Stets Posted November 3, 2004 Posted November 3, 2004 Hi All, This question may sound totally wierd but I can't find an answer anywhere else. I recently replaced all of the coax through my house, and all fly leads and interconnects, with Quad Shield RG6 (2 rolls purchased from Jaycar). Of course I ran out when I got to the last 2 flyleads and as it was nearby had to purchase 4 metres of RG6 from Dick Smith. When I have stripped this to crimp on the F type connector I have found that underneath the outer insulation there is 1 layer of braid, then 1 layer of foil, then the primary insulation.......Huh I thought that RG6 was all quad shielded, i.e. outer insulation, then braid, then foil, then braid, then foil, then finally the primary insulation. What gives....... Is Dick Smith selling bodgey RG6 or is there a Dual Shielded RG6 also? I did use the dual shield RG6 as I had nothing else available but now question whether this should be replaced with quad shield. Thanks Stets
ijd Posted November 3, 2004 Posted November 3, 2004 There is certainly dual-shield RG-6 - and probably single-shield as well! So you do need to insist on quad-shield when purchasing. I think you should replace the dual-shield with quad-shield for peace of mind and 'set-and-forget' - rather than having to replace the dual-shield sometime down the track if/when future video problems are encountered ('ants', 'haze', loss-of-definition, etc). Another alternative, which I have used for one or two RF flyleads using Foxtel 'leftovers', is RG-59 quad-shield. DSE sells a very good 'aircore' RG-59 quad-shield by the metre. Although it is thinner (and therefore more flexible) than RG-6, RG-59 is also 75-ohm - whereas RG-58/etc is 50-ohm (originally designed for 10-Base-2 ethernet).
djOS Posted November 3, 2004 Posted November 3, 2004 Yes, Dual Shield is susceptable to picking up interferance - Quad gives you a much cleaner signal.
gclark8 Posted November 3, 2004 Posted November 3, 2004 (edited) There is some very high quality dual shield RG6 on the market, it will have all copper conductor and over 90% shielding for each layer, such as Belden 1694A, http://www.belden.com.au/content.cfm?tds=1&productType=1694A , available from Madisons. http://www.madisontech.com/ Edited November 3, 2004 by gclark8
ijd Posted November 3, 2004 Posted November 3, 2004 There is some very high quality dual shield RG6 on the market, it will have all copper conductor and over 90% shielding for each layer, such as Belden 1694A George ... Don't encourage them to use dual-shield!! A 50m reel of Belden quad-shield RG-6 only cost me $1.40/metre at Jaycar (who don't even allow me to haggle!). A 100m reel of [no-name?] quad-shield RG-6 is only about $0.70c/metre at Ideal Elec. And I'm pretty sure that no-name quad-shield will offer much better shielding than Belden dual-shield.
gclark8 Posted November 3, 2004 Posted November 3, 2004 Not so, 100+95=195 50+25+50+25=150 the price is the best guide, much el-cheapo quad is steel inner, al foils (OK) al braid, no good for digital. Genuine RG59 is single shield, un-tinned copper braid, with copper core, not recomended above 300mHz RG58 is 50-52 ohm radio TX coax, not much good above 30mHz and no good for TV. buyers beware!!
