Use this to keep your analog TV's truly analog:

[zenithfan1]

You know, It would be feasible to study how it's made and what hooks to what and make your own on a bread board or point to point wire it in a home brew chassis. And possibly modify it just a bit and boost the power, you know, just a little I watched a lot of "Home Improvement" as a kid "Arrrh Arhhh AArrhh!!! MORE POWER!

[AnalogDigit]

Where can you get these transmitters? I want to get one! Even a kit would be nice.

[zenithfan1]

Check Doug's original post, there is a link. I got one but it's not here yet.

[richms]

I tried one of these (similar model but 5.5MHz audio) before I had dug for coax out to my work shed and was too cheap for 2.4GHz gears - and lets just say that the harmonics on it were somewhere they shouldn't have been. You should be fine inside a house with them, but slapping a UHF antenna on it pointing at your shed may not be the best of ideas. I was using it to send the output of the quad splitter and later the DVR so I could watch the driveway for deliverys when in the workshed.

I am always very cautious what I watch when using wireless video stuff since you are effectivly broadcasting it to your neighbourhood (so no pr0n or bootlegs of startrek over it)

[Whirled One]

I picked up one of these UHF transmitters on eBay based on Doug's recommendation, and it arrived today. Offhand, it seems to work pretty well for what it is, and it's definitely better than the Ramsey VHF TV transmitter kit. [Note: the Ramsey transmitter I have is the old original version; the current version (which is more expensive) may work better.]

The built-in pattern generator would definitely be handy for tuning the transmitter without having to connect a video source, but unfortunately isn't a terribly useful pattern from a service standpoint.

[wa2ise]

Originally Posted by zenithfan1

I was wondering that myself, I have many VHF only sets.

I modified a number of TV RF modulators, see my thread
http://www.audiokarma.org/forums/sho...d.php?t=220321

Changed the TV channel crystal to ones easily available from digikey or mouser. Did channel 2, 5 and 6, and even one for the old channel 1 that you sometimes see on early post war TV sets.

[zenithfan1]

My UHF Doowacky showed up today! It works nice, jus don tri ta reed da ownars emanual. The schineese needs to larn haows to speeel in anglash proparlet.
The good news is that it works anywhere around the house and back yard
I recommend buying them, I was pleasantly surprised.

[Jeffhs]

I'd suggest getting basic cable. I have Time-Warner cable (the lowest level they offer, local channels only) and have since found out that all of the local TV channels are transmitted along the cable (and they also arrive at your TV) in NTSC analog, not ATSC digital, no converter box required. There are no problems with the FCC as far as the TV stations are concerned, as these are video signals fed over coax cables or fiber optics, etc. directly to the cable headend and, at your TV, directly to the set over the cable. You could use a cable hookup like that and still have analog reception on old sets, although of course if you have more than one or two sets, the cable runs with splitters could get messy. Time Warner will connect every TV you have for no additional charge, if you subscribe to their basic cable package (they ran lots of ads for this in the last week or so before the DTV transition), although I wonder if they would balk at having to connect 50 antique sets in one house. They may do it, but I doubt if it would be for free with that many sets. Hmmm.

[zenithfan1]

That would be so funny! I'd love to see their face when they see all those tvs! I have satellite and am thinking of getting cable but I still need these for all the little guys around here. It's also nice to be able to take an old set out into the yard and use it the right way. I am also building an in home head end unit with commercial Blonder-Tongue RF modulators and combiners, it's gonna kick azz! I also have some other ideas too.

[fsjonsey]

I wonder how hard it would be to replace the RF output transistor with a more powerful one for better range? Or possibly add an external antenna connector as well?

[jhalphen]

Hi to All, Hi Fjonsey,

I've had good results using a wideband RF "Gain Block" (see pictures)

To get decent power, say 50mW, 100 mW,...1Watt, you're going to need a lot more gain than just adding an extra RF PA transistor. With the typical RF modulator, you will need 3 stages, 2 with high gain/low power + the final RF amp.

