Question: signals quality drops with bad weather conditions

scandiskwindows9x

Moderator of DTV Latino
#1
Hello everyone

was wondering the rain and extreme cold affects the signal quality of ATSC?

well my question is due today is raining and very cold the temperature and the signals rates have dropped of substantial way, the channels that had 100% of signal quality now are between 85-91% of signal strenght and the channel 11 from 80% now dropped to 57% the signal quality the only channel that keeps in 100% is the channel 13 and the 26 from 50% now dropped to 45% just is weird somebody have some idea of what can be?

well we use the japanesse system of DTV but i am seeing that the bad weather conditions affects to the signal quality of important way i use an rooftop antenna and gets those figures now, then would be worst with an indoor antenna.

any idea would be welcomed

best regards
Francisco
 

Tim58hsv

DTVUSA Member
#2
The weather does strange things to ota television reception and I don't really understand it myself. There's a station I pick up that has a very weak signal around here and it can go from around 70% signal strength to 30% in most any kind of weather conditions. Sometimes when the weather is nice the signal drops, sometimes when it's storming the signal stays high. Other times it's the exact opposite. I've heard atmospheric pressure has a lot to do with reception but I don't understand how or why so...
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#3
Francisco,

Do your TV "strength meters" report signal strength or quality of signal, as most do in the US?

I know in some instances rain soaked land can become an unpredictable reflector for RF signals, causing multipath signal reception. One possible remedy is to tilt the front of your antenna upward by (no more than) 10 degrees.

Jim
 

scandiskwindows9x

Moderator of DTV Latino
#4
well my set top box shows the signal strenght in percentage, my other set top box that is connected in HDMI2 have both meters signal quality and signal strenght ,

yesterday was reading about what happened in Spain , with the DTV there, well they uses the DVB-T system is basically almost the same than ISDB-T uses both COFDM modulation in the QAM 64 quadrature constellation , well in Spain in summertime the TV channels on DTV disappeared and found the explanation is two phenomens to consider .

the Fading effect occur when the heat and sea water that is getting evaporated and turned in mist creates a mirror effect over COFDM signals and the signal bounce back to the transmitter, this phenomen is caused by the heat. but is not the case because the temperature was here about 3°C /37°F and well is really unexplainable.

what are the chances that the rain cause signal attenuation?

i have read that the System of DTV DVB-T with an intense rain gets the signal lost or pixellations, as our System is based in COFDM can share the same defects than DVB-T

i really i do not know

suppose that the transmitter is located in the San Cristobal Hill in the town of providencia that is the highest place to locate and put an transmitter and i really i do not understand maybe if start to analyze what happen in a rainy day with the climate and the phenomens that occur in the environment maybe could get some conclusion, the only channel that kept the 100% of signal strenght was the channel 13.1 and 13.2, was reading and in test made in China with ISDB-T reported problems of reception using QAM 64 with indoor antennas and changing by QAM 16 the problems gets solved somewhat , also they report that is a Tidal fading too when cross peninsulas.

but already do not understand fully the core of the phenomen.
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#5
Francisco,

I receive KVOS-12 (35) which is 75 miles away from me and its signal rides over at least 25 miles of salt water to get here. When it was an analog signal, its strength changed dramatically with weather fronts that passed between their transmitter and Seattle: because digital signals here are 'quality' rather than strength based, I can only rely on the meter built into my TV set, but I "read" it as acting exactly the same way: sometimes there appears to be 'no signal' to be received. The diagnostic screen also shown BER and S/N ratio and when all reports drop to zero, that tells me (accurate or not) something is blocking the signal from me.

In the analog days I had to endure every large ship that passed thru Elliot Bay because they acted as signal reflectors: during extreme low and high tides, there were times that some channels were unuseable OR I received excellent reception: now with digital signals, I have seen absolutely no changes with passing ships or tidal changes.

I currently receive an analog LP translator from across Elliot Bay K62FS and I experience the same signal fading when strong weather fronts pass by: that station has a CP (construction permit) to move from real channel 62 to real channel 51, digital. It will be interesting to see if weather and tides interfere with its reception.

Here are two links with maps of the region that will help explain the terrain.

Jim
-----------------------------------------------------------------------
KVOS-12 (35)

Click VIEW MAP: I am on the 41 dBu ring.

http://cdbs.recnet.net:8080/fmq.php...&cmd=_s-xclick&hosted_button_id=A9BGM3QRPYT4C
----------------------------------------
K62FS-62 (soon to be 51)

Click VIEW MAP on the first (analog) listing: I am well beyond the 64 dBu ring.

Click VIEW MAP on the second (digital) listing: I am on the (anticipated) 41 dBu ring.

http://cdbs.recnet.net:8080/fmq.php...&cmd=_s-xclick&hosted_button_id=A9BGM3QRPYT4C
 

scandiskwindows9x

Moderator of DTV Latino
#6
interesting, i could not even get those figures , my converter box only shows quality in % do not show me the BER and S/N ratio, i wish have some machine to do those measurements, i am at 8,9 km from the transmitter, i already do not know the characteristics of the transmitter,

is something funny the transmitter is located but with obstruction in LOS is between some trees, so i am getting crazy or the brazileans that are working here are really stupids

where is a tv logo is the transmitter , the COFDM signals gets weaker with multipath not strong so not comments.

i would love to get such information of the experimental broadcasts in Santiago, would be useful as for think in why some things happens

well maybe am going too far in this

of anyway the 8 VSB modulation of ATSC would made less prone to Fading the signal due the pilot signal, ours just scatter thousand of carriers with Guard intervals and lets hope one carrier arrives to the receiver to be processed.


also well the power of broadcasts are very low as for a large city as Santiago, also i think when the ERP get increased would happen some problems by multipath, yesterday was reviewing the ISDB-T paper and there considered for indoor reception too the attenuation by the signal pass over the walls of a house were of 8Db aproximatelly., 8 Db sounds crazy.

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