Isolation: modulated signals & antenna

[TuxCoder]

First, a bit of background before I get to my question. I have many locally modulated channels on my in-home cabling. This includes a few devices with built-in Ch. 3/4, two Dish Network receivers capable of a few in the UHF/cable range, and two ChannelPlus 4-channel modulators. All in all, I have the capacity to create 2 VHF and I believe 11 UHF (12 if the ViP222 can put out two UHF but I think it might be 1 VHF and 1 UHF). I love this stuff.

Anyway, I also have an antenna (and will be adding another for a more distant city, but that's beside the point--I know what not to do with two antennas, etc.). Right now, I have my antenna split to a couple receivers/VCR for demodulation, and to my in-home cabling.

The "cabling" branch is the important one here. That line first goes into a Ch. 4 combiner. Coming out of that box, I have OTA VHF channels 2 and 7, and locally modulated 4 (I'm gonna add a Ch. 3 combiner soon). Then the line goes into a VHF/UHF combiner where it joins my modulated UHF channels (no OTA connection on that side). Out of that the fully combined line with VHF OTA, VHF mod, and UHF mod, is amplified, then split throughout the house.

Thus, my question: I would love to add my OTA UHF channels to those I am locally creating, but of course without sending them up the antenna, so what recommendations can you guys provide? You should be able to infer from the above that I don't want to simply use an A/B switch. But also, for a number of reasons, I do not want to use an amplifier unless it is absolutely necessary.

I am aware that amplifiers provide the isolation I need. But I imagine there should be a more standalone passive device, sorta like a diode I suppose, that yields the same isolation without requiring an amplifier. I don't think a low-pass filter or similar would be of any use. A sort of one-way filter is what I'm looking for.

Thanks for any help you can offer.

 

[bhelms]

If your OTA signals are strong enough then you might consider adding a 10dB attenuator into the path, like the one Dish supplies with its recevers. Of course that affects your signals in both directions. I can't think of a passive way to avoid that. As you noted, having an antenna preamp or distribution amp in the OTA system will prevent any unintended signals from your system reaching the antenna and I think that's your best option...

 

[TuxCoder]

I have seen the ChannelPlus/Open House HHR series of distribution "hubs" (HHR providing the isolation while BID not). They seem like pretty promising replacements for the amplifier & separate 8-way splitter I have now, but I suppose I'd still like to see if there's any simpler passive device.

There's the Open House H838HHR (here), the ChannelPlus DA550HHR (here), and the ChannelPlus DA8200HHR (here), all of which look intriguing.

Does anyone know what the difference is between the DA550HHR and the DA8200HHR?
Edit: looking at another site, I see the DA550 is for the 12V IR stuff and the DA8200 is for the 5V IR stuff.

 

[brantlew]

I guess I don't understand your setup that well because it sounds simple. It sounds like you just need to put a regular coax splitter/combiner in there. Just attach UHF antenna to one leg and the combined UHF modulated channels to the other leg and then connect the combined UHF signal to your VHF/UHF combiner. The isolation between the legs on the splitter should be enough (like -20dB or so) to avoid transmitting signal unless you are pumping the hell out of that signal. Am I reading you wrong?

On a side note - I suspect you may see interference trying to squeeze that channel 3 signal in there between 2 and 4.

 

[TuxCoder]

Thanks for the input (no pun intended). I always thought ordinary splitters don't have the proper isolation but if what you're saying is true, then yes that would be the simplest approach.

I have actually decided to get the DA8200 since it will replace 3 devices in my signal path along with reducing the AC adapter count by 1 (since my 5545 and 5645 are both capable of powering the DA8200). I'm literally leaving work right now to head to Parts Express and get it.

I do plan on drawing up some before & after diagrams, so I'll post them here soon to clarify my explanations above.

 

[brantlew]

Thanks for the input (no pun intended). I always thought ordinary splitters don't have the proper isolation but if what you're saying is true, then yes that would be the simplest approach.

I have actually decided to get the DA8200 since it will replace 3 devices in my signal path along with reducing the AC adapter count by 1 (since my 5545 and 5645 are both capable of powering the DA8200). I'm literally leaving work right now to head to Parts Express and get it.

I do plan on drawing up some before & after diagrams, so I'll post them here soon to clarify my explanations above.

You should consider the CVT28PIA II. Unlike most amps that isolate the outputs it has only -10dB isolation between the posts which allows you to use it as a backfeed distribution hub. You can just shoot your signals back up the line from any point in the home and distribute them to every other line - pretty cool. The only downside is that it only has +4db gain per post which is sometimes not enough. The CVT24PIA II has +8db gain but is harder to find. (I had to get mine on eBay)