Greetings all,

This is NOT the standard "I want to combine OTA and Cable in to a single RF input" question.

I'm trying to modulate 2 or 3 channels into my OTA signal, into the single RF input on my Hitachi plasma. The modulated channels are from my DVD and a couple TiVo's.

I have this working successfully - BUT, I can't get as many OTA channels with the modulator hooked up, as when its not hooked up. i.e. - if I do a direct OTA RF connection I'll get 20+ channels, and with the modulator connected I'll only get 4 or 5 OTA channels.

There's no direct channel conflict. I picked 3 channels that are not OTA for the modulator settings. (Its a Channel Plus 4 channel unit).

My conclusion is that the modulator is obviously interfering with the signal strength on the OTA channels.

So - since I only want to inject 3 or 4 channels into my OTA signal (again, not try and run an entire Cable channel selection into it), is there some way to do this?

Its almost like I need some kind of "inverse notch filter", so instead of blocking out channels 70 - 79 like a typical notch filter would do, I need to block all channels except 70 - 79 coming from the modulator.

Or is there some other inherent interference issue that I'm not thinking of?

I've tried things like running a channel scan without the modulator to get all the OTA channels, and then adding the modulator back into the loop, but the signal strength on most of the OTA stations then just goes away.

I've read a billion posts about how you can't combine Cable and OTA for obvious reasons. I'm just trying to inject 3 channels - there has to be a way....

FWIW - to combine the modulator signal with the OTA signal I'm using a standard splitter in reverse. Would this alone cause that much signal loss on the OTA side? I've seen devices from Channel plus that are designed for RF distribution that have a specific modulator input, but I didn't want to spend $150 to "see if it works".

Help!

Thanks,

Steve C.

Greetings all,

This is NOT the standard "I want to combine OTA and Cable in to a single RF input" question.

I'm trying to modulate 2 or 3 channels into my OTA signal, into the single RF input on my Hitachi plasma. The modulated channels are from my DVD and a couple TiVo's.

I have this working successfully - BUT, I can't get as many OTA channels with the modulator hooked up, as when its not hooked up. i.e. - if I do a direct OTA RF connection I'll get 20+ channels, and with the modulator connected I'll only get 4 or 5 OTA channels.

There's no direct channel conflict. I picked 3 channels that are not OTA for the modulator settings. (Its a Channel Plus 4 channel unit).

My conclusion is that the modulator is obviously interfering with the signal strength on the OTA channels.

So - since I only want to inject 3 or 4 channels into my OTA signal (again, not try and run an entire Cable channel selection into it), is there some way to do this?

Its almost like I need some kind of "inverse notch filter", so instead of blocking out channels 70 - 79 like a typical notch filter would do, I need to block all channels except 70 - 79 coming from the modulator.

Or is there some other inherent interference issue that I'm not thinking of?

I've tried things like running a channel scan without the modulator to get all the OTA channels, and then adding the modulator back into the loop, but the signal strength on most of the OTA stations then just goes away.

I've read a billion posts about how you can't combine Cable and OTA for obvious reasons. I'm just trying to inject 3 channels - there has to be a way....

FWIW - to combine the modulator signal with the OTA signal I'm using a standard splitter in reverse. Would this alone cause that much signal loss on the OTA side? I've seen devices from Channel plus that are designed for RF distribution that have a specific modulator input, but I didn't want to spend $150 to "see if it works".

Help!

Thanks,

Steve C.

The consumer modulators you are talking about are not professional models (for obvious reasons - cost being the least of which) and they put out trash well past the frequenicies they are set for, thus killing your OTA signal.

You will have to design something that will eliminate spurious signal from the modulated devices and OTA if you do not want to kill the OTA signals.

A professional grade 4 channel modulation system will most likely be your best option after all is said and done.

Thanks for your thoughts.

A pro model is out of the question for cost reasons.

I'm just trying to make it easier on my wife to watch casual stuff without having to fire up the HT unit to do the video switching.

Sounds like my first conclusion of an "inverse notch filter" was on target with what you were saying. (So the fillter would only pass a small range for the modulated channels like 70-79 and block everything else). I've never seen such a thing in the past - maybe I need to spend some more time googling.......

Steve C.

I'm just trying to make it easier on my wife to watch casual stuff without having to fire up the HT unit to do the video switching.
If that is the purpose, would it not be much simpler to connect the DVD player and Tivos directly to the TV or use the receiver as a video switched and get a programmable Logitech Harmony Remote? You can set the Harmony remote for 1 or 2 button presses to turn what is needed for TV watching, DVDs, or Tivos viewing, set the TV to the selected video input and set the receiver to the selected audio input? The Harmony remotes can be somewhat frustrating to program at times, but they do work quite well.

If that is the purpose, would it not be much simpler to connect the DVD player and Tivos directly to the TV or use the receiver as a video switched and get a programmable Logitech Harmony Remote?

Its a wiring issue. The plasma is mounted on a wall over my fireplace, and it will be extremely inconvenient to run all the extra wires I would need to connect the two tivo's directly.

I had empty conduit installed behind the walls when the house was built three years ago, but I wasn't thinking ahead enough and what I ran was too small. I had enough room for 3 RG6's for component, 2 audio line outs from the TV and a couple cat5's for the heck of it. To run any additional wire will be a major project. I'll have to do that eventually to get an HDMI cable there, but since I don't have any HDMI equipment right now I'm saving that for the future.

