmitter MUST be on an even numbered frequency, or you will get hetrodynes from the carriers of any other station on that frequency.

Grounding my transmitter killed most of the hum. I still get a little on radios which do not use a loop antenna. Another big source of hum is light dimmers. Touch control lamps and motion sensor lamps are also big offenders; the triac switches radiate a buzz, right up through the AM band and beyond.

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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Sat 29, 2018 4:25 pm 
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Posts: 13068
Unless there's a 1350 within 30-40 miles, at 1344 I would not think heterodyning would be a issue. Still I was never able to use that freq as we have a local 1350.

Tuned to 1440 I was receiving a small amount at night from my 9KC6 Tx. Bumped it to 1445, now totally silent.

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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Sat 29, 2018 9:29 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3903
Location: Cortez, Colorado
I did replace the 1.3344MHz oscillator with a 1.2288MHz and no whining. Can I get one of these 4 pin 5 volt oscillators to move 5-10 KHz?

Removing that Magic Jack USB power supply did wonders, not only did it remove 90% of the hum in the transmitters, but it also fixed the hum in a battery powered transmitter, and in a nearby Philco 38-7 that only would be hum free if I grounded the antenna.


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 Post subject: Re: Transmitters, how do you fix hum and noise?
PostPosted: Sep Sun 30, 2018 5:30 pm 
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Joined: Apr Thu 14, 2016 8:25 pm
Posts: 403
Location: pensacola fl
You would be surprised at how low a signal 6KHZ off of your own will produce a beat note in a receiver. Case in point, a strong oscillator + a weak carrier is how we receive CW. Many of today's AM radios have a very narrow passband down near 3 KHZ but may pass in the skirt the signal 6 KHZ off. Older AM radios had a wider bandwidth of around 5 KHZ and would easily let that 6KHZ off signal through to the detector. I suggest trying a LC trap placed as close as possible to the radio's antenna and see as you tune the trap capacitor if the tone goes down in volume. All you need is the antenna coil from a radio with it's variable capacitor.


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