Why does passthrough improve signal quality? (1 Viewer)

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trinidex

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So I have 2 receivers connected in series, LNB to #1, Passthrough of #1 to #2

I've noticed that if I feed #2 directly from the LNB the signal quality is lower by 5to10% than if I go through #1 !

Why is that?

Is there a device that will boost the quality?
 
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SatelliteAV

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I have always experienced the opposite. Pass-through ports usually degrade the quality.

Maybe the tuner in receiver one has a bandpass filter that cleans up some garbage noise in the signal before passing it to receiver two? The lack of noise can help provide a better signal to noise ratio and result in a higher BER (Signal Quality Reading). Easily determined if you have access to a spectrum analyzer.

Low quality can be the result of many variables. Any method that will increase the ratio of desirable good signal over the undesirable noise will provide increased Signal Quality. Examples: Larger dish, quality LNBF, quality cable, quality receiver / tuner, filters, and rarely a quality amplifier.
 
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AcWxRadar

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Apr 26, 2006
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40 miles NW of Omaha. Omaha?
SatelliteAV;2175058 Maybe the tuner in receiver one has a bandpass filter that cleans up some garbage noise in the signal before passing it to receiver two? [QUOTE said:
Hmmm? I had not thought of this. I thought it was almost a
straight through connection. More or less a repeater station. But, if the path reduces the noise in the process, it would be a blessing and an accidental attribute.

RADAR
 

B.J.

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Oct 15, 2008
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Western Maine
I originally thought that these passthru things were similar to splitters, ie pretty much a direct connection to the slave receiver except for DC block in at least one direction. However this does not seem to be the case. I think most of these tuners have some degree of amplification, and they are not at all "a
straight through connection".
Another thing that is obvious, is that different tuners are very different. The passthrus in some tuners seem to not only pass RF when the master is turned off, and some people report even passing the DC to power LNBs, while the passthru's in other tuners seem to go completely dead when the master is turned off.
Re to quality improving through the passthru, I have seen both better and worse through a passthru. I have also seen situations where one receiver will improve and another receiver will get worse when connected to the same passthru.
It seems logical that quality would always get worse with each step down the line when using passthrus, and that IS what I've normally observed, however in the cases where I've observed the quality improving, my suspicion (ie wild guess) is that the power supply in the slave receiver may be of poor quality, and when it's forced to actually power the LNB, that the signal from the LNB is of worse quality vs when the master receiver powers the LNB, if the master has a cleaner power supply, it might mean that better signal is coming from the LNB. In some cases, it could even be that the slave power supply isn't even good enough to provide adequate power to the LNB.
Anyway, although signal filtering might be involved, or even the master being somehow a preferred path for the noise due to differing impedances, or perhaps some form of the FM capture effect coupled with the amplification making the real signal predominate........... I really think that this is a power supply issue.
 

trinidex

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Interesting stuff!

Rcvr #1 still passes power to the LNB when in Standby - it retains the same polarity as when it was switched on.

Power supply is interesting, if that were the case, I could easily power my LNB with a separate injector setup - worth a go!
 

SatelliteAV

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Interesting stuff!

Rcvr #1 still passes power to the LNB when in Standby - it retains the same polarity as when it was switched on.

Power supply is interesting, if that were the case, I could easily power my LNB with a separate injector setup - worth a go!

  • Try turning off the Master Power Switch on the rear of the receiver and see if Receiver #2 voltage can pass through to control polarity.
  • If Receiver #1 has a TV/STB button on the remote, this may allow tuner bypass (I.E. Fortec Star Mercury II) while in Standby or even in Operate mode.
 

TMair

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Jan 12, 2010
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Midway, Utah
My receiver #2 is terrible even with #1 off, and if I have 2 off but the power swith in the rear on I can only use one polarity on #1, I think I am going to use an a b switch from now on, I think I will still have to turn the rear power off on #2 just to make sure I dont fry my disec switch, but the quality I think will be better.
Terry
 

Tron

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May 6, 2005
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Metro New Orleans, LA
The Visionsat IV-200 will not pass loop through signal if the receiver is powered off from the rear switch. It will if the unit is in standby. That indicates some form of processing is happening within the receiver, or perhaps there is only a relay (doubtful).
 
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