Because of the 'garbage' that can come down from an antenna.. in my case a local fm radio station plays havoc with the signaling.. I have to run fm traps too..
SWM - Wy would we need diplexers?
There's been talk here about diplexers that are supported on SWM installs. I have to wonder why we need a diplexer instead of just a simple splitter for OTA installs on the IRD side. (On the switch side I get the benefits of the respective low pass/high pass actions for the OTA and Satellite signals. I'm specifically considering the SWM-8 with onboard OTA scenario.)
Here's the frequency breakdown based on the information I've seen:
5-40MHz - SWM back channel
54-806 MHz - OTA frequencies
950-2150 - SWM channels
Since these are different frequency ranges, why is anything more than a splitter required? I could see it being an issue if the OTA frequencies confused the satellite tuner (or vice versa).
If you were paranoid about voltages hitting the OTA tuner, you could use single or no power pass splitters. I'd likely do that, as I would be concerned about the IRD getting misconfigured and sending 18V/13V down the line thinking that it was driving a legacy multiswitch or LNB.
What am I missing?
(Apologies for the thread title typo - mods could you please correct?)
Here's the frequency breakdown based on the information I've seen:
5-40MHz - SWM back channel
54-806 MHz - OTA frequencies
950-2150 - SWM channels
Since these are different frequency ranges, why is anything more than a splitter required? I could see it being an issue if the OTA frequencies confused the satellite tuner (or vice versa).
If you were paranoid about voltages hitting the OTA tuner, you could use single or no power pass splitters. I'd likely do that, as I would be concerned about the IRD getting misconfigured and sending 18V/13V down the line thinking that it was driving a legacy multiswitch or LNB.
What am I missing?
(Apologies for the thread title typo - mods could you please correct?)
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I also know that when a receiver is connected to a line, on many occassions it first sends 13v/18v trying to detect what it is connected to. Especially if it's a receiver that never had a SWM connected to it, I believe it will power up in its last known state. Sending 13v/18v.
If you used a normal combiner or splitter that passed power, you might be sending some voltage to your TV's antenna inputs and that would be a huge problem.
If you used a normal combiner or splitter that passed power, you might be sending some voltage to your TV's antenna inputs and that would be a huge problem.
18 Volts would probably make an Antenna input very unhappy. It might even cry bits of slag inside the TVNR4P said:I also know that when a receiver is connected to a line, on many occassions it first sends 13v/18v trying to detect what it is connected to. Especially if it's a receiver that never had a SWM connected to it, I believe it will power up in its last known state. Sending 13v/18v.
If you used a normal combiner or splitter that passed power, you might be sending some voltage to your TV's antenna inputs and that would be a huge problem.
But that would be passed to the OTA side even with a diplexer. I can see going from antenna through a low-pass filter to get rid of any higher frequencies that got picked up by the antenna. From there, into the OTA input on the SWM.houskamp said:Because of the 'garbage' that can come down from an antenna.. in my case a local fm radio station plays havoc with the signaling.. I have to run fm traps too..
Basicaly a diplexer is a high and low pass filter.. it separates the 2 signal ranges as well as keeps the sat power off the OTA..ebockelman said:But that would be passed to the OTA side even with a diplexer. I can see going from antenna through a low-pass filter to get rid of any higher frequencies that got picked up by the antenna. From there, into the OTA input on the SWM.
and FM is not at one end or the other. it is smack dab in the middle\houskamp said:Basicaly a diplexer is a high and low pass filter.. it separates the 2 signal ranges as well as keeps the sat power off the OTA..
Right. I can see placing an FM trap inline prior to the SWM as well (if needed in your area).curt8403 said:and FM is not at one end or the other. it is smack dab in the middle\
Right. That's why I mentioned power pass splitters in the original post. If you used a splitter that didn't power pass or only power passed one side you would avoid this.NR4P said:I also know that when a receiver is connected to a line, on many occassions it first sends 13v/18v trying to detect what it is connected to. Especially if it's a receiver that never had a SWM connected to it, I believe it will power up in its last known state. Sending 13v/18v.
If you used a normal combiner or splitter that passed power, you might be sending some voltage to your TV's antenna inputs and that would be a huge problem.
So you split instead of diplexing, what are you going to get?
Well you're going to send a 900+ signal to your OTA tuner, which will go "WTF"?, I don't want that and send it back. This is called a reflection that will bounce back to the incoming signal and if out of phase, will reduce it's level.
