Has anyone had problems with a C-band LNB acting up in cold temperatures?

[ancient]

I'm having kind of a weird issue and I'm not sure if the problem is with the LNB's or what. I have more than one C-band dish, each fixed on a specific satellite, and each has a dual LNB. The LNB's are of two different brands. One is an older model, which just so happens to be on my smallest dish, and it performs flawlessly in all weather and has done so for several years. The other type is a newer model. I should note that these are all modern style LNB's that use voltage switching for polarity; none are of the older type with mechanical polarity switching.

The thing I have noticed with the newer ones is that sometimes when it is really cold out (below around 20 degrees F) channels will come in really flaky, in that they have a lot of interference, purple lines or mini breakups in the signal, occasional small gaps in the audio, that sort of thing. You can watch the program but it is not a pleasant experience.

Last night I stumbled across something weird though. As it happened I tuned in a channel on the other side of the LNB, in other words, same satellite but different transponder while it was in the process of recording a program off the same satellite. And when I watched the playback of the recording, I noticed that all the interference cleared up right around the time I had tuned in that second channel and didn't reappear for the rest of the night. Now that could have been sheer coincidence, but it also made me wonder - I would imagine that when one side of the LNB is in use it generates a small amount of heat, but when both sides are in use a lot more heat is generated. Could the circuitry in the LNB have a thermal issue, where it's not happy until it reaches a certain temperature, and causes interference if the temperature is too low?

I only viewed that other transponder for about five minutes but unless it was just coincidence, the mere act of using the other side of that LNB seems to have cleared the interference on the first tuner, and I have not seen this issue occur when it's not several degrees below freezing. I wish I could get some more of those older dual LNBs (the ones sold about five years ago give or take a couple, I don't remember who made them but it was NOT DMS International), they seem to work reliably no matter what but nobody seems to have them anymore. Now I'm trying to determine whether I have a defective LNB, or if this is something common to the newer ones - has anyone else seen this particular problem?

 

[Titanium]

Next time the signal starts breaking up, take note of the current transponder frequency then delete the transponder. Blind scan the satellite. Is the new logged transponder frequency different? If so, how much higher/lower?

As DRO type LNBs age, the LO frequency often drifts. Temperature extremes will increase the amount of frequency drift. Likely the LO frequency is drifting during the temperature extremes and the receiver AFT (Automatic Fine Tuning) is able to track it to a point until the errors become to great or the tuner locks on another adjacent carrier.

 

[ancient]

Next time the signal starts breaking up, take note of the current transponder frequency then delete the transponder. Blind scan the satellite. Is the new logged transponder frequency different? If so, how much higher/lower?

That is an interesting thought and you may be right but unfortunately I don't have a receiver with blind scan. These LNB's all feed into TBS tuner cards and then into a PVR backend. And it all runs under Linux (just a server, no desktop) which I barely understand. I have heard that there are ways to run blind scanning software with those cards, but you either have to be running Windows and I don't have ANY computers that run Windows, or you have to install someone's special build of the operating system or special software that requires a considerable amount of Linux expertise to install. I can barely get the stupid TBS drivers installed and I've even messed that up before, so I'm not going to try to hack the operating system to install blind scanning software. And also, the blind scanning software I have come across is generally command line driven, which makes sense on a server with no desktop or GUI, but you have to know exactly what parameters to give to it and what I have found is a lot of times Linux guys write documentation for other Linux guys, and not for people who have never used anything like their software before and are just trying to figure out how to make it work.

In other words I think it would be a massive headache for me to set up blind scanning software on that machine, unless you know of something that can be easily installed under Ubuntu server and that does not require a lot of Linux knowledge to use.

I have just always manually programmed in the frequencies of the various transponders I want to receive, using an online source such as Lyngsat or from various forum posts, and it never really occurred to me that there might be a frequency shift. Once you have created a mux in the PVR software you can't just change the frequency on it to go up or down a little; if you do you have to delete the channel and re-add it, otherwise it will keep using the old frequency. Otherwise I could easily try one MHz lower, one MHz higher and see if going one way locks in the channel and the other loses it completely. As it is I can't really think of any easy way to try going up or down in frequency to see if it makes any difference. If I am going to try something like that I will probably do it on a weekend, not when I have things scheduled to record in an hour or two.

If you don't mind me asking, is this frequency drift an issue you've encountered before with any of the LNB's you sell or have sold in the past? I'm just curious whether this is a common problem.

 

[Titanium]

All LNBs experience thermal drift of the LO (Local Oscillator) frequency. Good quality DRO and PLL units drift less and this is one of the specifications that a factory presorts when qualifying the LNB hardware. As a DRO type LNB ages, the component values change and tuning slugs mechanically shifts. Often I run across quality LNBs with very little drift even after 20+ years.

As the TP frequencies are manually inputted in the software list, the frequency might be offset from the LNB IF to start with.

Sounds like your set-up makes it difficult to troubleshoot or even find new channels. That config would drive me crazy! Maybe time to buy a cheap DVBS2 receiver for troubleshooting?
or
Install dual boot OS or get a Goodwill cheap desktop running Windows so you can easily run software such as EBSpro or other user friendly software.

