Wikipedia:Reference desk/Archives/Miscellaneous/2013 July 14

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July 14

Digital TV information

I use a set-top box to subscribe to Digital terrestrial television in the United Kingdom. Every so often the box decides it needs to update itself, and asks me to confirm. if I say yes it displays a screen showing the progress of the update. This screen shows a table with a number of columns, as follows:

• Prog
• Channel
• Service name
• Net ID
• TS ID
• Quality

Apart from "Service name" I've no idea as to what all these mean. For instance none of them seems to correspond to the channel number that I use to select a particular channel to view. Any suggestions as to what all of these mean? --rossb (talk) 10:43, 14 July 2013 (UTC)

A "channel" is a section of the electromagnetic spectrum. C21 to C60 are the space for TV. C21 is at 474 MHz, C22 is 482 MHz, an so on. Different transmitter towers transmit on different frequencies (so that people in between, who can see both, don't get interference). In the old days of analog TV, from tower A you might get BBC1 on C21, BBC2 on C26, ITV on C31, etc. So e.g. if you lived in Fife, the engineer setting up your TV would figure out the bearing to the Craigkelly transmitting station (using a map), would point your antenna at that, orient it to match the antennas on the tower (he had a technical bulletin that told him that) , and then (again from the bulletin) he'd look up the channel numbers (and thus the frequencies) to which he'd tune individual program buttons on your TV. Now that analog has been replaced with digital, the process is similar, except that a "channel" now carries a digital stream called a multiplex. Each multiplex contains a bunch of TV programs (program-streams) all sharing the space (like watching ten YouTube videos at once). What's on each multiplex is listed here. You'll notice that they're ordered for commercial reasons - the BBC ones are all together, and separate from the ITV ones. You can look up the transmission details for each tower - so again for Craigkelly, we can see on this page that it transmits the BBC-A multiplex on C27 (522.0MHz), the D3&4 multiplex (ITV, channel 4, etc.) on C24 (498.0MHz), and so on. Each program has a LCN (logical channel number), also called EPG number, which determines where on your electronic program guide the program appears. Note that this has no relation to the multiplex, and certainly not to the actual chunk of radio spectrum (the channel) on which you're getting it. NetID (sometimes Service-id) and transmitter-service-id just identify the originator of a given program stream and identify that stream's ID as it moves through the network (for example, I think BBC1 has the same NID everywhere, but BBC1 Cumbria and BBC1 Wales and BBC1 Cornwall get different TSIDs). Service name is just a text embedded in a program stream identifying it ("BBC One Wales" etc.). And quality is just the strength of the signal being received. You can use that site I linked before (http://www.ukfree.tv/) to figure out which transmitter you're getting signal from (you might have a choice of two, depending on your location) and then you can see on which UHF channels the different multiplexes are sent over. -- Finlay McWalterჷTalk 13:51, 14 July 2013 (UTC)

I doubt most TV aerial installers would use a "technical bulletin" to decide where to point your aerial. They would simply look to see in which general direction your neighbour's aerials were pointing. And, since the introduction of auto-tuning, I also doubt they would use the bulletin to get the channel numbers. Only in particularly difficult reception areas, or for a special request from a customer, would they refer to any technical documentation or use a signal strength meter. Astronaut (talk) 11:32, 15 July 2013 (UTC)

Do I need to completely stop when changing from reverse to forward?

In a car with a traditional manual transmission, if I am backing my car in reverse and then want to suddenly drive forwards, do I need to completely stop my car before shifting into 1st gear and driving forwards? Or can I begin to slip the clutch and give it gas even as my car is rolling backwards?

I have a 01 Honda Civic with synchronized gears. My personal intuition tells me this should be ok, except that since I'll be slipping the clutch a bit longer (compared with if I had completely stopped the car), it will wear the clutch out just a bit more? Is that correct?

I don't think reverse gears are usually synchronized on production road cars right? Does this mean that we should avoid the opposite scenario: shifting into reverse and trying to drive backwards while the car is still rolling forwards?

Thanks Acceptable (talk) 16:06, 14 July 2013 (UTC)

My elderly mum drives like that and wears out clutches faster than most people can wear out a pair of shoes. This is purely original research though. Alansplodge (talk) 20:47, 14 July 2013 (UTC)

If you're doing about 1 mph it's unlikely to cause problems. Pulling away in first while the car is rolling backwards is similar to pulling away on a hill. But you have a brake pedal and you try using it. Itsmejudith (talk) 21:06, 14 July 2013 (UTC)

Why is it hard to shift the shifter into a low gear at high speeds?

I am driving a car with a traditional, synchronized manual transmission.

Suppose I am driving at, say, 40 MPH on 4th gear. Why is it hard to move the gear shifter into first gear, while still holding down the clutch pedal? I am well aware of that fact that on my car, 40 MPH is clearly out of the RPM range of first gear, so I should not try shift into and engage (by taking my foot off the clutch) first gear while travelling at 40 MPH. However, even when I keep the clutch dis-engaged (by keeping my foot firmly on the clutch and keeping it on the floor), I have to shove the shifter really hard for it to fall into first gear. Why is this?

Also another question. Sometimes when my car is at a standstill and on neutral, sometimes I just can't get it to shift into gear. I made sure my clutch is fully pressed against the floor, but the gear shifter just won't "click" into gear and when I try to give it gas, the engine just revs. I have to take my foot off the brakes and let the car slide just a bit before I can successfully shift the shifter into gear. Why does this happen? Is sometime misaligning? Acceptable (talk) 16:11, 14 July 2013 (UTC)

Not a direct answer to your questions, but have you read our article Manual transmission? Depending on your mechanical grasp, you may be able to find or deduce some of what you want to know in it.

