Homemade low power TV transmitter?
 

The end of broadcast TV is nearing, and come 2009, all of our sets will be forever stuck on channel 3, with some digital converter box. I am curious how hard it would be to build a low power, "housewide" TV transmitter. I don't know what the FCC rules on transmitting television are/will be, but is it possible or legal to build or buy some sort of small transmitter so that you could broadcast to all your old sets?

Imagine, a transmitter for each of five channels, broadcasting tapes (or re-broadcasting your favorite channels) on the standard analog TV band, so that all the sets in your house could use their own tuners! It's ambitious, to say the least. Having no knowledege of television transmission, I figured I'd post and ask the experts what they think.

Or, avoiding over the air broadcast, if you had some sort of modulator that could produce a signal on TV channels (more than just the normal 3 and 4) at suitable power to be cabled directly to all your sets, you could create your own, in-home cable network. That might be a better idea. No worries about broadcast license/rules, and everything nice and self contained.

Seeming as though I only watch a couple of cable chanels, it would be great if I could "remodulate" them, and send them out to a run of cable to all my sets, and have 12 channels that are all things I want to watch, or close to it. (Sci-fi, TV-Land, Discovery, etc).

Any ideas?

-Ian

In theory, the output of any common low power RF modulator could be hooked to a ham radio type linear amplifier and sent far and wide. The frequency of channel 3 which is 60-66 mhz would be slightly out of the ideal tuned range of such a linear amp and probably quite attenuated. But I bet anything you would get a noise free picture in the house. Problem is the transmit antenna design and the outright total illegality of it all. Your other idea of using a RF distribution amp and stringing wires is much safer but not as much fun. Linear amps were popular in the 40s and 50s until complaints from people who could not hear their table radios or watch their TVs brought FCC scrutiny and enforcement actions. I bet it would be quite hard to find one in working order. Plans for making your own are probably out there somewhere and would not involve huge expense for the parts. I salute you for seeking creative solution. --Tom in Tucson

The FCC allows a maximum radiated power of 100 mw. This won't cover a whole house, but will work within a rooom. You can find devices that broadcast TV on ch 3. with that power on Ebay.

It is very easy to connect sets using coaxial cable and splitters. Hook your channel 3 signal source to one of the 20 db VHF amplifiers that are sold at Radio Shack and you will have plenty of signal to feed at least 16 sets.

Ah. I knew that there was a limit, but wasn't sure what it was. Not enough for a whole house, so it probably won't be too useful for this particular application. I'll have to go with cable.

Good to know. I have never tried to drive more than two sets off one VCR before, so I wasn't sure what limitations I'd run into. The big question is if it's possible to modulate signals on other channels, and run them all together. The different signals should all be able to share the cable and amplifier, since that's what they are meant for, but how to generate them? Is it possible to modify a normal RF modulator to run on, say, channel 12 for instance?

If such hardware could be created or obtained, then you could have a stack of gear in the basement - 12 tuners(or DTV converter boxes), 12 modulators and an amplifier, and have a full spectrum of VHF channels available, sourced from 12 different cable channels/digital TV channels, etc. Feed it through the house using the standard cable lines. Then, you could hook up all your old sets, and just use the standard VHF tuner to choose the "station".

-Ian

I don't believe that the cable company would be thrilled to know that their signal is split into several different TV units throughout the house.

I'm pretty sure that the cable box is for ONE TV and if you want to watch cable (different channel) on another TV they will offer you a second TV discount and a second box.

If you want the hook up several TVs in series and watch the same channel on all of them (just in different rooms) then that ought to be fairly easy with a spliter (and perhaps a signal apmplifier), but I wouldn't advertise that to the cable co.

Splitting the signal into separate channels would be considered theft of service subject to a 3am visit by the Feral Broadcast Inquisitor Gestapo resulting in your mysterious dissapearance. :D

I don't see why it makes any difference to the cable company. It's not like they own or rent cable boxes. I mean, everything these days already has a cable tuner in it. And the tuners I would be using would probably just be old VCR's. (Pretty much what I do now). The only difference would be that now, instead of being on top of the TV, it would be in the basement. Connected through a long cable.

Likewise, if you chose to do this with digital television, you'd own the converter box, and it would be hooked up to a roof antenna. Provided that you didn't somehow wind up with more than your alotted two $40 off coupons, it doesn't matter what you do with your new digital TV converter box, or how many of them you buy.