gclark8 Posted November 3, 2004 Posted November 3, 2004 From: http://www.belden.com.au/content.cfm?tds=1&productType=1694A BELDEN AUSTRALIA PTY LTDTECHNICAL DATA SHEET Precision Video Cable For Analog and Digital Applications Product Type: 1694A Description: Coax, 1 coax, 18 AWG, Solid BC - Bare Copper conductors, Foam PE - Gas Injected Foam High Density Polyethylene insulation, Aluminum Foil-Polyester Tape-Aluminum Foil (Duofoil) shield with 100% shield coverage plus tinned copper Braid Shield with 95% shield coverage, PVC - Polyvinyl Chloride jacket, RG Type 6/U. Applicable Specifications: UL/NEC CMR, C(UL) CEC CMG. Flame Resistance: UL 1666 Vertical Shaft, CSA FT4. Use: Black suitable for indoor and outdoor aerial applications. Other colors suitable for indoor use only. 100% sweep tested, RG-6/U Type Precision Low Loss Serial Digital Video Coax. Coaxial. Brilliance. 75 ohm Precision Video Cables. SDI Digital video. For Plenum version, see 1695A. Analog Video - Belden precision video cables are used in critical analog video circuits and high quality applications such as live broadcast in network studios and pre- or post-production facilities. They should be used anywhere superior signal integrity is required. Precision video cables usually have solid center conductors and dual shields. The dielectrics can either be foam or solid. Tighter impedance and attenuation tolerances, superior structural return loss (SRL) specifications, and improved shielding give precision video cables their non-compromise performance. The frequency response loss curves of the solid dielectric cables, such as 8281, are different from those with foam dielectric, like 1505A. Therefore, different equalization equipment is necessary and commercially available. Avoid mixing 8281 and 1505A for this reason. Digital Broadcast - Precision video cables are also recommended for the latest digital video applications. Since its inception in the early 80's, digital broadcast is quickly becoming the preferred video format. The advantages of the digital format are many. Digital is very stable minimizing equipment adjustments. Copies or reproductions retain the quality of the original. Signal degradation is virtually eliminated, and noise immunity is greatly improved. Digital video is transmitted over a cable in either a Parallel or Serial format. DUOFOIL is a Belden registered trademark. BRILLIANCE is a Belden registered trademark. Applications: digital, video, coax, hd, hdtv, film, production, editing, high definition television, 75 ohm, post, rg-6, rg 6, rg6, rg-6u, rg 6u, rg6u, rg-6/u, rg 6/u, rg6/u, aes-3id, digital audio coax, ccir 601, sdi professional digital video, digital video, serial digital, sdi, serial digital interface, digital video, s/pdif, consumer digital audio on coax, serial digital, sdi, professional digital video, 601, ccir 601 professional digital video, smpte 259m, hdtv, smpte 292m, cable screened, screened cable cable, tv, tv station, headend, television, radio studio, recording studio, casino, hotel, radio broadcaster, corporate office, office, casino, training centers, stadiums, synagogue, auditorium, post production, tv broadcaster, production facility, cable tv operator, theater, corporate, board, mobile truck, broadcast, place of assembly, race track, digital upgrade, digital upgrade stations, digital upgrade tv stations, tv stations, head end, s/pdif, aes/ebu, Physical Characteristics: RG Type 6/U Total Number of Conductors 1 Number of Coax 1 AWG 18 Stranding Solid Nom. Core OD (in.) 0.18 Insulation Foam PE - Foam Polyethylene Insulation Thickness (in.) 0.068 Shield Foil/Braid Shield Detail Aluminum Foil-Polyester Tape-Aluminum Foil/Braid Shield Jacket PVC - Polyvinyl Chloride Jacket Thickness (in.) 0.034 Nom. OD (in.) 0.275 Nom. Cond. DCR (ohms/m) 6.4 Nom. Impedance (ohms) 75 Nom. Vel. Of Prop. (%) 82 Nom. Capacitance (pF/ft) 16.2 This information is supplied for your confidential use in the evaluation and application of the product involved. Any other use or reproduction requires prior written approval of Belden Australia Pty Ltd.
ijd Posted November 3, 2004 Posted November 3, 2004 50+25+50+25=150 Where the heck did you pluck that figure from? Is that really how bad the Matchmaster quad-shield RG-6 at Ideal Elec is - 'cos that is what most contractors will be using to re-wire our antennas!?!
gclark8 Posted November 3, 2004 Posted November 3, 2004 That is typical of most RG6 quad, i have seen much worse, one as low as 5% coverage from the braid.
ijd Posted November 3, 2004 Posted November 3, 2004 Well at least that explains why the single-shield 5% braid on the 'free' video cables and cheap supermarket RF flyleads gives such a great result (... NOT!! ...) with good equipment!
gclark8 Posted November 3, 2004 Posted November 3, 2004 The big advantage of the Belden 1694A RG6, it comes in black and 5 colours, so for Aerials, RGBHV, component, composite, Audio, it is THE cable to use.
