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post #8551 of 11052 Old 04-13-2012, 04:52 PM
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Originally Posted by mr. wally View Post

Weird i was watching 30 rock on kntv via dish and about 2/3 of the way through the show kntv went totally green screen. checked back to see if it was up when fallon was supposed to start, and still green screen.

weird how you were able to watch at 10:00 when i lost reception before 9:00.

What is so weird about it? You are on Dish, not Comcast or Direct! The OTA signal and the same signal that Dish gets its feed from was knocked out.

Comcast and Direct get a direct feed from fiber....

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post #8552 of 11052 Old 04-13-2012, 05:20 PM
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My recording of the Tonight Show was a title page saying that they knew the station was off the air, there was no need to call, and they would have the station back as soon as possible, along with background music. Prior to this I didn't know whether or not Dish Network got their feed for KNTV off the air.

Do Comcast and DirecTV get fiber feeds from all stations?

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post #8553 of 11052 Old 04-13-2012, 05:35 PM
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Quote:
Originally Posted by bobby94928 View Post

What is so weird about it? You are on Dish, not Comcast or Direct! The OTA signal and the same signal that Dish gets its feed from was knocked out.

Comcast and Direct get a direct feed from fiber....

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Originally Posted by Larry Kenney View Post

My recording of the Tonight Show was a title page saying that they knew the station was off the air, there was no need to call, and they would have the station back as soon as possible, along with background music. Prior to this I didn't know whether or not Dish Network got their feed for KNTV off the air.

Do Comcast and DirecTV get fiber feeds from all stations?

Larry
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hey bobby, larry's question is what makes it weird. how do comcast and direct get their signal as opposed to dish? and it is something dish subs should know especially if they live in a thunder storm prone areas.

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post #8554 of 11052 Old 04-13-2012, 05:49 PM
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Originally Posted by mr. wally View Post

hey bobby, larry's question is what makes it weird. how do comcast and direct get their signal as opposed to dish? and it is something dish subs should know especially if they live in a thunder storm prone areas.

Comcast gets fiber feeds from the Sutro Tower installation. Directv also gets a fiber feed from KNTV which broadcasts from San Bruno Mtn. I can't really remember the details but I think they get the feed as their OTA antenna farm near AT&T Park does not receive the KNTV signal well. Dish, I think, has their OTA antenna farm somewhere in the south bay area.
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post #8555 of 11052 Old 04-13-2012, 07:38 PM
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Originally Posted by mr. wally View Post

hey bobby, larry's question is what makes it weird. how do comcast and direct get their signal as opposed to dish? and it is something dish subs should know especially if they live in a thunder storm prone areas.


Considering that the Bay Area is not a thunder storm prone area, the question is moot...

That said, Comcast and Direct have the fiber feeds and Dish doesn't. It's a business decision.... Who's decision it was to spend the money for the feed is entirely on who had to pay for it....

Bobby 

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post #8556 of 11052 Old 04-13-2012, 07:58 PM
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Originally Posted by mr. wally View Post

...

weird how you were able to watch at 10:00 when I lost reception before 9:00.

I only checked at 10:50 PM, the face book page said ~ a hour ago, so with my edit time they reported they were off the air ~ 10:00 PM.

What was remarkable is that they said anything al all.

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post #8557 of 11052 Old 04-14-2012, 10:29 AM
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did not know about comcast and direct getting fiber feeds and dish not.

learn something new everyday, that's what i love about avs.

thanks guys

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post #8558 of 11052 Old 04-14-2012, 06:55 PM
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Originally Posted by 888CALLFCC View Post

Right now, The trees here are starting to bloom & leaf up. And they grow every year. Signals can be changed by this.

