Head Scratcher, 64772

[CowboyDren]

I just got back from a hunting trip at Grandma's house; Dad got a nice, 180-lb white tail, and I got heartburn.

Her zip code is 64772 (Nevada, MO), and she's pretty far out there. Her main goals are KOAM-7 (ch7, 48mi), KFJX-14 (ch13(!), 48mi), and KODE-12 (ch 43, 55mi). It's really unfortunate that two of the three channels are VHF, but she has a decent combo antenna (10' boom, forward-swept VHF section, big UHF reflector), which used to do the job just fine using analog signals. Up until recently, a little Craig DTV converter box would also sometimes work to pull in channels.

I went down there this weekend armed with my cable prep tool, compression fittings and a Channel Master 7777 combo preamp, hoping that I could get her some more signal. According to my cable toner, the circuit from the TV end of the cable to the antenna is complete. Plugging in the 7777 didn't help, though; both her new Panasonic TC-P50X1 and my Dish DTVPal came up with zeros doing automatic scans.

My first mistake was that I didn't bring the TVFool report with me, not even the broadcast channel numbers. I didn't know that I was looking for ch 7, 13, and 43, so I couldn't tune to them and see if they blipped.

My second mistake was assuming that the balun was good. Because I got continuity, and I didn't bring another balun with me, and I didn't feel like dropping a 20' 1-5/8" fence pole to replace the balun, I still don't know if it got fried in a recent electrical storm.

Did I make any other mistakes, or is that balun probably the answer?

PS - Who the hell would take a perfectly good UHF station (14) and move it into VHF-Hi (13) for the transition?!?! It's like these broadcast engineers were trying to cut off viewers. :rant:

 

[ericha]

VHF is actually better for propogation--channel 2 is the best. This is because for the same directionality, the antenna is bigger and intercepts more signal. What makes you think that VHF is worse?

 

[CowboyDren]

In RF theory, yes, VHF should be better (and was better for decades with analog transmissions). However, VHF and 8VSB is a provenly bad combination. Why do you think so many VHF channels are reapplying for UHF frequencies months after the digital transition? VHF vs UHF signal propagation shakes out to be about the same in the real world, if not actually favoring UHF in clear, flat terrain.

 

[GravelChan]

I don't quite understand the problem people are having with VHF signals except perhaps with an indoor antenna in a urban setting. I'm in south central South Dakota and pick up 10 and 13 which are 58 miles north, and channel 7 which is 59 miles south with 90-100 signal strength. Also a UHF channel 19 about 60 miles north. These antennas are at 50' which of course helps.

Cut channel 13 and separate UHF antenna pointed north with a 7777 amp. So I'm picking up channel 7 (NE PBS) off the back of these antennas with 90-100 signal strength.

However, I have a friend west of me that has an antenna similar to your grandma's mounted in his attic (no amp) that picks up these same channels. The signal strength isn't what mine is but they do lock in fine.

 

[wkomorow]

WRGB was digital rf 39 before the transition - I had a rough time getting the signal - they moved to rf 6 and reception is great. In fact 8 of my channels are VHF and I never have any problems with any of them. They are on the opposite side of a mountain - 30 miles away and all have strength in the 80s on my Dish receivers. The UHF stations on the same transmitter tower have more frequent drop outs. I had always though VHF hung better over mountainous terrain over UHF stations.

 

[ericha]

In RF theory, yes, VHF should be better (and was better for decades with analog transmissions). However, VHF and 8VSB is a provenly bad combination. Why do you think so many VHF channels are reapplying for UHF frequencies months after the digital transition? VHF vs UHF signal propagation shakes out to be about the same in the real world, if not actually favoring UHF in clear, flat terrain.

Do you have a comprehensive list of which stations VHF have reapplied for UHF, and which UHF stations have applied for VHF?

I don't particularly like 8VSB modulation, as it's not very good with multipath, but a good equalizer can deal with that. Can you show us some measurement data that 8VSB is worse at VHF? That would be quite interesting.

 

[CowboyDren]

I had always though VHF hung better over mountainous terrain over UHF stations.

That makes sense. But my grandma and I see a lot more amber waves of grain than purple mountains' majesty, ya' know?

Do you have a comprehensive list of which stations VHF have reapplied for UHF, and which UHF stations have applied for VHF?

I don't particularly like 8VSB modulation, as it's not very good with multipath, but a good equalizer can deal with that. Can you show us some measurement data that 8VSB is worse at VHF? That would be quite interesting.

I haven't been keeping track, because my hometown has been all-UHF since before the transition. It's mostly anecdotal, but the DX guys are all hacked off about the problems with low-frequency 8VSB. I've just been watching the chatter and reports of stations either applying to move or at least colocating (9.2 is a SD feed of 29.1, 29.2 is SD feed of 9.1, etc) to compensate for lost coverage. A bunch of stations, VHF and UHF alike, all bumped or applied to bump the power even more after the transition because too many people at the fringe (50-ish miles) lost signal.