TV4FREE Posted November 3, 2004 Posted November 3, 2004 Where the heck did you pluck that figure from? Is that really how bad the Matchmaster quad-shield RG-6 at Ideal Elec is - 'cos that is what most contractors will be using to re-wire our antennas!?! <{POST_SNAPBACK}> ijd, I don't think george was knocking a particular brand, more so many of the cheaper chinese alternatives. Your jaycar specials being the case. As for matchmaster cable it ain't cheap, the specs meet the world and are very very good. ELECTRICAL SPECIFICATIONSCable Type E6S/E6Q Shielding Effectiveness >100dB Impedance (Nominal) 75Ω Velocity of Propagation 85% Nominal IF your using matchmaster then your getting a decent cable however it's hard to beat the american belden designs......even if they are made in china Hence, use RG11 and then problems don't arise.
gclark8 Posted November 3, 2004 Posted November 3, 2004 Yes, for runs over 30m RG11 is better, however, on seeing your specs for shielding of better than 100db, it begs the question of proximity (mains) spikes of greater than 1 volt (120dBuV) being radiated into the receiving cable.
TV4FREE Posted November 5, 2004 Posted November 5, 2004 ? I seem to think the >100db can give some cause for concern however it could be worse. A trip to bunnings today revealed the worse possible cable called RG6Q. I was mighty surprised to see people reeling it off obviously thinking they were getting a good deal. And the price was astoundingly expensive. As you said beofre buyer beware.
bruiser333 Posted November 6, 2004 Posted November 6, 2004 Is everyone sure the interference comes in via the coax? I have run RG6 direct from the antenna to the STB (ie over the tiles, lawn and through a door so nowhere near any electrical cables), flick the light switch (my interference tester!) and it still glitches. Could it be the case that the interference is coming through the antenna (or the STB's power supply, less likely?), not the coax?. I'm not saying the RG6 doesn't knock out some of the interference, but if your antenna still picks it up then upgrading your coax is not the complete solution. Or looking at it differently, if the outer braid in the coax provides the shield by absorbing the interference, isn't that same braid connected to the STB anyway? Then again, the braid is also connected to the antenna, which is also connected to the inner core of the coax, which provides the signal to the STB. So wouldn't any interference picked up in the outer braid be transferred back through the antenna, into the inner core and then on the the STB? I'd be interested to hear from someone who can say exactly where and how interference enters the antenna system, and explain how the braid of the coax provides a shield against interference.
jamiep Posted November 6, 2004 Posted November 6, 2004 Bruiser, Try clipping a ferrite to the power lead of your STB, some of the noise may simply be coupling through the 240V, and the ferrite will help a little here. Also, if you are using a toppy or dual tuner device, take the little lead that goes between tuner 1 and tuner 2 and throw it as far as you can ... You can either make up a lead from good stuff, or get a splitter and run two runs ... one to each tuner. Works much Better! Jamie
PaulP33 Posted November 10, 2004 Posted November 10, 2004 Is everyone sure the interference comes in via the coax? I have run RG6 direct from the antenna to the STB (ie over the tiles, lawn and through a door so nowhere near any electrical cables), flick the light switch (my interference tester!) and it still glitches.Could it be the case that the interference is coming through the antenna (or the STB's power supply, less likely?), not the coax?. I'm not saying the RG6 doesn't knock out some of the interference, but if your antenna still picks it up then upgrading your coax is not the complete solution. <{POST_SNAPBACK}> I have the section of the antenna cable in the roof running through an earthed copper pipe, I still get glitches from the washing machine. I eliminated the power as the source by running the equipment off an unplugged UPS and still got the glitches. I'm pretty sure in my case it is the antenna that picks up most of the interference.