By using a Pro A/V modulator, you can get away with only 2 stages as these models can usually be cranked up to a pretty high output level.

For instance, looking at the spec sheet of the Blonder-Tongue AM Series agile NTSC A/V modulators, the output level is specified as +40dBmV to +60dBmV

That is 40 or 60 dB above 1mV defined as the 0dB level. If you convert to power on a 50 Ohm standard RF impedance,

42dBmV equates to 0.0032mW
60dBmV equates to 20.97mW

Hence the need for more power if you are to get any range for your transmitter.

Gain block RF amps are found in this E-Bay section:

http://business.listings.ebay.com/Pa...istingItemList

Mini-Circuits is still in business, Avantek also maker of interesting products, is defunct. I look for DC-1GHz amps or DC to a few hundred MHz. Personally, i stick to VHF Bands I & III and hate UHF because of its unpredictible field strength distribution in a house/condo appartment.

Also, from recent research i did on the frequency re-use of vacant ex-analogue TV bands, for instance in France VHF Band I will remain abandoned (so i am relocating all my transmitters there), VHF Band III is allocated to future DVB-MB digital radio broadcasting, a more advanced version of DAB radio, the UHF band remains committed to DVB-T television in SD & HD formats. The upper end of the UHF band (740-892 MHz) is being sheared off for "new digital services to mobiles", probably DVB-H H264 broadcasting to cellular phones.

To come back to RF power amps, each file name includes brand, bandwith, gain & output level.

As a low power, high gain "preamp", i like the Mini-Circuits ZFL-500:
20dB gain, +9dBm output, bandwith 50KHz-500MHz (see pdf).

As a high power final RF output chain, i like the Mini-Circuits ZHL-1042J:
20dB gain, +23dBm output, bandwith 10 MHz-4.2GHz (see pdf).

or the Mini-Circuits ZHL 2-8: 27dB gain, +29dBm out (a bit over 1W with full drive), bandwith 10MHz-1GHz.

To finish this long post, i feel it would be a worthwhile project to pool our knowledge here to achieve a sure & tried recipe of building block components so that each of us could enjoy OTA NTSC again via low-power TV transmitters.

Best Regards

jhalphen
Paris/France

[Adam]

I just got 2 of the B-T vhf modulators, one ch3 and one ch5. I hooked up the ch5 one to a dvd player. I hooked the output of the modulator to a pair of those "rabbit-ear" antennas fully extended, and have the output control cranked all the way up. I'm receiving it throughout the house, not just on the ground level, but also in the basement and upstairs. The picture is perfect downstairs and in the basement, not 100% upstairs, but still very good. I don't currently have one of those portable tvs, so I can't check to see how far it goes outside.

I want to eventually try having both units working at once, hoping that being 1 channel apart they won't interfere with one another. If the ch3 and 5 units will work together, I might pick up a couple more for the higher vhf band.

[zenithfan1]

Those B-T's are cool, I have a few too as well as a signal combiner. Fun to play with and I recommend we all get a few.

[jeyurkon]

I have two of the 60 dBmV B-T modulators. By matching a 1/4 dipole I get strong reception within the house. I also have a 45 dB unit, but I don't expect to get much range with it. I might boost it, but not to 1 watt.

With one of those 1 watt units, I'd probably have the whole block watching. Occaisionally the cable company, and more rarely the FCC, drive around checking for cable leakage. They might notice that!

John

[jhalphen]

Hi to all,

Well, i'm happy to see that the idea of private OTA NTSC is catching on!

John, i agree that 1Watt is overkill unless you have a big ranch in the wilderness.

Like you, i'm a city dweller. I operate a PAL B/G and NTSC transmitter 12 hours/day, 100 mW each. Absolutely no neighbor, nor "Big Brother" problems.

The trick to happy broadcasting is to not interfere with any signal someone else might want to watch.

Now that analogue NTSC is defunct, you should have channels 2-13 all to yourselves, lucky guys!

Best Regards

jhalphen
Paris/France