Really, the only deviation I'm suggesting is a way of modulating the signal on something other than just channel 3 or channel 4. And, if done through a cable and not over the air, there would be no "broadcasting", so therefore no FCC problems.

-Ian

The idea of modifying toy modulators (and that is really all they are) to run on the gamut of VHF band is a daunting task. The higher up you go in frequency, the more problematic it all becomes to get good clean well-modulated wideband color video on the antenna outputs. Industrial gear that already does this will soon be taken off the market, I suspect; but if you can find some used modulators such that the cable companies themselves or hotels might use, great. I am not sure how you would combine them on a single wire but again, there are likely combiners to do this in the used industrial arena.
I am the same person who speculated earlier about using a ham linear amp to beef up a toy modulator but on reflection, I caution that the transmit antenna and waveguide will be problematic for the amateur to rig up. Even if the linear amp could produce a big clean signal, it will be hard to load it properly while achieving wideband radiation. There is such a thing as ham TV and this would be the arena to find adaptable gear and expert advice.
--Tom

You can also buy kits. A Google search should turn them up.

I would not recommend the Ramsey kit. I built one a few years ago. The signal quality was abysmal, and the usable range was more like 3 feet than the claimed 300 feet.

Last year, I bought a Recoton video sender. Not really a TV transmitter, since it has receiving and transmitting units, and requires an RF modulator on the receiving end. It works OK in the same room, but the usable range is, again, far less than the manufacturer claims, which sort of defeats the purpose. If your range is 10 feet, you might as well just move your TV 10 feet closer to the source and make a direct connection.

If anyone knows of a better quality video sender, I'd love to hear about it. I would like to be able to tune a station on our satellite TV box and relay it to my workshop in the garage.

Splitters can't be used here. Our system detects them somehow and blocks the signal. When they installed the system, it wouldn't work at all in one room. The guys finally discovered an old splitter with an unused branch of coax in the crawl space under that room. (We used some existing wiring from a previous antenna system in the attic.)

Phil Nelson

I remember back in the 80's when cable ready receivers were making their debut and the cable company didn't take kindly to multiple in-house sets but I'm surprised to hear that mentality is still around today :scratch2:

I was doing some searching this morning before I stumbled upon this great thread and discovered "multi-channel" RF modulators capable of transmitting 2, 3, even 4 or 5 channels simultaneously over one coax, all from individual component inputs. The whole thing is digitally set up so you can configure the inputs to whatever channel you'd like, but it's a pricey affair at several hundred bucks.

Guess where I found it? None other than an audio/video security site, likely targetted so you can check multiple cameras over your in-house cable system. Just add digital converters (and maybe a dvd player for an in-house classics channel of your own) and you're set!

---

The TV6C? Yeah I had one too. With a few modifications I averaged about 25 feet signal range... Fried the transistor on it. That transistor gets hot as hell. Thing needs a heatsink on it.

Also, I couldn't get the damn thing to tune to channels 5 or 6 despite the kits claims that it could.

VCR modulators and similar cheap ones invade the lower adjacent channel, as they don't supress some of the lower sideband. Analog NTSC RF TV has the picture carrier 1.25MHz above the bottom end of the TV channel's 6Mhz of bandwidth. The sound is an FM carrier 1.25 + 4.5 MHz above the bottom edge of the TV channel. The video is AM modulated on teh picture carrier, with the sync tip at max modulation, black level a little lower than that, to white which is about 10% of sync tip. Real TV stations filter the lower sideband to stop at the bottom of the TV channel. Which requires a special filter, and this is the part VCR modulators leave out. As VCR modulators on channel 3 expect to feed nothing but a TV set tuned to channel 3, and not channel 2 when the modulator is on. But if you fed the VCR modulator into a splitter to combine it with a cable or antenna feed that has a channel 2 but an empty channel 3, oh, you would get a usable reception on channel 3, but channel 2 would be trashed by the unsupressed lower sideband of the channel 3 modulator.

Assuming that you can lay hands on some simple cheap Tv modulators that you can change the picture carrier frequency on, you'd have to put each on every other TV channel. Like 2,4,6,7,9,11,13. 6 is not adjacent to 7. To create your own analog CATV head end to feed your analog TV sets via coax.