Even though we are in the line of sight of Sutro, we have pesky Eucalyptus trees behind us which have branches which are apparently the cause of intermittent pixilation and drop outs during heavy winds up here on our hill. KPIX HD 5.1 is especially prone to it and we can almost predict a bad night of reception from that station.
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post #8559 of 11052 Old 04-14-2012, 08:03 PM
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Originally Posted by Bob Fosse View Post

Even though we are in the line of sight of Sutro, we have pesky Eucalyptus trees behind us which have branches which are apparently the cause of intermittent pixilation and drop outs during heavy winds up here on our hill. KPIX HD 5.1 is especially prone to it and we can almost predict a bad night of reception from that station.

It's a tough situation.
You can build a channel specific yagi antenna that has tons more gain than a basic broadband antenna. PM me for the design website.
Build two and you can stack and have some degree of signal controls.

I'm looking at building a ch36 yagi here.
15 feet long x 1 foot ... for 605MHz
16.7 dbd estimated gain
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post #8560 of 11052 Old 04-14-2012, 09:52 PM
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KGO RF 35, the channel 35 translator transmitter signal from Fremont for KGO-TV, is once again missing (and being missed) in the South Bay. It disappeared last Wednesday, April 11, and is still black on Saturday night, April 14.

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post #8561 of 11052 Old 04-15-2012, 10:22 AM
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Originally Posted by Rick_ View Post

KGO RF 35, the channel 35 translator transmitter signal from Fremont for KGO-TV, is once again missing (and being missed) in the South Bay. It disappeared last Wednesday, April 11, and is still black on Saturday night, April 14.

Rick

Weather related? Did something get fried? I still have KGO but on 7.1
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post #8562 of 11052 Old 04-15-2012, 07:14 PM
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Quote:
Originally Posted by 888CALLFCC View Post

It's a tough situation.
You can build a channel specific yagi antenna that has tons more gain than a basic broadband antenna.

His problem with the eucalyptus trees sounds the same as I saw at my cousin's house with KCSM also looking through eucalyptus trees. If it is the same then no amount of gain is going to fix the problem. I looked at KCSM on the spectrum analyzer and I saw a signal that was changing in amplitude by large amounts on a very short time scale. The trace on the analyzer was very chopped up with the sweep speed set so the channel was swept in 3 seconds. The display changed wildly with every sweep. I suspect the only solution would be to move the antenna.

Chuck
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post #8563 of 11052 Old 04-16-2012, 07:39 AM
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Looks like KGO RF35 is back up. Maybe somebody is following this forum
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post #8564 of 11052 Old 04-16-2012, 11:06 PM
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When KGO's channel 35 translator is off the air I get a great signal from KCRA 3 (RF35) from Sacramento. When KGO's translator is on the air, I don't get KCRA or KGO on channel 35. The two signals apparently desense each other and I end up with a signal of 12 to 13 dB no matter which way I point my antenna, and that's not strong enough to produce a picture.

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post #8565 of 11052 Old 04-16-2012, 11:43 PM
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I don't get it. What is the service area of this translator KGO 35 ?
I will guess this was intended to bring ABC to the Salinas Market from the bay area as that transmitter location does bring some signal down there. But now, there is a new ABC station in the Salinas market so is this translator unnecessary?
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post #8566 of 11052 Old 04-17-2012, 02:59 AM
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Quote:
Originally Posted by Larry Kenney View Post

When KGO's channel 35 translator is off the air I get a great signal from KCRA 3 (RF35) from Sacramento. When KGO's translator is on the air, I don't get KCRA or KGO on channel 35. The two signals apparently desense each other and I end up with a signal of 12 to 13 dB no matter which way I point my antenna, and that's not strong enough to produce a picture.

Larry
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It's not really "desense" per se. It's just a signal to noise ratio issue. One signal has to be the usual 15 dB above the other for a successful decode. Think of the signal with the lower level as setting the noise floor for the stronger signal.

