Thursday, October 6, 2011

DTV in Your Lazy Daze

Introduction:

• This article is intended to help you deal with television, especially DTV in your motor home.

• Notation: Since we are talking about both analog TV sets with DTV converters and DTV sets themselves, the word “set” here means any TV receiving device

Overview:

• The United States requires its larger (called full service) television stations to transmit DTV signals.

• There are other “secondary” TV services consisting of Low Power, class-A, translators and booster transmitters. Many are now transmitting DTV signals while others remain analog. These stations are typically found in the rural areas where we often camp.

• CATV systems in RV parks will typically have analog signals. Any digital signals on CATV systems will be in a different format than over the air DTV signals. Set top boxes typically will not decode them. Some DTV sets will

• Conclusion: The TV in your coach needs to have the ability to receive at both analog and over-the-air DTV signals.

The American DTV System:

• A DTV transmitter transmits 19.4 million bits per second.

• Computer networks typically send from 1 to 3 million bits per second.

• The DTV System is pretty spectacular, being able to send those 19.4 Mbits/sec under very difficult conditions.

• DTV has some other nice features

o Excellent picture quality

o Info button gives positive station ID

o Most sets have a program guide (what’s on right now and coming programs)

o Some sets are able to scan all stations and gather a full program guide

DTV Channel Numbering:

• DTV stations are able to send one very detailed program (HDTV) or several programs of varying definition. When they send several signals, it’s called multi-casting.

• A DTV signal’s channel number is always shown by the set as a number with a decimal or hyphen. For example, “10.1” or “10-1”. An analog signal may be shown as just the number. For example “10” or it may be shown as “10-0”.

• When multi-casting the signals are numbered thusly: 10.1, 10.2, 10.3, 10.4 etc

• But, DTV channel numbering is very different than analog in a very different way:

o There is the “Physical Channel”, which is the actual RF channel that the signal is being transmitted on. These are the numbers you have known all your life.

o Then there is the “Virtual” or “Display Channel”. This is the number that the station tells the DTV set to show as the channel number.

o For example, in Portland, OR, KOIN TV’s old analog transmitter was on channel 6 so everyone knows the station as KOIN 6. Its DTV transmitter is now on channel 40. KOIN sends a message to your set to show its channel as 6-1 so viewers recognize it as KOIN. TV people will say that KOIN is on virtual channel 6-1. You typically will only know the signal’s virtual channel number. Some sets have the ability to show you the real or RF channel number, but many don’t.

o Furthermore, translators carrying signals from distant transmitters often show the channel number of their parent station. Thus, along the north Oregon coast you will see channel 6-1 on your set while it’s actually tuned to physical channel 38, 41 or 23 depending where you are.

Connecting Your Converter Box:

• While you need to be able to tune in DTV, you must still be able to receive analog TV:

o Translators and Low Power analog TV stations not immediately converting to DTV.

o CATV in RV Parks will still mostly be analog TV for some time.

• There are two connections that must be made:

o A signal from the coach’s TV antenna must be connected to the DTV converter’s RF input.

o The signal(s) from the DTV converter must be directed to the TV set.

• There are essentially three ways to make each of those two connections. You can mix and match the antenna connections vs. the TV set connections.

Note: If the diagrams below are hard to read, just click on them and they will open in a larger view.

Method A:

Method A shows that if one can get to the back of the Winegard RV distribution box, there is an unused RF outlet available to provide the RF signal to the DTV converter set. This approach is good when the DTV converter box does not have a bypass mode (that mode feeds the unprocessed antenna signal directly thru to the TV set).

Method A also shows that one can connect the signal from the converter box to the TV set using audio/video connections. This approach creates the best picture quality.

Method B:

In Method B, the signal is provided to the DTV box by splitting the signal from the front of the Winegard unit. The big advandage of this approach is that no access to the back of the Winegard unit is required.

The analog TV signal on channel 3 or 4 RF signal created by the converter box is used to provide the TV set with a signal. Because it is necessary to be able to use the TV set to view analog TV signals, an A/B is needed as shown.

Method C:

Method C is the easiest but it requires a DTV converter box that has a bypass or feed-through mode.

Keep in mind that one can select any method to provide an antenna signal to the converter box and independently select another method to connect the converter’s output signal to the TV set; like a Chinese restaurant menu.

Connecting Your Power to your Converter Box:

• You must also connect power to the converter box.

• This is much more situational; depends heavily on the converter box and the RV.

• Some converter boxes have an attached AC line cord. You must provide it
110 VAC power via an inverter or shore power.

• Some converter boxes have external power supplies:

o You can plug the external supply into an 110 VAC inverter or shore power, or

o If the supply has a DC output, you may be able to use a DC to DC adapter.

• If the converter uses 12 VCD, one can plug it directly into the 12 VDC power in the coach.

DTV Background:

• To steal a line...”It’s not your father’s TV signal anymore!”

• DTV is like Frank Sinatra’s song a DTV signal is “All or Nothing at All”.

• DTV produces flawless (no ghosts, herring bone, etc.), noiseless (no snow or fuzz) pictures and sound ... until the signal amplitude falls to the receiver’s threshold .

It goes through a narrow “fuzzy” zone.

• And then:

IT FAILS COMPLETELY

As in ... NO Picture … NO Sound … NO Nothing.

• It goes from here...

.... to here...
To here...
... with a very small change (1 dB).

• It must be emphasized:

– Picture and sound are sent together.