Here is what Northlan Cable says about it on their website:

• How many television sets can I connect to digital cable?
You can connect to digital cable to any number of TVs in your home for a low fee per month for each additional TV. Alternatively, you can receive the Deluxe Basic lineup on each additional TV for no charge and without any additional equipment.
• Do I need a separate digital cable box for every TV?
No. You only need a digital cable box if you wish to view the channels above 99 or would like to use the digital guide.

Here is what Optimum says about a Theft of Service

Cable television theft is the illegal interception of cable programming services without the express authorization of, or payment to, a cable television system. There are two types of cable theft, passive and active. An example of passive theft is when a potential customer moves into a home, finds the cable service is on, but does not notify the cable company. Active theft occurs when someone knowingly and willfully makes an illegal physical connection to the cable system and/or attaches or tampers with equipment to allow the receipt of unauthorized services. Active theft can occur at either a consumer or commercial level. Commercial theft usually happens in an environment where the proprietor receives financial gains from the illegal services (i.e. a bar or restaurant).

Here is whare you can read about cable TV regulations:

http://www.fcc.gov/mb/facts/csgen.html

I've been looking at this unit...shown from ebay for info purposes only;

http://cgi.ebay.com/ChannelPlus-Mode...QQcmdZViewItem

It takes four inputs and can frequency synthesize your choice of four output channels within it's range. This unit is fine by itself if you want to cable all your sets individually. To add it to your existing cable, you need their insertion box which adds the output to a cable pass-through signal. It has four DA outputs I think. Search more for this info.

You might be able to use a splitter in reverse combining the incoming cable and Channelplus output on the output sides of a splitter and the input side then going to your main cable house wiring without the four output pass-through DA box. This would depend on signal strength needed around your house.

Using their insertion box, you would then assign your DVD, nannycam, laserdisc, etc. to unused channels on your cable feed. They have a variety of boxes for one or more channels. Obviously, the feed would have to hit a cable-ready device like a orphan VHS for a tuner and then on Ch 3 or 4 to your vintage set. In my case, cable channels 2 and 5 are open and would not need a tuner.

Anyone else ever try these boxes?

Dave A

Yes, but they're not as good as a good, so-called dedicated modulator. Dedicated as being dedicated to one channel. If you want to do it right, use something like a Pico commercial grade modulator, like a PCM-55, costs around $50 each. It puts out like 55 db and is adjustible. At that rate, you can power ALL your sets. Mount the ones you want in a rack mount or build your own. You won't believe the strong, clear signals!

Cory.....

You have the right solution. I even found one at Home depot. A 4 chanel modulator for $179. I think I will get one. Then I will buy 4 of those digital converters that the government is giving coupons for. I will tune each of the 4 convertors to a seperate local over the air digital chanel and feed the output of the converter to one of the 4 modulator inputs.

IN essence I will recieve the digital signal and remodulate it back to the old analog chanel and pump it down a 75Ohm antenna cable to my old tv sets. I think it should work pretty good. 4 analog chanels over the air is what I get now, 4,6,10, and 12. The neat thing is that if I ever want to watch a different chanel all I need to do is retune one of the digital converter boxes to different chanel.

You have solved my delima Cory. I was not aware of the multi chanel modulator box.

Here is the link to the one at Home Depot

http://www.homedepot.com/webapp/wcs/...7X-_-100598727

Bummer!!!! I just discovered that this unit does not modulate to the VHF band. Only to UHF and cable chanels.

Is there a unit that modulates to VHF???

Unless the amp was made for ATV, a typical ham radio linear amplifier's bandwidth is usually woefully too narrow to carry a 5MHz television signal, and most won't work outside the ham bands (6m, 2m, 70cm).

Theoretically you could try this setup instead (legal FCC/IC/PTT disclaimer intended and you've been warned, and if you're bright/dumb enough to try this you probably know the consequences :nono: ):

Cable head-end Modulator--->commercial cable distribution amp-->cable trunk amplifier--->single channel MATV antenna.

-the trunk amplifier is optional unless you need greater range.
-a real head end modulator is best since you can control output levels and it's true VSB, not a pro-sumer one.
-you'll need to use good quality coax cables like RG6 and RG-11.
-the antenna must be located in a manner that eliminates its feeding back into the amps, meaning away from the antenna. No rabbit ears here...
-older "~450MHz" cable amps that were used back in the day work better than the newer ones.
-stay away from ch4, as there are aeronautical users at 72+/- MHz and it would really suck if a 747 tried to land in your living room.

