Higher FEC Preventing Reception

[cyberham]

Today on 103W SES3 Ku, I was able to compare two NBC signals simultaneously:

Signal 1: DVB-S2 (8PSK) FEC 3/4 4600 kbps (NBC feed)

Signal 2: DVB-S2 (8PSK) FEC 5/6 20000 kbps (main NBC tps)

Though at a low SQ, I could lock Signal 1 and it was perfectly watchable. I could not (and can never) lock Signal 2 with my current 1m dish.

Technically, minimum lock threshold value for Signal 1 is 7.9 dB. Minimum lock for Signal 2 is 9.4 dB.

Am I correct to assume if the received signal into the LNB was 1.5 dB higher, then I could lock Signal 2? I assume the higher SR is not a factor for this.

A 1.2m Ku dish supposedly has a gain advantage over a 1m dish of 3 to 5 dB at Ku. Therefore a 1.2m dish would solve the above 1m dish results. This agrees with personal experience since a 1.2m dish has in past received the NBC tps.

Is there no simpler way to get just an extra 1.5 dB? This is very small. Loss of cable from dish to receiver is not a factor as this is a constant for both signals which follow the same path. I've also tested right beside the dish and had similar results.

Might a better receiver make a difference? In other words, would a better receiver be able to lock a lower signal such as received in the Signal 2 situation?

Why is a higher FEC used? Is it because a higher FEC transfers information faster which increases efficiency and reduces costs?

Sent from my SM-G950W using the SatelliteGuys app!

 

[Titanium]

Feed link budget, temperature, terrestrial noise threshold, reflector efficiency, feed placement, reflector illumination, cross polarity separation, conversion amplification noise, attenuation in coax type and length, switches, fittings and receiver sensitivity.

It all adds up... SNR (Signal to Noise Ratio)

Link budgets are based on the signal reliability based on cost, downlink hardware, location, etc.

While a hobbyist may attempt to gather enough signal to decode, the link budget downlink hardware choice is based on overbuilding to provide X amount of signal headroom above the base and extreeme signal attenuation factors to provide X percent of signal uptime.

 

[cyberham]

I know it's a complex subject. So I'm trying to understand why one signal versus another coming from the same satellite under identical conditions can be received whereas the other can't.

Many of the factors you mention are the same for each signal: temperature, terrestrial noise, reflector efficiency, feed placement, reflector illumination, amplification noise, coax attenuation, switches, fittings, receiver sensitivity. These are all the same for both signals.

The unreceivable signal is H polarity whereas the receivable one is V polarity. 11760 MHz does seem to be a common signal on satellites for data signals. I notice 105W has a strong data signal on 11760 MHz. I've wondered if it could be interfering with the desired signal of 11760 MHz on 103W, especially when using a smaller dish close to the edge of the satellite's footprint. But the 105W signal is on V polarity anyway so I doubt.

 

[Titanium]

I was primarily responding to how to have an increase in SNR or be able to lock with a lower SNR.

The higher the FEC, to more good data vs corrupted data must be received to play out the service.

An adjacent signal interference would need to overlap all or part of the target transponder's frequency range. Knowing the center frequency and the bandwidth of both carriers determines if there is overlap.

Cross pol separation is primarily a function of proper feed skew, but it could also be affected by improper FD and convergence point FL setting, parabola imperfections and feed design.

If using a voltage polarity switching LNBF, performance and specs are likely to be different for each polarity. The reflector efficiency and feedhorn design may favor one polarity over the other.

Many things that you view as being the same can be quite different. Just because both transponders are from the same satellite doesn't mean they are identical. Polarity variables with satellite hardware and geo/ionispheric disturbances, transponder receive/transmission hardware and electronic variables, uplink encoding/amplifiers/tracking, link budget, etc.

 

[primestar31]

Eliminating excess length of coax, or devices, (switches/splitters/positioners) between the receiver and the lnb is always useful, and can make useful gains. Doing a system tune-up in general is quite useful, replacing long RG-6 with RG-11 alone might get you 1.5db gain.