– When you have a picture you will have sound. When the signal fails,
Picture and Sound Fail Together.

– In fact, the first indication that the signal has fallen below threshold is the sound muting.

• For those few who know the term, the picture/sound can go from IDEAL to NOTHING with a 1 dB amplitude change.

• For those that don’t know what that means, 1 dB is about the change in volume one gets with one or two clicks of the volume control on a modern TV or radio.

• If you have just barely enough signal, small changes can cause the picture to become “pixilated” or vanish. Causes like:

o A storm.

o A vehicle moving.

o A new source of interference (like a fan.

• DTV troubleshooting is difficult

o When there is a picture, the picture is ideal.

o When there is no picture, you have nothing.

o There is little in between.

o You are flying blind.

• The only available strategy: just keep trying various things until something works.

Tuning In DTV Signals:

•If you are camping where the signal amplitudes are low, tuning in DTV signals can be ... uh … .....trying.

•The RF performance of most set top DTV converters is adequate to good for use in a RV. However, the user interface is quite variable with some MUCH better than others.

•DTV sets try to make finding signals “easy” by providing an automatic scanning mode to find the stations for you.

•Many sets won’t let you tune to a given channel until the set finds it for itself during some form of a scan, either manual or automatic.

•Other sets will tune to a new channel just by entering its channel number on the remote control.  Try your set to see if it works this way.  If it does ,and you know the new signal's RF channel number that is a fast way to tune the set.

• During an automatic scan, if a DTV signal is detected but is below threshold the set may or may not add the channel to its list.

• It’s very useful if it does so because it points to where to search for a DTV signal.

• If you don’t know what direction the signals are coming from, you may have to turn the antenna, scan, turn the antenna, scan, etc., which can be very time consuming (more below).

• A few sets have a manual add/delete mode or allow a manual scan. These sets are the best for use in an RV.

• The DTV set-top converters that have the best user interface for use in a RV are the Artec T3A, the Winegard RDCT-09, the Zenith DTT 900 and 901, The RCA STB 7766G-1, The Radio Shack stock # 15-149 and # 15-150, The Insignia NX-DTA 1. These units have an excellent manual scan add/delete mode that works very well in a RV. The Artec and the Wineguard are the only DC powered units.

Setting Up Camp:

• So, you just pulled into a new campsite. How do you find out if there’s any TV to watch?

• You may have a DTV set or a set top converter so there is a wide variation of user interfaces. This makes it impossible to give just one best method. Just some general guidance ...

• Where do you initially point the antenna?

o Ask someone where the TV stations are.

o If you are camping with other RVs, note where their antennas are pointing and point yours there too.

o If camping alone, start by pointing toward the nearest large population concentration.

• If you have a set and DTV converter, first scan the analog receiver to see what is around. Transmitters are typically found in groups so if there is an analog signal there may be DTV signals there also. Turn the antenna to get the best analog picture for a starting point.

• Now scan the DTV set. Hopefully, that will turn up at least one decodable DTV signal.

• Or perhaps after scanning, when you push the remote’s up/down the set stops at a channel but there is no picture. This might be a near miss.

o Slowly turn the antenna first one way and then the other and see if a picture will pop into view.

o Slowly equals one Winegard antenna azimuth notch every 5 sec.

• Perhaps the scan turned up one or more viewable DTV signals.

Slowly turn the antenna first one way and then the other to find the range over which the signal(s) are above threshold.

• Then center the antenna in the range.

• Signal strength indicators:

o Many sets have some sort of signal “goodness” indicator mode.

o If you have a signal above threshold, you can use the signal strength reading to aim the antenna directly at the station. (The strength indicators don’t seem to work until the signal is above threshold.)

• Aim the antenna at the center of the range that makes pictures on at least one channel.

• Run another scan to see if more DTV signals can now be found.

• If no signals are found on the first try, turn the antenna 45° and scan again.

• DTV transmitters are often, but not always, sited near each other so if you find one, you may find many.

• After finding station(s), you may want to try pointing the antenna in a different direction to see if there are more to be found.

• If your converter or TV set has a manual scan or manual add/delete mode it often can be used to find stations.

o Point the antenna in a likely direction.

o Manually tune the converter through the channels looking for the presence of a DTV signal on the unit’s signal strength indicator.

o Once a signal is found, slowly turn the antenna to maximize its strength.

• One of the oddities of DTV is that after the signal is above threshold, greater signal amplitude does not help. Therefore, if there are several signals, work to bring the smallest above threshold without loosing the larger signals.

The RV Batwing Antenna:

• Your present Winegard Sensar (batwing) antenna system works very well for DTV.

• For channels 2-13, the batwing is bi-directional: it gets its largest signal when you aim either of its flat sides toward the station. (There are very, very few DTV signals on channels 2 – 6).

• For channels 14-51, it’s directional: it gets its largest signal when you aim the flat side that’s away from its support posts toward the station. (Since DTV signals like to hide what channel you are actually tuned to, try to turn the antenna so that side is toward the station.)

• When looking for DTV signals be sure to turn the antenna completely around.

• Winegard introduced an accessory for the Batwing antenna called Wingman. Wingman improves performance and makes the antenna much more directional on channels 14-51. While the Wingman’s improvement is relatively small, because of DTV’s threshold, it can make the difference between receiving and not receiving a signal.

A Nag:

• Have you lubed your coach’s TV antenna mechanism lately?

• It gets stiff if you don’t.

Contributor: Linley Gumm


Revised: 6 Oct 11

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.