Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Jul Sat 11, 2020 6:19 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 194 posts ]  Go to page Previous  1 ... 5, 6, 7, 8, 9, 10  Next
Author Message
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 2:00 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 194
Tube Radio wrote:
Try feeding the signal in at U301B.


Wouldn't that require a stronger line input? I have my wife's laptop headphone output at 50%, so maybe 80-90% would be enough without the preamp. I might try bypassing it later today.

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 2:54 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 20612
Location: Warner Robins, GA
It may require a stronger signal.

That could be taken care of by getting the 15K to 15K version of the Edcor WSM series transformer and using 1/2 the primary and the full secondary. Plus it provides the necessary RF isolation between the source and transmitter.


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 5:23 pm 
Member

Joined: May Thu 04, 2017 1:08 pm
Posts: 361
Location: Raleigh, NC area
Regarding the source of the noise... I've been doing more reading about this. Yes, it is "because" of the TH. But indirectly. The TH is putting its signal onto the AC wires in the house, and those are re-radiating it, along with the hum.

I confess I don't seem to understand that mechanism very well, even though I passed the ham radio exams (!) I guess the unmodulated carrier from the TH is what gets onto the wires, and the AC current in the wires is providing modulation of the carrier, which we hear as hum on our radios. I would have thought that the TH antenna itself would be the "best" antenna in this equation, but apparently not.

Assuming the majority of the noise comes from the vertically-run wiring in a typical house, the electric field is vertically polarized. The magnetic field will therefore be horizontally polarized. Ferrite rods in portable radios respond to to the magnetic component of the EM wave. In my portable radio (Channel Master Super Fringe), the ferrite bar is horizontal, along the long axis of the radio. So when I look at the speaker and the controls on the front, I would be looking at the rod antenna broadside. That orientation is the best for picking up the horizontally-polarized magnetic field, being radiated from the electrical wires in the walls.

Back over at the TH, I have the antenna wire oriented horizontally. That is to attempt to minimize the amount of transmitted signal which is picked up by the vertical AC wiring. Clearly, even with this orientation, the hum level (at least in my house) is intolerable.

Really, what we want to do is maximize the signal received from the TH antenna, and minimize the signal received from the house wiring. I don't know how to do that. Perhaps, it would come from decreasing the amplitude of the TH carrier, which we know from measurements made by another ARF member, to be actually pretty high. I decided to check that.

It is not snowy here, but to me, it is cold at only 43 degrees. I took the portable radio outside, some 200 feet from the house, and could still hear the recorded message...and the hum. The signal faded away when I oriented the radio vertically, which should have broadside to the magnetic field of the horizontal TH antenna. The TH is doing a good job of infecting the AC wiring in the house, and I don't need to be able to hear that signal 200 feet or more away!

I expect that any transmitter would have a similar problem, depending somewhat on how well it was able to get its carrier onto the house wiring. The TH probably has other issues with the component choices, layout, grounding, etc., but I suspect my house wiring is the biggest component here.


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 5:35 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 20612
Location: Warner Robins, GA
If you're using the original power supply try putting a disc capacitor across the diode in the power supply.


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 6:26 pm 
Member

Joined: May Thu 04, 2017 1:08 pm
Posts: 361
Location: Raleigh, NC area
Tube Radio wrote:
If you're using the original power supply try putting a disc capacitor across the diode in the power supply.


Maybe that will work for someone else. In my case, I've already reported that I have identical hum, even using an 18V drill battery to power the TH.


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 7:05 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 194
DaveInNC wrote:
Tube Radio wrote:
If you're using the original power supply try putting a disc capacitor across the diode in the power supply.


Maybe that will work for someone else. In my case, I've already reported that I have identical hum, even using an 18V drill battery to power the TH.


My drill takes 20 volt batteries, which I decided not to try, since the TH reads about 15.8 volts under load. But I did decide to try a 12 volt battery. Believe it or not the TH works the same using a 12 volt battery as it does on the 18 V power supply. The volume received at my Sony is just as loud. I was thinking the carrier and/or modulation might be less, but I guess not. The Sony behaves exactly the same as with the 18 V supply. No noticeable hum/noise (in my case) aligned broadside to the TH. But, yes, lots of hum/noise, when the Sony is rotated, same as with the power supply.

When I say broadside, I mean I'm keeping the Sony vertical and orienting its horizontal antenna rod for maximum exposure to the TH antenna, which is vertical in my case. It's pretty obvious the hum isn't getting into the wiring or antenna through the power supply.

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 7:13 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 194
Another comment - if this hum is truly a 60 cycle hum, the TH antenna must be radiating its RF into the house wiring like Dave suspects. How else could it be a 60 cycle hum when running on a 12 V battery? Not even the TH's ground is connected to the house wiring.

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 7:54 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11578
Somewhere on net there is a article about a group setting up a college radio station. Weapon of choice was a Knight Broadcaster. Was stated it always had hum & they went so far as to power it using ten 12v car batteries, still hummed.

