Can cold kill one side of a C-Band LNBF??

[Mr Tony]

OK..this is weird

have a DMSI C-Band LNBF (ASC421 I think...its C-Band only) and the last two nights I have not been able to get the H side of it. Yes I have swapped cables.

Now here is where it gets weird. Its been -10 yesterday and tonight. I have a 6 foot Fortec dish that I wheel out of the garage because on the deck my LOS is AMC3-AnikF1 due to the roof so I brought it around to get other stuff
Wheeled it out and got the signal right away. Couple hours later the signal was gone (and confirmed still up). V side still up

Oh well I wheeled it back in the garage. Now this morning I took it back out and got signal. Couple hours later signal gone again. V side works fine.

So tonight I swapped to the old LNB that you need a analog box to control. Skewed it by hand (which when its -10 out you do pretty quick) and got H back to normal

Is it possible that the cold kills the H side? Like I say it works when I first wheel it out of the garage (the garage is probably 35 degrees) but a couple hours later the H side is kaput. Shows between 88-99 signal strength but 0 quality

 

[1inabillion]

yep i know the the cold weather will cause trouble with some Lnb i had.
i use a heat gun at times for a temp fix & heat tape works too

 

[voomvoom]

Maybe it's not that the H side isn't working, but that the voltage (13-18) isn't switching in the lnbf? Who knows?

Al

 

[gabshere]

i think it could go both ways
i have heard of cold zapping a lnb like that and also heard of cold bringing out bad connections too.

 

[photoman76]

I agree it might be a voltage problem. Have you checked it?
According to the specs vertical is 11.5 to 14 volts and horizontal is 16 to 19 volts. Perhaps the extreme cold is reducing the voltage at the lnbf and the voltage drops below 16 volts needed for horizontal polarity.

 

[DK_Sat]

LNBs work better on cold whether then hot whether it looks that the LNBF has a problem with voltage switching.

 

[Mr Tony]

I'm going to try today to see if its the LNB or a voltage thing. I'll wheel the dish out and aim at G16 to see what happens

 

[Mr Tony]

well I slapped the LNBF back on and aimed at G3 for the Equity mux which is H

77 quality so we'll see how long it holds. Temp is around -7 right now

 

[mikekohl]

A suggestion from the Siberian crowd:
Blind scan the satellite again.

Local oscillators tend to drift a lot when it gets below -20 F,
and I have repeatedly found, even with so-called "High stability"
C-band LNBs, which claim 500 KHz tolerance, can sometimes go
far enough out of tolerance that you may need to do a blind scan.
Some receivers may have problems if the channels are already in the memory,
and it might be necessary to delete them before re-scanning. Otherwise,
if you have a re-scan that turns up on a different frequency and symbol rate,
go back to the original TP, change the frequency to the newly scanned one,
and scan it again. As long as the blind scanned symbol rate is slightly off
(22001 instead of 22000) it should not trip the message TP already scanned.

All of this, plus the possibiity that your diode switch inside the LNBF is
not passing voltage higher than the 15.5 volt crossover point between
13 volts (vertical) and 18 volts (horizontal), could be reasons for what
you are observing. Should this be a constant problem, you might later
consider a dual port C-band feedhorn with separate LNBs and input them
separately into a DiSEqC switch located indoors so that it does not have
switching problems. In that case, a Power Inserter (Pico SPI-14/18 or equivalent)
keeping both polarities on hot standby at all times might be a good idea.

Don't freeze!

 

[Mr Tony]

Thanks Mike for the advise!

on Friday I kept doing a blind scan but couldn't get anything H polarity. Now I tuned the dish to G3 and its been 90 minutes and still a SOLID 77 on the Equity mux. All those feeds listed on lYngsat are across the board but I've flipped between H & V and it still is working.

must have been something last nite

 

[Mr Tony]

spoke to soon

2 hours later V is still pumping strong and H dropped like a rock to the threshold (65 on the Coolsat)

 

[Anole]

It's possible that the electronics that determine the voltage switching point are temperature sensitive, as suggested above.
You could check what that actual voltage is - maybe it's low from the receiver you are using?
You might test by putting this receiver on the loop-through output of a different receiver which could supply the selection voltage...

I guess you could take it apart and work on it (some cold spray should cause the problem to show on the bench).

You could send it back to the supplier.

Or, and this is my favorite...
Strap some 4w or 7w nightlight bulbs to the LNB.
Not only will you have the required heat, but a nice beacon , as well.
Wouldn't want any low-flying aircraft to run into your dish!
I strongly recommend Xmas bulbs in red, but the festive color is more a personal call, so feel free to exercise your creative choice.

 

[Mr Tony]

It's possible that the electronics that determine the voltage switching point are temperature sensitive, as suggested above.
You could check what that actual voltage is - maybe it's low from the receiver you are using?
You might test by putting this receiver on the loop-through output of a different receiver which could supply the selection voltage...

tried 3 boxes. Coolsat 5000, Pansat 1500 and Fortec Ultra. Same thing. Warm it up (brought the LNB in for an hour) and it works fine

You could send it back to the supplier.

too old. Got it last year around this time

Or, and this is my favorite...
Strap some 4w or 7w nightlight bulbs to the LNB.
Not only will you have the required heat, but a nice beacon , as well.
Wouldn't want any low-flying aircraft to run into your dish!
I strongly recommend Xmas bulbs in red, but the festive color is more a personal call, so feel free to exercise your creative choice.

maybe once it warms up later this week I'll see if the LNB works. It just is odd. The old one worked fine all last nite (hooked it up at 10PM and unhooked it this morning around 10AM)

 

[mikekohl]

Wrap a Heat Tape around the outside of the LNBF center and plug it in to 110 VAC with an extension cord. Definitely not UL approved. Not responsible for fires.
But it might stabilize the operation a bit.

 

[Hermitman]

Here's a couple of ideas for you. Most commercial electronics meets the COTS (commercial-off-the-shelf) temperature standards which is around -20 degrees C before operations are significantly effected. If you use electronics with a MIL-SPEC (military specifications meeting a MIL-STD 810E standard), the equipments' operational effectiveness will be down to around -55 degrees C. Of course, that will cost you big bucks. The alternative I use is cheaper. I have covers over my most important satellite dishes' LNBs. It's like a little igloo and the heat from the LNB keeps it warm and stable. I haven't had any problems on the LNBs with covers (it got down to -17F last night) but on some of the open LNBs, there was a noticable frequency shift. One went 4 mhz low which made me lose FTV (and that was a great loss until I rescanned and got it back). I don't know if your LNB is under cover but it might help. Have fun.

 

[Anole]

Well, that's a really good idea.!.

Either wrap the LNB with some sort of closed-cell foam, or maybe put it in a tupperware container, then flood it with the self-expanding insulating foam from the harware store.
Comes in an aerosol can.
Then, pull away the mold,.... uhhhh... or leave it....
Maybe use a plastic drinking glass from the 99¢ store?
Possibly one of the soft ones?

Or, and this is my best suggestion...
..if it's too damned cold outside for your LNB, then it's too damned cold to roll your 1.80 out of the garage!

 

[Mr Tony]

well I put the LNBF back on Sunday when I moved the dish out on the deck. Its been out there for 2 days now and still working (temp has bottomed out at +7)