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ch3 video to uhf upconversion
Hi all,
It's me again, attempting yet another mad science project, and I have practically googled the subject to death before thinking of asking this group for help: I am wanting to put video (preferably color but will settle for grayscale) onto a UHF TV channel for inhouse use only. I am considering doing it as follows: 1) Convert output of a VGA card to composite video using resistive combiner (found a few on net). 2) Place composite video on VHF channel 3 using a game modulator. 3) Upconvert the video signal on VHF to UHF by with a local oscillator whose frequence is the difference between the channels. I'd use an active mixer circuit from the VHF/UHF part of the Handbook to do this. 4) To test functionality, attempt to tune in using either an analog TV receiver or a TV tuner card. Question is this: Is point 3, upconverting video from VHF to UHF, a generally workable technique? Any other gotchas or pitfalls to my intended approach? Thanks in advance, The Eternal Squire |
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Did some research on Alps UHF modulator, these are limited to channels
30 - 37. I am wanting more channel range, but these would be good for experiments I suppose. What I want is to ask if upconverting the HF television signal to the center frequency of the UHF channel would have the same overall effect as using a direct modulator.. The physics says probably yes, but are there any showstoppers other than physics? The Eternal Squire |
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Andrew VK3BFA wrote:
The easiest way is to gt a hard rubbish vcr, (most have been dumped because of tape transport faults) use the av inputs, and output on a UHF channel - the modern ones have tunable UHF output. Not in the States. VCR modulators here output on VHF channels 3 or 4. (60-66 or 66-72MHz) If the OP can find a foreign UHF modulator, it should work with US signals, with two possible issues: - The sound-video separation is different. This means the sound will be on the wrong frequency for an American TV. If the OP doesn't care about sound then this isn't a problem! - TV channel frequencies are different in different countries. Most Australian channels don't coincide with American channels. (if a modulator tunes Australian channels 30-37, the only channel in that range that corresponds to an American channel is 32, which is American channel 28) Are European/Australian VCR modulators continuously tunable? Or can they only be set to discrete channels? http://www.73.com/a/0019.shtml offers a "block converter". (among dozens of other items! It's about 3/4 down the page on the left-hand side, stock #AE047) It's a broadband frequency converter that will convert a US channel 3 RF signal up to US channel 37. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
Doug Smith W9WI wrote: Andrew VK3BFA wrote: The easiest way is to gt a hard rubbish vcr, (most have been dumped because of tape transport faults) use the av inputs, and output on a UHF channel - the modern ones have tunable UHF output. Not in the States. VCR modulators here output on VHF channels 3 or 4. (60-66 or 66-72MHz) If the OP can find a foreign UHF modulator, it should work with US signals, with two possible issues: - The sound-video separation is different. This means the sound will be on the wrong frequency for an American TV. If the OP doesn't care about sound then this isn't a problem! - TV channel frequencies are different in different countries. Most Australian channels don't coincide with American channels. (if a modulator tunes Australian channels 30-37, the only channel in that range that corresponds to an American channel is 32, which is American channel 28) Are European/Australian VCR modulators continuously tunable? Or can they only be set to discrete channels? http://www.73.com/a/0019.shtml offers a "block converter". (among dozens of other items! It's about 3/4 down the page on the left-hand side, stock #AE047) It's a broadband frequency converter that will convert a US channel 3 RF signal up to US channel 37. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com Hi Doug, thats interesting - us in OZ had the same VHF output system years ago, but when we got UHF broadcasting, all the VCR's went to UHF output. Most (if not all) are tunable over a narrow range,(via a trimmer cap on the rear panel) some of the more exotic ones (even from dumpster diving) have user settable(sp) output with the actual RF frequency on screen - makes a crude UHF sig gen. The advantage of the UHF output over the older VHF only is no co-channel QRM from the strong Ch3 signal to local on air channels. Agree with the different standards - nowadays, this is not an issue as even the el cheapo VCR's are multi-standard. Saves having to manufacture for different markets, and the new chipsets for this are dirt cheap. Most new ones have an integrated tuner/if/video conversion "can" - unfortunately, bus controlled so difficult to experiment with unless you are comfortable with microprocessors. I aint - firmly rooted in the analog domain! 73 de VK3BFA Andrew |
Andrew VK3BFA wrote:
