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Guest Message by DevFuse

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rain fade with hd channles


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8 replies to this topic

#1 OFFLINE   prop

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Posted 11 June 2013 - 07:04 AM

i have an hd24 dvr reciver as well as other standard and dvr recievers.all 101 transponders are in the 90 to 100 quality range and  the avaliable 99 and 103 transponders all in the 80`s and above.it seems like with just a moderate amount of rain i lose some of the hd channels like the weather channel and local nbc stations here in the ny city area.the heavier the rain the more lost channels.no issues with standard def dvr.i have done my own installs for 20 years and started with c-band dishes,so i have been around the block a few times.i use an old birdog as well as an acutrack meter.i understand the  the narrow bandwidth of the ka birds so i`m just wondering if it`s just something i have to live with or is it possible to install a bigger dish for hd birds or is there any way to get the standard def channels on the hd reciever?thanks



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#2 OFFLINE   jimmie57

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Posted 11 June 2013 - 07:15 AM

To get the SD channels to show on the HD receivers,

Menu, Settings, Display, Preferences, Guide HD Channels ( choose "Show All Channels" ).

 

When you are using your favorites they will not show. When it rains and you lose the channel, get the guide on the screen and then press the yellow button and change the "Change Favorites List" to "Channels I get". The SD channels will show on the guide now so that you can change to the SD version of the channel you were watching.


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#3 OFFLINE   gpg

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Posted 11 June 2013 - 07:19 AM

We've had some exceptionally heavy rain in the NYC area the past few days, so I'm not surprised that you had some rain fade on the HD channels. So did I.

In any event, you can add the SD duplicates to your guide by going to Settings>Display>Preferences and then selecting Show All Channels on the Guide HD Channels line. This will place the SD duplicate of an HD channel one position up from the HD version. So if WNBC 4 HD went out, pressing channel up would take you to WNBC 4 SD. If you simply press "4" on your remote, you would still automatically go to the HD version of the channel.

Hope this helps, and that the rain gives us a break.
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#4 OFFLINE   prop

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Posted 11 June 2013 - 09:19 AM

thanks guys .i should have thought of that



#5 OFFLINE   jimmie57

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Posted 11 June 2013 - 09:24 AM

You are welcome.


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#6 OFFLINE   Diana C

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Posted 11 June 2013 - 10:04 AM

Here in NE New Jersey we have 90's on most of the HD transponders.  We only had rainfade last Friday night when the worst of Andrea's remnants came through. You might need a repeaking of your dish.


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#7 OFFLINE   texasbrit

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Posted 11 June 2013 - 11:45 AM

Yes, a correctly aligned dish will have signals on 99c/103ca/103cb in at least the low 90s. Mine are all 94-96



#8 OFFLINE   harsh

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Posted 11 June 2013 - 12:49 PM

i understand the  the narrow bandwidth of the ka birds so i`m just wondering if it`s just something i have to live with or is it possible to install a bigger dish for hd birds or is there any way to get the standard def channels on the hd reciever?thanks

There aren't any affordable reflector options. Taking great pains in accurate aiming is the only practical solution to reducing fade as Ka is substantially unforgiving.

Too often we enjoy the comfort of opinion without the discomfort of thought. -- JFK


#9 OFFLINE   TomCat

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Posted 11 June 2013 - 08:10 PM

...i have done my own installs for 20 years and started with c-band dishes,so i have been around the block a few times.i use an old birdog as well as an acutrack meter.i understand the  the narrow bandwidth of the ka birds so i`m just wondering if it`s just something i have to live with...

 

What you have to live with is the max possible signal level.

 

What I mean by that is that if you understand how this all works, as you apparently do, if you tune your dish for max reception, your HD channels will not fade faster than your SD channels, generally speaking. But more precisely, Ka does not have a narrower bandwidth (and that would not make a difference anyway). What is has is the tendency to focus at a tighter (smaller grouping) focal point that implies a need for more accurate tuning to receive with full rain fade margin overhead, as compared to Ku, simply because the downlink frequency is higher.

 

The prominent reason for HD channels fading before SD channels is because of mistuning. IOW, even if you are mistuned a bit for Ku, the larger focal point with slower dropoff means you still get most of the signal. For Ka, slight mistuning means much more dropoff comparatively speaking, and quicker rain fade due to less rain fade margin. If you are precisely tuned, this takes that difference completely out of the picture, leveling that playing field.

 

And the reason I qualified this with "generally speaking", is because what causes rain to interfere is not so much diffraction of the signal as absorption. If rain drops are a similar wavelength to a signal, they are more likely to actually absorb the signal (the signal enters the raindrop and bounces back and forth inside the raindrop until attenuated because the similar size causes the drop to act like a little antenna). If drops are a dissimilar size to wavelength, the signal mostly passes through, is diffracted, but not attenuated.

 

Why is that important?  Because we are dealing with two wavelengths (or bands of wavelengths) on downlink. If the rain particles match in size the wavelength of Ku but not Ka, Ku might fall off faster, and vice versa.

 

One might suspect that this is a factor in uplink as well, but it isn't, really. The uplink site dynamically varies the signal level to fully illuminate the sat regardless of what weather conditions might be intervening, so theoretically, the uplink signal as received is about the same under all conditions regardless. Downlink is at the mercy of where you happen to be. Intervening weather will be a factor, and the only technique at your disposal (barring a larger or hotter antenna) is as harsh says, which is to tune precisely.


Edited by TomCat, 11 June 2013 - 08:37 PM.

It's usually safe to talk honestly and openly with people because they typically are not really listening anyway.




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