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Guest Message by DevFuse

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Signal Strength


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30 replies to this topic

#1 OFFLINE   Mike109

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Posted 25 November 2010 - 02:14 AM

I have a problem with one OTA channel, CBS. Every so often I get the signal loss message. Sometimes I get green pixels at the bottom of the screen. These problems last only a second or two & occur maybe once or twice during a program. It does not happen with satellite CBS.

The OTA signal strength reading on the 722K DVR is typically from 78% to 82%. Once I saw it dip to 74. At what point would a signal loss usually occur?

A lot of my channels are 90% to 100% indicated signal strength. I thought about installing an amp, but am concerned about having too high of signal level on these channels & overdriving the DVR.

I do have a couple 4 way splitters that I could change to 3 way ones. Then use the -3.5dB (instead of -7dB) outputs to feed the Dish DVR. This should increase my signal strength by 7dB. Is there any rule of thumb that correlates a change in dB to signal strength percentage?

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#2 OFFLINE   Larry Kenney

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Posted 25 November 2010 - 03:06 AM

The OTA signal strength reading on the 722K DVR is typically from 78% to 82%. Once I saw it dip to 74. At what point would a signal loss usually occur?

I do have a couple 4 way splitters that I could change to 3 way ones. Then use the -3.5dB (instead of -7dB) outputs to feed the Dish DVR. This should increase my signal strength by 7dB. Is there any rule of thumb that correlates a change in dB to signal strength percentage?


I've found that anything below 80 is subject to occasional drop out. Signals vary a lot due to multipath, weather, atmospheric conditions, aircraft flying by, etc., so the higher your signal reading is the more solid your reception will be. One of the stations I watch regularly averages about 73 to 74, and I occasionally get drop outs, while another station that only has a signal of 68 seems solid all the time. It all depends on what's happening in the direction that you're getting the signal from. Any signal you see that's below 65 will probably be unreliable... there sometimes, gone at other times.

There is no dB signal strength indicator on the Dish receivers, but I've done a comparison of Signal to Noise Ratio (SNR) strength in dB on my Sony XBR5 receiver to the signal strength reading on my Dish ViP622 using the same antenna for input. I have come up with the following comparisons:
A signal of 15-16 dB is the point where I get a picture on the Sony. That signal equals a reading of 61 to 64 on the Dish receiver.
17 dB = 64
18 dB = 66
20 dB = 68
21 dB = 73
23 dB = 76
24 dB = 78
27 dB = 82
28 dB = 85
30 dB = 90
31 dB = 93
33 dB = 98 - 100
(I didn't have any signals at the values that are missing.)

As you can see, the two don't go up linearly, but at least from this you can get an idea of what SNR signal levels equal on the Dish scale. Your receiver might perform differently than mine, but this will give you a general idea of the values.

Larry
SF

#3 OFFLINE   Mike109

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Posted 26 November 2010 - 06:52 AM

Larry,

Thanks for the information. One splitter is easy to access, the other is not. I'll take out the one & see what happens. As I think about it, the second one may not have much impact due to the way a pair of diplexers are connected to it.

From what I could find out, a diplexer has only a small amount of loss. Maybe .5 to 1.0 dB. Does that sound right?

Mike

#4 OFFLINE   Larry Kenney

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Posted 27 November 2010 - 02:10 AM

I don't know about the loss in a diplexer, but splitters can have different loss values, so you really won't know how much of a difference removing one will make until you try it. Good luck. I hope it helps enough get rid of your problem with CBS.

Larry
SF

#5 OFFLINE   P Smith

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Posted 27 November 2010 - 02:03 PM

Larry,

Thanks for the information. One splitter is easy to access, the other is not. I'll take out the one & see what happens. As I think about it, the second one may not have much impact due to the way a pair of diplexers are connected to it.

From what I could find out, a diplexer has only a small amount of loss. Maybe .5 to 1.0 dB. Does that sound right?

Mike


Nope. The your number is close to two F-connector and one barrel junction.
Splitters as passive device starting from -4 dB for 2-way, -7 dB for 4-way, etc.

