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Boston area TV stations changed their antennas... weaker signal


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  #41  
Old 09-18-2019, 12:40:32 AM
Zephyr7 Zephyr7 is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

I’m a little late here, but since I’m an EE with a background in RF and microwave (even though I don’t do that professionally anymore), I thought I’d clear up some stuff:

The VHF channels were made to move to UHF primarily due to issues with tropospheric ducting. This is the phenomena that would sometimes let you watch a very distant channel 2 or 3 on occasion. Digital systems are less tolerant of interference like that. The wireless data guys actually usually prefer the higher frequencies since they can stuff more data through those.

UHF is not less efficient. It doesn’t penetrate structures as well in some cases, but it actually can do better in others. It depends on the type of structure. Power is measured at peak of sync, which is the highest power part of the analog TV waveform, the so called “blacker than black” since a fully black frame is the highest average power signal. Digital signals are more evenly distributed in terms of energy density which requires higher average power.

ERP, effective radiated power, has to do with antenna gain in dB. Height doesn’t matter. Height has to do with pushing the visible horizon out farther so that more receivers can “see” the transmitter antenna without obstruction. Digital transmission is more susceptible to multipath (signals bouncing off of things and arriving at the receiver at slightly different times). That had the effect of causing some surprises during the digital transition.

You lost a lot of tv transmitters on 9/11 because ALL the broadcasters had their transmit sites up there, on the building with the antenna tower on top. There was only one station (I forget which one) with a backup transmitter on the Empire State Building. That one station helped others to get back on the air on an emergency basis. Since the trade centers were the tallest place to put a transmitter, they also gave the best coverage. Everything else has a reduced coverage area due to reduced height.

I’m not so sure I agree with the flyswatter antenna being best here. It would be more prone to multipath, and it won’t do any diversity reception stuff (which needs some smarts to implement, a passive antenna won’t do it), which is what the “one bow tie might receive it better” would be implying. I’d stick with a high-gain corner reflector (the classic old UHF antenna), and aim it carefully.

One of the problems is that the ATSC digital system used in North America uses an inferior coding to the terrestrial DVB variants used in most other countries. The original thinking was that DVB would be more costly to implement, but with the economies of scale of the semiconductor industry that doesn’t matter anymore. We’re still stuck with the deficiencies of the system that was chosen though.

We’re likely to see other changes in the future as spectrum gets shifted around. Congress critters like spectrum auctions because it’s “free” money that doesn’t make voters mad. They have no idea of the technical issues though.

I have a friend who is a station engineer at one of the local TV stations. He says the broadcast guys have always seen cable as “the enemy”. Broadcasters aren’t pushing people into cable.

Bill
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  #42  
Old 09-18-2019, 06:45:23 PM
Pete Deets Pete Deets is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Bill,
Thanks for the further information and making me realize I need to clarify on one point.

ERP is absolutely independent of antenna height and I fell into the trap of speaking in shorthand. From the standpoint of the FCC each station is allowed a maximum ERP at a stated height above average terrain. If you choose to build above that height then you must reduce the ERP in order not to interfere with other broadcasters. The funny thing is they won't allow a higher ERP if you build below maximum height.

To muddy the digital waters even further there is another modulation scheme that has been approved but unlike the switch to ATSC 1.0 (our current digital transmissions) which was mandatory, broadcasters may switch to ATSC 3.0 on a voluntary basis. Like the original switch to digital, the 3.0 signal cannot be decoded by current equipment and will require convertors or new receivers.

The 3.0 signal has been shown to be much more robust and resistant to interference and multipath and is extremely flexible as to what channels or subchannels you can put on it. That being said, since it would require consumers to change their equipment again I really wonder if I'll see widespread implementation before I retire.............PD
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  #43  
Old 09-19-2019, 08:35:02 PM
EICBob EICBob is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Quote:
Originally Posted by Power View Post
You have internet......
Hi Power...
A small caveat to that, yes I do have internet, just NOT, NO WAY, IMPOSSIBLE, to stream video in any format. I live in what my state lists as the “Best wired county” in the state. One BIG problem with that, not every road in my county is being served by high speed internet. I have the fastest DSL available. On a good day I get 2.5 MBs down and .25MB up.

We have options if I want to pay the cable company $3700.00 to run a cable to my house, then pay the monthly bill on top of that.
Yes satellite is available to me, but again there are limits on data, speed and in the case of satellite the latency in the down, versus up prevents me from using my VPN connection to my work.
I agree that if it were available to me at a reasonable price, I to might try streaming to cut what I pay in satellite bills for TV.
OTA, I get 21 stations, except when it rains terribly hard then the multi path tends to cause un-locking of the receivers.

