Those of you involved with domestic TV systems in any way may find this story a familiar one. Make yourselves comfortable......
A guy I've done work for before seems to have gotten into whole-house TV in a big way. A couple of years ago I installed a satellite system for him using an older analog receiver and dish that he'd been given. Since then, he's swapped over to a digital receiver and run his own distribution system around the house. The feeder from the regular UHF roof antenna was looped through the satellite unit, then through the VCR, back up into the attic to a 4-way distribution amplifier, and from there back down to the main TV in the living room and to three other sets around the house. He also had direct SCART (audio-video) connections between the satellite/VCR/main TV.
All normal broadcast TV in the U.K. is on UHF. The four main networks on the local transmitter are up near the top end of the band on channels 55, 59, 62, and 65. By the time I looked at this set-up, the four off-air UHF signals viewed directly on any of the sets around the house were poor, to say the least. Apparently it hadn't bothered him too much, as all are available on the satellite anyway, so they only watched one direct if the satellite receiver was being used to watch/record something else at the same time. They could also switch the VCR to one of the networks and watch the VCR output around the the house, which resulted in much improved picture quality. So the set-up was far from perfect, but it had satisfied them for a while.
Now, came the problem. He'd gone out and bought a new digital terrestrial receiver which he wanted to add to the system. This needed a feed from the UHF roof antenna, and obviously its RF output would also need to be distributed to everything so it was yet another box for the line to loop through.
The result was that the four analog UHF signals were now varying in quality from very poor to terrible when viewed directly. He'd connected the new digi-box to the main TV with a SCART lead, but had run into big problems with trying to tune in the new signal on that set's tuner and around the rest of the house. He'd also got a pre-amplifier to insert in the attic on the incoming feeder from the antenna to try to boost the signals. That had worked (I should hope so, as it provided 20dB gain!) and the four analog UHF signals were now excellent throughout the house, but the satellite signal now had bad patterning. It was at this point he became totally confused and called yours truly (probably at the behest of his wife, who didn't understand why he wanted yet another box anyway ).
It's already too late to cut a long story short, but I found that the reason he couldn't properly tune in the signal from the new digi-box was that its output was set to channel 36. The VCR was already feeding its signal out on ch. 35. Retuning the digi-box output to a clear spot at ch. 48 fixed that.
The patterning on the satellite signal around the house was caused by the now very strong analog broadcast signals coming down from the attic. The digital satellite receiver he'd acquired had its RF output tuned to channel 68, and with the now 20dB stronger off-air signals the distribution amplifier in the attic was cross-modulating and throwing out all sorts of spurious signals across the band. One of them happened to be right on ch. 68. I retuned the satellite output down to the bottom of the band at ch. 21, and also found several bad joints at coax plugs. Fixing them resulted in good picture from the satellite receiver throughout the house.
Now one of the problems this guy faced with setting up all this equipment is the complicated on-screen menus used on all this equipment. Obviously we had to go around the house and re-tune every TV to the new frequencies, but every set was different, and a couple of them had such complex menus (and no instruction books!) that it took me at least ten minutes on each to figure out how to even get into the tuning menus.
The digital satellite box has a whole batch of set-up menus, but anyone looking for a way to change the RF output channel would be out of luck. You can go through every menu you can see and not find it, because it's on a hidden "installer" menu which isn't even mentioned in the user's manual. You just have to know to press 0, 1, Select. I can see how they might want to prevent Mr. Average from messing around with the LNB IF offset, 22kHz switching signal, etc., but why hide the option to change the output channel? More and more people are getting complex set-ups like this these days, so they're bound to need to change the output from the default at some point to avoid clashes.
Anyway, both the lady and gentleman of the house were satisfied with the eventual quality of all pictures, and I left them with consistent settings on all TVs: 1 thru 4 = normal networks, 7 = digital terrestrial, 8 = VCR, 9 = satellite.
I'm not sure they've quite mastered how to switch to direct A-V inputs on the main TV in the living room or quite figured out just exactly what combinations of channels they can watch and/or record at the same time, so I wouldn't be surprised to get another call sometime soon.
Did I mention that he also bought a new widescreen TV for the living room? I'll save my comments on that for next time!
[This message has been edited by pauluk (edited 07-31-2003).]
Sounds as though you have been quite busy. I know that poor connector connections can be blamed for a whole lot of interference problems, poor signals, etc. Multiply that by 3 connectors and they're lucky to have had much of a signal at all.
BTW, there was an excellent article on spectrum analyzers and coaxial cable (diagnosing problems on the coax) in this month's S&VC.
Paul, That's a great story. In all the times that I have repaired TV systems like the type that you mentioned, the problem has been caused by the homeowner, who has used the original coax (normally single-screened R-206) or twin lead (ribbon) cable and fitted the highest gain amp in the land, to the system, in the hope that there will be MORE signal at the other end of the cable. With respect to Output channels on Decoders, the Sky UHF Decoders over here, have a pair of 10 position (0-9) Rotary switches on the rear panel and these are used to set the Output frequency. On the Digital decoders, the presets can only be accessed by inputting an installer code. One thing I do know about Digital TV recievers, is that if there is a small fault in the input signal quality, you don't get a picture at all, as opposed to the snowy picture on an Analouge TV. How do the Minimum Signal levels required for a Digital TV compare with that of an Analouge TV?. Were F-connector type plugs and splitters used in this installation?.
