TV Fool  

Go Back   TV Fool > Over The Air Services > Help With Reception

Notices

Reply
 
Thread Tools
Old 20-Sep-2011, 8:41 PM   #21
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Quote:
Originally Posted by mtownsend View Post
Keep in mind that analog (NTSC) signals NEEDED much more power to achieve a clear picture. They need a fairly high signal to noise ratio (say roughly a 27 dB SNR) to produce a clean (like VHS tape quality) image.

Digital (ATSC) signals can produce a clean (like DVD quality) image while using less signal power (roughly a 15 dB SNR).

The lower power of digital broadcasts does not make it harder to receive. The power was reduced to maintain roughly the same amount of coverage as the old analog systems. Since the threshold for reception has been reduced, it takes less power to get to that threshold. The high ERPs with analog stations was mostly out of necessity due to the spectral inefficiency of that signal format (developed in the 1940s and 50s).

In general, ERP is a bad way to look at station effectiveness because it does not take into account the signal type (ATSC vs. NTSC) and it does not take into account the frequency (high frequency channels require much more power than low frequency channels). For example, a 50 kW digital station on channel 7 will cover the same area as (actually even more than) a 5000 kW analog station on channel 51.
Ah, ok, got it... ATSC requires less power than NTSC...

And yes, I knew about VHF signals go further in distance than UHF, which is why I was disappointed to know that those Vancouver stations went from VHF to UHF.

For example, I was able to receive analog channels 6, 8, 10 ERPs like 200-300kW (fuzzy, but watchable) at 100 miles away with my current antenna system... now they are at UHF at 40Kw... So I am just disappointed that it will take another big antenna in any hope of receiving these signals.

But like I said in my earlier post, I had Artec DTV box and once in a while, I would see a "signal" blip in its signal meter on channel RF 22 (CHAN) at 100 miles and 40kw... and my location shows it is at -9.8 dB NM.

This gives me hope to pick up this channel somehow if the best GAIN UHF antenna (either DB8 or Clearstream 4?)
be236 is offline   Reply With Quote
Old 20-Sep-2011, 9:00 PM   #22
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Closed or open loop?

Another question... I have an ohmmeter so I can measure the RG6 cable, the inside and outside shielding... Once I connect my RG6 cable to antenna leads via twin-lead to coaxial adapter, and I measure for ohms across the terminal of either the RG6 itself or directly on the antenna leads, is it open (infinite resistance) or closed (some ohm readings)?
be236 is offline   Reply With Quote
Old 20-Sep-2011, 9:05 PM   #23
John Candle
Senior Member
 
Join Date: Jun 2010
Posts: 2,697
Tv Antennas and Reception

http://forum.tvfool.com/showthread.php?t=1999. This can go on for ever. I will provide no more information
John Candle is offline   Reply With Quote
Old 20-Sep-2011, 9:14 PM   #24
rickcain
Member
 
Join Date: Dec 2010
Posts: 65
What's frustrating is now legitimate sites like SolidSignal are starting to sell scam antennas, shame on them.
rickcain is offline   Reply With Quote
Old 20-Sep-2011, 9:37 PM   #25
GroundUrMast
Moderator
 
GroundUrMast's Avatar
 
Join Date: Oct 2010
Location: Greater Seattle Area
Posts: 4,773
Quote:
Originally Posted by be236 View Post
Yes, you're correct.. when I said signal of -5 dBm, I mean that's the NM value I get here in Tvfool when it shows channels for my specific location.

So back to my actual problem that I started for this thread.

The channels I want show up to -16 dB NM value. Then I need to find an antenna that is spec-ed/claimed to be +16 dB gain or higher , right so that I can get above the 0 dB threshold to get a signal lock?

That Lava antenna claims +30 dB gain (but not sure if they meant that is for the pre-amp gain and not the antenna gain itself).