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post #8567 of 11052 Old 04-17-2012, 07:31 AM
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Quote:
Originally Posted by 888CALLFCC View Post

I don't get it. What is the service area of this translator KGO 35 ?
I will guess this was intended to bring ABC to the Salinas Market from the bay area as that transmitter location does bring some signal down there. But now, there is a new ABC station in the Salinas market so is this translator unnecessary?

It's for people in the South Bay having trouble with KGO from Sutro. ABC is carried by KSBW on 8.2.

Chuck
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post #8568 of 11052 Old 04-17-2012, 08:30 AM
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I tried to find a good link to explain receiver desensitization (desense) but I couldn't find one. They just talk about it as though everyone knows what it is. So I'll take a stab at it. If I say something wrong I'm open to correction.

An amplifier has a maximum output. Increasing the the input signal above a certain level will not make the output go higher. An amplifier with such an input signal is operating in saturation. If a very strong signal is present in the passband of an amplifier and there are also weaker signals in the passband, the strong signal essentially steals power from the weaker signals thus reducing the gain of the amplifier for the weaker signals. The weaker signals are said to be suffering from desense.

This is an insidious problem because it's not obvious that weaker signals are suffering from desense. Strong signals can be received but weak signals have a reduced SNR or cannot be received at all. It's a very difficult problem to diagnose without being able to measure the signals on a spectrum analyzer and knowing the preamp maximum output. Preamp manufacturers do provide output numbers but they are not standardized in any way. Tinlee gives the saturated output for 8 input signals. Winegard gives the maximum input signal in uV which is useless until you convert it into dBm and add the preamp gain.

When one reads comments about preamps being overloaded, this mostly means desense. It could mean 3rd order intermodulation problems but that's another topic.

Desense is the main reason that preamps don't work well in strong signal environments. One signal can drive the amplifier into saturation. Even if one signal is not enough to do it, multiple strong signals can drive the amplifier into saturation because the summation of the individual signals can exceed the maximum amplifier output. San Francisco would be a prime example of this. All the Sutro and San Bruno stations might come in fine but few if any other stations can be received because the amplifier is in saturation. Even the TV tuner itself can suffer from desense if the signals are strong enough. This is why preamps are not recommended in strong signal environments.

When I first put up my antennas I had a very high gain preamp and I had all kinds of problems which I traced to desense from KUVS on channel 18. Now that I know more I've been able to select a preamp that KUVS doesn't drive into saturation and I'm using a notch filter just before the TV to reduce that huge signal from reaching the TV tuner. All the other signals in the UHF band don't sum to be as strong as KUVS by itself!

The ideal solution would be to use a preamp with a tuned input, one that passed only the channel you were tuned to, but that would be prohibitively expensive for a consumer TV installation.

I believe the assumption is made that if you have very strong signals that you'll be watching just those channels and not trying to watch weak channels. If you have only weak channels (fringe area) then you can take full advantage of the added sensitivity of a preamp.

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post #8569 of 11052 Old 04-17-2012, 12:21 PM
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Quote:
Originally Posted by Calaveras View Post

Winegard gives the maximum input signal in uV which is useless until you convert it into dBm and add the preamp gain.

Chuck

This spec is not useless, it is in fact the only way to accurately specify the limitation of the amplifier.

Amplifiers operate from a power supply, and can not output voltages beyond their power supply. If you have an amplifier running off 12V DC, it can not output more than 12V peak to peak (the limit is actually likely to be significantly less). Unless you know the shape of the waveform, you can not translate a peak to peak value into dBm. dBm is a power measurement, and does not translate directly into a peak to peak voltage. Two signals that measure the same power in dBm can have wildly different peak to peak voltages.

The worst thing about over driving an amplifier is that it expands the spectrum of the over driving signal. Thus energy from the over driving signal can appear on top of other weaker stations, wiping them out.
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post #8570 of 11052 Old 04-17-2012, 06:34 PM
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Quote:
Originally Posted by Calaveras View Post



Desense is the main reason that preamps don't work well in strong signal environments. One signal can drive the amplifier into saturation. Even if one signal is not enough to do it, multiple strong signals can drive the amplifier into saturation because the summation of the individual signals can exceed the maximum amplifier output.