As to your specific queries in this section: the first is not something I've noticed, but then I doubt I've ever needed or wanted to do it, and on the rare occasions I've done it accidentally I had other immediate concerns than remembering how much resistence there'd been!

The second is in my experience not uncommon, and I've always assumed that the gears involved happen on occasion to be sitting exactly "tooth-to-tooth" rather than offset enough to mesh smoothly – this one needs actual mechanical expertise rather than mere driver experience. A similar similar phenomenon used to happen when the starter motor was in "dead top" position and so couldn't start the engine, and the same tactic of rolling the car slightly was the cure: I haven't had this happen in a long time, and suspect modern starter motor design has elimitated the problem.

In general, experience tells me that as a car ages the "gate" of a manual gearbox seems gradually to wear and become sloppier, and individual gears may become more finicky to select, but again this has become less prevalent in recent years, again perhaps due to more advanced design.

There's an awful lot of personal presumptions in the above: hopefully a qualified mechanic will be along eventually to give informed and referenced answers.

Which reminds me, I must remember to book my car in for its annual service and MOT soon . . . . {The poster formerly known as 87.81.230.195} 90.213.246.168 (talk) 20:19, 14 July 2013 (UTC)

On the second question, you should give the engine a _little_ rev with the gears in neutral and the clutch engaged, then declutch and select first gear. This will ensure all the gearbox components are rotating so that the synchro dogs can engage. See Manual transmission#Synchronized transmission. Tevildo (talk) 23:16, 14 July 2013 (UTC)

I've had an older (1983 Toyota) manual transmission where it wouldn't go into gear (it didn't have a preference up-to-down or down-to-up, it would just sometimes do it), the shifter just would pretend that the gear I wanted to go into wasn't there. I would just release the clutch in neutral, reclutch, and then it would almost always shift fine. I always assumed it was because something that was supposed to line up wasn't lining up any more (at the time the car was about 15 years old). So I can confirm the above advice as having worked on my car at the time. --Jayron32 00:28, 15 July 2013 (UTC)

Think I might know the answer to this. If you have convention H shift can you move it out of fourth and into the horizontal only to find you can’t move it forwards fully into first? I ask this because back in the 80's some of my friends and myself found – and over came this - when we showed off (not on the public highway I might add) and we found this very problem at first. Note: this was with contemporary front wheel drive cars without a long prop-shaft to the rear in which to store rotational energy. Eventually, with practice, we found we could spin a car through a 180 degrees and when the wheels were going in reverse, release the clutch in reverse at high revs. Then after driving in reverse for a bit, depress the clutch again, spin another 180 degrees and release the clutch in second gear. At no time did the car stop. The problem we found at first, was not being able to engage between reverse and second gear when we wanted to. However, when we leant to get the engine rev's to match the drive shaft speeds the gears engaged with ease. The guy in this video calls it block:[1] In other words, if there is too much speed miss-match, the synchro will not synchro and so the gear will not engage. The gear leaver therefore, can not fully move into it final position.--Aspro (talk) 01:18, 15 July 2013 (UTC)

To show you that it ain’t that difficult here is another guy doing it at 3 min and 21 sec into the video:[2] So, there you see it, the car doesn't stop and yet it goes from forward to reverse gear. --Aspro (talk) 01:52, 15 July 2013 (UTC)

My strawberry plants' leaves are turning red, can anyone help?

Several of my strawberry plants' leaves on our allotment have started to turn red, or have turned completely red. Can any gardening experts help me? Have they got a disease or is there something I'm doing wrong or is this just natural? I don't know what variety the strawberries are but they have just finished fruiting and are planted in the ground rather than in a pot. They get watered twice or three times a day (how much water they get depends on how hot it is, so today as it was 32 degrees they got a lot of water) and the strawberry patch is weeded pretty much every day or couple of days, it depends how much time I have. They spend most of the day in direct sunlight, getting the most out of all the plants on the allotment. They are, however, rather closely packed together but there is not much I can do about that. I'm really starting to get quite worried as this has been going on for a week and my gardening expert grandmother can't explain it. Please help!!! PS I live in south-east England. Ej02 (talk) 19:24, 14 July 2013 (UTC)

How are you watering them? The disease section at Strawberry#Diseases says to make sure you don't water the leaves, otherwise you can get fungus growth. If you take a couple of leaves to a local nursery, they can probably tell you what is wrong and how to remedy or prevent it. Our article on List_of_strawberry_diseases doesn't have many photos, so I'm not sure which leaf problem you have. RudolfRed (talk) 19:38, 14 July 2013 (UTC)

Natural for them to be red. Itsmejudith (talk) 21:03, 14 July 2013 (UTC)

Yes, I worked on a college farm and they turn a rich red after they fruit. Only worry is if they are black or wilted or spotting as from a fungus. This is to b expected. Kinda nice, actually. μηδείς (talk) 00:36, 15 July 2013 (UTC)

Yep, depending on where in the world this is in South England (or any temperate climate), I'd expect strawberries to be senescing about this time (i.e. as pictured in Medeis' link above). Much like fall color on trees, the chlorophyll gets retranslocated (redlink, google /nitrogen retranslocation/) so that that nitrogen can be stored, and used to make next year's leaves. SemanticMantis (talk) 14:59, 15 July 2013 (UTC)

Oh, and if they do look like the pic above (not diseased), leave all the leaves there, until they are totally brown and dead in the fall. Some people cut off old leaves to make a plant look better, but that can rob the plants of resources. SemanticMantis (talk) 15:04, 15 July 2013 (UTC)

Thanks for the help everyone, all much appreciated! They have just fruited so if that's natural then panic over. Phew.Ej02 (talk) 16:41, 20 July 2013 (UTC)