The DB8 antenna I see in various sites show a gain of +16 dB, which would get me to this 0 dB threshold... but looks like I need more gain to get signal... would I have to string 2 DB8s together or something like that (would look unslightly)...
If the prediction is 100% accurate, and if there is never any fading, and if there is no interference, and if you have a perfect receiver, then reception of a signal with a NM of -16 dB would require an antenna that has 16 dB of gain on the channel of interest plus the additional gain needed to overcome the noise figure of any amplifier used. That equates to antenna gain of 19 dB in theory (assuming a preamp NF of 3 dB).

In the real world, a 10 dB 'fade' margin is cutting it quite close. Engineering for a margin of 15 dB is not overkill by any means (IMO). So I'm suggesting an antenna with 29 to 34 dB of forward gain. (I know of no such antenna on the consumer or commercial market.)

Reception of a signal arriving at a NM of -16 dB is going to be impossible in some cases, unreliable in others. In a few cases, you'll get lucky and find that the prediction was off in some way.

It may be more practical to find a friend in Bellingham or Lynden who would allow you to operate a HTPC or Slingbox remotely.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

(Please direct account activation inquiries to 'admin')

Last edited by GroundUrMast; 20-Sep-2011 at 9:51 PM.
GroundUrMast is offline   Reply With Quote
Old 20-Sep-2011, 10:09 PM   #26
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Quote:
Originally Posted by rickcain View Post
What's frustrating is now legitimate sites like SolidSignal are starting to sell scam antennas, shame on them.
Ya, I noticed that too on their website.
be236 is offline   Reply With Quote
Old 20-Sep-2011, 10:13 PM   #27
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Quote:
Originally Posted by GroundUrMast View Post
If the prediction is 100% accurate, and if there is never any fading, and if there is no interference, and if you have a perfect receiver, then reception of a signal with a NM of -16 dB would require an antenna that has 16 dB of gain on the channel of interest plus the additional gain needed to overcome the noise figure of any amplifier used. That equates to antenna gain of 19 dB in theory (assuming a preamp NF of 3 dB).

In the real world, a 10 dB 'fade' margin is cutting it quite close. Engineering for a margin of 15 dB is not overkill by any means (IMO). So I'm suggesting an antenna with 29 to 34 dB of forward gain. (I know of no such antenna on the consumer or commercial market.)

Reception of a signal arriving at a NM of -16 dB is going to be impossible in some cases, unreliable in others. In a few cases, you'll get lucky and find that the prediction was off in some way.

It may be more practical to find a friend in Bellingham or Lynden who would allow you to operate a HTPC or Slingbox remotely.
What's funny is that I can get CHEK 6 VHF analog and they show NM of -10 dB. Heheh...

As for that slingbox idea, yeah, I thought about that.. wonder why there's not a website that would do something like this? I guess it would be a copyright issue, huh?
be236 is offline   Reply With Quote
Old 20-Sep-2011, 10:28 PM   #28
GroundUrMast
Moderator
 
GroundUrMast's Avatar
 
Join Date: Oct 2010
Location: Greater Seattle Area
Posts: 4,773
Quote:
Originally Posted by be236 View Post
What's funny is that I can get CHEK 6 VHF analog and they show NM of -10 dB. Heheh...

As for that slingbox idea, yeah, I thought about that.. wonder why there's not a website that would do something like this? I guess it would be a copyright issue, huh?
I can still see a couple of analog Canadian stations here in Seattle. They're quite noisy (snowy). Analog kept working when the signal got weak. OTA DTV has quite a bit of forward error correction ability engineered into the ATSC standard so it looks perfect right up to the point where the receiver can no longer decode valid data. Digital signals are prone to that phenomenon, referred to as 'cliff effect' where, when close to the minimum, a slight decrease in signal to noise will produce a dramatic increase in error rate.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

