- Antennae Booster - 4 Updates
- Carvin B2000 bass amp won't power on, need schematic. - 3 Updates
- keys - 2 Updates
| dplatt@coop.radagast.org (Dave Platt): Sep 24 01:41PM -0700 In article <56unmfhd8j3h69650rfhu107426r70pj2n@4ax.com>, >Masthead amps make good targets for lightning hits. I've seen a few >where every semiconductor in the amp was fried. Yeah... probably need to consider them to be a potentially-sacrificial component. The really troublesome ones I've heard/read about, are the cheapies... sometimes using just a single broadband transistor as a gain element. Some of these have been known to break into oscillation, for some reason (or no reason) and blast broadband noise all over the place. https://www.gpsworld.com/the-hunt-rfi/#:~:text=Reports%20of%20other%20GPS%20users,narrow%20harbor%20entrance%20in%20fog. talks about one such case, in which several on-shipboard "active TV antenna" systems were emitting enough RF crud to blank out GPS reception in the harbor in Moss Landing, CA. Not a good thing to lose your GPS when you're trying to come into a foggy harbor at night. This is one reason why which buying a well-tested, professional-grade mast-head amplifier would probably be a better idea than buying a generic cheapie. |
| Jeff Liebermann <jeffl@cruzio.com>: Sep 24 09:35PM -0700 On Thu, 24 Sep 2020 13:41:43 -0700, dplatt@coop.radagast.org (Dave Platt) wrote: >>where every semiconductor in the amp was fried. >Yeah... probably need to consider them to be a potentially-sacrificial >component. I had one mounted on a redwood tree. It wasn't hit by lightning. Instead, it was invaded by ants, dripping formic acid, which ate the copper traces on the PCB. I was prepared to replace all the active components, but not the entire amplifier. >oscillation, for some reason (or no reason) and blast broadband noise >all over the place. >https://www.gpsworld.com/the-hunt-rfi/#:~:text=Reports%20of%20other%20GPS%20users,narrow%20harbor%20entrance%20in%20fog. This might fill in a few details: <http://www.learnbydestroying.com/jeffl/GPS%20Jamming%20Moss%20Landing/> Note the photo of the antenna. The cloverleaf pattern is NOT a broadband device and will not present a 75 ohm impedance to the amplifier input. Designing a broadband amplifier to be unconditionally stable and provide a low NF (noise figure) as well as high gain into such an antenna is difficult. There will be some frequency, where the antenna presents the perfect impedance to cause the amplifier to oscillate. Also, such an antenna construction is not very tolerant of the corrosive effects of a marine environment and probably should have been potted or conformal coated. >talks about one such case, in which several on-shipboard "active TV >antenna" systems were emitting enough RF crud to blank out GPS >reception in the harbor in Moss Landing, CA. Yep. That happened near me. Although I knew some of the participants, I didn't know that there had been a transmitter hunt until two years after it was over and the article appeared in GSP World. >Not a good thing to lose >your GPS when you're trying to come into a foggy harbor at night. GPS selective availability was finally turned off on May 1, 2000, navigating a 150 ft wide harbor entrance channel by GPS would have been theoretically possible. At the time, MBARI did operate their own DGPS transmitter on Mt Toro, but that was for precision vessel and buoy location in the bay. Today, even with WAAS, GALILEO and GLONAS satellites added to improve GPS precision, I'm told it's still tricky due to reflections from moving metal masts and rigging, plus a very large steel building at the power plant. Once into the channel, I would probably switch to navigating by the harbor lights: <https://geographic.org/nautical_charts/map_img/18685_3-t.png> >This is one reason why which buying a well-tested, professional-grade >mast-head amplifier would probably be a better idea than buying a >generic cheapie. Yep. In my never humble opinion, there was probably nothing wrong with the amplifier. Instead, it was the design of the antenna, which had the misfortune of not being properly matched to the RF amplifier causing the amp to oscillate. A properly designed Yagi, Bow-Tie, LPDA (log periodic dipole array), or other broadband design, would worked better, and not oscillated. <http://www.hdtvprimer.com/ANTENNAS/comparing.html> <http://www.hdtvprimer.com/SIMS/> -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Chris K-Man <thekmanrocks@gmail.com>: Sep 25 01:15AM -0700 On Tuesday, September 22, 2020 at 4:54:39 PM UTC-4, Stu jaxon wrote: > Hi Group, can someone help please, I have an antenna booster that requires a power supply of 6v 100ma, can i use a variable power supply 6v 300ma??? > Thanks, ____________ My idea of a "booster" or "signal amp" is a bigger/higher gain antenna. As far as language differences are concerned, England and India are forever bound by their use of English. Compared to them, what is spoken in the States is called AMERICAN: a rebellious corruption and bastardisation of what is spoken/written in the two aforementioned nations. Where else do you hear "nucular" routinely substitute for nuclear? Or plural's of item's succeeded with an apostrphe s? LOL! |