Not to mention I already had the modulator in place to serve all the rest of the TV'sin the house, so I already had that infrastructure. Its just that the rest of the TV's didn't need an OTA HD signal so I didn't encounter the problem until now.

Steve C.

Woohoo!

I think I have this working.

I'm getting MOST of my HD channels, and decent image for the TiVo's on the injected channels (as decent as I can expect on an RF line).

I did lose some of the very far away HD channels (like the ones 45 miles out or more), but really what do you need for OTA besides ABC,NBC, CBA, FOX and PBS. Its not like I needed 5 PBS stations or 3 ABC stations anyway.

Once I make sure its all stable and everthing else still works in the rest of the house I'll post how its connected for posterity and future searchers....

Steve C.

Did you try lowering the injected signal levels to reduce intermod distortion,
which would reduce sensitivity for some (but probably not all) OTA channels??

I would also worry about re-radiating your injected signals into your local neighborhood via the OTA antenna.
Check the signal levels and isolation specs on the RF Combiner....
You should be under (10 mW???) of radiated power....or thereabouts....

Did you try lowering the injected signal levels to reduce intermod distortion,
which would reduce sensitivity for some (but probably not all) OTA channels??

I would also worry about re-radiating your injected signals into your local neighborhood via the OTA antenna.
Check the signal levels and isolation specs on the RF Combiner....
You should be under (10 mW???) of radiated power....or thereabouts....

Actually - that's exactly what I ended up doing. (Although it never would have occurred to me to phrase it like that, I'll use that line on my brother-in-law when I tell him what I did.)

I took a low-tech approach: I previously had a combiner (splitter in reverse) running into my RF distribution amp to all my TV's, including the plasma. I used a splitter to remove the distribution amp from the plasma circuit. The splitter on the initial input side reduced the signal strength of the modulator. But, having it all tapped in my distribution amp was causing also part of my problem. I had previously also tried an attenuator on the modulator input line and that didn't help.

So now I have:

Modulator into a splitter
One output of splitter going to distribution amp for other house TV's
One output of splitter going to combiner (splitter in reverse)
OTA input into same combiner
Output of combiner into Plasma

I was still having minor PQ issues on the injected channels, so I moved them way down on the band (channels 18,32,34 on the modulator) and added a 600mhz low-pass filter coming off the modulator into the initial splitter.

That filter was probably overkill, but I had it laying around....just moving the injected channels to the low end, instead of 60, 64, etc made a huge difference in PQ on its own.

I surfed for well over a week to find out if this was possible, and all I could find was the ubiquitous "can't inject cable onto OTA" threads. This was not the same thing, but I hope my experience can help someone down the road.

re: re-radiating -

errrr - hadn't thought of that......

Steve C.

Modulator into a splitter
One output of splitter going to distribution amp for other house TV's
One output of splitter going to combiner (splitter in reverse)
OTA input into same combiner
Output of combiner into Plasma

did you try
modulator to port 1 of combiner
off air to port 2 of combiner
output of combiner to 2way splitter
port 1 off splitter to short runs
port 2 off splitter to distribution amp for long runs.

if all the runs are long...output off the combiner to the distribution amp.

if you attach the filter to create the clean space and pick the right combination of channels, interferences should be tamed.

although similar, this may take some of the edge off the signal prior to the amp and only amplify the long run since amplifying the short run may cause overload.

you may want to leave a larger space (32,34) if you can find one. like a space of at least 6 channels if you have room.

filters are great. I am blessed with 3 filter companies less than 10 miles from my home. Call in the morning to order, pickup in the afternoon.

did you amplify the off air antenna?

I have been using the winegard hdp269 preamp as a distribution amp the last few years. less gain and more overload tolerance than the distribution amps out there. sometimes not at the antenna but at the distribution point if I see interference on the less powerful channels.

If the user has a vhf/uhf combo or a cm4228 (hi vhf is rather stong) for that matter I would amplify uhf only and pass vhf or filter vhf completely using a setup of 2 cm0549 vhf/uhf splitter combiners...separating vhf and uhf, amplifying uhf, passing vhf then recombining. I also like doing this cause I do not like to amplify fm and this allows flexibility to manipulate the fm signal which can also cause interference issues.

a couple cat5's for the heck of it. To run any additional wire will be a major project. I'll have to do that eventually to get an HDMI cable there, but since I don't have any HDMI equipment right now I'm saving that for the future.



I run hdmi over dual cat6 cables with converters on both ends. Expensive, but probably
less expensive than ripping up walls for rewiring for hdmi. If you don't have a long
run, the cat5 might work. Just a thought.

FYI: Here is FCC Bulletin re allowable radiation limits for "Part 15" Low Power, Unlicensed Transmitters:
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf

Simpler check would be to make sure you CAN'T pick up the "injected" channels on a second TV using indoor antenna....
after making sure to disconnect coax inputs.

I have a question on Modulater. Can you use them on ATSC tuner equip TV ? I never really see they say are analog or digital format? All they say is Ch2-69 or certain channel on the cable again don't say analog or digital either. I know they will work with analog tuners but digital is what I am wondering about.

I have a question on Modulater. Can you use them on ATSC tuner equip TV ? I never really see they say are analog or digital format? All they say is Ch2-69 or certain channel on the cable again don't say analog or digital either. I know they will work with analog tuners but digital is what I am wondering about.

No.