Chuck

Chuck.

I am in northern santa rosa and basicaly in a fringe area from sutro tower. Kfty channel 50 is really strong here. Is it possible that this could cause desense for me? Or, is desense only a problem with adjacent channels?

Thanks
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post #8571 of 11052 Old 04-17-2012, 08:55 PM
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Quote:
Originally Posted by DAP View Post

This spec is not useless, it is in fact the only way to accurately specify the limitation of the amplifier.

Microvolts is just another way of saying dBm, or in the TV business dBmV. The Winegard spec is not useful for comparing to other manufacturer specs that give the maximum output of their amplifiers in dBmV. You have to convert to dBmV and then add the gain of the amplifier to obtain max output in dBmV for the Winegard preamps. The Winegard spec has nothing to do with peak-to-peak voltage.

Quote:


Amplifiers operate from a power supply, and can not output voltages beyond their power supply. If you have an amplifier running off 12V DC, it can not output more than 12V peak to peak (the limit is actually likely to be significantly less). Unless you know the shape of the waveform, you can not translate a peak to peak value into dBm. dBm is a power measurement, and does not translate directly into a peak to peak voltage. Two signals that measure the same power in dBm can have wildly different peak to peak voltages.

Well, what you say is correct but RF amplifiers are not spec'd in peak-to-peak output voltage. The only output specs I've ever seen are 3rd order intercept point, 1dB gain compression, and saturated output, all in dBm.

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The worst thing about over driving an amplifier is that it expands the spectrum of the over driving signal. Thus energy from the over driving signal can appear on top of other weaker stations, wiping them out.

Yes, that's the intermod products I mentioned. It all depends on where the intermod products fall. Intermod can affect weak signals long before the amplifier goes into saturation. Intermod can be a huge problem or not. It depends on how many big signals are in the passband and where the weak signals are located. It only takes one big signal to desense an amplifier and affect all the signals, which was the only point I was trying to make.

Chuck
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post #8572 of 11052 Old 04-17-2012, 09:08 PM
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Quote:
Originally Posted by iitywygms View Post

Chuck.

I am in northern santa rosa and basicaly in a fringe area from sutro tower. Kfty channel 50 is really strong here. Is it possible that this could cause desense for me? Or, is desense only a problem with adjacent channels?

Thanks

Looks like northern Santa Rosa is about 13 miles from Mt. St. Helena. KEMO has only 4KW in your direction. I assume you have a directional antenna pointed to Sutro with some front to back ratio. Under those assumptions it's unlikely that KEMO is strong enough to cause desense. It may be strong enough to bleed over onto RF 31 and 33. Do you have trouble with KMTP more so than anything else from Sutro?

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post #8573 of 11052 Old 04-17-2012, 10:05 PM
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I do have a directional antenna pointed at Sutro.
I do not watch kmtp much so I cant give a good answer. But right now looking at my hdhr, it shows about 20% less than the other stations.
I was just curious. I get the major networks up here fairly solid and that is all I really need. They do drop out during the hot summer days, but that is another subject.
I appreciate the info Chuck. You and others on this forum are very enlightening.
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post #8574 of 11052 Old 04-17-2012, 10:45 PM
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Originally Posted by Calaveras View Post


His problem with the eucalyptus trees sounds the same as I saw at my cousin's house with KCSM also looking through eucalyptus trees. If it is the same then no amount of gain is going to fix the problem. I looked at KCSM on the spectrum analyzer and I saw a signal that was changing in amplitude by large amounts on a very short time scale. The trace on the analyzer was very chopped up with the sweep speed set so the channel was swept in 3 seconds. The display changed wildly with every sweep. I suspect the only solution would be to move the antenna.

