That should work nicely, of course one of the advantages of getting the frequency up is to use a smaller inductor. It's almost into reasonable air-core range, which could be helpful at one end.
I keep thinking I'm missing some obvious possibility with those chokes, but maybe not.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Pity. Common-mode signalling would probably be the easier to implement.
An inductor at each end of the line might be used to raise the impedance at the carrier frequency. This would allow capacitively-coupled differential signalling.
Perhaps look for inductors from switchers, in the range 20-50uH at 50Adc polarisation. Use Speff's 455KHz carrier frequency.
-- Tony Williams.
How about the PoE trick, center-tapping both ends and communicating via the center-taps, presumably against ground. For a 455 KHz signal, the ct's could be just two caps on each end.
You can make a nice stable FM discriminator out of a ceramic resonator and an xor gate.
John
Once you get a bandlimited, saturated signal, apply it to one input of an xor. Also run it through a resonator into the other xor input, and lowpass filter the xor output. The resonator must produce a 90 degree phase shift at the cf, and should have a 3 dB bw about twice the fm deviation. You can get the phase shift from an r-l-c (technically a lowpass filter, but with a big amplitude peak at cf) or better yet a ceramic res circuit, which won't/might not require tuning.
John
Now that looks darn near perfect....
Your series inductive coupling requires you to break the high power utility circuit, you do not need to break the circuit to install a shunt source and the components do not have to be rated to withstand 10KA surges and whatnots. ASK is the last kind of modulation anyone would want to use. A high frequency trap driving a comparator/limiter combination into his 455KHz resonator for gain/slope detection of an FSK signal in MARK-NULL-SPACE format is much more impervious to interference- there should be more than a few reference designs he can use.
The input is 12V and is dedicated. Probably the secondary of a fat
60Hz 120:12VAC transformer (up to 600VA). I have control over the noise on the branch circuit(s), but there may be substantial transients.Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
I don't think I've got access to ground. Otherwise that would be very nice.
That sounds like an interesting trick. How do you do that?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
I think that is a variation of the common-mode signalling that has already been mentioned Mike.
Hot +-------------------- Black ------------------+
60Hz supply Load L1 L2 +------///----+------ White -----+------///---+ |? | | |? GND +-------------|---+-- Green -+---|------------+ | | | | C1=== | | ===C2 | | | | Tx RxL1 and L2 are still handy additions because they isolate the comms-driven section of line, away from any Grounding that may happen at either end.
-- Tony Williams.
Thanks, Tony. I didn't see it was already mentioned.
As far as isolation inductors, many power supplies have bypass caps from hot and neutral to case gnd, which is connected to the green wire. So there is a possible short for rf, which would negate the effect of the isolation inductors.
If the driver can supply sufficient current, some voltage will be developed across the power cable connecting the device to the line and allow the signal to propagate. It's a bit like common-mode noise on a scope ground.
In this case, perhaps the series inductors may not be needed. There are many examples of carrier current devices on the market, such as intercoms, baby-sitting units, and so on. I'm sure they don't use series inductors, which would be expensive and difficult to install.
Mike Monett
You probably want to stay away from 455KHz - that could block every AM radio on your street:)
Perhaps also try to avoid frequencies used by local low-power non-directional beacons (NDB) for aircraft navigation. These are often used to establish holding patterns for aircraft during storms.
I'd look at some commercial products using carrier current, such as intercoms and baby-sitting devices, and figure out how they manage to work without series inductors.
Here's one that simply injects the signal into the neutral, like my proposal in another post that was quickly shot down:)
Mike Monett
and here's a complete transceiver at 135KHz
Some signal processing may be needed to reduce interference from line noise, but it seems you can simply inject the signal wherever you feel like.
Mike Monett
Here's a 5 watt AM carrier current broadcast transmitter for college campuses that shows another way of injecting the signal:
OK, that's enough examples. Fire up your soldering iron and get one working:)
Mike Monett
In article , Tony Williams wrote: [....] Notes added to drawing:
The white and green are hooked together by being grounded at the power entry point. There should not be any other connection between the two anywhere in the wiring.
The EMI reduction filters at the input of electronic equipment usually have a lowish AC impedance at high frequencies because they are commonly pi filters.
Watch that you don't run up against the NEC. Anything that introduces an impedance in the white wire is frowned on. They flat hate anything that could cause an open white wire. Since the impedance at the RF frequencies is fairly low, L1 and L2 can be darn near zero at 60Hz.
L2 faces some unknown capacitance. It would be a real bummer if it went into series resonance at the working frequency. C3 can prevent this by making the series resonance alway appear below the working frequency.
Also: You may want to make L1 and L2 go into parallel resonance somewhat above the working frequency. This makes their impedance higher in the working band.
-- -- kensmith@rahul.net forging knowledge
Yes, that seems most reasonable. I listed urls for examples of three different injection methods in other posts.
Perhaps the small inductance of a few feet of line cord is enough to allow the signal to propagate. Protection against spikes is definitely good. Also may be a good idea to think about transients due to nearby lightning stikes.
Some carrier current transmitters may go up to 50 Watts. That might overcome the attenuation from a few line filters:)
Mike Monett
Cute. A bit like the type I phase comparator in a 4046.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Yes, probably a good idea!
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
the
From cost and EMI considerations, I was thinking more of
That might work if the transmitter and receiver share the same plug:)
Mike Monett
OK, but some people might be too embarassed to come back.
I try to soften the blow with something like "I got lucky on that one, I think Clyde said something that made me think of it" or some such, even if Clyde is in fact a dimmish bulb. I try to be "on their team" instead of the outsider smart-alec; I don't want the glory, just the money.
I also like brainstorming meetings where ideas just happen without really distinct authorship. I did this a couple of weeks ago at P****&W******, and it sure seems to have worked.
There are people in this ng who brag about their ability to deliver calibrated insults to their customers' intelligence, and further complain about being unemployed.
John
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