I've had good luck using horizontally strung antennas.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 10:14 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 35179
Location: SoCal, 91387
I think one very relevant aspect of the Talking House transmitters is the simple fact that they were designed to broadcast to car radios, which of course are nowhere near house wiring.

Try picking up the TH signal with your car radio, parked outside the garage, and see how it sounds.

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


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 10:35 pm 
Member
User avatar

Joined: Jun Sun 22, 2008 2:03 am
Posts: 908
Location: Burke, VA 22015
With the TH powered by a 4S Li-Po battery (14.4V), an audio source battery operated, a 40-inch telescopic vertical antenna, C348 removed, and 1.54MHz unmodulated carrier, the hum was pretty loud on an AC powered radio regardless on its orientation. The hum was less on a battery radio.

At 810kHz and 710kHz, the hum was also almost non-existent when the TH is AC powered and the AC radio was carefully oriented. The custom AC adapter has a lot of EMI filters inside, probably more effective at lower frequencies.

I took out my homemade transmitter which transmits an unmodulated RF at 1.536MHz. When powered by an AC adapter, the same kind of hum was heard on an AC powered radio. The hum was practically gone when the transmitter was battery powered whereas it didn't make any difference for the TH. My transmitter operates on the same principle as the TH. The difference is the antenna ground is isolated from the DC ground and connected to the top of a metal lamp post where the transmitter is mounted. The cable that supplies power and audio to the transmitter is inside the post. The metal post and telescopic antenna short of form a very short sleeve dipole.

I think that Dave was right. The RF somehow gets into the house wiring and modulated by the 60Hz AC.

_________________
Binh


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 10:59 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 194
fifties wrote:
I think one very relevant aspect of the Talking House transmitters is the simple fact that they were designed to broadcast to car radios, which of course are nowhere near house wiring.

Try picking up the TH signal with your car radio, parked outside the garage, and see how it sounds.

That's a good suggestion, especially since a car has a different type of antenna, more or less an omni-directional one. I had to pick my wife up, so I gave it a try. Unfortunately, it has substantial hum all the way out to about 200' when it looses the signal. With my Sony portable, I can orient the radio in such a way to eliminate the hum. There isn't any way to do that with a car radio.

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Sun 22, 2019 11:02 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 35179
Location: SoCal, 91387
moallen wrote:
fifties wrote:
I think one very relevant aspect of the Talking House transmitters is the simple fact that they were designed to broadcast to car radios, which of course are nowhere near house wiring.

Try picking up the TH signal with your car radio, parked outside the garage, and see how it sounds.

That's a good suggestion, especially since a car has a different type of antenna, more or less an omni-directional one. I had to pick my wife up, so I gave it a try. Unfortunately, it has substantial hum all the way out to about 200' when it looses the signal. With my Sony portable, I can orient the radio in such a way to eliminate the hum. There isn't any way to do that with a car radio.

It sounds then like the fault is with that particular transmitter. Have you modified it? I haven't read the entire thread.

I have two transmitters, an SSTrans, and a Transistor unit I bought off eBay; with either of them, orienting the receiving radio changes the reception AFA volume level and hum, so that's not unusual.

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


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Mon 23, 2019 12:53 am 
Member

Joined: May Thu 04, 2017 1:08 pm
Posts: 361
Location: Raleigh, NC area
fifties wrote:
I think one very relevant aspect of the Talking House transmitters is the simple fact that they were designed to broadcast to car radios, which of course are nowhere near house wiring.

Try picking up the TH signal with your car radio, parked outside the garage, and see how it sounds.

I also did this, in a post on this page. 200 feet away from the house, standing in the cul-de-sac, with the battery Channel Master. Plenty of loud hum.


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Mon 23, 2019 2:58 am 
Member
User avatar

Joined: Jun Sun 22, 2008 2:03 am
Posts: 908
Location: Burke, VA 22015
We have a teeny tiny transmitter with a hum problem and it doesn't seem we can find a way to resolve it. Wondering how the people who design a commercial transmitter half a million times more powerful manage to keep the RF out of the AC power line. Probably it's about time for me to call a quit since I don't have enough technical knowledge to continue

_________________
Binh


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Mon 23, 2019 4:46 am 
Member

Joined: May Thu 04, 2017 1:08 pm
Posts: 361
Location: Raleigh, NC area
Inverse square law. Power from an antenna falls off as the square of the distance.

Let's do a wierd calculation.

TH is supposed to be under 100mW, but someone (on ARF I believe it was) measured 400mW, while also measuring about 100mW from the SStran, using the same technique. (So I think the measurement could have been valid.) This TH antenna is maybe five feet from the closest electrical wire in my wall. Probably closer. Now let's start backing away, and see what power we need to get the same interfering signal power into the AC wiring:

50ft = 10x the distance, so 100x the power = 40W
500ft = 4000W
5000ft (or about a mile) = 400,000W

Are you within 1 mile of an AM station, broadcasting with 400kW of power? I doubt it. You'd probably have some hum. :wink:

Yeah, yeah, I know, antenna gain, efficiency, blah, blah. It makes a point though, I think...