thats interesting - us in OZ had the same VHF output system years ago, but when we got UHF broadcasting, all the VCR's went to UHF output. Most (if not all) are tunable over a narrow range,(via a trimmer cap on the rear panel) some of the more exotic ones (even from dumpster diving) have user settable(sp) output with the actual RF frequency on screen - makes a crude UHF sig gen. UHF in the States long predates the VCR. But that may be why we stuck with VHF output -- because early UHF tuners were pretty bad and many Americans had experience with their poor stability and difficult tuning. So the VCRs with on-screen frequency setting are also continuously variable? I mean, you can select a RF frequency that doesn't correspond to a valid Australian channel? The advantage of the UHF output over the older VHF only is no co-channel QRM from the strong Ch3 signal to local on air channels. True. (though with the dawn of digital TV in the States I'm not so sure that's enough anymore! Here in the Nashville area we have stations on channels 20, 21, 23, 24, 26, 27, 28, and 30 among many others...) Cable TV boxes use the same modulators as VCRs. CBS-TV had a serious problem when they began digital broadcasts in Chicago a few years ago. They'd been assigned channel 3 for their digital transmitter, and it clobbered the cable boxes. Of course, QRM on the boxes' output channel meant that it clobbered *every* channel on the cable! Agree with the different standards - nowadays, this is not an issue as even the el cheapo VCR's are multi-standard. Saves having to manufacture for different markets, and the new chipsets for this are dirt cheap. Most new ones have an integrated tuner/if/video conversion "can" - unfortunately, bus controlled so difficult to experiment with unless you are comfortable with microprocessors. I aint - firmly rooted in the analog domain! Multistandard equipment is more common in the US than it used to be, but it's still pretty rare. I only know of two variants of NTSC - the one used in Japan, and the one used in all other NTSC countries including the US - and they vary only in the RF carrier frequencies used. (even sound-vision separation is the same) Still, American equipment cannot (usually) be switched to receive Japanese frequencies. Yeah, my microcontroller experience is pretty limited as well! -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
-ex- wrote: Doug Smith W9WI wrote: Andrew VK3BFA wrote: thats interesting - us in OZ had the same VHF output system years ago, but when we got UHF broadcasting, all the VCR's went to UHF output. Most (if not all) are tunable over a narrow range,(via a trimmer cap on the rear panel) some of the more exotic ones (even from dumpster diving) have user settable(sp) output with the actual RF frequency on screen - makes a crude UHF sig gen. UHF in the States long predates the VCR. But that may be why we stuck with VHF output -- because early UHF tuners were pretty bad and many Americans had experience with their poor stability and difficult tuning. For the most part, USA VCRs or cable boxes have always had a switch for ch 3/4, or to a lesser extent, 2/3. The way the channel allocations are done in the US you won't find adjacent channels broadcasting in a given area so one or the other is supposed to work. Guys halfway between Philadelphia and New York City will of course explain why thats not always workable. Nowadays they have dropped in the digital channels, yes in VHF too, with no need to regard adjacent channels which turns the cake upside down. Given the capabilities of modern tuners it makes much more sense to have selectable UHF channel outputs on consumer gear. There's still some free slots in the most crowded metro areas...although the "digital data" people are lobbying hard to get access to those unused frequencies. -Bill Hi Bill, digital here has been a mixed bag - where I am, its line of sight to the hills which is full of UHF translators - thats not so bad for analog, as you can "see" the QRM underneath the ch you have chosen as a RF out. Digital, well, you dont get nothing on screen, so it looks like the front end of the VCR has died. Took me a while to twig to that one - even the local agents for a very well known brand didnt know it and were trying to sell me a new front end to fix the problem! Hitachi have had OSD of RF frequency out for a while now - Philips also in some of their tv;s, and TEAC as well, so it will pretty well be universal before long. The Chinese are really gearing up - they do make some pretty sophisticated gear, but will happily sell us rubbish if we want it as well! We also have a FM broadcast channel on the same tower as the VHF transmitters - it QRM's TV ch 10 depending on how good the tuner front end is. - Funnily enough, (well, it isnt really, more obvious) the older style rotary UHF tuners with ganged RF and LO tuning dont seem to have any trouble, only the varactor tuned ones. But then, they are the sweepings of the factory floors of Asia - bought on price rather than performance. Try telling the customer this tho.... Andrew VK3BFA |
Andrew VK3BFA wrote:
-ex- wrote: We also have a FM broadcast channel on the same tower as the VHF transmitters - it QRM's TV ch 10 depending on how good the tuner front end is. - Funnily enough, (well, it isnt really, more obvious) the older style rotary UHF tuners with ganged RF and LO tuning dont seem to have any trouble, only the varactor tuned ones. But then, they are the sweepings of the factory floors of Asia - bought on price rather than performance. Try telling the customer this tho.... Andrew VK3BFA The Keyword here is how 'bad' the tuner front end is :) Its probably a tossup if there's a harmonic being received instead of a mixing beat but at least tunable sets have a chance of getting away from it. Here in the US, gear usually has options of off-air, cable, cable HRC (harmonically related channels) or cable IRC (incrementally related channels) . Depending on the freq of the FM station *sometimes* you can force the set away from the FM harmonic by selecting one of the oddballs. But if its beating with the video there's no cure. Do you still have folks with rotary tuner sets down there? I haven't seen one in a customer's home for 30 years on this side! -Bill |
