- Antennae Booster - 5 Updates
- VCR plays color tapes in B&W only? - 1 Update
| Jeff Liebermann <jeffl@cruzio.com>: Sep 26 05:05PM -0700 On Fri, 25 Sep 2020 12:36:44 -0700 (PDT), "Ron D." >Antenna is pretty big, A Winegard HD-8200U and the CM-7777 antenna mounted amp. <https://winegard.com/products/hdtv-digital-antennas/hdtv-antenna-amplifiers/boost/hd8200u-platinum-hd-series-antenna> <https://www.channelmaster.com/TV_Antenna_Preamplifier_p/cm-7777v3.htm> Unless you're dealing with weak signals and fringe coverage, a high gain (26dB in this case) amp is an invitation to overload problems. Quoting the Channelmaster data sheet: The Titan 2 High Gain Preamplifier is recommended for professional installers only. Due to the high gain output of this product, it can result in over amplification if not used in the appropriate scenario. Over amplification can cause issues with the television tuner's ability to receive and display some or all channels. Note that there were 3 radically different versions of the CM-7777 amplifier. Which version do you have? <https://photos.imageevent.com/holl_ands/files/ota//CM7777%20Ckt%20Brd%20Rear%20Photo%20-%20damaged%20rlongfield.jpg> The original Titan 2 amp had a phenolic PCB. V2 had separate VHF and UHF outputs, while V3 has them combined into one output. Therefore, my guess is that it's a V2. >but they were not done at the same time. I measures the signal >at the antenna and the NEXT day the signal after the power >injector (about 30') Are you trying to measure amplifier gain using an OTA (over the air) signal? The amplifier gain is not the same for the VHF and UHF sections. It's also has some intentional "tilt" in the frequency response intended to compensate for the higher coax cable losses at the higher UHF channels. >Gain varied from 15.6 (physical channel 3) and 27.1 for channel 21. >I'm at least 30 miles outside of Philly and aimed toward Philly >stations. Due to intentional "tilt" in the frequency response, that's too much "tilt" for the amplifier. CH3 = 60 MHz, CH21 = 512 MHz. Cable loss for 100ft of RG-6/u is 1.6dB at 60 Mhz and 5.2dB at 512 MHz. Therefore, I would expect to see a corresponding: 5.2 - 1.6 = 3.6dB difference in gain between CH21 and CH3. Comparing with your measurement: 27.1 - 15.6 = 11.8dB Yep, way too much "tilt" in your measurement. Do it again, this time with a spectrum analyzer and an RF sweep generator. >The rotor also has a bypass braid around it which many people >forget. What is a bypass braid? I've never heard of the term. Neither has Google search. Do you mean something like quad shielded RG-6/u? >A large tree is going to hit by lightning first. Large height or large girth? -- 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 |
| Ralph Mowery <rmowery28146@earthlink.net>: Sep 26 08:13PM -0400 In article <sljvmflff4bfi51udegldlovgb03cg13s5@4ax.com>, jeffl@cruzio.com says... > >A large tree is going to hit by lightning first. > Large height or large girth? Bypass braid for a rotator is for lightning protection. You put a piece of wire to the mast above the rotator and then to the mast below the rotator. That is suppose to make a good connection from the top mast to the bottom mast. It is not so much the actual gain of the amplifiers, but the noise figure. If just feeding one or two tv sets all the gain needs to be is just to make up for the loss of the feedline if the amp is very near the antenna and a little more depending on the noise figure of the TV set. If the amp is near the TV, it needs very little gain (maybe 10 db) and better have a noise figure much lower than the TV tuner. Hopefully a tall tree will get hit first,but no guarentee. |
| Michael Terrell <terrell.michael.a@gmail.com>: Sep 26 05:21PM -0700 > What is a bypass braid? I've never heard of the term. It was a piece of heavy braid to connect the upper mast to the lower mast for grounding. It was supposed to prevent lightning or static discharges from damaging the ball bearings or their races. The grease wasn't conductive, and would harden into an insulating layer of varnish. That forced the downlead to carry the discharge current. |
| Jeff Liebermann <jeffl@cruzio.com>: Sep 26 08:14PM -0700 On Sat, 26 Sep 2020 17:21:21 -0700 (PDT), Michael Terrell >to the lower mast for grounding. It was supposed to prevent >lightning or static discharges from damaging the ball >bearings or their races. Thanks. Even with the magic buzzwords, I wasn't able to find any rotator or tower installation instructions that involved such a bypass braid. I don't think it will do much to prevent 20,000 Amps from turning a big antenna rotator into a metal recycling candidate. I double if it will do much to prevent arcing from pitting the bearings. The are a large number of bearings in the rotator and it only take a decent connection through one bearing to discharge a static electricity buildup. I've taken apart a few rotators and found plenty of rust, considerable loss of grease, but no pitting (except from the rust). The bypass wire might also protect against an unusual situation where a ham operator uses a tower or mast as both a monopole antenna and a rotator mount. In transmit, the RF current will go through the rotator