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Mon 23, 2019 5:51 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 35179
Location: SoCal, 91387
DaveInNC wrote:
fifties wrote:
I think one very relevant aspect of the Talking House transmitters is the simple fact that they were designed to broadcast to car radios, which of course are nowhere near house wiring.

Try picking up the TH signal with your car radio, parked outside the garage, and see how it sounds.

I also did this, in a post on this page. 200 feet away from the house, standing in the cul-de-sac, with the battery Channel Master. Plenty of loud hum.

How did it sound when using your car radio?

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


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Mon 23, 2019 2:19 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 194
fifties wrote:
fifties wrote:
I think one very relevant aspect of the Talking House transmitters is the simple fact that they were designed to broadcast to car radios, which of course are nowhere near house wiring.

Try picking up the TH signal with your car radio, parked outside the garage, and see how it sounds.


How did it sound when using your car radio?

My TH was playing music from Pandora on the Internet using a ground loop isolator between the laptop and the TH's line input. I could hear the music just fine on my car radio. No garble or distortion, but frequency response seemed poor. I could also hear a low-frequency hum that I would estimate to be about 1/3 the level of the music. Had I been receiving on my portable radio, I could have oriented the antenna to nearly eliminate the hum, but no way to do that with a car radio.

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Mon 23, 2019 2:29 pm 
Member
User avatar

Joined: Jun Sun 22, 2008 2:03 am
Posts: 908
Location: Burke, VA 22015
DaveInNC wrote:
Are you within 1 mile of an AM station, broadcasting with 400kW of power? I doubt it. You'd probably have some hum.

Interesting, never thought about that. Likely I won't have a chance to test that theory because 50kW AM transmit towers are usually protected by fences surrounding a large field.

DaveInNC wrote:
TH is supposed to be under 100mW, but someone (on ARF I believe it was) measured 400mW, ...


R358 (10 Ohms) at the output of the modulation amplifier allows you to measure the average power into the modulator. For my TH, the voltage at one leg of R358 is 8.6V and the voltage at the other leg is 8.2V. There is another 10 Ohm resistor (R305) at the low side of the envelope chopper in the modulator. So the average power into the modulator is 7.8V * 40mA = 312mW. The load seen by the modulation amp is 195 Ohm. Assuming that the switches (TR305 and TR306) of the chopper are driven by a 50% duty cycle square wave, the average voltage across the primary of the output toroidal transformer is 1/2 of 7.8V. The antenna load reflected to the primary transformer side is therefore 1/4 of 195 Ohms or magically about 50 Ohms. The power of the fundamental component that gets transmitted by the antenna tuner is about 40% of the total power or 125mW. If you take into account the switch losses (25mW), the TH is compliant (otherwise it would not have passed the FCC). The power can be lowered by increasing the value of R305.


Attachments:
TH5_sch_sm5_RFAmplitudeModulator.jpg
TH5_sch_sm5_RFAmplitudeModulator.jpg [ 122.84 KiB | Viewed 859 times ]

_________________
Binh
Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Mon 23, 2019 5:06 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 194
Yet - another test. The middle of my basement rec room is the farthest I can get from any power lines, without going out and wading through the snow. The nearest AC line to the TH was about 10 feet. Everything in that room was unplugged. I was running it on a 12V battery with a mp3 player connected to the line input. So, the TH was completely isolated, even from ground.

I wasn't getting any hum in that room, no matter how I oriented my Sony portable radio. If I turned the mp3 player off and turned my portable radio up all the way, I could hear a tone (maybe a couple of kHz?). But no low frequency hum. This tone is definitely being generated by the TH, because if I turn the TH off, I don't get the tone on the radio. The tone isn't loud enough to hear when playing music at a normal level.

My Tecsun PL-880 (much better radio) isn't picking up any hum either. Oddly, it doesn't pick up that tone I hear on the Sony, unless I fine tune the Tecsun off frequency a little. Not sure what that means.

I know Dave did the same sort of test outside using an 18V battery and had hum. Is it possible a 12V battery reduces the output power enough to drop the hum?

I wanted one of these to do some experimenting, but this may be more frustrating than I had in mind!

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Dec Mon 23, 2019 5:27 pm 
Member
User avatar

Joined: Sep Mon 10, 2012 10:41 pm
Posts: 4034
Location: Phoenix, AZ
power the unit with a ground pin not connected to ground.

ground the TH case run the antenna in the same plane as the ground plane 1/2 the distance of the antenna length to ground. then turn on the unit.

that's what I did.

_________________
Everyone you meet is fighting a battle you know nothing about.


Top
 Profile  
 
Post New Topic Post Reply  [ 194 posts ]  Go to page Previous  1 ... 5, 6, 7, 8, 9, 10  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 10 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB