What would be a good modulator/transmitter, that would transmit in both VHF/UHF for TVs inside my house?

Look on that auction site for "Blonder Tongue" modulators. Many cable companies are going all digital, and unloading their analog equipment.

Ya, I've been thinking of the Blonder Tongue AM-60-550B AM Series..

Those are not bad units unless you get a damaged one.

What I recommend is to use a DTV box or a decent web search to find which RF channels are occupied with DTV carriers in your area, and avoid using those channels.

If you want more than one modulator get an agile modulator (one where you can pick any given channel) first, and test different frequencies, and antennas*. I would recommend getting blonder tongue BAVM-z modulators once you have found which channels work good. BAVM-z modulators come with the channel permanently fixed, but are cheaper, and come in a variety channel options. *I've had DTV adjacent channel interference prevent me from using some channels I wanted.

Shango66 has a good video on youtube on making a custom tuned TV transmitting antenna out of lamp cord that you may want to watch.

...and stay away from any "T" channel modulators - they are upstream modulators and not what you are looking for. I mistakenly bought two at an auction and was disappointed tof ind out what they were.

Cheers,

I received my Blonder Tongue AM-60-550B today, it was preset to 16 on the dip switches.. I'm trying to go into the UHF channels and can't get anything out of UHF.. and have the same antenna set up with the loop antenna as he has in this video.. I don't have a manual or dip switch card but I did download the card from here http://antiqueradio.org/HomeTVTransmitter.htm.. I'm able set presents for the single digit channels, but on the UHF channels I can't get anything out of it, I think with the UHF the left side is used to add up for first digit and right side is used for the second.. Anyways I tried different combinations, and nothing.. This guy in the video is able to get strong signal with just a loop antenna and not even any antennas on his sets..

https://www.youtube.com/watch?v=V3k4e-0_Wy8

I'd go with a UHF bowtie dipole. Those loops are shorts. 75ohm cable is transmission line. if you short transmission line and it is at the wrong fraction (or multiple of) the wave length of the transmitted signal then some or ALL of the transmitter signal power will not be transmitted but instead reflected back to the transmitter (which can damage some transmitters).

Also I'm leery of using matching transformers/baluns designed for receiving antennas...The transmitter power may be sufficient to damage them, and cause poor or NO performance.

I'm VHF exclusive right now, and this video has been my guide.
https://www.youtube.com/watch?v=z4dhRt7tmd4
I'd give it a try on VHF this way first, then start trying UHF if I were you....That video you posted is the first talk of using a BT mod for UHF that I've seen.

I'm using VHF and made an antenna similar to the video you posted and signal is very weak, doesn't even come in good 3 feet away from it.. And can't get anything from it outside the room that's viewable.... 7 8 and 9 seem to be the better channels.. All other VHF channels seem to either not be anything or something very weak.. I had it hook directly at one time and still could not get a UHF signal to the TV.. While hooked directly with using a VHF channel still pic is not 100% clear, still slight noticeable fuzz and noise pattern on screen.. If I adjust to channel 10, 11 or 12 the green light starts blinking.. I don't think this thing is working right at all..

First off make sure your antenna is TUNED TO (ie cut to the proper wavelength for) the channel you wish to transmit on.
I first tried my modulator on a pair of all band rabbit ears, and could hardly get 30' of range at max transmitter output, but with a tuned dipole I could could get the same range with MINIMUM transmitter output, and several times that distance with the output maxed.......

...Which reminds me, do you know what all the pots with flat head screw driver adjustment on the unit do? If not here is a run down on how to set them: Output level should be maxed (until you know the max transmit range, then back it off a bit if the signal travels farther than you are comfortable with). The audio and video level controls are also important to set. Tune in a TV to the signal and increase the video level until you see fine bars/noise in the picture and the synch gets messed up, then back off until the picture is normal. The audio and aural carrier should be tweaked the same way up until distortion, then back off until good again. Some models have over-modulation indicator LEDs....You don't want them to light more than the faintest amount...Back off controls till they JUST go out.

Channel 7 seems to work best on my BT agile modulator too. Channel 2 gives me about 2-300' radius, channel 7 gives me about 1 block radius, and 9 gives me about 3/4 block radius. 3 and 4 are not used to protect VCRs being used with their RF out, 5 is DTV occupied here, 6 has too much interference from 5 to be used, 8 is also DTV, and I don't have enough modulators to bother with channels over 9 presently.

BTW I don't recommend using wire thinner than lamp cord strands for the dipole antenna leads....Thickness of the dipole wires is directly related to antenna bandwidth and a 6MHz NTSC TV signal has a whole lotta bandwidth....They did not make roof top TV antenna wires finger thickness just for resistance to wind damage, they wanted the entire bandwidth of the signal to be strong, clear and flat.

output level is maxed, all other levels are adjusted and were backed off until indicators went out for both audio and video.. But I would think to have a clear pic with this thing hooked directly to the TV right? I'm getting a bit of fuzz and a slight barley visible line pattern on the screen.. I'm not aware of those pots.. Probably under the cover where the little screw is..

Was using 18 gauge stranded wire.. I didn't cut them to the proper range though.. I also have lamp cord if that would make a difference.. I don't have a VHF/UHF Antenna Analyzer like Shango has, they are in the $300 range on eBay..

I have the model AM-60-550B I know there is a model AM60-550 without the "B", not sure what the difference is...

That spatsbear guy on Youtube just has that loop antenna, and TVs with no antennas hooked up and he get a perfect raster with UHF, even in a next room over.. I can't get nothing to come up with UHF, nor even a perfect raster hard wired.. I do have a UHF bowtie dipole antenna in storage that's connected to a 85" GE portable that I can take off and use.. But this thing is not giving me any UHF..

Hooked directly to a TV you may have TOO MUCH signal power for the tuner to handle. With a direct connection start with minimum output power and slowly increase it until it is decent, if it even needs any increase (which it should not). The pots I mentioned and named are on the front and back panels and can be adjusted without opening the unit....

Try again with lamp cord and cut to the appropriate length for the channel you are going to use.
I do NOT have an antenna analyzer either....The math process Shango uses was sufficient for me to cut antennas that work well. Cutting them to proper length is rather important...You will get VERY little transmission range if you use an antenna that is not tuned to the station you wish to transmit on (case in point the crappy results I got with an off the shelf UHF/VHF all band antenna). Also make sure your dipole is high up in the room you are using it in, the two ends of the dipole are pointed away from each other, the dipole leads are taught, and the antenna does not sway, vibrate or move in any noticable way.

Lets not worry too much about UHF for the moment. UHF is much more finicky to transmit and receive on, so lets first get good results with simple VHF frequencies and methods to prove your modulator is working before working with UHF.

By the way do you know what RF channels (as opposed to those stupid, fake 'virtual channel numbers') your regions DTV stations are transmitting on? That is important to know. If you transmit on the same channel as a regional DTV carrier your modulator will likely be drowned out by the DTV station, or at least severely interfered with by it (or if you look at it another way you may be jamming your neighbor's attempts to receive that DTV station, which could bring the FCC to your door). If you can, also avoid channels next to DTV stations (at least until you confirm your modulator is good) as adjacent channel interference may result.

Also the test TV is important. I'd test the antenna with a newer solid state TV (preferably a portable that you can walk outside with to check the signal range once you get it right) if I were you. It is hard to be certain of the calibration and performance of the receiver sections of older TVs. If it works with a newer set, but your old one is not liking it then that old set will need some work.

Remember over modulation and under modulation can cause many strange effects just as too much signal or too little signal can cause undesirable effects.

I'd rather trouble shoot this wired directly to the TVs first, it will better determine there is a problem much easier.... Comes to find out that it's only channel 3 that has a slight line pattern.. Hard wired with it set to channel 7.. I adjusted the audio/video peak controls and the level and aural control, and still there is a bit of noise in the pic like the station isn't coming in at 100%... I notice there is 3 or 4 holes on the top front of the unit, they seem to be pot controls. 2 of them are adjustable, I adjusted those two, and they didn't do anything, and they don't have any kind of label on them either.. No pots on the front and back panels, other than the front what everyone already knows (Audio/Video Aural and Level Controls)..

On the other forum, someone mentioned that this unit may have a power supply problem, which results in weak signals.. They said they have a bunch of these units and one with power supply problem..

Looks like I'm going to have to return this.. Just my luck I received a unit with problems.. Seems like this always happens to me when I get a new item I learn about..

Here's a short video of what I'm talking about.. That's as clear as It can get:
https://www.youtube.com/watch?v=8-OH56RL1b8&feature=youtu.be

Don't tweak the ones other than already mentioned unless they are labeled, you know they need adjustment, and you know how to properly set them.....A modulator is essentially the opposite operation of a TV tuner/IF system, and just like a tuner IF system if the adjustments don't look like user controls then they should not be casually messed with.

