combining multiple units through a modulator?

[Anole]

two success stories

The hard way:
One of my friends is a retired engineer from a major L.A. TV station.
I just got off the phone with him, to verify these facts...
He moved out into the boonies where there are only a couple of VHF stations around: 3, 6, & 12.
From the TV antenna, he runs through three band pass filters, one for each channel.
Next, he's got a pre amp, and then runs that via RG 6 into the house.
Somewhere along the way, he picked up some surplus commercial modulators.
They're made by Blonder Tongue, and would have been around $350 each, new.
He's set them on channels 7, 8 , 9, & 10.
Because they're commercial quality, they can actually be placed on adjacent channels, unlike consumer units!
The modulators feed some sort of rack-mount commercial combiner, which he says is a pretty simple box.
The combiner's output is fed through the house, where any TV can select the three local stations, or the output of his four satellite receivers.
Yes, he actually leaves three of them on fixed channels for easy access.

The easy way:
Another buddy wanted to combine his cable TV with the output of several satellite receivers.
Obviously, most of the channel frequencies were already in use.
We experimented with some frequency agile modulators like the ones Sadoun sells.
These came from a close-out deal at Radio Shack last year, and look almost identical.
The features are certainly the same.
His cable went up through about channel 79, as I recall.
He tried using a standard high frequency TV splitter backwards to combine the two signals, but had interference between cable and his modulator.
In the end, he got a $30 filter from Minicircuits (I think it was a low-pass) at channel 80
The output of the filter cut the cable-carried garbage above channel 80.
Then, he used a 4-way TV splitter -backwards-, and combined the filtered cable with 3 modulators set to channels 82, 84, and 86.
That seemed to work fine, with no more cross interference.
Now he feeds his three video sources throughout the house, along with regular cable TV.

I described this approach to my TV engineer, and he was impressed.
He didn't knock the design at all. :up

-[30]-

 

[MotleyFool]

Reviving this thread to preserve the good information and discussion...

I need to use an RF modulator to route my FTA receivers' output to other rooms. In the past, I used a wireless transmitter, but when I dug that out of storage, I discovered that it used the same 2.4ghz bandwidth as my more recently installed WiFi router (turning on the video transmitter caused the previously stable WiFi to start having frequent interruptions - even using theoretically non-overlapping channels did not help).

SNIP

Thanks!

You could change over to 5.8 GHz 802.11a. I'm running 802.11a/b/g Trendnet dual radio APs that cost me under US$80. Of course if you're using 5.8GHz cordless phones 802.11a will conflict with them.

Whatever happened to the FCC keeping the spectrum separated? Not in this day and age I guess.

 

[kstuart]

You could change over to 5.8 GHz 802.11a. I'm running 802.11a/b/g Trendnet dual radio APs that cost me under US$80. Of course if you're using 5.8GHz cordless phones 802.11a will conflict with them.

Whatever happened to the FCC keeping the spectrum separated? Not in this day and age I guess.

While researching online I came across this ad copy for 2.4ghz senders:

Superior quality 2.4 GHz transmission avoids the crowded 900 MHz band used by most wireless items

Undoubtedly this text was written several years ago when 2.4ghz was new, prior to WiFi Routers and 2.4ghz phones.
I did price 5.8ghz video senders and they cost 3 figures since they are so new.
Changing my 802.11 would cost me a lot more than that - I would need a new router and 3 new wireless cards for the laptops.

 

[kstuart]

Someone PM'ed me that Radio Shack still sells the 15-2525 as part of the 15-2541 "installation kit", which is now priced for clearance at $19.99 (includes several cables).
My local RS did not stock this, and they don't participate in the "free ship-to-store" program. So, I checked ebay and someone is selling the 15-2541 kit new for $7 plus a padded shipping price. But that enabled me to buy two kits for the same price as one from RS.
I've come across three different threads at Forums where people verified that the RS modulator outputs true stereo; and here is one:

starneml 06-12-2006 04:49 PM
--------------------------------------------------------------------------------
i have a Radio Shack RF Modulator that actually modulates to an MTS Stereo Signal. My test (so I dont have to hunt down a channel) is done by using an MP3 I created with one song in the left channel and a completely differnet song in the right channel and feed that baseband audio into the RF modulator and then feed that via channel 3 or 4 into the DT.
Very easy to tell Stereo (seperate audio) or Mono (mixed in both speakers)

I'm giving all this info to help anyone who comes across this thread later and is looking for the same thing.

 

[Anole]

That's a good test trick!

The disco RS modulator I have, is frequency agile.
This one shown does channel 4 or 3, which may satisfy many folks.

 

[vfrjim]

The hard way:
One of my friends is a retired engineer from a major L.A. TV station.
I just got off the phone with him, to verify these facts...
He moved out into the boonies where there are only a couple of VHF stations around: 3, 6, & 12.
From the TV antenna, he runs through three band pass filters, one for each channel.
Next, he's got a pre amp, and then runs that via RG 6 into the house.
Somewhere along the way, he picked up some surplus commercial modulators.
They're made by Blonder Tongue, and would have been around $350 each, new.
He's set them on channels 7, 8 , 9, & 10.
Because they're commercial quality, they can actually be placed on adjacent channels, unlike consumer units!
The modulators feed some sort of rack-mount commercial combiner, which he says is a pretty simple box.
The combiner's output is fed through the house, where any TV can select the three local stations, or the output of his four satellite receivers.
Yes, he actually leaves three of them on fixed channels for easy access.


