UHF modulated home 'cable' system

DavidEC2955 · Post by **DavidEC2955** » Sat Apr 15, 2006 5:25 am

I have two questions:
1: What started out as a single two channel modulated home 'cable' system has now ended up being a multi-unit-modulator system.... What is the best way to combine these devices to a single house wide coaxial cable for distribution through out the house?
2: Some of the modulators used are mono, so when connected to my DirecTV receiver they change both out-put lines to combined mono signal, how can I keep stereo on audio line one and allow for mono-combined on audio line two?

Post by **The Robman** » Sat Apr 15, 2006 9:36 am

You will probably need to give a much more detailed description of your setup in order for anyone to comment. You should list all of the devices and describe how they are wired together.

zaphod7501 · Post by **zaphod7501** » Sat Apr 15, 2006 10:25 am

Are you adding the modulated signals to an existing CATV system or an OTA (over the air) antenna system? It can be done but requires some knowledge of your cable system and exact channels to be added/combined.

There are modulators that have antenna/cable input and output that add the new channels to the output. These can be connected in series for multiple channel additions; again, exact channels involved are a consideration.

To combine one L/R audio line output to mono without causing the other line output to become mono, you need some isolation. One way is to use 1 Kohm resistors in series with the left and right outputs. The resistors cause some lowering of the signal level but conbining them brings it back up. Some modulators (mono modulator but stereo input) do this internally anyway.

The other way to handle audio is to add a distribution amp to the output of the DirecTV. This would give you 4 (typically) isolated line outputs from the box. (one for the TV, one for the modulator, one for the VCR, one for the DVR or other device or a line output for second TV.

True stereo modulators are now available also. They run in the $100 to $250 range rather than the $25 - $100 range.

DavidEC2955 · Post by **DavidEC2955** » Sat Apr 15, 2006 12:21 pm

The Robman wrote:You will probably need to give a much more detailed description of your setup in order for anyone to comment. You should list all of the devices and describe how they are wired together.

All right lets see if I can out line the current setup.. just trying to outline basic "RF" signals and A/V input into modulators... I would have to have colored graphing program to outline the A/V interconnects....

External/off-air ant VHF/UHF/DTV channels...
3,3.1,5,8,10,10.0,12,12.1,12.2,24,24.1,26,33,33.1,36,36.1,40,45,51,53,59....>>
......> two way splitter>
[E1]HD/TV Receiver
[E2]rest of the system......>Four Way RF Combiner/spliter<......>

<......>single channel mono UHF/RF UHF 48 <......A/V1[E1]HD/TV Receiver
<......>single channel Stereo UHF/RF UHF 64 <......DirecTIVO#1
<......>single channel mono UHF/RF UHF 38 <......Phillips DVD+R-Recorder
<......>single channel mono UHF/RF UHF 44<......VHS/VCR
......>Four Way RF Combiner/splitter Out<......
\
\>>......>>>......>two Way RF Combiner/spliter<......><<<>>......>>No name brand "Skywalker" 3 channel mono UHF/RF UHF 14/17/27
<<......"Skywalker" 3 channel mono UHF/RF UHF<<--DirecTIVO#2
<<......"Skywalker" 3 channel mono UHF/RF UHF<<--iLo DVD+R
<<......"Skywalker" 3 channel mono UHF/RF UHF<<--Computer video out [personal weather channel {'"hacked"' together full screen web page that goes out and gets weather data from a number of local and nation sources and displays it 24 hours a day with reports from NOAA weather reports and MPEG music mix}]
......>two Way RF Combiner/splitter out<......>
\
\>>......>>>>......>>Sony MRD-D1 two channel mono UHF/RF UHF 20/22
<<.....Sony DRD1<<--DVD Player#1
<<.....Sony DRD1<<--ReplayTV 5040+80
\
\>>......>>Sony DRD1 four lines out >> Main TV and to other areas of the house>>>>[these might be split close to their final point]

All the above controlled with 'IR Repeaters' and JP1 programed remotes...

--David

zaphod7501 · Post by **zaphod7501** » Sat Apr 15, 2006 3:55 pm

Without spending hours redesigning your house, I can offer a couple of ideas/suggestions. RF modulators, with passthrough, can be cascaded, one right after the other. Each modulator would add another channel (or 2 or 3) to the main line "passing through". Modulators that don't have passthrough will be difficult to add since the splitter/combiners tend to have very high insertion loss. The Sony MRD-D1 would have to be the last in the add-in sequence.

Two difficulties that I see are the physical location of all the equipment (need to be on the same grounding location) and the possible frequency overlaps. You will have to determine what frequencies channels like 3.1 12.1 33.1 36.1 etc are actually at (3.1 is probably not at VHF ch3, it is most likely a UHF channel) in order to avoid interference.

DavidEC2955 · Post by **DavidEC2955** » Sat Apr 15, 2006 8:36 pm

zaphod7501 wrote:Without spending hours redesigning your house, I can offer a couple of ideas/suggestions. RF modulators, with passthrough, can be cascaded, one right after the other. Each modulator would add another channel (or 2 or 3) to the main line "passing through". Modulators that don't have passthrough will be difficult to add since the splitter/combiners tend to have very high insertion loss. The Sony MRD-D1 would have to be the last in the add-in sequence.

Two difficulties that I see are the physical location of all the equipment (need to be on the same grounding location) and the possible frequency overlaps. You will have to determine what frequencies channels like 3.1 12.1 33.1 36.1 etc are actually at (3.1 is probably not at VHF ch3, it is most likely a UHF channel) in order to avoid interference.

I have a list of the "Digital/HD" true UHF channels but can not find it .. but I do know that I had to move a few of my channels so that none of the channels over lapped...

My biggest troubles seems to be with grounding and the audio..
If I disconnect the external antenna the pictures are all clean... and the picture is clean when it is raining.. but when it is dry the picture is full of noise... and none of my current modulators have RF pass through other than the 'Sony MRDD1'...

About the audio.. where can I get a pre-made "One Way" stereo audio jumper??

A local radio station is so powerfull that even with all devices unplugged I can hear the station in my speakers.....

--David