One thing I did was to make sure in my OTA install, all my down lead was a good quality RG6, good quality “F” connectors and to limit any splitters on any line to 1 2 way splitter. The signal loss with 4 and 6 port splitters can really impact how well your receiver will decode and lock on.
I used a 1 x 6 powered, adjustable distribution amp to send the signal around the house, and on the closest set to the antenna I had to add a 3 dB pad. Sometimes too much signal is just as bad as not enough.

Of course your mileage will vary!

(I miss my days at the television station, but glad I am not around for round 2 of the repack. I was there for the analog to digital conversion.)

-BobC
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  #44  
Old 09-19-2019, 09:54:38 PM
Zephyr7 Zephyr7 is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

You can get more flexibility with directional taps. Put one amp ahead of the system where your antenna lead comes in, and pick it carefully — you don’t want too much gain, but you want good drive (output) capability so that you don’t push it into compression. Ideally all the channels coming in will be the same level, or at least close.

Put taps with however many ports you need wherever you need them. The tap’s isolation value is how far down the tap output will be from whatever the level in the trunk (cable from the amp) is at the point the tap is installed. An example: if the trunk is at +15dBV at the tap location, and you’re using a -10dB tap, each output port of the tap (the usually have one, two, or four outputs) will be +5dBV. MATV guys like to design for +10dBV at each receiver, but part of the reason for that is to overpower any local interference so if you’re out in the boonies you can get by with less.

Loss on the trunk is dB loss for the coax, plus dB loss (“through loss”) for each tap. Note that the through loss for a tap is absolute and it doesn’t matter how many ports the tap has. The taps will specify their through loss in the datasheets.

If you’re using splitters, three 2 port splitters in a tree should be equivalent to one 4 port splitter. The trouble is when you split a split of a split, and you end up with vary unbalanced outputs on different ports.

I always liked designing MATV systems. I did a lot of schools back in the day, complete with mini head ends for local channel injection for video announcements or broadcast videos. Fun times

Bill
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  #45  
Old 09-20-2019, 12:21:23 PM
EICBob EICBob is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Thanks Bill
I want to go check what I have for signal strength at my antenna, as I recall it is somewhere near +5 as an average across all the channels, some a bit higher and some a bit lower.


I am not familiar with directional taps, will have to look into them.


I did not have the fun of designing internal RF distribution systems but always had to trouble shoot them.


Cheers


-BobC
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  #46  
Old 09-20-2019, 05:05:30 PM
Power Power is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Quote:
Originally Posted by EICBob View Post
Hi Power...
A small caveat to that, yes I do have internet, just NOT, NO WAY, IMPOSSIBLE, to stream video in any format. I live in what my state lists as the “Best wired county” in the state. One BIG problem with that, not every road in my county is being served by high speed internet. I have the fastest DSL available. On a good day I get 2.5 MBs down and .25MB up.

We have options if I want to pay the cable company $3700.00 to run a cable to my house, then pay the monthly bill on top of that.
Yes satellite is available to me, but again there are limits on data, speed and in the case of satellite the latency in the down, versus up prevents me from using my VPN connection to my work.
I agree that if it were available to me at a reasonable price, I to might try streaming to cut what I pay in satellite bills for TV.
OTA, I get 21 stations, except when it rains terribly hard then the multi path tends to cause un-locking of the receivers.

One thing I did was to make sure in my OTA install, all my down lead was a good quality RG6, good quality “F” connectors and to limit any splitters on any line to 1 2 way splitter. The signal loss with 4 and 6 port splitters can really impact how well your receiver will decode and lock on.
I used a 1 x 6 powered, adjustable distribution amp to send the signal around the house, and on the closest set to the antenna I had to add a 3 dB pad. Sometimes too much signal is just as bad as not enough.

Of course your mileage will vary!

(I miss my days at the television station, but glad I am not around for round 2 of the repack. I was there for the analog to digital conversion.)