-ex- wrote: Andrew VK3BFA wrote: -ex- wrote: We also have a FM broadcast channel on the same tower as the VHF transmitters - it QRM's TV ch 10 depending on how good the tuner front end is. - Funnily enough, (well, it isnt really, more obvious) the older style rotary UHF tuners with ganged RF and LO tuning dont seem to have any trouble, only the varactor tuned ones. But then, they are the sweepings of the factory floors of Asia - bought on price rather than performance. Try telling the customer this tho.... Andrew VK3BFA The Keyword here is how 'bad' the tuner front end is :) Its probably a tossup if there's a harmonic being received instead of a mixing beat but at least tunable sets have a chance of getting away from it. Here in the US, gear usually has options of off-air, cable, cable HRC (harmonically related channels) or cable IRC (incrementally related channels) . Depending on the freq of the FM station *sometimes* you can force the set away from the FM harmonic by selecting one of the oddballs. But if its beating with the video there's no cure. Do you still have folks with rotary tuner sets down there? I haven't seen one in a customer's home for 30 years on this side! -Bill Hi Bill, nope, not many left with rotary tuners (on UHF) - but I still get called in to fix them occassionally, and even more so that some of them still have good tubes in them! Andrew VK3BFA |
One pitfall not already mentioned is that simply combining the R-G-B and
sync signals coming out of a VGA card won't produce a US standard NTSC signal. A US television signal (NTSC compatible) uses a 15.750 kHz horizontal sweep rate. The lowest VGA resolution (640 X 480) uses a 31.5 kHz sweep. Higher resolutions use higher sweep rates. This scan rate incompatibility may complicate your project. Of course, there are some specialty video cards around that have an NTSC video output, in addition to VGA. Those cards have an on-board scan converter. Good luck, Roger K6XQ |
Roger,
Wouldn't this be be exactly double of NTSC, in which case the TV would see every other frame of the composited VGA? Or, because I am intending to run the card in Linux, could I create a resolution below 640X480? But you may be right, a surplus video card with S-video out would sidestep this problem. The Eternal Squire |
Roger,
Wouldn't this be be exactly double of NTSC, in which case the TV would see every other frame of the composited VGA? Or, because I am intending to run the card in Linux, could I create a resolution below 640X480? But you may be right, a surplus video card with S-video out would sidestep this problem. The Eternal Squire |
Wouldn't this be be exactly double of NTSC, in which case the TV would see every other frame of the composited VGA? If the TV would ignore the sync pulses that arrived too soon, you might get two images, side by side. But that ignores the other complications that I didn't mention: VGA and NTSC don't use the same vertical sweep frequency. And NTSC is an interlaced vertical scan, meaning you get alternating lines of display, rather than a complete image scanned top down. NTSC requires two complete top down scans to get all lines of an image. VGA is non-interlaced. Or, because I am intending to run the card in Linux, could I create a resolution below 640X480? But you may be right, a surplus video card with S-video out would sidestep this problem. The video card has more to do with the VGA scan rates than the operating system. You often see crystal controlled oscillators on video cards so you are locked into what the card manufacturer provides. I can't rule out some flexibility here, but I think a video card with NTSC video output would be the surest way to get this idea to work. Roger |
I looked at the article. Nice try, but I don't have the equipment or
eyesight to work with TSSOP-24 package, nor the money to play with a $300 evaluation board :) The Eternal Squire |
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On Sun, 12 Jun 2005 13:41:29 GMT, Doug Smith W9WI
wrote: [snip] http://www.73.com/a/0019.shtml offers a "block converter". (among dozens of other items! It's about 3/4 down the page on the left-hand side, stock #AE047) It's a broadband frequency converter that will convert a US channel 3 RF signal up to US channel 37. I called these bozos to inquire about buying one of these. You get an answering machine but not the courtesy of a call back. The items have also disappeared from their web site inventory. Any other sources? Wes N7WS |
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Gudmundur wrote:
In article . com, says... Hi all, It's me again, attempting yet another mad science project, and I have practically googled the subject to death before thinking of asking this group for help: I am wanting to put video (preferably color but will settle for grayscale) onto a UHF TV channel for inhouse use only. I am considering doing it as follows: 1) Convert output of a VGA card to composite video using resistive combiner (found a few on net). And what magic resistive combiner makes VGA into NTSC??? There is no such thing. There are active models which do this, but if your VGA output is 640X480 or more, then NTSC will make the video suck. NTSC does not have the bandwidth. Yes you can take a properly modulated channel 3 signal, run it into a balanced mixer (well almost any mixer) and add your favorite local oscillator signal and get 2 signals in the uhf band. LO + ch3 and LO - ch3. Good luck. Here's looking at ya or at least the unviewable signal. There are a number of video cards with a NTSC video output in the S-video format. I still have a couple I used in old PCs to drive a Commodore 1701 monitor to trick people. My Commodore 128 was connected to an IBM PC Junior monitor in CGA mode. The look on people's faces was worth the effort. -- Former professional electron wrangler. Michael A. Terrell Central Florida |
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