- HDTV half Screen Horiz Hold - 1 Update
- Small VHF Transmitter - 4 Updates
| vjp2.at@at.BioStrategist.dot.dot.com: Sep 05 03:55PM Don't understand it. Portable LCD HDTV right part of screen looks like it is scrolling and flickering. Even during the local (ie not broadcast) station resampling mode. All stations. -- Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus blog: panix.com/~vjp2/ruminatn.htm - = - web: panix.com/~vjp2/vasos.htm facebook.com/vasjpan2 - linkedin.com/in/vasjpan02 - biostrategist.com ---{Nothing herein constitutes advice. Everything fully disclaimed.}--- |
| Michael_A_Terrell <terrell.michael.a@gmail.com>: Sep 04 08:09PM -0400 Fox's Mercantile wrote: > The correction factor is -48.75, so the actual output in dBm is > -8.25 dBm. Or, about, 0.15 miliwatts. > I seriously doubt this modulator puts out 31.625 Watts. I seriously doubt that you've ever built any CATV head ends. I expressed the output stage gain in dB, not dBm. Working in system design, you work with gain and attenuation levels, not dBmv, dBm or any other variation. To get the gain required for a line amp, the module dissipates real power in Watts, not puny mW. Those modules are mounted on a heavy bar that is bolted to the amplifier's case to dissipate that heat. If you overdrive the input on a TV, you can damage the input amplifier. At the very least, intermod and sync compression happens when the tuners are overdriven. One system had over 10,000 TVs connected to it. The systems that I worked with in the Military used Jerrold tube based CARS to link two channels to every airfield around Ft. Rucker. That system could also take control of the civilian CATV system at the point where it entered the base. This was t allow emergency weather alerts, or disaster information to be sent into the housing areas. When I built an interface to connect two incompatible Community loops, our lead tech radioed the office to complain that my design was off. By just under +0.2dB. Not dBm or dBmv, but dB. Cable losses, connector losses and insertion losses for passives is what eats up your gain budget. I wrote software back n the early '80s to simplify system design. Our company specification was +10 dBmv at the output port of the tap. In most cases, that allowed four TVs and the drop loss at the highest channel. The software stored data for every brand of coax we used for feeder, trunk and super trunk. It held the specs for every brand of tap for the feeders, so all you needed was an accurate strand map to design a reliable and flat system. The only thing that it couldn't do was stop lazy techs from changing taps to drive more TVs in some homes. That dropped the signal for every drop past that point. Johnny Bench was one of our customers. We had drops to both ends of his home, and one TV was on a floating bar in his pool. I not only did system design, I maintained the microwave equipment. Rockwell-Collins had soaked the industry for a crappy, modified fixed tuned model that was a downgraded Military design. They ran so hot that the PC boards would burn, and they refused to repair them. The design was so bad that they used a 1500uF electrolytic in the video output stage, rather than a properly designed amplifier that could handle the DC offset. That series was listed as impossible to use with the Videocypher II descramblers. I had already removed a trap from all of them, because they didn't work with any channel carrying a secondary service as a subcarrier. The idiot manager freaked out, but he wasn't as smart as he thought he was. He would set the Sat equipment up to output the 1V of video, without terminating the Tektronix 528 waveform monitor. Then he had to crank the modulator gain wide open to come close to 90% of noisy video modulation. He claimed that Tektronix didn't know how to design test equipment. Those Rockwell-Collins receivers had a 225 ohm resistor in series with the output, so he was setting them for .25 volts of video. For anyone who is interested in this subject, Blonder Tongue publishes handy reference books. This is an older edition that still covers NTSC equipment. That large system had a RCA headend that was miswired at their factor. When you tried to use the emergency alert system, all the outputs dropped by just under 40dB. They had wired a splitter wrong. One port work, the other didn't. Once again, the pointy haired boss insisted that RCA NEVER made mistakes. I not only fixed that, but I modified it so the individal Hetrodyne Signal Processors could detect a lost input and switch to the auxilary IF inputs. These were fed by a single modsulator with no upconverer. I used a spare video output from a character generator to display, "This channel is off the air. Please consult your program guide." During an emergency that message was automatically switched out for a different video feed. This eliminated a lot of phone calls from customers, and it only took a dozen 1N4001 diodes. The line, bridger and extender amplifiers were Sylvania, which was sold to Tekscan. The original taps were built in Canada by Lindsay. They were absolute shit. Instead of a cast face plate and water tight seals, it used cheap chassis mount F connectors which were tinned brass, and mounted on a pot metal face plate. They corroded quickly in the Cincinnati area, thanks to road salt. That caused all kinds of intermod, system leakage and poor signal quality. <https://www.blondertongue.com%2Fpage%2Fmedia%2F2014_BRG_lo-res.pdf> Stick to your used business radios, where you can do that simple job. -- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-) |
| Fox's Mercantile <jdangus@att.net>: Sep 04 07:35PM -0500 On 9/4/20 7:09 PM, Michael_A_Terrell wrote: > Stick to your used business radios, where you can do that simple job. Ya know what? Go fuck yourself. Nobody gives two shits about what you claim to have done. And your entire post was just a bunch of non-related crap. I have the manual. It clearly stated the output in dBmV. I used to use it with a DVD player supplying video and audio to it to show off various vintage TV sets in shop. There was never any sign of overloading. The crown jewel was my 1948 Andrea Sharp Focus VK-12 that I restored. AM/FM and channels 1-13. The only concern I have, is that 0.15 mW of output power it might not have the range necessary -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
| Michael_A_Terrell <terrell.michael.a@gmail.com>: Sep 05 12:17AM -0400 Fox's Mercantile wrote: >> Stick to your used business radios, where you can do that simple job. > Ya know what? Go fuck yourself. > Nobody gives two shits about what you claim to have done. Take your own advice. You've done it to yourself, for years. > And your entire post was just a bunch of non-related crap. That's your standard response when you are caught out. > I have the manual. It clearly stated the output in dBmV. Of course it is. It is a signal SOURCE. They write the specs that way for the simple minded. Modulators are intended to be a component in a system. As a stand also device, the output would be much lower. In the range of +3 to +6 dBmv. The combiner panels use a lot of the extra power gain to overcome their insertion losses. Our head ends were flat to a fraction of a dBmv at 20, leaving the building. Each trunk amplifier raised it to reach the next amplifier at +20dBmv from 54 to 300 MHz. I'm sure this is all gibberish to you, because you don't ever admit that you are wrong. I don't know what happened to you after you moved out of California, and I don't want to. Prior to the move your actually tried to help people, instead of being a total waste of skin and oxygen. If I was as miserable as you, I would either get help, or step in front of a semi on the interstate. > AM/FM and channels 1-13. > The only concern I have, is that 0.15 mW of output power it might not > have the range necessary Then build a 100KW linear for Peter. Most of the old VJF spectrum has been realocated. You don't want to get cught running too much power on those frequencies. Not that you would give a damn. -- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-) |
| Fox's Mercantile <jdangus@att.net>: Sep 05 12:23AM -0500 On 9/4/20 11:17 PM, Michael_A_Terrell wrote: > [ Nothing worth quoting ] Exactly what I'd expect from you. More non-related crap. And and implied death threat. You're pathetic. -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
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