 

[ancient]

Sounds like your set-up makes it difficult to troubleshoot or even find new channels. That config would drive me crazy! Maybe time to buy a cheap DVBS2 receiver for troubleshooting?
or
Install dual boot OS or get a Goodwill cheap desktop running Windows so you can easily run software such as EBSpro or other user friendly software.

Well I do wish I had the capability, but I don't have any systems running Windows, therefore no copy of Windows to install even if I knew how to set up dual booting, which I don't. Getting a separate computer wouldn't help because I'm not going to start swapping cards between machines. EBSpro looks like interesting software, too bad they don't have a Linux version, although the fact that it's a GUI-based program means it would not work on a server with no desktop anyway.

I did a little searching and came across this article: How to do DVB-S2/S blindscan on Linux, which says "There is already blindscan capability in TBS Linux driver,but to make full use it, you need to write a ‘shell-script’ which consists of several simpler steps." It ends by saying, "Since not so experienced linux users will have difficulty in writing this “shell-script” by themselves, TBS will prepare such ‘shell-script’ and include it in the next driver release for easy use of every Linux user." But if they ever did this, I don't see it in their drivers package. I do see two programs:

- szap-s2.tar.bz2 (szap tool compatible with new DVB-S2 aware S2 API for Linux)
- scan-s2.tar.bz2 (scan tool compatible with new DVB-S2 aware S2 API for Linux)

But as best I can tell from the README (which is really confusing to me) it appears that scan-s2 will only scan frequencies from a predetermined list for whatever satellite you are attempting to scan, also it appears it has to be built and then you have to figure out exactly what options to use. Not even remotely as easy to use as the Windows program. There are also Linux programs not specific to the TBS cards, called scan and dvbscan, but they appear to have the same limitations other than that they do not need to be built, at least under Ubuntu, I think you just have to install the dvb-apps package. The thing I don't understand about all those programs is if they will only scan the frequencies in a predetermined list, which is how it appears from the limited documentation provided, what good are they? You're trying to find new channels or determine the correct frequencies, not just scan frequencies you already know about.

Anyway thanks for the response, I don't know if frequency drift is the problem but I guess it is something to consider.

 

[BigRyan]

Could you just manually enter the transponder and frequencies at + or - say 10 or something and see if the signal improves at all? since you don't have blind scan and you enter them manually, I would think manually entering is your best troubleshooting method at first. Maybe enter them incorrectly on purpose in both directions and see if it changes the signal.

 

[ancient]

I thought of that. There are two problems with that approach. First, it's a very intermittent problem that only occurs sometimes, so the trick would be to catch it while it's happening and not when you go to watch a recording two hours later or the next day (by which point the problem has often disappeared for the moment, possibly because the LNB finally warmed up?). The other problem is that the backend software makes this a difficult task, since you can't just change the mux frequency and have it automatically applied to all channels on that mux. Instead, after editing the mux frequency you'd need to delete the channel, delete the service, and then rescan the mux, remap the service, and find the new channel. Also, when you say up or down by 10, isn't that a pretty huge jump? If a transponder is at say 3800, just to pull a frequency out of thin air, I would think that going to 3810 or 3790 would be too much; I don't know what how close to the frequency the tuner needs to be to lock but on a typical LNB but wouldn't you want to first try increments of 1 or 2, for example 3802 or 3798?

The other thing I have wondered is I sometimes see people touting these expensive satellite meters with digital displays that would possibly provide this type of information, and those are fine if you are a satellite professional that uses such an item several times in a week. But I have wondered if it would be possible to make a poor man's version using something like a raspberry pi and a USB DVB-S2 tuner, or even by connecting a UBS tuner to an Android-based tablet or phone and running an app, assuming the tablet or phone has an active USB connection and you can find an adapter to connect to the mini USB connector on those things. I am just thinking out loud here, I have no plans to try and build such a device, not that I would have the slightest idea how in the first place. But, last week I was talking to a guy I know from way back in High School who is now a ham radio operator and he was telling me how the ham community is embracing Raspberry Pi's and in some cases tablet computers to perform functions that in the past would have required some piece of expensive and/or complicated hardware device, and usually at a very significant cost reduction. So I am just throwing that thought out there, not expecting anyone to rush off and build something, but just planting the idea and if it's already been done, I apologize but I am unaware of any such thing.

 

[Titanium]

Several of us on SatelliteGuys have Pi2 / USB DVBS2 systems running various software for the past year. Quite a long SatGuys thread on the projects.

UpdateLee has provided great support for UpdateDVB on the Pi2. There is an active thread on Ricks site .

Haven't gotten around to loading Win10 on the Pi2, but I was thinking that it might open the DVBS software options and ease of operation for more hobbyists.

 

[KE4EST]

Go grab a glass of your favorite beverage and have a read in this thread: http://www.satelliteguys.us/xen/thr...-receiver-raspberry-pi-2.346824/#post-3618133