The same would be for the OTA going to the receiver.
You want everything "matched" so the reflections are at a minimum. "The end" of every line should be something that the signal can be terminated in, be it a receiver tuned to that frequency or a resistor.
Well you're going to send a 900+ signal to your OTA tuner, which will go "WTF"?, I don't want that and send it back. This is called a reflection that will bounce back to the incoming signal and if out of phase, will reduce it's level.
The same would be for the OTA going to the receiver.
You want everything "matched" so the reflections are at a minimum. "The end" of every line should be something that the signal can be terminated in, be it a receiver tuned to that frequency or a resistor.
normal splitters do pass power, so there is no such thing as a non power passing splitterebockelman said:Right. That's why I mentioned power pass splitters in the original post. If you used a splitter that didn't power pass or only power passed one side you would avoid this.
Guess this would depend on your definition of "normal". "Normal" for a SAT system would pass DC.curt8403 said:normal splitters do pass power, so there is no such thing as a non power passing splitter
So what's this?curt8403 said:normal splitters do pass power, so there is no such thing as a non power passing splitter
http://www.thesatelliteshop.net/perfect-vision-8-way-non-power-passing-splitter-51000mhz-p-624.html
(Yes, I realize this one doesn't go up to 2150, but it was the first example that came up.)
So an OTA tuner will reflect the higher frequency SAT signals? Have you seen this happen?veryoldschool said:So you split instead of diplexing, what are you going to get?
Well you're going to send a 900+ signal to your OTA tuner, which will go "WTF"?, I don't want that and send it back. This is called a reflection that will bounce back to the incoming signal and if out of phase, will reduce it's level.
The same would be for the OTA going to the receiver.
You want everything "matched" so the reflections are at a minimum. "The end" of every line should be something that the signal can be terminated in, be it a receiver tuned to that frequency or a resistor.
I would also think that if the OTA frequencies reflecting back from the SAT tuners was an issue, a single box without the B-Band converter installed would be reflecting back and affecting other IRDs in a legacy system.
And they do.ebockelman said:So an OTA tuner will reflect the higher frequency SAT signals? Have you seen this happen?
I would also think that if the OTA frequencies reflecting back from the SAT tuners was an issue, a single box without the B-Band converter installed would be reflecting back and affecting other IRDs in a legacy system.
This is just the nature of RF transmission. The whole concept is a ratio of forward to reverse voltage/power. Fundamental measuring is VSWR for matching/impecdance of a line.
RF is pretty complex, I don't fully understand it. But you really can think of the different frequency ranges as if they were different wires. So one of these "virtual wires" can be terminated properly, unterminated, or even grounded (meaning no signal can be sent because it would go right into ground).
But you want each "virtual wire" to be properly terminated. The problem is you cannot tell what happens at the receiver, does it have a filter in it that will separate off the OTA "virtual wire" before receiving the signal? If so, then the OTA "virtual wire" will just end, unterminated. This is like leaving the end of the wire unconnected, and will reflect signal back. This is bad. Conversely, what does the OTA input on the receiver do? Does it leave the SAT "virtual wire" unterminated too?
No one here seems to know. You could put a network analyzer on it and see what it does. But in the end, it doesn't really matter anyway. Because if you use a splitter, you'll end up cutting the input signal down 3dB anyway, because you'll in essence create two ends to the SAT "virtual wire" and to ends to the OTA "virtual wire". Instead, a diplexer just separates the "virtual wires" from each other, allowing you to route each to the right place without any splitting, and no 3dB loss.
So even if you could make a splitter work in place of a diplexer, you'd be throwing away signal, and you don't want to do that.
But you want each "virtual wire" to be properly terminated. The problem is you cannot tell what happens at the receiver, does it have a filter in it that will separate off the OTA "virtual wire" before receiving the signal? If so, then the OTA "virtual wire" will just end, unterminated. This is like leaving the end of the wire unconnected, and will reflect signal back. This is bad. Conversely, what does the OTA input on the receiver do? Does it leave the SAT "virtual wire" unterminated too?
No one here seems to know. You could put a network analyzer on it and see what it does. But in the end, it doesn't really matter anyway. Because if you use a splitter, you'll end up cutting the input signal down 3dB anyway, because you'll in essence create two ends to the SAT "virtual wire" and to ends to the OTA "virtual wire". Instead, a diplexer just separates the "virtual wires" from each other, allowing you to route each to the right place without any splitting, and no 3dB loss.