Try lowering the Video, audio, and aural carrier levels, and see if the interference goes away.

Also there should be a short IF patch cable on the back connecting 2 75ohm jacks together...Try another cable in it's place (the one it came with may be damaged).

I've done all that, and more than once.. And just tried replacing the cable.. Now I notice the audio and video over modulation light stays lit, even with it all the way down as the unit gets warm..


Here's a video of what the issue is:

https://www.youtube.com/watch?v=8-OH56RL1b8&feature=youtu.be

The over modulation light issues were the pot controls on the top I had adjusted.. I got them to where they should illuminate.. That was a whole problem in it's self that I created and fixed..

I can't see a problem in the video....

If the over modulation lights stay lit with the controls all the way down, then that is a problem with hum (probably 60Hz) getting into the signal. It could be a result of your AV source having a different ground voltage than the modulator, or mod output being connected to something with a different ground potential. Using a power line isolation transformer to power things independently may work to fix it. You can trace the source by unplugging things till the lights go out.

My agile mod likes to randomly introduce hum in it's output, and interfere with my fixed modulators....Some BT modulators are old enough that the lytics have gone bad, and I suspect mine is one....Yours could also be one.

I fixed the over modulation lights as mentioned above.. The problem is there.. You don't see the noisy video? actually the camera picks it up more that what I actually see, that's not a pixely youtube video, that's actual noisy video from the TV screen, it's very noticeable...

Sorry bout that. You posted while I was writing my previous post.
I could not see video noise...Granted digital video systems try to suppress noise to get better compression and fine noise is harder to record.

If you have been using a cheaper modulator before this how much more noise can you see with the BT modulator? It is hard to get noise free RF video, so there should be a threshold where (say at normal viewing distance) it is very difficult to notice which should count as good enough.

I was using a regular cheap RF modulator to run from the digital cable box RCA outputs to the modulator and output coax to the TVs, seeing how the cable box doesn't have a coax output, and there is no noise with the cheap RF modulator..

Here is another youtube video with someone outputting directly to TV with their Blonder Tongue and the video is perfect..
https://www.youtube.com/watch?v=KQ_83G8UEgs

I'd go with a UHF bowtie dipole.


I'll also :sing: the praises for good old oven-rack in fancy-dress with bowtie(s) style of antenna. Damned good at what they do.


The discussion on baluns in this thread so far is spot on. That is to say, your bog-standard 75 to 300 ohm TV balun is absolute crap if you're trying to transmit power through it. (TBFH, the average TV balun is just crap, full stop.)


http://www.kyes.com/antenna/balun.html has a good writeup/table on the kind of losses you'll be facing. -3dB means you're losing HALF your power, -6 means you're losing THREE-QUARTERS. So for VHF use, you'll be lucky to see 40% of what you put into it come out the other end. For UHF it's a roulette wheel style thing where on a given channel you might only lose 30% of your power, but if you slightly alter the length of the cable at some point suddenly you're losing 90% but on a previously unusable channel you're getting great throughput.

The page I linked also includes information on rolling your own 4:1 balun, but this link will make things a bit easier. http://n-lemma.com/calcs/dipole/balun.htm The important thing here is that you do need to know with some level of confidence what the velocity factor of the cable you're using actually is. Dig through your coax stash until you find something that has a series number on it that you can turn into a spec-sheet with google. (If you see Belden, you've got it made.) Once you plug the known velocity factor into the calc, next you'll plug in the video carrier center frequency(Not the channel center frequency.) for your channel of choice, and the calculator will return a length value with a hilarious number of digits east of the decimal point. For your purposes here you can round to the nearest 0.1" and be OK. Good cable-prep and soldering skills will help, but if this is your first time making RF signal transmission line connections, spending half an hour practicing on a few feet of junk coax is a good idea, so that you get a feel for where and how to begin the cutting/stripping process so that your finished length is as close as possible to the ideal desired length.


I'm also in agreement that you probably want to attenuate the output of the modulator if you're direct wiring it to a set.

Thanks for all the info.. I suspect that will come in handy when I get a unit that's functioning properly..