Chuck

Yep, that could help, but we are limited on placement and size of our 8 ft RS antenna which we prefer to keep in the attic. Since the dropouts and pixilation are not a major problem most of the time we will continue to use the same antenna. A few years back I did try an amplified antenna, but with no avail and much worse reception despite claims of superior reception.
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post #8575 of 11052 Old 04-18-2012, 01:01 AM
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Quote:
Originally Posted by dr1394 View Post

It's not really "desense" per se. It's just a signal to noise ratio issue. One signal has to be the usual 15 dB above the other for a successful decode. Think of the signal with the lower level as setting the noise floor for the stronger signal.

Ron

Thanks for the explanation, Ron. I got a good demonstration of this phenomenon earlier today.

Signals from the north and northeast were about 5 to 6 dB stronger than normal this afternoon while the signals from the South Bay were weaker than normal. (This often happens. When 22, 50 and the signals from Walnut Grove are up, the signals from Mt. Allison and Monument Peak are often down.) KAXT 1 dropped below the cliff edge here today, so KGO 35 must have been down, too. KCRA was actually strong enough during this period to rise above KGO on channel 35 and it gave me a signal of 17 dB SNR.

By the way, signals were up on both VHF and UHF today. Often it's one band or the other, but 3, 6, 10, 13, 31 and 58 from Walnut Grove, 42 and 52 from Mt. Diablo, and 22 and 50 from up north were all way up today.

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post #8576 of 11052 Old 04-18-2012, 01:13 AM
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Quote:
Originally Posted by Calaveras View Post

An amplifier has a maximum output. Increasing the the input signal above a certain level will not make the output go higher. An amplifier with such an input signal is operating in saturation. If a very strong signal is present in the passband of an amplifier and there are also weaker signals in the passband, the strong signal essentially steals power from the weaker signals thus reducing the gain of the amplifier for the weaker signals. The weaker signals are said to be suffering from desense.

Chuck

That's the situation I have here. I've tried a couple of different preamps to see if it'd help with the weaker Walnut Grove stations, but in both cases, any added gain would cause the distant stations to get weaker. I got the best signals when the preamps were turned all the way down.

I don't seem to have any trouble with a distribution amp that I have here for feeding four TV's. I actually get a 1 dB increase in signal from the amp over the strength of the signals going into it. 16 dB SNR in = 17 db out; 32 dB in = 33 dB out -- those real strong signals from Sutro don't seem to bother it at all.

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post #8577 of 11052 Old 04-18-2012, 07:36 AM
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Quote:
Originally Posted by Larry Kenney View Post

By the way, signals were up on both VHF and UHF today. Often it's one band or the other, but 3, 6, 10, 13, 31 and 58 from Walnut Grove, 42 and 52 from Mt. Diablo, and 22 and 50 from up north were all way up today.

Exactly how this works is somewhat of a mystery. This morning all the stations from Mt. San Bruno are coming in, at least the ones that don't have co-channel interference but no station from Sutro is coming in. Walnut Grove signals are both good and bad. KVIE/KXTL on the same tower are 10 dB above average. On the next tower over KMAX is 20 dB below average, KCRA is a little bit down and KQCA is average. All three use the same antenna.

In a couple of hours things will likely be back to normal.

Chuck
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post #8578 of 11052 Old 04-21-2012, 05:02 PM
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Ok, almost time for the hot weather inversion layers to kick in.
North bay reception
South bay reception
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post #8579 of 11052 Old 04-21-2012, 10:35 PM
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Originally Posted by 888CALLFCC View Post

Ok, almost time for the hot weather inversion layers to kick in.
North bay reception
South bay reception

Here where we are in the North Bay, our signal strength is much better in the summer than during the winter.
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post #8580 of 11052 Old 04-23-2012, 05:04 PM
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Really?
Opposite for me.
I lose KNTV when the temps get above 85 or so. KGO gets iffy too.
KPIX will also disappear to but not near as much as the above two.
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