There's going to be a number of analog low power UHF translators going up for replacement (read: disposal) when the "event horizon" comes up. Most of these are solid state, have a proper "channel converter" to take channel "x" and make it into channel "Y", are reasonably compact and don't take up a room, and make some power (=range). If your head-end modulator can generate channel "x" the translator won't know the difference.

Enjoy...

Ah, see - you're talking about digital cable. That's proprietary and each cable company rents out the boxes. I don't get digital cable. I don't intend to. I tried it for a month but the picture was abysmal. But no. I'm not going to be stealing service. I pay for it. I'm not going to be circumventing anything, because with analog cable, I'm not renting a box - only using tuners in consumer equipment. In my computer room, I have an early 80's Mitsubishi 15" television. It's connected to a Sanyo Betamax VCR. The VCR does the tuning of the analog cable. No cable company equipment in my house at all.

With analog cable, it doesn't matter to the cable company if I have one set or a hundred, I don't get charged extra per set. Analog cable must be called "Deluxe Basic" by your provider.

-Ian

http://www.audiokarma.org/forums/sho...d.php?t=102105

$10 TV transmitter.

Somewhere in storage here I have the remains of the TV distribution system from a hotel that was dumped when they renovated. It consisted of 6 modulators (with A2 stereo, I've yet to see a stereo consumer modulator) set to various UHF channels fed from a bank of now long obsolete MDS receivers and 3 distribution amplifiers.

I doubt I'll ever have a place big enough to need such a set up, but it would be almost ideal (I would prefer VHF modulators as I have a few VHF only sets, but for some reason every setup I've seen like this uses UHF modulators). Just replace the old receivers with a few SD set top boxes and your ready to go.

---

I've been to a few big hamfests and there are always guys with piles of commercial equipment that has gone obsolete. I'll have to pay attention on the next trip. Some of that stuff goes very cheap.

Most low power UHF translators are fed from an existing NTSC transmitter which is transposed from one RF channel to another without taking it down to baseband (video/audio).

If they are exempt in the U.S. (they won't be in Canada), they will be in an interesting position. When the feeding analog transmitter (usually VHF, sometimes another UHF translator/transmitter) is no longer available, they will cease to function.

I haven't yet tried transposing a digital signal from one channel to another.

I suppose you could use a digital receiver STB with a channel 3 RF output jack to feed the translator input (assuming the translator input can be set to channel 3) to create an analog translated output.

A commercial "agile modulator" is probably the best device to use for in-house VHF signal creation. There is at least one on Ebay right now, item #120206024645. It goes down to 40 MHz, so you could even use it for Channel 1.

Good day Gentlemen,

Try this Greek made 100mW transmitter:

http://www.aspisys.com/tvpll.htm

All modern world standards (NTSC-M, PAL B/G, PAL-I, SECAM L, B/DK) in one unit. Synthesized, fully programmable.

Full choice of channels VHF and UHF + hyperband cable channels.

Enough power for full coverage of a normal house with near broadcast quality, however, DSB output (no vestigial sideband filtering) so technically can't qualify as "Broadcast".

I've got 6, ready for analog blackout if/when it ever happens.

I repackage in metal box, (i don't like plastic) and the metal provides good heat-sinking for the + 5VDC, +12VDC which otherwise run hot.

Not my company, just a happy customer.

Best Regards

jhalphen
Paris/France

---

I just emailed that greek outfit on that modulator. I could not find a US price on their site.
Sorry if I sounded ignorant on the ham radio linear idea. My buddy the ex-ham told me that a linear would not pass the full 6 mhz needed for such a task. It was just a thought but this aspisys thing seems much better IF it can be brought into the country legally and IF it works and IF it is not expensive. I shall advise if I hear from them. --Tom

Hi Thomas,

Some help:

Aspisys home page:
http://www.aspisys.com

Pricelist:
http://www.aspisys.com/pricelist.htm

The UTV-100TX is currently at Euros 132.00

Contact Engineer/Owner Mr Sotiris:
info@aspisys.com
sales@aspisys.com

As said previously, i have 6 units.

3 of which are the first generation model i purchased in 2002:

http://www.aspisys.com/tvpll2.htm

The newer model is even better & more powerful

BTW, my NTSC & PAL B/G transmitters are transmitting about 15 hours/day

Before these products i tinkered with broadcast quality agile modulators + wideband "Gain Blocks" from Avantek & Mini-Circuits to reach + 28 dBM RF out. Works well, but 19" rack units + the RF amps takes up precious real-estate...