bruiser333 Posted November 10, 2004 Posted November 10, 2004 Thanks PaulP33, Your UPS test would seem to confirm the antenna as the culprit, that is what I have been suspecting in my case also. By the way, what VHF band(s) does your antenna cover ie 1-3 or just 3? BTW JamieP, I have tried the ferrite core on the STB lead before with no improvement, and using a quad shield lead on the Toppy's RF 2 In regrettably did not improve my situation either - thanks anyway. Cheers, Bruiser
PaulP33 Posted November 10, 2004 Posted November 10, 2004 Thanks PaulP33,Your UPS test would seem to confirm the antenna as the culprit, that is what I have been suspecting in my case also. By the way, what VHF band(s) does your antenna cover ie 1-3 or just 3? BTW JamieP, I have tried the ferrite core on the STB lead before with no improvement, and using a quad shield lead on the Toppy's RF 2 In regrettably did not improve my situation either - thanks anyway. Cheers, Bruiser <{POST_SNAPBACK}> I have a typical antenna with bands 1-3 and also a fracarro, both pick up the impulse emissions. I have also tried a power filter on the washing machine, which did not stop the problem, to try and rule out nosie from the device radiating from the power cables to the antenna cables. This combined with the copper pipe has convinced me that the point of entry into the distribution system is the antenna. I also tried moving the antenna to another part of the roof away from the washing machine (but using the same cabling). This improved the impulse problem but reduced my overall reception so I moved it back and banned use of the washing machine during peak viewing times.
gclark8 Posted November 10, 2004 Posted November 10, 2004 I recently insulated my Fracarro from the mast, it eliminated my local (75m away) HT power line problem. Still have lots of noise on the FM band (88-108), but that's another antenna (vertical dipole). Also, back in the DGTEC days, I replaced the Hoover with a Fisher & Paykel Smart Drive Washer, they are digital friendly.
bruiser333 Posted November 11, 2004 Posted November 11, 2004 Both log periodic antennas and Band 1 dipoles have a lot of metal connected to the downlead, and AlanH in other posts has said this leaves them susceptible to picking up interference. I think the only thing left for me to try is a Band 3 only antenna which has a much smaller dipole, however after already forking out a heap on my antenna system I might have to put up with the glitches for a while... (unless someone can suggest a silver bullet solution like an impulse noise filter - wishful thinking methinks).
poidahl Posted December 7, 2004 Posted December 7, 2004 Interesting topic. Why Quadshield is a very good question. A US TFC (one of the worlds best coax manufacturers) authority told me a few years ago he agreed that it was the Cable TV industry that needed Quadshield to limit emissions and ingress from their aerial suspended cables. Then Foxtel & Austar mandated Quadshield for their systems. The benefits for terrestrial analogue or digital are hard to see other than the 'oh I had it in the van anyway' electricians who run in RG6Quad everywhere. The English CAI guidlines for minimisation of impulse noise feature impedance match of antenna to cable as the no1 issue. Beyond that I think we are all going to have to get better at suppressing the washing machines etc. that generate impulse noise. To expect to stop it with an external filter might be a tall order, so what to do. It's an inside job - for licenced electrical people only - fitting suppression capacitors across the controllers contacts responsible for the impulses and ferrite filters to the wires near the controller. External filters are like trying to stop a radio signal once it has been transmitted - pretty difficult.
bruiser333 Posted December 7, 2004 Posted December 7, 2004 Poidahl, The English CAI guidlines for minimisation of impulse noise feature impedance match of antenna to cable as the no1 issue. OK, what exactly does that mean? Does it simply mean that if you use 75ohm coax you should be right? Or is there something else that needs to be done to impedance match the antenna to the coax? Cheers, Bruiser
poidahl Posted December 7, 2004 Posted December 7, 2004 You need the best possible impedance match from aerial to cable. TV cables are mostly 75Ohm but the antennas can be all over the shop. Follow the CAI's links on this subject to benchmarked areials, a fascinating subject in itself that has not surfaced down-under yet. The only ones available in Aus. are a certain FR brand I can't promote here.
poidahl Posted December 7, 2004 Posted December 7, 2004 Omitted to add the benchmarking system covers UHF only so it will be helpful in regional Aus. but unlikely to be in the Capital cities.
Recommended Posts