-BobC
Bob, that comment was for UglyBlue. I have been in NC, and believe Concord has cable.
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  #47  
Old 09-20-2019, 05:10:29 PM
Power Power is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Quote:
Originally Posted by EICBob View Post
Hi Power...
A small caveat to that, yes I do have internet, just NOT, NO WAY, IMPOSSIBLE, to stream video in any format. I live in what my state lists as the “Best wired county” in the state. One BIG problem with that, not every road in my county is being served by high speed internet. I have the fastest DSL available. On a good day I get 2.5 MBs down and .25MB up.
BobC
Bob, that comment was for UglyBlue. I have been in NC. Concord is good sized, and has a lot of hotels/ motels. It is around 100,000 people, and believe it has cable and Fios. Leastways, the hotels had wi-Fi & cable
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  #48  
Old 09-20-2019, 08:13:32 PM
Birken Vogt Birken Vogt is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Quote:
Originally Posted by EICBob View Post
Hi Power...
A small caveat to that, yes I do have internet, just NOT, NO WAY, IMPOSSIBLE, to stream video in any format. I live in what my state lists as the “Best wired county” in the state. One BIG problem with that, not every road in my county is being served by high speed internet. I have the fastest DSL available. On a good day I get 2.5 MBs down and .25MB up.
I must add here that we ran streaming for years on DSL 2.5 meg actual throughput with similar slow upload. Data caps eventually started to bite us though.
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  #49  
Old 09-20-2019, 10:05:06 PM
Zephyr7 Zephyr7 is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Quote:
Originally Posted by EICBob View Post
I am not familiar with directional taps, will have to look into them.

-BobC
They’re just little indoor versions of the things used to build CATV networks. Blonder tongue is a manufacturer that makes good stuff. I’ve used a lot of their parts in my designs, amps, taps And other things.

The nice thing about taps is you can hang them off of a random length trunk and still keep all your drop levels where you want them, you don’t have to worry about what is split how many times. Remember to put a terminator at the end of the trunk.

In a house, your system will be too small to worry about gain tilt, so the only really tricky part of MATV design (and it’s really not all that bad to deal with) won’t be an issue.

Bill
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Old 09-21-2019, 05:51:04 AM
EICBob EICBob is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Quote:
Originally Posted by Power View Post
Bob, that comment was for UglyBlue. I have been in NC. Concord is good sized, and has a lot of hotels/ motels. It is around 100,000 people, and believe it has cable and Fios. Leastways, the hotels had wi-Fi & cable
Hi Power
I apologize for ms-quoting you, no disrespect intended.

In Maine there has been a huge push for streaming services and cord cutting. I have been seriously trying to work on successfully streamng. I can at times watch some video, but after about 10 minutes the stream will start to degrad and pixelate and buffer. Not very enjoyable.
I use wired connections right to my DSL modem so I am pretty sure it is not related to using WiFi.
At any rate, this has been an enjoyable thread.

Again, sorry about the mis-quote

-BobC
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Old 09-21-2019, 05:54:45 AM
EICBob EICBob is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Hi Bill
I am familiar with Blonder Tongue gear, they do indeed make nice stuff. My DA is a BT unit and it works very well.



-BobC
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Old 09-21-2019, 02:51:11 PM
len k len k is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Interesting that cable compaies are hyping 50 and 100 megbit/sec speeds. When I talked with them about what I needed to downstream good quality video for TV ( or was it just you tube) they said only need 2 meg/sec INSTANTANEOUS speed ...BUT it CAN'T drop below that..


But as ISP drops your speed after a while I guess you need to pay them a LOT of money so 50-100 M/sec doesn't drop to 2 M/sec. They got max profit all figured out.

Think is I remember the old days when you could download the whole movie then watch it without dropouts..... that seems like a better way to go.
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Old 09-21-2019, 03:58:54 PM
Zephyr7 Zephyr7 is offline
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Default Re: Boston area TV stations changed their antennas... weaker signal

Comcast just sent me a flyer this week saying they’re upgrading me for free from 250Mb/s down to 300Mb/s. Still only 20Mb/s up though. I’ve never had any problems aside from power outages knocking the cable system out (it has about 5 hours of battery running my node), but they have been surprisingly good about getting a generator on the local node quickly and keeping it running.

I do actually see more speed than they claim when I run tests. Comcast over provisions as a matter of policy, probably to avoid arguments with customers. They do this on their commercial fiber optic circuits too.

They don’t “drop your speed” after a while. If you see that issue, you probably have your system not handling packet errors well and/or have a lot of latency on your connection. There are some optimizations you can do (look up “TCP window size”) to help.

The industry for the most part doesn’t do any sneaky speed games — it’s too much hassle. They’d rather just sell you a fast circuit and not deal with it. There are very real issues with congestion, latency, bursts, and other things that can cause issues though. The telecom industry just wants to bill you monthly and not hear from you all the time. It’s not worth the hassle to do sneaky things to try to get you to upgrade, and it’s easier to just upgrade core networks than it is to put in sneaky things and then manage them.

Bill
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