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 Post subject: Two tube transmitter question
PostPosted: Jan Wed 31, 2018 4:28 am 
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Location: Warner Robins, GA
I saw in a recent topic about a part 15 transmitter where one could use the carrier current method for part 15 transmitters.

What would I need to properly match the output of a two tube 6GY6 transmitter to the neutral connection of its power cord?

Also how well would that work far as hum is concerned?


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 Post subject: Re: Two tube transmitter question
PostPosted: Jan Wed 31, 2018 6:48 am 
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Matching is usually in low impedances. A T net usually works great.

Blocking couple via a .1uF is plenty, go to hot side of line.

Not tough to do, you can easily cover a whole house with 5W.

Dennis

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 Post subject: Re: Two tube transmitter question
PostPosted: Jan Wed 31, 2018 12:32 pm 
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Would the 100mW output of the typical part 15 transmitter be enough to cover the whole house?

If not then it isn't really worth my time unless I build a 5 watt transmitter and then it would also have to be able to reach my 12' X 12' building which is maybe 10-20' from the house with static free reception.


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 Post subject: Re: Two tube transmitter question
PostPosted: Jan Wed 31, 2018 1:15 pm 
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You'll need more than 100mW.

Since you're loading into the power line rather than a free antenna that poopy FCC power limitation doesn't apply, and that is good as CC operation is very lossy.

The LPB transmitters I cared for were 25W into 50Z, and used separate couplers. One TX did a whole 100-room dormitory, and maybe 25' out to the parking lot.

Fresh from the fun police:

https://www.fcc.gov/media/radio/low-pow ... on#CARRIER

Dennis

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 Post subject: Re: Two tube transmitter question
PostPosted: Jan Wed 31, 2018 1:47 pm 
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I might have to look into making a higher powered transmitter just for that purpose.

Someone in the other topic did post an antenna coupler he used specifically for carrier current systems.


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 Post subject: Re: Two tube transmitter question
PostPosted: Jan Wed 31, 2018 9:32 pm 
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Location: pensacola fl
Hi. I did as safety comes first one could build a similar device even one with standard coils instead of toroids and variable caps instead of the switched system used in the coupler and get a flat swr. You will not need that much power to get to your out building if it is powered from your breaker box in the main house. Counting coupler loss 400mw will prove to be more than enough even if you insert a resistor bridge to read the swr before the coupler. I can provide the resistor swr bridge diagram as I found it out here online. The other coupler diagrams are also out here on the net.


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 Post subject: Re: Two tube transmitter question
PostPosted: Jan Wed 31, 2018 11:08 pm 
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My building is powered from the panel in my dad's shop which is on its own meter.


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 Post subject: Re: Two tube transmitter question
PostPosted: Jan Wed 31, 2018 11:17 pm 
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If there two distribution transformers (pole pig or ground mount) between your buildings, it is really tough to get coverage.

With no big restriction on TPO, why settle for milliwatts?

DDG

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 Post subject: Re: Two tube transmitter question
PostPosted: Feb Thu 01, 2018 12:14 am 
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Ok. If they are connected to the same pole then the neutrals will be bonded and even if there is a transformer the two services may be on the same feed from that transformer so it should work on traditional feed or neutral feed.


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 Post subject: Re: Two tube transmitter question
PostPosted: Feb Thu 01, 2018 11:44 am 
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Yes only one pole pig, but at least 4 homes share it.


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 Post subject: Re: Two tube transmitter question
PostPosted: Feb Thu 01, 2018 8:01 pm 
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Ok then you have four homes that will receive your signal if you use traditional feeding the hots of the ac line. Carrier current works by the fact that the radio is connected to the transmitter by wire but some does leak out so a portable can pick it up short over limited distance.


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 Post subject: Re: Two tube transmitter question
PostPosted: Feb Thu 01, 2018 8:21 pm 
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Having four homes receiving it might be a problem, although I don't know if any of them listen to AM.


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 Post subject: Re: Two tube transmitter question
PostPosted: Feb Fri 02, 2018 5:46 am 
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What problem if they dont like what you play they do not have to tune it in wont mess with you.


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 Post subject: Re: Two tube transmitter question
PostPosted: Feb Fri 02, 2018 2:16 pm 
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True, although would any sources of RFI cause any interference though.

I know in my place I have tried to reduce RFI as best I can, but I don't know if the other homes have.


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 Post subject: Re: Two tube transmitter question
PostPosted: Feb Fri 02, 2018 10:43 pm 
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Hi. There are several differences between the two methods as far as behavior of the system goes. Traditional loading of the hots and neutral means anything connected across the line that changes the line impedance can change the swr your transmitter sees and if they were to inject a signal that is able to interfere with you then you are likely to notice it. For example a device generating a carrier at your frequency would beat with yours. This is true even if it were a neighbor broadcasting over the air they couild interfere with your over the air signal. If they were to have a device that was tuned to your frequency such as a series tuned circuit that type of trap would be reflected down the line to your transmitter as an impedance change. Neither of those is likely to occur unless they want to cause you trouble. Incidental noise from led or switch mode power supplies is more likely what you will have. This is similar to over the air conditions though the levels can be different. On the other hand loaded neutral has much less to deal with on those fronts. The signal in the traditional system is delivered across the line pair from neutral to hot but in a neutral loaded system only the neutral is a common conductor so loads on your neighbors outlets are less likely to be a problem. In the neutral load system the earth itself is the return path just like over the air antenna operation is. The losses may be higher but you can make that up. I bet you wont need anywhere near one watt to make a clean trip unless the noise level is incredible. Of course there is another refinement. Back in the 1970s radio shack for one had plug n play intercoms. The cheaper and first version were am the later and upper end versions were fm on the same frequency. They ran down below the am band but were carrier current and worked well. The fm models were better. Also back in the 1960s GE had extension speakers for their stereo system that had a carrier current transmitter at the stereo and a receiver and low power amp inside of the speaker box. These were also fm and tube type to boot. They work well too.


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 Post subject: Re: Two tube transmitter question
PostPosted: Feb Sat 03, 2018 2:11 pm 
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Cool.

Might be something I play with in the future.

Would be nice if I could find one of those Radio Shack AM intercoms and modify it for the AM band.


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