This kind of stuff doesn't affect most people, but the ones affected get seriously messed up. If grandma had a 50' tower, we would be having a different conversation.

Back on track, though, do you guys think it could be the balun, or am I barking up the wrong tree? It looks like an HBU44 would do the job, or a Y10-7-13 and a U4000, but I'm looking for a simple fix right now.

 

[Tower Guy]

PS - Who the hell would take a perfectly good UHF station (14) and move it into VHF-Hi (13) for the transition?!?! It's like these broadcast engineers were trying to cut off viewers. :rant:

That's a common feeling, but in your case it's wrong.

VHF usually works better for outdoor antennas than UHF. UHF outperforms VHF when you use indoor antennas.

 

[ericha]

That's a common feeling, but in your case it's wrong.

VHF usually works better for outdoor antennas than UHF. UHF outperforms VHF when you use indoor antennas.

Why is that (UHF being better than VHF with an indoor antenna)? Is it because you can fit a higher-gain UHF antenna inside? For the same antenna gain, UHF should always be worse (since for the same gain the UHF antenna is smaller).

 

[CowboyDren]

Higher frequency usually means better penetration, making it work better inside than VHF signals that get attenuated by your wall and roof. The higher frequency also means the potential for more bandwidth (more Hz = more bits), but I don't think ATSC:8VSB actually takes advantage of this.

I also find that a 4-bay bowtie antenna works outstandingly well outside for UHF-only, usually they have gain in the 8-10dB range. They're also compact, lightweight, and durable. You have to buy a pretty big VHF/UHF combo antenna to get 8dB of gain on the UHF side of a fishbone.

 

[JB Antennaman]

Before I correct anyone for any mistakes that they made with their understanding of how UHF / VHF works on digital - let's fix your problem.

You have one antenna of unknown origin and several DTV converters.

If everything worked before you started, then the first guess would be that you did something wrong. The road to h311 is paved with good intentions.

Without knowing what wire you used, how long the length was and what kind of F type terminals you used, there is no way for me to diagnose what you did or did wrong. I was in the same situation a couple of months ago with a neighbors antenna. 32 feet off the ground, a 350 lbs man standing on a 250 lbs Werner Ladder. Trying to hook up a pre amp on the side of a 9/12 pitch roof - 3 tab granulated shingles with nothing below it but rocks and dirt. Not the kind of place where you would want to fall.

I gave my brother a safety line and a harness and sent him up on the roof while I worked off the ladder. I came to find out that one of the wires that I had crimped, I crimped wrong and it was shorting out. I cut every terminal off except one - and it was the one that was giving me fits. Right off the antenna going into the pre amp. 10 feet above the peak of the roof.

Give me the co ordinates for that location and the height of the antenna, so I can look at the real TV fool report and not just a picture of it and maybe I can make some suggestions. Keep in mind that I like to spend money - even more than a politician so don't be alarmed when I tell you what equipment you need to get reliable reception.

My guess is that channel 7 is the easiest channel to receive and you would not need any type of amplification for the VHF since the only other station VHF is channel 10 KLOR

A Winegard AP 4800 or a CM 7775 would be a better choice for a pre amplifier.

A CM 94444 balun is a pretty good choice if you are bound and determined to reuse the old antenna.

 

[JB Antennaman]

VHF is actually better for propogation--channel 2 is the best. This is because for the same directionality, the antenna is bigger and intercepts more signal. What makes you think that VHF is worse?

VHF reception is more susceptible to interference then UHF. The lower down in frequency you go the worse it becomes.

Channel 2 is the worst for reception. Band 1 stations often had very tall antenna's due to their long wave length, it allows them to use much less transmitter output.
It saves on the electric bill and standby generators, they are limited by the FCC to a maximum output of 45 kW digital 8vsb ERP.

Stations on band III can go up in power to 160KW.

Most countries abandoned the VHF and moved all reception up into the UHF.

If the United States would have done this, it would have required us to all use one type of antenna and one type of pre amp - just like in Great Britain today.

UHF is less susceptible to noise, be it ignition noise from gasoline engines, electric fences, power lines, motor brush noise, even electrical light switches inside your home will all interfere with your reception. In time, I look for either the FCC to take away all the VHF or limit the amount of licenses it sells in the VHF - due to all the problems it has.

Florida, which is at or even slightly below sea level and surrounded on 3 sides of by water was once a mecca for VHF reception. Now with digital, the customers complains in the summertime that they have too much reception and in the wintertime that they do not have enough reception. There is no happy medium.

You cannot judge the reception in one location to be the same as what it might be in another.

The test bed for digital television transmissions was I think down in Maryland.