However, NOTHING beats getting good PASSIVE gain more than a larger antenna. IE, in this case, a larger dish. If you really want to go for it, find a 6 foot offset Prodelin dish in your area. They are around at gas stations and the like for internet uplinks. Tell EVERYBODY you are looking for one, and perhaps you'll get one.

 

[a33]

FECs and needed CNR:
Does this help:

Satbroadcasts.com - no. 1 source for professional work

www.satbroadcasts.com

There's also a graph somewhere on the internet showing data like these; cannot find that right away though.
Edit: here, pag 13 and 14.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwiFz5nxov_oAhVMnaQKHb-nAzQQFjAAegQIARAB&url=https%3A%2F%2Fwww.satelliteguys.us%2Fxen%2Fattachments%2Fdvbs-2_guide-pdf.33411%2F&usg=AOvVaw3lOZD3WMKipycZeC2Lj_Nw

Don't know if it could be found without the google-interference in the webpage-address? It seems to be on this forum....

Greetz,
A33

 

[cyberham]

Eliminating excess length of coax, or devices, (switches/splitters/positioners) between the receiver and the lnb is always useful, and can make useful gains. Doing a system tune-up in general is quite useful, replacing long RG-6 with RG-11 alone might get you 1.5db gain.

However, NOTHING beats getting good PASSIVE gain more than a larger antenna. IE, in this case, a larger dish. If you really want to go for it, find a 6 foot offset Prodelin dish in your area. They are around at gas stations and the like for internet uplinks. Tell EVERYBODY you are looking for one, and perhaps you'll get one.

All good advice. Though these suggestions are about reducing loss en route to the receiver. I think I need extra C/N at the LNB to be able to pull in the troublesome NBC tp. A better LNB might help with that. Or simply a 1.2m dish. If I went all the way to a 6-foot dish, I'd be doing C-band!

 

[cyberham]

FECs and needed CNR:
Does this help:

Greetz,
A33

I was able to download the doc. I'll take a read through. The charts of DVB-S and DVB-S2 against their C/N values for different FEC are bookmarked on my PC and phone already. Did you know that using DVB-S2 with QPSK allows you to lock at a lower C/N than using DVB-S QPSK? I didn't until I studied the charts.

 

[comfortably_numb]

Did you know that using DVB-S2 with QPSK allows you to lock at a lower C/N than using DVB-S QPSK?

I think you meant 8PSK in the second half of your sentence

Personally I don't recall seeing many DVB-S2 QPSK feeds anymore. Seems like most are DVB-S2 8PSK, and we're starting to see 16PSK feeds creeping in....

 

[cyberham]

I meant it as I wrote, though I could have added "for a given FEC".

For example:
DVB-S: QPSK, FEC 3/4: C/N lock is at 5.5 dB
DVB-S2: QPSK, FEC 3/4: C/N lock is at 4 dB

I always thought DVB-S2 was harder to lock but not so. It was just a technical observation after looking at the charts. I don't know if there actually are any DVB-S2 QPSK signals. I mostly see DVB-S2 8PSK.

 

[comfortably_numb]

I meant it as I wrote, though I could have added "for a given FEC".

For example:
DVB-S: QPSK, FEC 3/4: C/N lock is at 5.5 dB
DVB-S2: QPSK, FEC 3/4: C/N lock is at 4 dB

I always thought DVB-S2 was harder to lock but not so. It was just a technical observation after looking at the charts. I don't know if there actually are any DVB-S2 QPSK signals. I mostly see DVB-S2 8PSK.

Sorry, I misread what you wrote- I thought you were saying it's easier to lock DVB-S2 QPSK than it is DVB-S2 8PSK.

 

[Martyn]

Is there no simpler way to get just an extra 1.5 dB? This is very small.

Interesting discussion. I think FEC is too often missed in discussions about satellite reception.