bearings. That's not a problem if the rotator is not in motion, but potentially a big problem if the bearings are moving, arcing merrily as they roll along. To be fair, I haven't proven that this is happening, but I'm fairly certain it could easily be tested. >The grease wasn't conductive, and would harden into an insulating >layer of varnish. That forced the downlead to carry the discharge current. I've seen grease turned to varnish, usually in salty marine atmospheres or after using the wrong type of grease to lubricate the rotator. I sometimes find some water in the bearing race. In my never humble opinion, what's happening is the grease is getting washed away by rain, fog and condensation. The idea grease would be something that can (in order of most important to least important): 1. Will not wash out (i.e. marine grade grease). 2. Inhibits galvanic corrosion and rust formation. 3. Does no "foam" or create abscesses that collect water. 4. Slightly conductive to discharge static electricity. 5. Tolerates high temperatures by NOT evaporating or dripping. 6. Handles a heavy load. What I've been using are various marine lithium based grease concoctions such as WD-40 Specialist Marine-Grade Grease: <https://www.amazon.com/WD-40-Specialist-Marine-Grade-Resistant-Grease/dp/B071R943VS/> <https://www.wd40.com/products/water-resistant-grease/> Note that this is lithium based and not white-lithium grease. Please note that very little of this has much to do with a receive only TV antenna, rotator, and mast/tower. -- 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 |
| Jeff Liebermann <jeffl@cruzio.com>: Sep 26 08:35PM -0700 On Sat, 26 Sep 2020 20:13:15 -0400, Ralph Mowery >> >A large tree is going to hit by lightning first. >> Large height or large girth? >Bypass braid for a rotator is for lightning protection. Methinks it has more to do with discharging a static electricity buildup (St Elmo's Fire) than protecting against a lightning hit or lightning induced current. >of wire to the mast above the rotator and then to the mast below the >rotator. That is suppose to make a good connection from the top mast to >the bottom mast. Well, I've never seen such a thing, never had anyone request it, and couldn't find with Google any installation instructions recommending such a practice. >antenna and a little more depending on the noise figure of the TV set. >If the amp is near the TV, it needs very little gain (maybe 10 db) and >better have a noise figure much lower than the TV tuner. Agreed. I think I mumbled something about too much gain causing intermod problems further up this thread. Another problem is loss of dynamic range when the added gain also raises the noise floor but not changing the overload point. Way back in the dark ages of TV, the receivers were stone deaf and any kind of RF preamplifier offered a performance improvement. These days, with GaAs low noise front ends, the best that a preamp can offer is to compensate for coax cable losses. >Hopefully a tall tree will get hit first,but no guarentee. We don't get much lightning here on the left coast[1]. I live in a forest full of 100ft and higher trees. I know of three local trees (out of millions) that were hit by lightning in the past 40 odd years. Both were in rather odd locations, such as the bottom of a canyon or surrounded by taller trees. My best guess is the tree holding the most water has the highest conductivity and therefore gets hit first. [1] Mother nature delivered our accumulated savings (with interest) of lightning on Aug 15, 2020, with a really impressive display of flashing lights, and starting 500+ big fires that are currently trying to incinerate California, Oregon, and Washington states. 5 million acres burned and climbing. -- 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 |
| Guy Patterson <str00ntz@aol.com>: Sep 26 10:14AM -0700 On Friday, September 25, 2020 at 10:02:18 PM UTC-4, crazy chicken wrote: > I am having the exact same problem. What is broken, the VCR or VHS that is making it B&W. Is everything B&W because my VHS tapes are too old and have eroded? I have tapes since 1990, so do they still work 30 years later? Is there no solution to this problem? I am trying to get my tapes to digital, and I need to solve this problem. > Thanks for reading! > - A Chicken A specific model number would be helpful. I may still have service records somewhere on VCRs. But no, the age of the tape has nothing to do with a loss of chroma in playback assuming the signal to noise ratio is still respectable (viewable image without severe noise). The chroma sub carrier won't degrade any faster than any other part of the composite waveform will. Old VCRs suffer the same issues as modern garbage does: lazy electrolytic caps as they age. If you only need this to run long enough to do a digital transfer, try taking the cover off the VCR and heating the innards for about 10 minutes with a hair dryer (don't use a real heat gun). With a good hot soak, a weak electro cap can increase it's value and lower it's ESR enough to allow the color to work as it should. If it responds to heat, make all your transfers while it stays hot. |
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