Hi All - I am this close (this close) to getting a Black Cat .1 mfd 1kw capacitor in line with a fuse and a Talking House transmitter (I have four in case this one blows up) - anyone have any advice? A coupler is way out of my means right now & would like to maximize station coverage....
Your best off to find a proper coupler. For now, I would advise using a 3Kv cap instead.
For inductance, place in series a 20 to 150uF inductor, variable if you have one. Put a 350pF variable cap across the inductor to tune out excess capacitive reactance.
Use .5 amp fast blow fuses.
Though this approach is NOT recommended, it is a good learning tool and way to find out how CC works.
Just be careful around those hots. And always remember regardless of coupling method..ie neutral or hot, there is voltage potential in that breaker box or power socket.
RFB
Your stuff is some of the most inspiring CC stuff out there. I can only drool at your setup in the the pics on your site. I would love if one day our station could have the part 15 impact yours has.
I see in your forum that you specifically mentioned the TH units. I have 4 just sitting here right now. Is it true they can drive a coupler OK for CC? I also see you once mentioned building a special coupler for the TH units themselves. Did it include an amp circuit? If you're selling, I am definitely buying...
thank you again, you have me sold on CC - I know there are variables... but overall, it is exactly what I am looking for. I am very grateful for your experiences in this forum and am thankful to connect with you.
As for the 20uF-150uF variable inductors, have any idea where I can buy one? Closest ebay has is one that is around 30uF-80uF...
"I see in your forum that you specifically mentioned the TH units. I have 4 just sitting here right now. Is it true they can drive a coupler OK for CC?"
Yes. The TH external antenna output (F connector) is 50 ohms, just like the LPB and RS transmitters are, and is the input of the TCU couplers and CP couplers.
The TH outputs about 135mW at that port. Enough to drive the couplers and inject usable signal on the lines.
As seen in the pictures of my CC station setup, the coupler connections were the same when connecting the TH unit up to it, and the signal was able to cover a 4 block area at about 30 feet from the lines. At the 2 block point, the signal extends away from the lines about 80 feet. Beyond the 4 block area the signal goes another 2 blocks but only about 5 feet from the lines.
We are more interested in "down line" of the signal than "off the line". The above example with a TH shows just how a CC system is supposed to function, keeping that signal mostly ON the lines and not producing far field emissions.
"I also see you once mentioned building a special coupler for the TH units themselves."
Yes I did build one, though it is not a tunable unit, but built specifically for my station's frequency, 1670Khz. It is experimental and further improvements are being done along with some tuning ability, mostly for peak coupling. It is based on the TCU couplers by use of toroid core transformers, though much smaller as it does not need to be capable of handling watts as the TH does not output in the watt range.
"Did it include an amp circuit? If you're selling, I am definitely buying"
No. The concept was to design a coupler for the low power level TH transmitter and make it workable. The idea of an linear amplifier was not considered because of that.
It's been some time since messing with that little coupler, other projects etc.
RFB
is there an easy amp circuit anyone could build that I (even a caveman could do it) could be tutored through?
Well I ordered a 3kv .1 mfd cap and got the 15uF-59uF coil and the Air Variable Capacitor Tuning Capacitor (350pF) coming. I will also put the thickest rubber mat I can find at the coupler.... I might even buy an RF amp tonight to up the TH power. any advice where to get one? I am thinking about the pallet amps I am seeing on ebay... know anything about those?
Gosh I wish I could build a transmitter!
I have a power line interface that may work for you if your interested.
Hit me up with an email if you want.
just sent you an email.....
" I am thinking about the pallet amps I am seeing on ebay... know anything about those?"
Those pallets could be a good choice if they push no more than 20 watts or so. Anything higher will cause localized receiver saturation and could extend some distance down the line from your coupling point.
Using the "simple" coupler..ie the inductor, cap, fuse arrangement would basically "force" signal onto the lines and may put too much on those lines using a pallet amp or other linear. The result is severely saturated receivers that could occur within a range of 2 blocks, most certainly within range of a few houses, and enough so that if there is improper matching taking place, the pallet amp or linear could produce spurs and splatter on modulation peaks scattered across the spectrum dancing with high frequency audio.
A proper coupler takes the 50 ohm impedance and matches up to the very low impedance/inductance which varies constantly. Fed with 10 watts on the coupler input side, your effective radiated power on the line will be as low as 1/4 watt, maybe even less.
Imagine even a 1/4 watt radiator sitting right next to a typical AM radio, which will have AGC and high sensitivity. That radio will be so saturated and possibly blow the front end, or hopefully worst case is your audio will sound crunched, scratchy and highly distorted.
If the signal is coupled and matched correctly, it won't take very much power at all to get down range results, given power grid configuration, frequency of operation and the swing of inductance/impedance change on the lines.
For my setup, on 1670 a TX TPO applied to the coupler is at 1/2 watt. At that level the signal in the near field from the coupling point hits about 80 feet at 30 meters (15.221) which running the formula, the maximum distance off the lines for 1670 is around 93 feet. Down range on the lines covers about 5 miles which for the city of Casper, laid out very tight spaced and still using much of the older power grid system, provides excellent coverage where I want it to be..in homes and businesses with radios plugged into AC power, hence the table top radio capable of receiving it across town 3 miles away from the coupling point.
Again we are shooting for down range on the lines, not distance off the lines or producing high level far field radiation. CC systems are not intended to produce far fields. CC works by near field inductive coupling to the receivers where the signal on the power wire or neutral has a very very short distance to travel to that receiver front end.
Excuse my bad manners..welcome to the Part 15 forums! (slaps self in face)
RFB
Thank you sir! I am glad to be here... plus... I may be about to purchase a T-8 Power Line Interface! Maybe matching won't be such a problem!
talking house... check.
couple.... almost check.
I have four talking houses... one is already built into an outdoor weatherproof box with the standard wire antenna mounted in a 9 foot pvc pipe (so the house still matches it and a 5.8 video sender receive unit & 17db gain antenna... and 20 watt solar panel (still testing hope it's enough) with battery.... waiting on China to send the power controller before it cranks up... on it's own far away from the house.
Thought about grounding it to the 75 ohm connector on the back and sending that to a ground rod or radials. Gotta test.
Though, I may drop everything when the coupler arrives!
Guess I ought to try each talking house unit as they may not put out the same power? Guess the one in the outdoor box will need to be disassembled for testing...
The T-8 is LPB's first coupler using the ferrite core toroid transformers and provides a good matching capability and good return AC rejection. It is FAR better than the "quickie" approach with the inductor/capacitor/fuse arrangement, and will also help provide constant match to the TX with the varying inductance and load changes on the lines.
It doesn't quite match up to the vastly improved TCU series, but it is a darn good coupler and was sold like hotcakes after it's introduction, replacing those early lump component couplers that were a CC engineer's worst nightmare.
Keep us all updated!
RFB