#6 OFFLINE   Mike109

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Posted 28 November 2010 - 02:55 AM

I bypassed the 4-way splitter which had a 7dB loss. This increased the signal strength by 3%. I went back & forth a couple times and always got the same results. Basically my nominal 80% went to 83%. I don't know how linear the increase is, but if it is then to go from 80% to 90% would need about a 23dB preamp.

Is it best to install a preamp between the OTA antenna & the diplexer and then power it from its own power supply? Or insert it after the diplexer (IOW after the signals are mixed) and let the Dish DVR provide power to the preamp? Obviously I'd have to make sure the preamp operates on the proper voltage, but will that be too much of a load on the Dish DVR? And how would the sat signal be affected by having it go through the preamp?

Any advice would be appreciated.
Thanks in advance.

#7 OFFLINE   Jim148

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Posted 28 November 2010 - 11:54 AM

.....Any advice would be appreciated.....


Well, you did say ANY advice would be appreciated, right? Do you have any RG-59 coaxial feedline anywhere in you system? even the short patch cords? The reason I ask is because I would buy feedline on price yers ago, but I learned the hard way that even short runs of RG-59 can be pretty lossy. I am not saying that it will cure your problem, but it might be worth looking at. Cable can be misleading because you can look at it and it will look out of the package new, but who knows how much shielding is actually inside their? I learned the hard way as a ham radio operator that cheap feedline is NOT the way to go because it looses too much signal.

#8 OFFLINE   Mike109

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Posted 29 November 2010 - 01:14 AM

Everything appears to be RG-6, based on the visible coax.

#9 OFFLINE   Larry Kenney

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Posted 30 November 2010 - 06:35 PM

A pre-amp should be installed at the antenna so that it amplifies just the signal and not the noise picked up in the coax. The power supply is usually at the TV end of the coax, so you need a complete connection between the two.

I'm not sure what this diplexer you're talking about is doing in the line. Do you really mean splitter where you're sending the signal to two TVs?

Larry
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#10 OFFLINE   Mike109

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Posted 01 December 2010 - 01:15 AM

The diplexer is combining the OTA antenna coax and the sat coax. This is done in my attic. There also are 2 more diplexers & a splitter which feed the rest of the house.

I do have electrical power in the attic, so it could power the preamp power supply if located near the antenna.

#11 OFFLINE   Mike109

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Posted 08 December 2010 - 06:05 PM

I looked at signal strengths for my area on tvfool.com. Of the major networks, Fox is the strongest at -29.8 dBm and CBS the weakest at -40.5 dBm.

The signal strength indicator on the DVR tends to follow the tvfool.com power figures, however there are a couple of noticeable exceptions. My highest signal strength of 100% is on a station with -30.5 dBm.

Would it therefore follow that by using a 10 dB preamp it would increase the signal level of CBS from -40.5 to -30.5, and thereby give me a DVR signal strength reading of about 100% just like the other station?

IOW I would not need a lot of gain.
Any thoughts on this?

Edited by Mike109, 08 December 2010 - 06:16 PM.


#12 OFFLINE   Mike109

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Posted 10 December 2010 - 12:34 AM

My townhouse OTA antenna is in the attic because all the units were built that way. There is no mast & the antenna is is held up by wires. It's really a tight fit & very little room for adjustment. But I was able to swing it around about 5 or 10 degrees. CBS signal strength jumped to 92%. Two other channels increased and most stayed the same. But two minor PBS channels went from 81% down to 76%.

So I've been checking CBS frequently because that was my problem channel. One thing I noticed is that CBS and NBC sometimes indicate about 77% signal strength for the same programs that gave the higher readings. I look again a second later & they are back into the 90s. What the heck would cause them to drop 15% for a few seconds & then bounce back up?