Unless I calculated it wrong, 1.5dB is about a 40 percent difference in signal, so it is quite a lot.

Luckily, a 1.2m dish has about 40 percent greater area than a 1 meter dish.

Why is a higher FEC used? Is it because a higher FEC transfers information faster which increases efficiency and reduces costs?

Less wasted bandwidth. Why use one in every 4 bits for error correction when you can use 1 in 6. Because broadcasters use larger dishes, they can get away with less error correction. That it makes it more difficult for hobbyists to receive is probably an added benefit but not something that influences the decision.

 

[cyberham]

FEC is interesting since it is critical in determining if a hobbyist can receive a signal or not.

I said "just 1.5 dB" improvement but that may not be so anyway. I assumed the signal I was locking was at minimum lock level. It could be higher. So the difference between the signal that can be locked and the other one could be even higher.

When weather warms, I'm sure I won't be able to resist pulling my slightly damaged 1.2m from its fixed duty on 123W and re-installing it back on the motor at 8-feet high as it once was. It's just a bit of work. Previously, I could lock everything on the NBC mux with that configuration.

Sent from my SM-G950W using the SatelliteGuys app!

 

[Martyn]

The meter that Titanium sells is great for this. You get all the measurements of the signal and it's great for peaking a dish. Also makes finding a signal super easy as you have the spectrum scope and you can easily visualize transponders from adjacent satellites and whether they might interfere. If you can afford it, I recommend getting one.

 

[cyberham]

That's a good tip. I now use a GeosatPro microHD receiver which has an excellent almost full screen bar graph that's easy to see (and hear) from a distance. On that portion of the arc, there are signals on 101W and 105W as well as other strong signals on 103W so finding where the the NBC tp is located is pretty easy.

Also, even with the current 1m dish, there is a noticeable "bobbling" of SQ as appears just prior to lock when aimed at the tp in question.

My bigger desire would be to source a new Edision Mio. But that will wait for now.

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[comfortably_numb]

Using Facetime with 2 iPhones (or iPads) works great for dish pointing as well. Put one phone in front of the TV with signal meter displayed, and take one outside with you

 

[cyberham]

I do similar if lazy or if bad weather. I use VNC software on PC, point PC camera at TV screen in the house, then use a VNC app on my Android phone with wifi. It's OK but receiver and a little TV monitor at the dish is much better method. Also, had to install a wifi extender (from my junkbox) to get wifi coverage down near the dish.

Sent from my SM-G950W using the SatelliteGuys app!

 

[Brct203]

Using Facetime with 2 iPhones (or iPads) works great for dish pointing as well. Put one phone in front of the TV with signal meter displayed, and take one outside with you

I've done that, also tried with Skype. The delay was a bit annoying though. Now with my OSMIO4K I use e2remotelite on my phone. It's definitely not perfect, but a lot nicer to bring up on the roof than a tv and receiver

About the topic of FEC and whether or not one can lock a signal, well, like Brian indicated, there are many factor in the transmission budget. One fact that is important to remember is that not all transponders on the same satellite, same beam, transmit with the same signal strength. That's one factor. Then the modulation is another. Then the FEC. also the uplink signal quality. Do they have phase noise? are they uplinking with a garbage can cover (I'm exagerating of course, but not all uplink stations are the same).

As a result, on some satellite, there are transponders we can easily lock and others that are more tricky. For me, 43W is a perfect example, many channels that I get (and don't watch), but the ones I really want, I can no longer get as their signal strength dropped a bit and they are on an 8psk 30000 5/6 transponder, so not particularly forgiving.

Now an interesting observation, in some cases, where you have a Direct-to-Home service, not all transponders use the same modulation and FEC.
DN and Bell use a mix of 8psk 2/3 and QPSK (5/6 or 7/8?) on the same satellites
Canal Caraibes on 34.5W has some transponders using 8PSK 2/3 (6.6 dB to lock) and others using QPSK 5/6 (5.2dB to lock). That's quite a difference (1.4 dB).