Short version: Looking for a booster amp because my convertor box isn't finding enough signal on the cable to work.

Long version: we have cable using a digital cable box (Mediacom) upstairs on our flat screen TV. Downstairs we have the old 35" Mitsu beast, still running after 17 yrs. and 2 minor repairs.

I know the cable has a group of channels (not all of them) accessible even before the cable box. We can watch them on our bedroom LCD w/o a cable box. I ran a line to the old Mitsu and figured I could insert a DTV convertor box and get those stations. It can't find a single station. I can hook up an antenna and get a couple over the air so I know the box works, more or less.

I know these boxes suck, do I need a booster amp? I don't wanna spring for $10/mo for another Mediacom box.

I am not sure that I understand the question... If you are trying to use an off-the-air (ATSC) DTV converter box to decode cable digital (QAM), It may not work, because the standards are different. Your Flat TV can likely decode both standards, but the typical $40 coupon boxes that were sold for use with antennas likely will not.
jr

Your flatscreen likely has a QAM tuner, which can decode clear QAM cable channels. Usually, only the minimum basic (local) channels are delivered in clear QAM format. The other digital channels are usually encoded and require a digital cable box.

The typical DTV converter box is designed to receive ATSC broadcast and convert them to analog for use on older TV's. Although ATSC and QAM are both digital, the formats still have differences and are not compatible. In rare cases, some cable companies deliver local channels in ATSC format. My digitalstream DTV converter actually has a menu selection for cable or air. Even on cable, it looks for ATSC signals; which, are not on our cable. Therefore, the box finds zero channels when connected to cable.

If you want to receive digital cable channels on the old TV, your only option will be to obtain a digital converter from your cable company.

In my area, Comcast offers two types of digital cable converters. One type is the large Motorola box that enables the user to access pay-per-view movies, program guides, etc. The other type is what they call a digital transport adapter (DTA). This is a basic digital cable converter that does nothing more than convert the digital cable channels to analog channel 3 or 4. These DTA's don't even have A/V output jacks. Basically, these are a modern version of the older analog cable boxes that were popular in the '80's.

When you obtain a digital cable box, you first connect it to your TV and turn everything on with the TV set to channel 3 or 4 (whatever the output channel of the box is set for). Then, you contact the cable company with the box serial number and your account number. They will then send a signal down the line to activate your box for the level of service that you are supposed to receive.

Something to consider with ATSC signals -- RF Signal strength doesn't necissarily translate to better reception. I'm only 10 miles from the transmitter field, so I get clear, strong signals. What kills my ATSC reception is the reflections I get off of the downtown buildings just 3 miles NE to me. ATSC is terrible at filtering out interference of any kind. It wants a perfect clean RF signal -- not ghosty, staticy, or other anomolies we were so used to getting with analog transmissions -- or it will refuse to extract the A/V it contains. Fussy fussy fussy.

What really annoys me is that ATSC tuners, TVs and Converter boxes alike, tend to show their signal stringth diagnostic infomration based on something OTHER than true RF strength or the noise figure. I can't determine what they're actually measuring to get that strength display. Just by moving an antenna a couple of inches I can go from 22->66->22 alternating to solid 71-75 on my Sony XBR 32". I can't imagine there's that much change in the RF domain. In the digital domain, what is it measuring to get that 22->66->22 jump

Unless you know that your "digital" cable has no analog channels at all, you should just try hooking the cable to the Mitsubishi's RF input and have it do a scan. It should find the analog channels without a box.

Signal strength indicators on digital devices usually measure bit error rate, not RF intensity. That is the best indicator of the expected performance for the consumer. As noted earlier, lots of RF does not guarantee satisfactory results.

In the digital domain, what is it measuring to get that 22->66->22 jump

What it typically is measuring is the signal-to-crud ratio, where crud refers to both noise and ghosts (intersymbol interference). If you have a lot of ghosts, you will have good spots and bad, as you note by moving your antenna. Listening to FM radio in the car, this shows up as "picket fencing" and "stop light fades."

By the way, what kind of antenna?

An interesting thread. Antenna is everything as usual, and whats most important is that its directional. Boosters add to the noise floor and make things worse unless you are very rural have weak rf and a good antenna.

... Boosters add to the noise floor and make things worse unless you are very rural have weak rf and a good antenna.

Most boosters will create lots of intermod from strong stations and trash up the desired weak signal. A directional antenna that has deep enough nulls in its reception pattern may allow you to aim one of the nulls at the strong ghost sources and allow the box to decode the main signal. Or aim for the ghost and null the main signal.

---

Why so many replys? It is all ATSC. Over the air is 8VSB with higher error correction, and QAM is a proprietary cable format. Quit being cheap and get a device with the tuner you need.

Thank you for all the replies and especially your wonderful bedside manner, mirayge. :tongue: I am paying near $150/mo for TV and Internet, and if there is something I can get without spending more, I don't think that makes me cheap. I am cheap, though, no doubt about that. :yes:

I think the first two replies have nailed it, the expanded basic is probably in QAM format and the flatscreen will decode it but the old TV will not, and neither will the converter boxes. I may check with the cable co. and see if they have the simple box that radiotvnut suggested. Good idea. We're already paying ten bucks a month for the fancy box.

Thanks y'all!

Well I got this fixed. Channels above 13 are in fact all scrambled, and I now have a $2/mo tiny descrambler box like radiotvnut described. Getting channels up past 70 now, and we can still watch any of our higher channels on the 2d antenna input off the line from the big box upstairs. Thanks for the help!