Made an Antenna.. Haven't cut the lamp cord yet.. Waiting on another unit..

http://i1220.photobucket.com/albums/dd458/vintageceilingfans/Misc%20TV%20Video%20Stuff/DSCF3223.jpg
http://i1220.photobucket.com/albums/dd458/vintageceilingfans/Misc%20TV%20Video%20Stuff/DSCF3215.jpg
http://i1220.photobucket.com/albums/dd458/vintageceilingfans/Misc%20TV%20Video%20Stuff/DSCF3219.jpg

I wonder what kind of antenna would be needed with multiple modulators and an active combiner.

I'd cut all but the coax connector side off of the box and make it so that the closest the wires come to each other is the point at which they are soldered to the connector....

I'm able to keep this unit and get a full refund.. Right now I'm testing all the electrolytic caps on power supply board with my ohm meter and eico cap checker.. So far all the bigger caps are either testing out of range, not giving a reading at all, and the Eico leakage test eye opens slightly instead of all the way at their 35v ratings.. And small cap is not even making contact with one lead (pictured)

http://i1220.photobucket.com/albums/dd458/vintageceilingfans/Misc%20TV%20Video%20Stuff/DSCF3224.jpg

For shits and giggles I'd order up all the standard electrolytics from capacitorworld and see what happens.

I'm going to, then I'll have 2 units working hopefully.. Look at the pic, that's the way that cap was when I opened it, not even making contact.. I suppose I should replace those rectifier diodes too..

I'm going to, then I'll have 2 units working hopefully.. Look at the pic, that's the way that cap was when I opened it, not even making contact.. I suppose I should replace those rectifier diodes too..

They seem to have gotten a bit toasty... Granted they probably have eleventy-million hours in a hot and cramped headend rack on them. Looks like there's room to stand the replacement rectifiers up off the board when the lid is on, plus an extra 5 cents per diode x4 for the good ones isn't a big deal when the shipping charge is considered. :yes:

I just got my second BT modulator model "A" model, and it's preset for UHF 23, which I'm going to leave it, and it's working great, and I'm just using a bowtie dipole antenna that I don't have extended yet.. I'm able to pick up signal at the end of the block.. I tried the GE set, and the UHF actually comes in on that set.. No pic though, but sound comes through.. The caps arrived today for the problem modulator, I'll recap that and use it for a VHF channel.. Probably 7 or 8..

What would you recommend broadcasting with UHF? just a standard botie Antenna or shango066's method?

I just got my second BT modulator model "A" model, and it's preset for UHF 23, which I'm going to leave it, and it's working great, and I'm just using a bowtie dipole antenna that I don't have extended yet.. I'm able to pick up signal at the end of the block.. I tried the GE set, and the UHF actually comes in on that set.. No pic though, but sound comes through.. The caps arrived today for the problem modulator, I'll recap that and use it for a VHF channel.. Probably 7 or 8..

What would you recommend broadcasting with UHF? just a standard botie Antenna or shango066's method?
Glad you got a working mod. I'd probably go with a UHF bowtie. Odds are at UHF, without a SWR meeter like Shango has, it will be hard to cut the length close enough to optimum frequency/ impedance match for there to be much benefit....But you could try if you are curious, and I could be wrong.

Thanks!!

I recapped the other mod, and replaced the bigger rectifier diodes, it's noticeably better, and able to program it for UHF frequencies now, but it still has issues with reception, it's still weak, not as weak as it was before but still much weaker than my second mod.. I did order up the three transistors, and the smaller rectifier diodes, I'll try replacing those tomorrow to see if it makes a difference..

With the bowtie I'm able to get reception about a block radius with an area where it's completely dead.. I thought it would go a bit farther with UHF..

Thanks!!

I recapped the other mod, and replaced the bigger rectifier diodes, it's noticeably better, and able to program it for UHF frequencies now, but it still has issues with reception, it's still weak, not as weak as it was before but still much weaker than my second mod.. I did order up the three transistors, and the smaller rectifier diodes, I'll try replacing those tomorrow to see if it makes a difference..

With the bowtie I'm able to get reception about a block radius with an area where it's completely dead.. I thought it would go a bit farther with UHF..

About a block with the unit on the second floor is what channel 7 gives me....I always figured VHF (especially low band) would give better range since the lower the frequency the less a TV signal behaves like light/FM radio (line of sight transmission), and the more it behaves like AM/SW signal (sky waves and skip)...I hear tales of people with just a few trees between them and the towers loosing DTV signal when the wind blows the trees, so if there is something like a brick or metal wall, vent ducts in the walls, a fence, or something of that nature between your transmitter and and your receiver in your UHF dead zone odds are it is the cause of your dead zone.