| Jeff Liebermann <jeffl@cruzio.com>: Sep 25 08:50AM -0700 On Fri, 25 Sep 2020 01:15:02 -0700 (PDT), Chris K-Man >My idea of a "booster" or "signal amp" is a bigger/higher gain antenna. Do you mean that a "bigger" box is your idea of a better TV antenna amplifier? This looks plenty big: <http://www.ambery.com/rfmp-w50.html> Dimension: 498mm (W) x 360mm (D) x 280mm (H) Or, perhaps you mean't something other than size? Higher gain does not buy you much in the way of a performance improvment. At best, all you need for gain is a bit more than the coax cable loss between the amp and the TV (or distribution amp). Too much gain just generates intermodulation products, AGC overload, and other receiver problems caused by too much signal. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| David Farber <farberbear.unspam@aol.com>: Sep 24 04:38PM -0700 On 9/20/2020 10:40 PM, Phil Allison wrote: > ** 20A at 120VAC at least. > .... Phil Before I went to the trouble of dismantling my audio dummy load resistor setup, I found two, 3.3 ohm, 1 watt resistors, put them in series, and soldered them in place of the thermistor. (My supply of resistors in the low ohm, high power range is almost nil.) I know you said to use at least a 5 watt resistor but I wanted to get some idea of what kind of current the amp would draw on power up. I did put a 200 watt lamp in series. By the time the line voltage was up to 50 ACV, the lamp was glowing at about half strength and the AC current was about 1 amp. The voltage across the resistors was over 3 volts so they were already overloading. At that point I aborted the test. If I do repeat this test with the 8 ohm, audio, 25 watt dummy load resistor, should I leave the light bulb in series? Would it take more than 2 amps of continuous AC power even when bringing up the voltage slowly? What if I bypass the relay contacts and eliminate the resistors? There shouldn't be any inrush surge while bringing the voltage up slowly, right? I should also mention that the power amp has a 25 amp line fuse inside. Does that sound reasonable? Neither the schematic nor the PC board indicate what the fuse rating should be. Thanks for your reply. -- David Farber Los Osos, CA |
| Phil Allison <pallison49@gmail.com>: Sep 24 08:18PM -0700 David Farber wrote ==================: > least a 5 watt resistor but I wanted to get some idea of what kind of > current the amp would draw on power up. I did put a 200 watt lamp in > series. ** Completely spoils the test. > By the time the line voltage was up to 50 ACV, the lamp was > glowing at about half strength and the AC current was about 1 amp. ** So nearly 50V AC was across the 200W lamp. Odds are very high the PSU is a dead short to the AC supply - though the bridge rectifier may be OK. Check that and some FETs with a multimeter on diode tests. .... Phil |
| David Farber <farberbear.unspam@aol.com>: Sep 24 09:56PM -0700 On 9/24/2020 8:18 PM, Phil Allison wrote: > Odds are very high the PSU is a dead short to the AC supply - though the bridge rectifier may be OK. Check that and some FETs with a multimeter on diode tests. > .... Phil I will recheck for shorts in the PSU. Thanks for your reply. -- David Farber Los Osos, CA |
| Eli the Bearded <*@eli.users.panix.com>: Sep 25 12:00AM > https://stackoverflow.com/questions/3075130/what-is-the-difference-between-and-regular-expressions I would have guessed he was asking about keyboard keys not working, not regular expressions. https://www.wikihow.com/Fix-Sticky-Keyboard-Keys > The internet is your friend. Is it? That same internet that foments conspiracy theories like mushrooms after a rain and gives nobodies who would be ignored shouting from a street corner rapt audiences? The internet is powerful, but not friendly. Elijah ------ advice on replacing the keyswitches would require more information |
| Jeff Liebermann <jeffl@cruzio.com>: Sep 24 09:45PM -0700 On Wed, 23 Sep 2020 14:05:38 -0700 (PDT), Robert Long >I'm confused. When I program my unit it tell me to ?*?. What keys do I hit. Or better yet, what is ?*? Sounds like a questions involving military hardware. 56th Artillery is US Army, but your email address suggests Marine Corp. ?*? is what a printer or display would produce if it doesn't recognize some characters. In the case, the "?" is a place holder for a character that can't be displayed or printed. My guess(tm) is that it's something like "*" where the two quote marks were replaced by the question marks. On an Apple computer, they would be replaced by square black boxes. So, the single key that you press (not hit) is just an asterisk or an *. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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