(Please direct account activation inquiries to 'admin')
GroundUrMast is offline   Reply With Quote
Old 20-Sep-2011, 10:54 PM   #29
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Quote:
Originally Posted by GroundUrMast View Post
I can still see a couple of analog Canadian stations here in Seattle. They're quite noisy (snowy). Analog kept working when the signal got weak. OTA DTV has quite a bit of forward error correction ability engineered into the ATSC standard so it looks perfect right up to the point where the receiver can no longer decode valid data. Digital signals are prone to that phenomenon, referred to as 'cliff effect' where, when close to the minimum, a slight decrease in signal to noise will produce a dramatic increase in error rate.
Wow... you're just down the road from me? Nice... Do you have any good recommendations for antenna installer? Or have you done any yourself?

Basically I'd like to do a J-mount (under-the-eave mount) so as not to alter the roof itself, plus I'm afraid of heights.

The only BC station (lower mainland) that is still analog is CHEK 6 that I know of... the fact that you can get it in Seattle (maybe you live on Queen Anne hill).
be236 is offline   Reply With Quote
Old 21-Sep-2011, 7:21 PM   #30
GroundUrMast
Moderator
 
GroundUrMast's Avatar
 
Join Date: Oct 2010
Location: Greater Seattle Area
Posts: 4,773
Using consumer grade (priced) equipment, you best hope for seeing any signals from Canada would be an Antennas Direct XG-91, their CPA-18 or CPA-19 preamp, mounted on a 5' tripod + 10' HD mast at the roof peak.

I would expect that you would see some signals, at least intermittently, weather and atmospheric conditions would often rule.

Mounting at eave height would likely rob you of precious signal.

(From Canada, I now see only CHEK-6)

Sorry, I don't have a recommendation for antenna installers.

A while back you asked,
Quote:
Closed or open loop?

Another question... I have an ohmmeter so I can measure the RG6 cable, the inside and outside shielding... Once I connect my RG6 cable to antenna leads via twin-lead to coaxial adapter, and I measure for ohms across the terminal of either the RG6 itself or directly on the antenna leads, is it open (infinite resistance) or closed (some ohm readings)?
It depends on the matching transformer design. Many will have low resistance from center conductor to shield. There are designs that appear 'open', virtually infinite resistance.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

(Please direct account activation inquiries to 'admin')

Last edited by GroundUrMast; 21-Sep-2011 at 7:23 PM.
GroundUrMast is offline   Reply With Quote
Old 21-Sep-2011, 7:27 PM   #31
Tower Guy
Senior Member
 
Join Date: Dec 2009
Location: Delmar, NY
Posts: 1,225
Quote:
Originally Posted by be236 View Post
wonder why there's not a website that would do something like this?
Bamboom http://bamboom.com/

http://arstechnica.com/tech-policy/n...n-new-york.ars
Tower Guy is offline   Reply With Quote
Old 21-Sep-2011, 8:12 PM   #32
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Quote:
Originally Posted by Tower Guy View Post
Thanks for the links! I'll check it out!
be236 is offline   Reply With Quote
Old 21-Sep-2011, 8:19 PM   #33
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Quote:
Originally Posted by GroundUrMast View Post
Using consumer grade (priced) equipment, you best hope for seeing any signals from Canada would be an Antennas Direct XG-91, their CPA-18 or CPA-19 preamp, mounted on a 5' tripod + 10' HD mast at the roof peak.

I would expect that you would see some signals, at least intermittently, weather and atmospheric conditions would often rule.

Mounting at eave height would likely rob you of precious signal.

(From Canada, I now see only CHEK-6)
Just last night, I got a good signal on CHEK-6 (less snowy than normal).. so just for fun, on my Artec box, I scanned on BC's DTV 17, 22, and 26 and got a 'signal' blimp, meaning some signal on it... gives me hope!

Yes, I do intend to get that XG-91 model, that seems the best UHF gain antenna (they claim 16.7db gain) to pick up deep fringe , which is my situation.