Best Regards

jhalphen

They would have to modify the translator to make it a full transmitter by adding the exciter (the modulator if you will), thus making it no longer a translator. Like someone said earlier, the modulator from a stb would be double sideband, and would therefore not meet FCC technical requirements on the air.

Broadcasters are always trying to one-up one another. So if some broadcaster in a given area runs digital, they all will, or if they do what they did near my dad's place, a number of SD stations went in and put up one digital transmitter and each runs on a sub channel.

---

Why bother with all that? Get a VHS machine or similar (with an RF modulator), daisy chain 3 or 4 aerial signal boosters in line off of it (those ones you use to boost output from TV aerials in poor signal areas - nothing fancy), and wire the output of that into a standard TV aerial.

My mates and I did this in college (using my mid-80s Panasonic PAL VHS machine, and 4 Labgear signal boosters) and were able to broadcast fairly well over a 40 metre range or so. Not sure if the metal-framed building we were in added to the effect or not, but friends in an adjacent dormitary block were able to pick it up well.

We "debuted" "THe LoSt BoYS" the night before BBC1 showed it - but ours was uncut. Also broadcast other interesting titbits including soft porn, but had to dismantle the rig after 3 weeks or so as some neighbours just off the college campus were complaining about interference.

The staff never did suss out it was us, but they had their suspicions ;)

I see Blonder-Tounge Tube RF amps on ebay quite often. Some of them have very high gain, 50-90db. They would probably work well for a LPTV station.

There were at least two. I bought it and another one and will try them out and let you all know how they work. Unfortunately, buying them on that ePay place, the shipping tends to cost more than the item, and buying 13 of them could get a little pricey. Maybe I'll check the local hamfests/surplus stores for some more.

If anybody ever finds a tube type CATV modulator from the early 60's let me know. I want to restore one and have it on display and able to be operated at a real master headend. If the output was good I might even be able to put it out on the system for a while in the middle of the night. As far as real CATV modulators it's sad but we can't find anybody to buy em they have been going to scrap dealers for the metal.

ChrisW6ATV,

I just did a deal with a seller on epay for 5 Holland modulators to build my own VHF in home cable system. I got a chanel 3, 6, 8, 10, and 12. I will feed them with 4 digital converters all tuned to a different chanel, and also a DVD player on the 5th chanel.

Specific question for Chris, I will need some sort of combiner, I was thinking of a 6 in 1 out passive combiner spliter, but I am not well versed on this sort of thing. Will this approach work? And how many sets would I be able to power on the outpout of the combiner?

I also will have eventually a large number of tv sets to feed, probably 20 to 30 sets in my collection. Typically, how would you feed this many sets?

Thanks,
Bob

A combiner spliter will work just fine. Lets say you have an 8 port spliter you will lose about 11 to 12 dB going through it. Do you know what the output level of your modulators are? Most single channel CATV modulators will do +60dB.
It's all math you only need 0 to +3 at the back of the set. Each 2 port spliter you lose 3 to 4 dB.

Good Lock,
Steve

Spec for the modulators claim 55db output. I also got a commercial Holland 12 input combiner thrown in the deal for a few extra bucks. So worse case now would be that I might need a distribution amp at some point in the system, after I have lots of set hooked up to the output of the combiner. That will be down the road a bit. I only have 5 sets restored at this point, and about 30 more waiting to be restored.

These modulators rarely work well at their maximum output. Count on running them at +50 dbMV. The combiner will have a loss of about 20 db, leaving +30 for your splitters. If you split for 16 output, the splitter loss is about 14 db, leaving +16, which is plenty for the TV sets. You could easily drive 32 sets.

I found this:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=150202318726

It does 12 inputs to one output, not amplified (passive). Looks brand new. I'd get it but I just snagged a used one here:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=280189609459
along with two modulators.

From what I gather, some B-T rackmount units are set to one specific channel at the factory, others have DIP switches to select your desired channel. Presumably the latter were more expensive. The channel 9 one I can leave as-is, the chanel 17 one will be a science project. Hopefully just a crystal swap? The other ones I bought are a channel 7 and the switch-settable one mentioned earler. I paid way too much for the channel-7 one, in hindsight and after some research. I've seen a couple go for 5 dollars already. But I should have a good start sometime next week when it all arrives and it should be entertaining to say the least.