Thursday, May 10, 2012

Over The Air Digital TV/HDTV Signals & Multipath…. Oh Boy….

Trying to explain frequencies isn’t easy and my memory when people ask always fails only to return when away from the person who asked the question. Confused smile  I’m always much better explaining via email or blog because I can gather my thoughts and hopefully say them better than I can verbally.

Since the invention of TV and before cable we all had antennas on our roofs or rabbit ears on top of the TV. They looked funny and had these long to short spikes for lack of a better word on them. The length of the spike determined what frequency the antenna would pull in. You pointed it at the city and hoped for the best. How many Dad’s went up there to tweak the signal? Mine did A LOT!

Lucy & Ethel, I loved that TV show! Why are they up there I wonder? Smile 

TV Antenna

I’m sure everybody who is old enough remembers the rabbit ears that tried to soak up all signals but never did it very well or had to be adjusted frequently. Some of the fancier ones could be tuned.

Rabbit Ears

How many of you were your fathers antenna adjuster and personal remote control? Until 1979 that was me, I was good at it too! The good thing about TV back then was you could still watch a program if it didn’t come in very well, it was snowy and sometimes hard to watch but there weren’t many stations to choose from so if that one was playing something good you watched it anyway, snow and all. With digital TV it’s off or on or gets blocky as it drops out, not fun.

Our Government in it’s selfish wisdom decided to force everybody to digital TV, heck it’s not their money so why not? It spent about a “Billion” to market the idea and then between 650 million to 900 million to give away converter boxes to the masses, the digital to analogue converter box program lasted until September of 2009. All paid for by you and me, was the Government ready for this conversion? No, were the broadcast TV stations? No, but it’s done now and people can argue the merits of it but in my view, nearly 2 Billion was wasted… radio is also making the switch which will make using my antique radios a real pain to set up…again I digress…

The great thing about digital TV is a good picture right? Well, on a tube TV a good analogue signal looked plenty sharp, a digital signal looks pretty sharp too but better? Hardly. It’s the HDTV signals that really pop but of course you need the proper TV to display them.

TV Bands, VHF is technically broken into VHF-LOW, channels 2 - 6 (54 - 88 MHZ) and VHF-HI, channels 7 - 13 (174 - 216 MHZ). Pre analogue shut off the UHF band was channels 14 - 69 (470 - 806 MHZ) while Post transition is channels 14 - 51 (470 – 698 MHZ). Channel 37 is not used for TV broadcasting, it’s allocated to Radio Astronomy.

Digital TV is NOT the same as HDTV, of course HDTV is digital but it’s at higher resolutions than standard definition digital TV. Standard definition is typically 480p these days, getting into what the p stands for would be too much to get into here but I’ll go this far, the “p” is for progressive while the “i” is for interlaced, click this LINK to get into the technical aspects of it.

Regarding resolution think about it this way, when you buy a laptop they come in different resolution screens. Back in the day the standard was 640x480, if you wanted to fit more onto the screen and get a better picture you bought a monitor that could support higher resolutions. In generic terms the higher the resolution the better the image quality would be. Of course this is being pretty generic since there were many high resolution screens with horrible pictures but again, in theory this is sound. For more information click this LINK to read more. 

Todays flat panel TV’s come in typically 2 resolution flavors 720p (1280x720) or 1080p (1920x1080), this didn’t used to be the case but if you go into a store these days I don’t think you’ll find a TV that’s running 1080i anymore so we’ll just look at 720p and 1080p. If the TV you buy is 1080p it has to be better than a TV that is 720p right? Wrong, the box stores want you to believe that of course but there are some TV’s running 720p with incredible pictures and there are some 1080p TV’s out there with horrid pictures. I could give examples but keep this in mind, if you buy a 55” TV for $800.00 on sale and it boasts huge numbers plus 1080p it’s likely a poorly performing TV not worthy of buying.

With TV’s & computers my motto is buy the best you can afford since you’ll be using it a lot for the next several years. This could mean spending more than you would like but then again you’ll be staring at the screen for years to come, why look at a bad one?

Moving on, some of you may have run into a situation in your RV where a TV station has a very strong signal but still drops out on you. The reason for this? Multipath, or of course, distance from the tower. Multipath is a signal that took different routes to get to your antenna. The main signal is supposed to come from the tower directly to your antenna in a perfect world but unfortunately in many cases it bounces off of many objects like buildings or other large objects. So, you could be standing there seeing a very strong signal but the station is still dropping out. Changing the direction of the antenna can help here but often times it takes moving the entire rig to fix the situation. To understand Multipath problems here is another LINK to help explain it. Good equipment is supposed to reject multipath signals but RV manufacturers aren’t into installing the best TV and audio hardware. You stereo buffs may remember back in the 70’s there was a button on the stereo called multipath to help with the situation, it rarely did.

For the average RV’er who bought their rig prior to 2009 this means you likely have the old style analogue batwing antenna and a digital converter box installed in the rig that you use to tune channels. Mine has a menu option that tells me signal strength and the ability to scan for channels. It also has station info and can arrow forward to tell me what program is coming up next. Unfortunately batwing antennas lack good UHF reception unless close to the tower, say between 15 and 20 miles. Mine seems to be less sensitive and is drastically affected by multipath as many stations that come in strong drop off as night kicks in and multipath is affected by the atmosphere more.

By installing a digital TV antenna like the JACK antenna you don’t need the converter box anymore and you can tune in everything with the TV tuner. I ordered a signal finder because I have this nerdy need to tweak everything, I don’t think it’s really necessary but that I’ll find out for sure once I install the new antenna.

I don’t know if this actually helps anybody or not, I may have gone too in  depth but that’s the nerd in me. If people have corrections let me know, my memory isn’t perfect and I started this at 4:00am!


Big Matt said...

I originally was looking at that Signal Finder jobby, since my antenna has to be aimed from outside, but I later found the antenna web application for my phone which allows me to aim myself at the local towers in an area, then simply match my antenna up to that, reducing the number of times I need to go in and out of the RV to get the maximum number of channels on a scan.

I do need to make my antenna taller, though, every time I get a neighbor in site #4 next to my antenna, the signal goes wonky because the neighboring rig creates a partial blockage of the signal path.

Merikay said...

Good explanations. Now if there were just something on that was worth watching!

Kathy's Klothesline said...

You did well with your explanation. I was intrigued, having been in the pager business before I went insane and bought a kampground. Try explaining UHF and VHF to a stoned reseller having his pagers recrystaled! My employees told me that I got a certian tone to my voice, like I was talking to morons. Condescending was the word they needed.

Teri said...

I hate fighting with electronic things so I do not have a TV in my RV. I have a really good radio/stereo in the dash and they installed speakers in the motorhome and I purchased a really good laptop with BluRay and Beats Audio for watching movies. Life is a lot simpler this way.

Diana said...

Ha! I had a feeling that you were up late writing this post. Never thought super early!!!
Very informative Erik. You gave me some insight into how it all works.
That in itself is an accomplishment! Thanks for all the info.
Love Di ♥