RF Splitter/Combiner ??

I beg to differ.

Please note that "combine" does not mean "add" or "sum". In my explanation above, the signals in question are on two radically different frequencies and therefore not in phase. Also note that all this is about a splitter/combiner, and has little in common with how a directional coupler or "tap" operates, which is Jim's question.

I'm not combining or summing the two signals. I'm passing the two signals unchanged (less a little loss in the xformer) from the split ports to the common port. The point of contention is whether there is any loss doing this. I say there is none (except for some slight xformer loss).

That's an audio combiner. I'm talking about this device like this: borrowed from: I think this is the original patent: It's what you'll find inside the better CATV splitters. If you tear apart a common CATV splitter and look inside: Note that the good splitter has two xformers and follows the aforementioned schematic, while the cheap piece of disgusting junk on the right is ummm.... disgusting junk.

I'm not sure I can properly explain exactly how it works. I'm also short on sleep and time today. I'll see if I can find a sane explanation, maybe run a bench test, and if I get really ambitious, I'll throw together a SPICE model. There is an explanation at 0006 to

0009 in the patent: but it's not terribly clear (to me).

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

OK, yes we are talking about the same devices. I am not talking about addi ng voltages or adding current, I am talking about adding powers as are you.

And I guess we disagree about the loss issue.

The devices you show __will__ have a 3 dB loss when used to combine two dif ferent signals.

"The power combiner will exhibit an insertion loss that varies depending up on the phase and amplitude relationship of the signals being combined. For

ignals are equal in amplitude and are in-phase then the insertion loss is z

infinite. And, if the two signals are at different frequencies, the inserti on loss will equal the theoretical insertion loss shown above." (Which is 3 dB for a 2 way combiner)

Consider that there is no*** way to combine two 10 Watt Tx on 100 MHz and a 10 Watt Tx on 101 MHz and feed them both a common antenna without loosing 3 dB in each path. As I said before, if you know a way to do this, contac t me and we will be millionares. (Hint... There is no way)

Do the analysis and figure out what the resistor does. If it doesn't dissi pate any power, why is it there?

see also

slide 6

"It can be shown that the S-matrix of a 3-port network cannot be matched, lossless and reciprocal at the same time. One of these characteristics has to be given up if the 3-port network is to be physically realizable....."

*** there __is__ a way to losslessly combine different frequencie using fr equency selective filters, but there is no way to do it with broadband devi ces.****

Jeff, thank you for having a civil conversation without name calling which is bec oming rare on Usenet.

Mark

Those are cheap directional couplers intended for MATV systems. I replaced quite a few of those in schools in the '70s & '80s. That model provides a VHF to UHF & FM signal at 9 dB down from the feeder. Each model has a different insertion loss. Common models ranged from 3 dB to

26 dB, with an inverse amount of insertion loss. I wrote software back in the '80s to design CATV distribution systems, but I haven't see a copy in about 20 years. It allowed you to enter the maximum system frequency, then chose the brand and type of coax. You entered the available signal level into the coax, and it calculated the level at each port, for the desired output level. It also did back feeds, which other commercial software often ignored. I also wrote a program to generate a two page printout of the look angles for every C-band satellite. That one was fun, because several needed functions weren't available on a Commodore 64. The only commercial software ran on a VAX, or an NCR 2600 and was only available via a leased phone line at 9600 baud.

Here is a link to a pre digital TV version of the BT reference guide. It has plenty of RF information for anyone interested in a TV antenna of other distribution system. What you really want is a channel combiner, and possibly a tunable notch filter.

At least these are the newer die cast versions. The ones that gave me fits were stamped steel, and were easy to be filled with water if someone used them outdoors. I worked on one school, after a winter of a severely curtailed natural gas supply. The idiots had run the wiring in the concrete gutters, and the ice that formed had crushed the cases. That was real fun, working on a steel slate roof. I slipped, and almost went over the edge. It was about 70 feet to the ground, and I would have landed on concrete. There was no place to secure a safety belt, on that

1940s building.

Maybe putting a channel on his home cable wiring to monitor a camera? " What was that noise?" Flip to channel 3 to see all 6 security cameras!

Mikek

Adding in a DVR on an unused channel. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

No cigar for me! Mikek :-)

There are boxes to do that (at least for analog NTSC)- I presume they use an attenuator, LC trap, amplifier to null out the input signal on a few channels, then inject the 'new' signal, in regular old vestigial sideband analog fashion. Like this:

The more modern approach, though, is to do it on Ethernet (or WiFi, according to taste), using a streaming protocol and either smart TV or a streaming-equipped game console, Roku, BluRay player...

Or, if you don't want to run CAT5, use IP cameras and MoCA for moving the video over the coax cable:

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558