Let's face it, these days if you're not young, you're old - Red Green
Thanks for the link. I'll read it tomorrow over my coffee break (getting rather late now) -- Looks interesting.
That's one of the problems with these sort of high frequencies: It takes only one bad joint to cause an impedance mismatch, set up standing waves on the coax, and cause all sorts of interference problems.
Trumpy, The F-connectors are only really used here on the coax from satellite dish to satellite receiver. All the regular UHF antenna connections are the Belling-Lee coax plugs (U.S.-style 300-ohm balanced feeders never caught on here for TV).
There were actually a lot more plug and socket connections even than my description might have led you to believe. The drop from the roof antenna had a splice in the attic on its way down to the living room. Each coax cable entered a coax socket in the corner of the room with a fly lead to the various equipments. B-L coax plugs were used to connect to the input and outputs of the distribution amplifier.
So with all that lot plus the connections at each box, the signal was actually going through no less than 13 plug/socket combinations on route from antenna to TV. With several bad joints you can see why the signal was poor, and that before you even include the attenuation through the threediplexer/combiners in the digi-box, satellite receiver, and VCR.
If you think that TV installation's complex don't look into an attic over here in Cork, Ireland!
In the days before BBC 1 & 2 were carried on SKY digital Co. Cork was exclusively served by a few systems (operated by a monopoly cable company): Cable in the city and larger towns. MMDS in the non-urban areas.
(ITV/C4 still are not on the Republic of Ireland's SKY package..the irish terestrial channels are on 101-104 and BBC 1/2 on 214/215 so cable/mmds are still the only legal ways of receiving ITV or C4)
However, MMDS coverage isn't exactly universal and the company who operates the cable and mmds systems tends to be pricy and seem to have employed ex-gestapo agents as customer service people!
The result was that during the 1980s a community owned and operated UHF rebroadcasting system was established (without a licence) to rebroadcast BBC 1, BBC 2, ITV and C4 from overspill signal picked up on the east coast (130 miles away). The system picked up the UK broadcasts on a huge tower antenna and beamed them back to a network of distribution TX's around the county. Since cutting off people's favourite TV channels goes down like a lead balloon in an election, not to mention the fact that the TV community group inserted help messages after popular programmes like coronation street to rally the "troops" (community tv campaigners) to come out and march if anyone dared to raid their facilities , the system has been allowed to continue to operate as long as it respects the frequency allocations used by RTE and other broadcasters. However, I suspect that the advent of full "freeview" digital terrestrial type TV here will be the end of the line for the rebroadcasting system.
Anyway, back to the point:
RTE 1 / Network 2 broadcasts on a mix of VHF and UHF (along with TV3 and TG4 only on UHF)
Southcoast community television broadcasts 4-5 channels on UHF (for years this included sky one and eurosport!!!)
So the average house has 2 flat panel wideband (UHF/VHF) antennas on the roof pointing at different transmitters.
Using a completely weird mix of diplexers, filters and attenuators tuned to filter out unwanted signals the feeds from the two antennas are merged into one cable and usually fed from there to a distribution amplifier feeding at least 3-4 (if not all) rooms in the house. It would be quite common to add a door security camera on UHF, maybe the feed from the VCR/SAT box too !!
Our antenna installers tend to have to be able to resolve all sorts of ghosting, crosstalk, patterning, weak signals, etc etc..
Basically you have:
2 X antennas (with inline amplifiers on the pole)
feeding through all the attenuators etc..
the internal stuff (sat boxes, door cameras etc) is added in.. possibily more attenuators if there are problems with interference / crosstalk.
then on to the distribution amp..
it can get as complicated as a mini-cable tv system!
Generally analogue reception is excellent though!
[This message has been edited by djk (edited 07-31-2003).]
[This message has been edited by djk (edited 07-31-2003).]
Ah yes...... I wish I had a nickel for every time I've tried to explain that to somebody. A wideband amplifier does just what it says and amplifies everything you feed into it, noise and spurious signals included.
The dual-use of VHF/UHF in Ireland (and most other countries) certainly makes the situation more complicated.
In the days of 405-line VHF television in the U.K., people often needed two antennas. In all but a few places, BBC and ITA (Independent TV) had their transmitter sites in different locations, so rooftops often had a band I (BBC) aerial pointing one direction and a band III (ITA) pointing in another.
By the time the UHF 625-line network was planned in the 1960s, the BBC and ITA had agreed to co-site their transmitters to use shared facilities, and the band was planned so that an eventual four networks could be broadcast from every site, the channels assigned in groups to allow higher-gain aerials to be employed (hence the four channels in this area being on 55, 59, 62, and 65).
It was only BBC2 on UHF at first, so many rooftops then added a third antenna for that, but when BBC1 and ITA went onto UHF from the late 1960s onward, it was possible to abandon the two tons of rooftop art and receive all three (later four) stations on a single UHF antenna.
This is one area where British planning was actually excellent, for once.
It's just a pity they've made such a mess of it in recent years with the fifth network and digital.
ThinkGood, You're on to it!. Like Paul said, most people don't understand that RF amplifiers amplify EVERYTHING that is fed into them, noise included. All a masthead-type amp, does, is maintains the signal at a given level, to remove some of the loss in the downlead, a bit like having your TV on the roof!. Customers that I've spoken to in the past, seem to think that an amp will make up for a poor Terrestrial signal or a shoddy installation job and man have I had some funny looks when I have told them the truth!.
Let's face it, these days if you're not young, you're old - Red Green