Once I order it, I can do a quick test by just putting it in my 2nd story room and aiming it outside my open window and connecting it with a 6 feet RG6 cable directly to my TV tuner (hence no need for an amplifier just yet, since I really dont have any signal loss downstream)...

SO, here's the deal.. currently my antenna is mounted on a fence post about 12 feet high that bypasses a big tree towards the direction of those BC stations.

If I mount it on the house rooftop, the big tree (about 50-60 feet tall big tree) will be in direct line-of-sight of the house and the stations. d'oh...

.. so which is better? Lower height, no tree, or higher height, but big tree with leaves about 30 feet away?
be236 is offline   Reply With Quote
Old 21-Sep-2011, 9:37 PM   #34
GroundUrMast
Moderator
 
GroundUrMast's Avatar
 
Join Date: Oct 2010
Location: Greater Seattle Area
Posts: 4,773
Which mounting option is best... you'll need to try both to know for sure.

In the winter with all the leaves off the tree, I'll bet a cup of coffee on the shot through the tree.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

(Please direct account activation inquiries to 'admin')
GroundUrMast is offline   Reply With Quote
Old 23-Sep-2011, 6:19 PM   #35
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Quote:
Originally Posted by GroundUrMast View Post
Which mounting option is best... you'll need to try both to know for sure.

In the winter with all the leaves off the tree, I'll bet a cup of coffee on the shot through the tree.
It's funny. Using tvfool's map, I zoomed into my lot, placed my marker on my current fence post antenna at 10feet, and got CHAN to show at -6.8 dB.

Then I put the marker on my roof , about 30 feet high), and it shows CHAN at like -7.5 dB.

So, it's almost like better to keep it at my fence post antenna location than going on the roof the house... weird...

Also, I played with the height setting at the fence post location and if I set it to 20 feet, my dB when down to like -7.2 dB...

Weird, eh? Guess in *some* rare situation it's better not to have a higher antenna... oh well...

some of this "picking up signals" is an art-form and not so much science (though most is science and math). eheeh...
be236 is offline   Reply With Quote
Old 23-Sep-2011, 6:31 PM   #36
GroundUrMast
Moderator
 
GroundUrMast's Avatar
 
Join Date: Oct 2010
Location: Greater Seattle Area
Posts: 4,773
The mathematical model used by TV fool is only able to predict based on the information is has access to. It does not have an absolute picture of every tree, building, rock, etc. The terrain data is finite in resolution.

Yes, in some cases, you'll get better reception close to the ground. That's the exception, not the rule, in the real world. Simulation is a valuable aid but the real world is where it happens.

Per TV Fool:
Quote:
About the signal strengths and coverage overlays
- They DO take into account the transmitter power, frequency, antenna pattern, and height
- They DO account for propagation losses due to terrain
- They DO account for curvature of the Earth
- They DO NOT take into account your antenna gain, amps, or receiver sensitivity
- They DO NOT account for building obstructions or indoor penetration
- They DO NOT account for multipath
...
Please understand that this is a simulation and can only be treated as a rough approximation. Reception at your location is affected by many factors such as multipath, antenna gain, receiver sensitivity, buildings, and trees - which are not taken into account. Your mileage may vary.
(Emphasis added)
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

(Please direct account activation inquiries to 'admin')

Last edited by GroundUrMast; 23-Sep-2011 at 6:40 PM.
GroundUrMast is offline   Reply With Quote
Old 23-Sep-2011, 9:04 PM   #37
be236
Senior Member
 
Join Date: Sep 2011
Posts: 135
Yup.. understand those points...

... next, I picked up what looked like a DB4 antenna off Craigslist. All the V-shaped elements are quite rusted. Given this antenna claims a -13 dB gain... with all that rust, how much gain did I "lose?" Maybe -5 db ?
be236 is offline   Reply With Quote
Reply

Bookmarks

Go Back   TV Fool > Over The Air Services > Help With Reception


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off




All times are GMT. The time now is 8:21 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright © TV Fool, LLC