#13 OFFLINE   Davenlr

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Posted 10 December 2010 - 12:45 AM

Multipath

Tivo Premier XL4, Tivo Premier, Tivo HD whole home on Xfinity HD, DirecTv Whole Home with 39" high gain KaKu dish, Roku3,SageTv 8 TB Win8 Server -> DVDO Edge-> Denon AVR, Klipsch KB15's/Panasonic 55ST60 plasma"


#14 OFFLINE   RasputinAXP

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Posted 10 December 2010 - 07:45 AM

Same for me. I have pretty bad multipathing but there's not much I can do without relocating my antenna. It so happens that my OTA transmitters are geographically north from my house, and my antenna is on the old mast from my Dish 500.

"Belligerent and numerous."

Sometimes I update the Dish Network FAQ

AT200, Hopper & 360 via HDMI to Onkyo 505 to basement 42" Westy, Hopper via Comp-over-Cat5 to living room 42" Vizio with a Roku 3, Joey to Toshiba 32" LCD with a Logitech Revue. You want fries with that? Pull up to the 2nd window.


#15 OFFLINE   Mike109

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Posted 11 December 2010 - 02:45 PM

I thought multipathing was having the signal bounce off buildings, etc & arriving at the antenna at different times than the main signal. That this would create ghosting in the picture in the old analog days.

But why would a modern digital tuner tune in a strong signal & then decide to momentarily use the weaker signal?

#16 OFFLINE   P Smith

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Posted 11 December 2010 - 02:58 PM

Short answer is here http://en.wikipedia....th_interference

#17 OFFLINE   Mike109

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Posted 13 December 2010 - 03:28 AM

Short answer is here http://en.wikipedia....th_interference


Thanks for the link. I understand the signals arrive at different times. But what would make the time difference vary? I am still at the same distance from the transmitting tower and any buildings that are in the path are also fixed in location.

Sunday evening I time-shifted & watched a recording in progress. CBS was back down to 79% signal strength. I checked frequently because I was disappointed that the level dropped. I never changed channels and later I watched whatever was on after the late news and now I was getting 93% strength on CBS all the time. IOW it went from a couple hours at 79% to an hour or so at 93%. I wish it was the other way around because the recording had a few green pixels for a second or two at the very bottom of the picture.

This has only happened with CBS which is real channel 12 in the Chicago area. This is the only high VHF channel in the area, at least of any major station. Is VHF more prone to multipathing than UHF?

#18 OFFLINE   RasputinAXP

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Posted 13 December 2010 - 08:22 AM

Yes. Also, depending on your antenna you could have greater issues with multipath than other antenna types.

My kingdom for something that picks up VHF-LO and isn't 12 feet around.

"Belligerent and numerous."

Sometimes I update the Dish Network FAQ

AT200, Hopper & 360 via HDMI to Onkyo 505 to basement 42" Westy, Hopper via Comp-over-Cat5 to living room 42" Vizio with a Roku 3, Joey to Toshiba 32" LCD with a Logitech Revue. You want fries with that? Pull up to the 2nd window.


#19 OFFLINE   P Smith

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Posted 13 December 2010 - 12:01 PM

Thanks for the link. I understand the signals arrive at different times. But what would make the time difference vary? I am still at the same distance from the transmitting tower and any buildings that are in the path are also fixed in location.

Sunday evening I time-shifted & watched a recording in progress. CBS was back down to 79% signal strength. I checked frequently because I was disappointed that the level dropped. I never changed channels and later I watched whatever was on after the late news and now I was getting 93% strength on CBS all the time. IOW it went from a couple hours at 79% to an hour or so at 93%. I wish it was the other way around because the recording had a few green pixels for a second or two at the very bottom of the picture.

This has only happened with CBS which is real channel 12 in the Chicago area. This is the only high VHF channel in the area, at least of any major station. Is VHF more prone to multipathing than UHF?


Absolutely, you can see same process in a pond.
Temp, wind, jitter in source signal, etc are contributing factors to multipath variation.

#20 OFFLINE   Mike109

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Posted 27 December 2010 - 12:52 AM

Regarding Multipath -

For the last week or so my max signal strength has changed. Instead of having a high of about 92-93% and sometimes a dip to about 77-79%, the max is now about 84% with the same dip to about 77%.

If the 77% was due to multipath & I presume one signal canceling out the other, could the 93% have been from two signals in phase and therefore adding to other?




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