I've got a few of these, perhaps they've been discussed before. Now with the DTV transition, I think now is a good time to inform those who want to still use their old TV how it was meant to be. I like the idea of the TV doing all the work, that is, no cables hooked up to it, no converters etc. While the days of the old TV being independent and receiving signals without any other source are nearly gone, heres something I think all the TV guys should own if you're like me:

http://cgi.ebay.com/Wireless-UHF-Audio-Video-Transmitter-Sender-TV-DSS-DVR_W0QQitemZ170342607387QQcmdZViewItemQQptZLH_Def aultDomain_0?hash=item27a935ea1b&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1205%7C 240%3A1308%7C301%3A1%7C293%3A1%7C294%3A50

Its small low powered UHF transmitter. Transmitts on channels 14-31, channels adjusted via potentiometer on the unit. Its actually a pretty decent little transmitter. In a metal case, self contained power supply, totally analog (lots of resistors, transistors and caps) so its completely serviceable if it ever breaks down. No chips or digital microscopic parts on the board like whats inside the converter boxes.

I will say one thing, when you first power it up, it does want to drift off frequency a bit, so you'll be touching the fine tuning of your TV set a few times through out the hour. After its been on for a few hours, its nice and stable. I leave mine on all the time, and it does have very good range. They work best on RCA sets because of the way the IF is tuned. You'll get some intercarrier buzz though any zenith tube type set using this box, which can be aligned out of course. Another plus is that you can adjust the luminance signal, and sound signal at the transmitter, and also has a switch so you can transmit a cross hatched test pattern, which is pretty nice. I have three of these hooked up to three converters of some of my favorite channels. This way, if I want to watch an old set (having UHF of course), I simply hook up the loop antenna to the set, tune the UHF dial and the only cord going to the TV is the power cord, which is the way I like it. Just thought I'd pass the word on. For what its worth, I used to see TONS of these on ebay from numerous sellers. Now, it appears that there is only one seller left. I suggest you grab them before they are all obsoleted, which is probably going to be very soon.

Exactly what I use. Bought it off flea bay about 3 years ago to use with a security camera. It runs 24/7 and it still works great to this day.

Or you could pick up an old analog broadcast transmitter on the cheap. Some Stations don't know what to with them.

old analog broadcast transmitter on the cheap. Some Stations don't know what to with them.

Probably a market for them in 3rd world countries. :banana::D

Thanks for the tip Doug. I'm glad to see you posting again!
-Tony

Hey Doug! Nice to see you back. I just bought one, I hope it works as good as you say.

I was searching for one of those, but didn't find one until you showed this one... Thank you! I'll get one and play with it. I wonder if anyone makes a VHF version?

Charles

I was wondering that myself, I have many VHF only sets. I hope to find some commercial modulators on different VHF channels but no luck yet.

I too wanted to find an equivalent set up for VHF only. I looked everywhere, and the best I could come up with was one of those little ramsey kits, it was for VHF channels 2-6 only. They're expensive, around $100 for the kit, but don't know how good the design is.

This UHF one works well on most any TV, but I noticed that on Zenith tube type sets, I get that intercarrier buzzing. Its not existant on an RCA type set though. The IF's are different on the Zenith and RCA's, so you'd have to touch up your IF on the zeniths to get it spot on.

I like the UHF one, even though its really slapped together. Hopefully he's not the same guy who ships these in nothing more than a bubble wrap envelope. I bought one and it came that way a while ago and it was all smashed up!

I stocked up and bought 6 of them last week. Ironically, they arrived on my door step on the 12th. I do remember the build quality being alot better on the older ones from about 5 years ago. I let some guy at work barrow it and then he quit and never heard from him again.

Here's a pic of the inside, notice mine was a factory defect. Apparently a bad diode was chopped out and a new one tacked in.

http://img.villagephotos.com/p/2009-3/1337386/DSCF8220.JPG

Just gotta love the lack of quality control and pride put into the cheap crap we're forced to buy. Look how crooked all the other part are put in. I may disassemble mine when it comes and put the G*d d*mn parts in right if it looks like that. I did better work at age 12.

Yeah, no wonder the stuff fails...:scratch2:

Sad thing is, it was probably put together in a sweatshop by a kid YOUNGER than 12.

probably true. Atleast they tested the thing and fixed it as opposed to just passing the defective unit. Normally, when I buy new electronics, I end up getting the defect then best buy wants to charge me the 15% restocking fee because I opened the box.

Yep, been there too. I once bought some "KLH" speakers at Best Buy about 9 years ago. They were on sale for 99 bucks for some "12s" so I was all happy, I get them home, hook 'em up and what crap. Back in the box they went and I took them back (after peeking inside at a woofer). Turns out there was a bunch of defective ones and they had 'em fixed with cheap horrible woofers that didn't match the specs of the originals in any way. They had a little sticker on the magnet that said made in china, all the other drivers were labeled KLH. I took them back and they were all rude and said Oh, we're going to have to test them, in a smart ass tone. He came out of the room a few minutes later and said go get new ones. I opened 6 boxes and finally the last box had the right woofers installed. I sealed all the others with their tape gun that said best buy over and over on the tape and went on my happy way, they are in my living room right now because I'm restoring my CV D9s and Klipsch Forte II's. Sorry for the OT comment but wanted to share it.

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.:thmbsp: And possibly modify it just a bit and boost the power, you know, just a little:cool: I watched a lot of "Home Improvement" as a kid:D "Arrrh Arhhh AArrhh!!! MORE POWER!

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

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

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)

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.

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/showthread.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.

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:thmbsp:
I recommend buying them, I was pleasantly surprised.

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. :scratch2:

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.

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?

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/Parts-Accessories-Plug-Ins_Amplifiers_W0QQfclZ3QQfromZR11QQfsooZ2QQfsopZ2 QQsacatZ25392QQsbrsrtZdQQsocmdZListingItemList

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

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.

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.

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

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