Question About Side Lobe Interference

[wvman]

Brian, I have a question. The other day we were discussing a group of channels that just went off and it was decided that it was possibly side lobe interference. For no apparent reason, I lost the signal on those channels. Later, they came back on without me doing anything to the dish. Last night, I lost all the channels in the Luken MUX.

Today, they're back on. Last evening, I unhooked the cable going to my switch and checked the signal at the switch. The signal bounced in and out, just like the other channels we spoke of earlier. This has happened within the last three or four days on 101W and now on 87W. I'm not quite sure what's going on since the problem migrated from 101W to 87W.

I understand about side lobe interference, but isn't it a bit strange that it would happen on two satellites so far apart. I always had a great signal on the Luken MUX since they moved from 101W to 87W. I would think if it's a side lobe problem, wouldn't it be an ongoing problem instead of an intermittent problem. What's your take on it?

 

[mikekohl]

At this time of the year, I would look carefully at the possibility of drifting and/or erratic operation of LNBs and LNBFs from extremely cold temperatures. Cheap C- band LNBFs can easily be 4 or 5 MHz off frequency when it's below zero. If you scanned in your transponders when temps were more normal, there may not be enough leeway to lock them in when the LNBF is oscillating off the deep end. If you are certain things are on the satellite, do a blind scan and see if the Luken Mux shows up, but at a slightly different frequency, perhaps 2 or 3 MHz away. I also do not remember Luken ever being on 101 West...they were on 87 West, and then moved to 83 West last year. If moved back to 87, it would be news to me.

 

[danristheman]

Luken mux went to 101w for a short time do to the loss of amc 9. I have noticed at certain time midnight to 2 am lesea channels go out then come back. I noticed i have a minibud dont remind me.

 

[wvman]

At this time of the year, I would look carefully at the possibility of drifting and/or erratic operation of LNBs and LNBFs from extremely cold temperatures. Cheap C- band LNBFs can easily be 4 or 5 MHz off frequency when it's below zero. If you scanned in your transponders when temps were more normal, there may not be enough leeway to lock them in when the LNBF is oscillating off the deep end. If you are certain things are on the satellite, do a blind scan and see if the Luken Mux shows up, but at a slightly different frequency, perhaps 2 or 3 MHz away. I also do not remember Luken ever being on 101 West...they were on 87 West, and then moved to 83 West last year. If moved back to 87, it would be news to me.

I'm running all Titanium LNBF's. No cheap LNBF's on any of my 5 dishes. However, I did consider the possibility of drift considering the Luken channels came back on today after it warmed up, and went off again shortly before 5PM. I just checked them and they are still off. Can't do a re-scan right now, recording a movie. I did consider it drifting off frequency as it is 5 below zero here right now.

However, I'd be surprised if a Titanium LNBF was off frequency, but it is possible. I am reasonably sure the dish is still on the satellite since it has a lock down bar on it. It would have to bend the bar to move the dish and we have not had winds high enough here to do that. If the temperature is affecting it, I may end up putting a heating tape around the LNBF. I do not want to mess with changing it in these temperatures, especially since I've had my toe operated on twice and it's not healed good yet.

I appreciate the info. My movie is about done recording and I will re-scan after it's done. Thanks again.

 

[Titanium]

Since you are using fixed dishes and not a single motorized, I would suspect interference rather than multiple random LNB failures. I also base this on your multiple reports of problems locking many channels on different satellites with different dishes over the past year.

PLL LNBs are crystal referenced and unless the circuit is damaged, the frequency drift is typically less than 20KHz within 1 minute of power application. Temperature variations of +/- 50f would not shift the frequency beyond 10-20KHz. The auto tuning circuitry of the set-top box would easily correct +/-3 - 5 MHz on these fat TPs.

Losing one fat transponder and not another on the same satellite would indicate that the LNB LO frequency is not drifting.

 

[wvman]

Since you are using fixed dishes and not a single motorized, I would suspect interference rather than multiple random LNB failures. I also base this on your multiple reports of problems locking many channels on different satellites with different dishes over the past year.

PLL LNBs are crystal referenced and unless the circuit is damaged, the frequency drift is typically less than 20KHz within 1 minute of power application. Temperature variations of +/- 50f would not shift the frequency beyond 10-20KHz. The auto tuning circuitry of the set-top box would easily correct +/-3 - 5 MHz on these fat TPs.

Losing one fat transponder and not another on the same satellite would indicate that the LNB LO frequency is not drifting.

Weather is as weird as this problem. We had a heatwave overnight. Went from 5 below to 20 degrees this morning. My neighbor stopped in a few minutes ago on his way to town. He went outside to check a couple things at the dish. When he came back in he grabbed my toolbox and went back outside. When he came back in he was carrying two F-Connectors. We plugged everything back and fired it up and all the channels were working. As it turned out, both connectors had failed where the nut attached to the body of the connector.

We both remembered having this problem with connectors several years ago, and I thought we had weeded out all the connectors from that batch, but apparently we missed a few. When we discovered the problem, they always broke off when tightening down the connector. Wasn't the case with these. When time and weather permits, we're going to change all the connectors in the system to avoid this problem again later. this would explain the problems I was having all along.

It seems the possibility of having another one somewhere in the system is likely. When you buy connectors by thousand lots, it's hard to keep track of which ones were bought when. Anyway, thanks for the input and help. I can always count on Brian and the rest of you guys to jump in help solve a problem. Have a happy new year gang, and thanks again.