Technical Issues

Receiving Free Over the Air Digital TV Translator Signals

Dan Mooney

South Lane Television Engineering

With the transition to digital over the air broadcasting, South Lane Television has undertaken a major upgrade to its television translator system. Presently there are 37 program choices from a tower atop Hansen Butte southeast of Cottage Grove, 16 program choices from a tower just northwest of London, and 8 program choices from a tower on Hawley Butte northeast of Culp Creek. I will attempt to clarify some of the confusion about digital broadcasting and provide some tips on how best to receive the signals.

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Virtual Channel Numbers

After connecting your antenna and performing a scan for available channels, some viewers will notice that they have multiple listings for the same channel, such as two copies of 9.1, 9.2 and 9.3. This happens because you are receiving signals both directly from the Eugene parent station and from the Cottage Grove translator system. This can be an annoyance and most viewers will want to delete from the program list the programs that are coming directly from Eugene and keep the ones from the translator system as these will probably be the most reliable. There will be no difference in picture quality. How can you determine which ones to delete? The answer lies in gaining a little knowledge about how the channel numbering system works in digital broadcasting. The channel numbers that you see on screen are called “virtual channel numbers” and can be set by station engineers to display any number they choose. These numbers may or may not be the actual television channels (FCC frequency assignments) by which the signals propagate from the tower to your antenna. Some set top converters and digital TV sets have provisions for displaying the “actual” or “RF” (radio frequency) channel although you will probably need to go into the menu system to find it, possibly under “manual tuning”, “setup” or something similar. Here is a table showing how the virtual and actual channel numbers match up for available signals in our area:

So, as an example, if you are watching the SLTV Cottage Grove translator system and receiving two copies of virtual channels 9.1, 9.2 and 9.3 go into your menus and try to determine which ones are on actual channel 9 and which are on actual channel 24. Delete from the program list the ones which are on actual channel 9. If you are unable to determine which actual channel you are watching, find your on screen signal quality meter which usually looks like a colored bar graph. This varies among different set top converters and digital TV sets but is usually found in the menu section under “setup” or something similar. Delete the program set that has the weakest signal quality reception.

SLTV Stations

Maximize Your Reception

Broadcast engineers refer to what they call the “cliff effect”. This is a reference to the fact that digital reception is an all or nothing proposition. When signal quality goes below a certain threshold, the picture goes over a “cliff” and disappears entirely. There are no more snowy pictures or ghosts. Initially, some areas of the picture may “freeze” and you may hear dropouts in the sound. Then a blank screen will appear with a message that says “no signal” or something similar. This makes it difficult to set your antenna for the strongest signal. In the old days of analog TV you could move your antenna around and see if the picture gets better or worse. In the digital age, the way to accomplish this task is to display your on screen signal quality meter and adjust your antenna for the highest reading. Do this for the weakest channel you are receiving. You may then need to check the other channels and fine tune your antenna to get a good reading on all channels.

It does not take much signal to get full performance from set top converters or digital TV sets. Therefore it is not usually necessary to install a mast mounted preamplifier or “booster”. In fact, this may do more harm than good because the amplifier may be overloaded by other strong signals in the area, causing interference to your receiver. An exception would be in a situation where there is a great distance between the antenna and receiver, say fifty feet or more. In this case a preamplifier would compensate for the loss in a long cable run. This compensation must take place before the cable loss, not after, so it does no good to install an amplifier right behind your TV set. As usual there is an exception to that rule. If you have a network of splitters feeding several receivers, you may need to amplify the signal before splitting it.

Outdoor Antennas

In the early days of translator reception it was understood that you were going to need an outdoor antenna. Translators then (and now) put out only a small fraction of the power that their high powered parent stations do. Of course some people could get a picture with rabbit ears or indoor loop antennas, and with analog you could still tell what was happening and hear the sound even with snowy pictures. With digital, if you are operating near the “cliff” it is highly recommended that you upgrade to an outdoor antenna. A good antenna for UHF reception (Cottage Grove and London) is a “bowtie” style antenna such as the Channel Master model 4221HD or the Xtreme Signal HDB4X, available for around $50 to $75. These have a rectangular screen of about 2 X 3 feet with what looks like four wire “bowties” or “cat’s whiskers” mounted a few inches in front of it. Use RG-6 coaxial cable coming into the house, which is normally available at local electronics or building supply stores. Do not use the flat “twin lead” cable so common in years past. Waterproof outdoor connections by wrapping with rubber tape or mastic then apply vinyl electrician’s tape over that.

For those receiving channel 11 in the Row River area, the best antenna is one designed for the “VHF high band” such as the Winegard HD7694P. This would have a horizontal boom about 6 feet long with several cross arms of about 2.5 feet long and costs about $60. For very low signal areas, The Winegard HD7697P is larger, has higher performance, and costs a little more.

Indoor Antennas

In some areas you can get by with an indoor or “set top” antenna and in apartment buildings you may not have the option to install an antenna on the roof. These antennas come in various shapes, some with a small wire loop for UHF (Cottage Grove and London) and extendable rods or “rabbit ears” for VHF (Row River system). In Cottage Grove and London, the loop is all that matters; push the rabbit ears in all the way. In the Row River area, extend the rabbit ears about half way out. There are higher performance indoor antennas such as the Terk HDTVa for about $40 which has a boom of about 14 inches long with cross arms of varying lengths. This works better than a simple loop for UHF reception in Cottage Grove and London. It also has rabbit ears for VHF which fold up out of the way when not needed.

With any indoor antenna, it is important to move the antenna around and aim it in different directions to find an adequate signal, again using the on screen signal meter as a reference. The transmitter signals bounce around, reflecting from nearby objects to create hot spots and dead spots. A hot spot may be only a foot or two from a dead spot, so moving an antenna just a small distance can make a big difference. Complicating matters, due to the various frequencies in use, a hot spot on one channel may be a not so hot spot on another. If you need to move your antenna around when switching from one channel to another, consider moving to an outdoor antenna, then just set it and forget it.

When to Re-Scan

If you are experiencing trouble and have determined that your system is connected properly, you should re-scan for available channels. The receivers are like computers in many ways and like most digital devices, they can crash. Unplug the receiver, wait 10 seconds, plug it in again and then re-scan. Sometimes faulty data from the digital transmitter can cause a receiver to get “scrambled”. So if anything odd is happening, the solution may be to re-boot and re-scan. Finally you should re-scan periodically to see if anything new has come on the air since the last scan. The parent stations or South Lane Television may add programs in the future or make changes to the program names or numbers. Your receiver may or may not display new programs until the next scan. If you lose some programs that you once had, you should re-scan.

When not to Re-Scan

There is a downside to performing a re-scan. If your antenna happens to be sitting in a weak spot for a given channel then that channel may disappear from your channel list after the scan. If that happens, move or re-aim your antenna and scan again. This happens most frequently when using indoor antennas. If there have been power outages in the area and you suspect the translator system may be off air temporarily, it is best to leave things alone for now. If you scan when some or all of the translators are not transmitting, then your receiver may never display those channels even after they come back on air. You must scan only when everything is up and running.

Conclusion

The digital broadcasting standard has proven to work very well with low powered translator systems and has many advantages; excellent pictures, high definition on some programs, theater quality sound, more program choices, and on screen program guides for some programs. The disadvantage is that in marginal reception situations, it does not degrade gracefully like analog did. So give your antenna system a good tune up, become familiar with your receiver’s menu structure, and enjoy!

Revised June 10, 2018