-[30]-

I actually do this with mine(Also, there are different manufacturers then Blonder Tounge that are less costly, if you need manufacturers, just ask), but it is not difficult (or even expensive when you find the modulator and combiners on ebay) and since analog transmissions are going away, they are very common to find on ebay for the CHEAP. The pluses out way the minuses due to the fact that the quality of the picture is OUTSTANDING. I HIGHLY recommend this method, especially if you have a rack to mount it all in.

Jim

 

[V_H]

The output of the filter cut the cable-carried garbage above channel 80.

That's bad to hear. I was expecting the channels without any TV signals to be clean. I was going to do the same thing as your friend and combined cable TV with 2 FTA channels. Thrown into the mix is a cable modem and one digital cable box.

My plan was that the cable TV signal feed a 1-to-4 bidirectional amplifier. One output would go to a cable modem. The other output would go to a reversed splitter used as a combiner. The other input to the combiner came from the modulated output of the ChannelPlus 3025 which is fed from 2 FTA boxes. The combined output would go to a 1-to-8 anplifier which distributes the signal to the rest of house.

Considering your information, I may have to use a filter if I can't find 2 clean channels. I can either use a notch filter before the combiner or use a low pass filter and connect the cable box directly to the 1x4 (which may be a good thing if I ever want to use the PPV).

The top analog cable channel is 75 and I was vaguely planning on using 90 and 92. Does anybody see any problems? Is the channels safely far away from the data channels? Suggestion for source of filter?

 

[V_H]

I actually do this with mine(Also, there are different manufacturers then Blonder Tounge that are less costly, if you need manufacturers, just ask)

I am asking. Please elaborate on which manufaturers, type of equipments, lines of products, model numbers etc. to look for on ebay.

Thanks.

 

[vfrjim]

I am asking. Please elaborate on which manufaturers, type of equipments, lines of products, model numbers etc. to look for on ebay.

Thanks.

I currently have a few Drake VM2410A modulators and a Holland Electronics HMA-500H , these are all Mono and are too hot (too much signal to feed my distribution amp) so they need to be reduced in power and combined by my Blonder Tongue Headend Combiner model ZHC-12 does the job fine. I use a Channel Vision model T2/8PIA-II that I got here : http://www.asihome.com/ASIshop/product_info.php?manufacturers_id=31&products_id=155 as my distribution amp.

Hope this helps you.

 

[V_H]

Hope this helps you.

Thanks.

 

[kstuart]

So, the Radio Shack 15-2541 kits arrived today, and they do indeed include a RS 15-2525 RF modulator.
I hooked up the modulator to my Fortec Mercury II, and - voila - stereo on FTV - over RF - as indicated by both the Wega's onscreen "STEREO" indication as well as the obviously stereo sound. Visual PQ is fine too - as good as the Mercury's onboard modulator.
So, it seems that - just as with many other electronic devices - a several hundred dollar printed circuit board can be replaced by an entirely equivalent IC chip costing pennies.

 

[Sat_addict]

Modulators

I made my own three channel modulator out of some chips sold by New Japan Radio (NJR). The three cable channels are 84, 86, and 88. I have CCTV cameras installed on the front/back of my house on 84,86 and my Pansat 2500a on 88. I bought the Pansat UHF kit so I can have Sat TV on any TV in my house with one 2500 unit. I just bring the UHF remote to the room I want to watch TV in. If I hear something outside I switch to the CCTV channels to see what's going on. The setup works out nice. We live out in the woods so it's also nice to eavesdrop on the deer and other animals that visit us through the CCTV cameras.


I don't think it was mentioned here, but the best place to feed the cable with a modulator is right where it enters the house. This way it will feed subsequent splitters as splitters and not as combiners which could add signal loss to your modulators injected signal. I have a channel 80 low-pass filter installed on the cable where it enters the house to eliminate the digital cable channels (I pay for Analog only) that would interfere with my three injected channels. after the LPF I use a 1 to 2 splitter backwards as a way to combine the analog cable and the output of my home made three channel modulator.

I spaced the channels apart a bit so I would not have to do extensive filtering to the lower sideband which would step on the lower adjacent channel. NTSC is normally vestigial side band (upper side band and fraction of lower) modulated. At times my three channels perform better that what I receive from the cable company.

 

[Anole]

I made my own three channel modulator out of some chips sold by New Japan Radio (NJR).
The three cable channels are 84, 86, and 88.

Sounds identical to my doing it "The Easy Way" description above.
What's the source of those chips? Got a site with a schematic?

 

[Sat_addict]

Sounds identical to my doing it "The Easy Way" description above.
What's the source of those chips? Got a site with a schematic?

The part # from JRM is NJM2259 and they are available from Mouser for about a buck. I just used the typical circuit out of the data sheet which you can easily find doing a search or maybe Mouser has it. I deviated from the data sheet by adding a varactor diode in the oscillator circuit so I could use a 10-turn pot for easier tuning.

I did not document the filter circuit and amp that I added after the output of the chips so I don't have anything I can give you. I have a habit of designing as I go without documenting it when I'm playing at home. I have an old spectrum analyzer which makes RF work easier. The filter was was a double tuned filter for knocking down the lower sideband a bit on each channel and reducing any harmonics. Since I have three channels, I created three separate circuits which obviously needed three 2259's. I combined all three circuits into a 1 to 3 splitter inserted backwards as a combiner. The output power from each channel was about +15 dbmV which equates to about -33 dBm. You may be able to just drive the cable system with the output of the chip without filtering or anything if you can tolerate the sidebands. In my case, even with the filtering, I needed to separate the channels two apart to avoid the lower sideband which was not quite attenuated to standard.