Two other things to consider: All antennas are directional to some degree (google radiation pattern of antenna in question, in your case UHF bowtie dipole, to see it), and dipoles have the weakest reception at an angle at which the transmit antenna is pointing at you*. Also the RF power of the BT seems to vary from channel to channel (which is not too surprising given is is hard to make wide band tuned circuits and reflected wave traps completely flat over the whole TV spectrum).

*Another side effect of directionality is what IIRC is called polarity mismatch....If the TX and RX dipoles are oriented to face 90 degrees different from each other then minimal signal transfer for the other given conditions will be minimal.

I took an antennas elective last year, and despite it being the first time the class was offered and the professor diving way to deep and spending way too much time on the maths of infinitesimal dipoles I did take some useful stuff away from it.

Walking with the TV, it's mostly in and out, static and picture after about 2 houses down. I tried it with VHF and 7 seems to be the channel that goes the farthest.. Channel 6 Seems to work better closer, but a radio station interferes..

I opened the other modulator and realized that one of the 10mf 50volt caps I took out during the week, I forgot to replace, so I was actually operating the modulator without a cap that is needed.. I replaced it, no change in performance, and I also changed out the rest of the diodes and the 3 transistors, and it's still very weak.. I'll switch the mods and use the same channel and antenna and the TVs will come in crystal clear with the new one, and an unwatchable pic with the one that has problems..

Walking with the TV, it's mostly in and out, static and picture after about 2 houses down. I tried it with VHF and 7 seems to be the channel that goes the farthest.. Channel 6 Seems to work better closer, but a radio station interferes..

I opened the other modulator and realized that one of the 10mf 50volt caps I took out during the week, I forgot to replace, so I was actually operating the modulator without a cap that is needed.. I replaced it, no change in performance, and I also changed out the rest of the diodes and the 3 transistors, and it's still very weak.. I'll switch the mods and use the same channel and antenna and the TVs will come in crystal clear with the new one, and an unwatchable pic with the one that has problems..

You might just have a dead one. You gotta remember these modulators are extremely high hour devices. Some might be dead.

I got mine from some seller down in Texas. It works good. I'm pretty happy with it. All my video devices are plugged in to it. I love wireless video

One thing to be aware of is reflection damage. It is a phenomenon caused by impedance mismatch. If you connect a 50 ohm antenna to a transmitter and coax system designed for 75 ohms there is an impedance mismatch. Impedance mismatch on a transmission line (75 ohm coax is a good example of transmission line) has varying effects depending on how long the line is relative to the wavelength of the transmitters signal (google Smith Chart to learn more about this and it's uses). If it is at one fraction of a wavelength the transmitter will see an open circuit as the device connected to it's antenna terminals (which may or may not be good, can't remember), if it is at another fraction of a wavelength the transmitter sees a short circuit (because all the output power is reflected back into the transmitter) which means no power is transmitted and the transmitter is in danger, and at still another fraction it sees the 50 ohm antenna as a 75 ohm load (which is ideal).

In the early days of SS transmitters the short condition (all power reflected back) would usually destroy the output transistors....More recently reflection traps were devised to protect the outputs, but they are not infallible, and if damaged can block/attenuate forward signal flow, or allow enough reflected power to reach the outputs to cause damage. Your units traps or outputs could be damaged.

Here's my setup.. I just got another one that's a 450A model that only does the lower end VHF.. I got a good deal on the 450 model and took a chance with an as is auction, and it also works great.. I've got it the broadcast channel 10 which I can go down a few houses with my Sony Watchman and it still having a viewable pic.. I don't even have antennas on the TVs in the house other than the coax cable hookup and they come in clear.. I'm broadcasting on a VHF and a UHF channel between the two.. I may go as far as putting an antenna outside with a transformer to see if I can get several blocks of a watchable signal.. I found an old computer power station last Saturday at a local thrift for $3.. So that's good for shutting things off.. TV below it has slight hum bars and the one in the living room does too, but the other sets don't.. I think it's because they are plugged into a power strip, or near the cable hookups..

http://i1220.photobucket.com/albums/dd458/vintageceilingfans/Misc%20TV%20Video%20Stuff/DSCF0053.jpg

One thing I do is power my mods through a line voltage isolation transformer. Sometimes the power supply and grounding of the BT mods does not like to play nice with the PS and jack grounding of video sources creating hum bars....