Maryland was a very poor place to test television reception because of the lack of mountains and valleys. What worked great in Maryland did not work at all in Pennsylvania - just 100 - 200 miles away! The engineers all agreed with the 8 VSB - with no regard to other systems used other places in the world which would have served us better.

I belive that SECAM would have been a better choice. NTSC is not good enough for challenging terrain such as Pennsylvania with its high mountains and deep valleys and long distances between markets.

 

[JB Antennaman]

I don't quite understand the problem people are having with VHF signals except perhaps with an indoor antenna in a urban setting. I'm in south central South Dakota and pick up 10 and 13 which are 58 miles north, and channel 7 which is 59 miles south with 90-100 signal strength. Also a UHF channel 19 about 60 miles north. These antennas are at 50' which of course helps.

Cut channel 13 and separate UHF antenna pointed north with a 7777 amp. So I'm picking up channel 7 (NE PBS) off the back of these antennas with 90-100 signal strength.

However, I have a friend west of me that has an antenna similar to your grandma's mounted in his attic (no amp) that picks up these same channels. The signal strength isn't what mine is but they do lock in fine.

Signal strength means nothing to us due to the fact that there is no standard SWR - standing wave ratio between receivers and what is considered to be a strong signal by one manufacturer is not as good by another manufactures standards. What matters is the sensitivity of the receiver. In the old days it was determined by the quality of the first transistor in the front end of the receiver.

By determining what you have in your link budget, line loss, splitter loss, antenna gain, amplifier gain, free space loss, what ever is in your first and second fresnel zone and the power of the transmitter and the distance between the transmitter and the receive antenna - you can figure out how much signal is being received at your location.

Attic antenna's is a poor comparison due to the fact that although wood is not opaque to UHF signals, the building materials such as aluminum is. A piece of aluminum 6 inches wide between the antenna and the signal can be enough to block your signals. A vent stack in the attic will not block your signals, but the moisture inside of the pipe can. The same holds true with shingles. The shingles and plywood and trusses might not block your signal, but the moisture in the wood and the moisture under your shingles will.

You can loose 6 db or more just through the wall. Although this might be a acceptable amount of loss in a urban area, in a fringe reception area, it might be the difference between watching a television station and no reception at all.

With a digital signal, you can loose 70% of the signal and still have a good signal. BUT - once you loose 70% of the signal, anytime something comes between you and the signal you will experience drop outs. Be it rain, snow, fog, a airplane, a flock of birds, a swarm of bees, leaves in the trees, evergreens which never loose all it's needles at the same time etc.

Front to back is not a real reception term, it is just a generalization to explain how a antenna works and what you need to take into account when designing equipment for proper reception. If a antenna has a high front to back ratio, it also has poor rejection qualities and with a digital signal, it could cause more problems then it solves. Analog signals - you would experience ghosting - due to two of the same signals reaching the tuner at the same time. With a digital signal - it is all or nothing. The information that the tuner receives is all ones and zero's and when you corrupt digital information - it is worse then not having any information at all.

Like scratching a CD and then trying to play it in a CD player.

 

[CowboyDren]

Before I correct anyone for any mistakes that they made with their understanding of how UHF / VHF works on digital - let's fix your problem.

You have one antenna of unknown origin and several DTV converters.

If everything worked before you started, then the first guess would be that you did something wrong.

No. Only one tuner matters, the one in the TV, and it has never worked, because the TV is a week old. Several weeks ago, there was a heavy electrical storm that fried most of the telephone and TV gear inside and outside the house. The DTV converter box she has stopped working at the same time everything else did. I'm checking the balun and it's connection to the antenna next, but it's going to be a while.

 

[dodge]

Replace the balun, it may be gone!!!
They are cheap
have you tried another tv or other convertor box??? They may be bad due to the storm!!!

 

[Tower Guy]

Why do you think so many VHF channels are reapplying for UHF frequencies months after the digital transition?

There are many reasons;

Mobile TV to handheld devices works better on UHF than VHF. A station's future may depend on the income from handheld receivers.
Converter Boxes and DTV receivers have omitted FM traps needed to deal with strong FM stations. FM bothers VHF more than UHF. (All analog TVs had them.)
Many companies market UHF only antennas as DTV antennas.
Many viewers made the mistake of installing UHF antennas for DTV.
Distributed transmitters work better on UHF than VHF. The FCC approval for DTS took years to get approved.
The higher power needed to improve indoor VHF reception will cause interference to other nearby co-channel VHF stations.
There was a knee jerk reaction to converter box rescanning problems.

VHF continues to work better with outdoor antennas than UHF.

 

[Tower Guy]

Why is that (UHF being better than VHF with an indoor antenna)? Is it because you can fit a higher-gain UHF antenna inside? For the same antenna gain, UHF should always be worse (since for the same gain the UHF antenna is smaller).

In simple terms, the smaller waves on UHF fit through the windows better.