So even if you could make a splitter work in place of a diplexer, you'd be throwing away signal, and you don't want to do that.
Even without the B-Band converter installed, it can be reflecting OTA frequencies back to the head. As long as your wires are relatively short, you won't necessarily notice, the reflected signals will be close enough in time alignment to the true signals to not cause problems. If you have long enough wires, you'll get multipath (edit: this is wrong, see below). In essence, it's the same as leaving the ends of a cable wire in your house unterminated, which people do all the time and still get signal through.ebockelman said:So an OTA tuner will reflect the higher frequency SAT signals? Have you seen this happen?
I would also think that if the OTA frequencies reflecting back from the SAT tuners was an issue, a single box without the B-Band converter installed would be reflecting back and affecting other IRDs in a legacy system.
If you have a receiver that doesn't use OTA, and you have OTA diplexed on, you should technically put a diplexer on there with a terminator on the OTA side.
I'm starting to wonder if I should put a receiver on a network analyzer and get a Smith Chart. I used to have access to a network analyzer at work. Then we would know if using a diplexer to separate and terminate like this is strictly necessary.
A "normal" satellite splitter passes power on one leg and blocks it on the other(s). There are other model satellite splitters that pass power on all legs, and some of them are "diode steered", so that if the voltages of the sources are different, there won't be any damaging backfeeds to any of the other components. I don't think I've ever seen a satellite frequency that blocks DC on all ports.
There are a lot of old satellite splitters that are rated 450-1,750 MHz. I have seen them wreak havoc on channels 4 and cable 17, so they cannot be used to diplex cable or even the full spectrum of broadcast, but I have never had any low frequency problems using satellite splitters that were rated 950-2,000(+) GHz. Of course, YMMV.
There are a lot of old satellite splitters that are rated 450-1,750 MHz. I have seen them wreak havoc on channels 4 and cable 17, so they cannot be used to diplex cable or even the full spectrum of broadcast, but I have never had any low frequency problems using satellite splitters that were rated 950-2,000(+) GHz. Of course, YMMV.
I would like a "do over" on my answer, and perhaps I can get it right this time. Not sure where my head was.
If you have an unterminated end (including because you didn't put a diplexer in with terminator before a box that isn't using OTA), you create what's known as a "stub". It's basically a piece of wire carrying an RF signal that isn't terminated. The stub runs from where the signal last split to the unterminated end.
A stub is two things.
1. It is a notch filter centered at C/(2*stub length) (I think). So, if you have a stub that is 10M long, you've created a filter centered at 30MHz. This will cut your OTA channel 2 signal down some.
2. It is also an antenna, it will radiate out all that lost energy into the air, so you'll be broadcasting at 30MHz.
You can in theory get what you really would consider multipath because of stubs, but they would have to be very long stubs, like over 1km I think. In practice, I don't think this ever comes into play.
So terminate those ends, even "virtual ends".
If you have an unterminated end (including because you didn't put a diplexer in with terminator before a box that isn't using OTA), you create what's known as a "stub". It's basically a piece of wire carrying an RF signal that isn't terminated. The stub runs from where the signal last split to the unterminated end.
A stub is two things.
1. It is a notch filter centered at C/(2*stub length) (I think). So, if you have a stub that is 10M long, you've created a filter centered at 30MHz. This will cut your OTA channel 2 signal down some.
2. It is also an antenna, it will radiate out all that lost energy into the air, so you'll be broadcasting at 30MHz.
You can in theory get what you really would consider multipath because of stubs, but they would have to be very long stubs, like over 1km I think. In practice, I don't think this ever comes into play.
So terminate those ends, even "virtual ends".
So if you worked with a N-A and know a Smith or two, you know that both open and shorts reflect. The first reflects voltage and the second reflects [180 out of phase] the current.flipptyfloppity said:I'm starting to wonder if I should put a receiver on a network analyzer and get a Smith Chart. I used to have access to a network analyzer at work. Then we would know if using a diplexer to separate and terminate like this is strictly necessary.
This is why "matching" is a load [which with SAT systems is 75 ohms]. Anything not 100% resistive 75 ohms, will at some frequency reflect.
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