Oscillation Fixes/Cures?

[Greg Mueller]

I have been having problems with my system for a week or two. It seems to come and go. Yesterday it got worse and just to check I replaced my expensive Norsat 8115 with an old Cal-Amp Mag 90 that I had in the junk box. It seems to have cured the problem, but I will watch it for a few days just to make sure.

The only thing I have been able to figure is that the Norsat was going into oscillation for some reason. But that is just a guess. The symptoms were that it would be fine with good Q then the Q would drop sharply and then come back up. I also noticed that the S would drop for a split second at the same time.
I was thinking of buying a second 8115 for my dual LNB feedhorn but that's a lot of money for 6 mos use, which is about how long I have been using this Norsat.

Could this be a power supply intermittent failure in the 922?
Is there any cure for this or is the lnb just scrap?
Can it be sent somewhere to get fixed?
Is there number for Norsat?

 

[B.J.]

I have been having problems with my system for a week or two. It seems to come and go. Yesterday it got worse and just to check I replaced my expensive Norsat 8115 with an old Cal-Amp Mag 90 that I had in the junk box. It seems to have cured the problem, but I will watch it for a few days just to make sure.

The only thing I have been able to figure is that the Norsat was going into oscillation for some reason. But that is just a guess. The symptoms were that it would be fine with good Q then the Q would drop sharply and then come back up. I also noticed that the S would drop for a split second at the same time.
I was thinking of buying a second 8115 for my dual LNB feedhorn but that's a lot of money for 6 mos use, which is about how long I have been using this Norsat.

Could this be a power supply intermittent failure in the 922?
Is there any cure for this or is the lnb just scrap?
Can it be sent somewhere to get fixed?
Is there number for Norsat?

I used to have a CalAmp LNB that after about 5 years of good service started having this oscillation problem. It was temperature dependent. I used to notice it at the same temperature each day on one specific channel. I would see the problem every time the temperature would drop into the 10-15 deg F range in the evening. What I'd observe on analog was that the screen would be completely black, and I'd have a maximum reading on signal strength. I found that I could STOP the oscillation by unplugging the receiver for just a couple seconds, so I put the receiver on an X-10 switch, and when this happened, I'd just flip it on and off by my UHF X-10 remote, and all would be well. I eventually discovered that the actual oscillation was moving across the whole sat band, channel by channel, and that I only happened to be noticing it on one channel.
But the power cycle seemed to stop the oscillation, and it wouldn't come back until the next evening. I suffered with this for about 3 years, then finally replaced the LNB with a Norsat, which has been fine since.
Anyway, only thing I could figure was that there was some bad solder joint or something that lost contact due to contraction at low temperatures.
I had one other LNB that suddenly changed LO freq by exactly 20 MHz one VERY HOT afternoon in the summertime. I was able to deal with that for quite a while too by using a freq offset setting on my analog receiver.
But anyway, sometimes temperature can cause some problems with LNBs. They are really rated only over a very narrow temperature range, and if it gets hot or cold, strange things can happen, although usually it's just a bit of drift, not oscillation. But you might try a power cycle on the receiver the next time it happens.

 

[Corrado]

If it was the LNB that you swapped out, then by reinstalling it the problem should return. I would test it out for a bit longer as it is to rule it out.

Sometimes cable connectors with a stray strand of shielding can cause such issues. Perhaps just disconnecting and reconnecting the fitting restored the connection. Any chance something was wet, loose, ice accumulation, etc?

 

[Anole]

WAG:

I see Greg was using a 922 to power his LNB.
What voltage to those put out?
Any chance a self-powered switch or power inserter would change the conditions?

Also, is the LNB open to the cold air, or under a cover?
Several members have described odd problems at super low temperatures.
I've suggested a small lamp in the nose cone, to act as a heater/stabilizer.
However, I don't think anyone has ever taken me seriously.

There is pretty obviously something causing this.
What are the variables?
- voltage
- temperature
- moisture
- corrosion
- time
? ? ?

 

[knowmiddlename]

Norsat America
93 Main Street
Third Floor, Suite A
Annapolis, MD 21401 USA
tel: +1 410 263 8165

 

[Greg Mueller]

I see Greg was using a 922 to power his LNB.
What voltage to those put out?
Any chance a self-powered switch or power inserter would change the conditions?

Also, is the LNB open to the cold air, or under a cover?
Several members have described odd problems at super low temperatures.
I've suggested a small lamp in the nose cone, to act as a heater/stabilizer.
However, I don't think anyone has ever taken me seriously.

There is pretty obviously something causing this.
What are the variables?
- voltage
- temperature
- moisture
- corrosion
- time
? ? ?

I was just thinking about the voltage output of the 922 myself and it's failing is my biggest worry.
Since I am going to go to a dual LNB feedhorn (in the future) I was wondering about having a switch that would insert power to the LNBs and would have multiple outputs so I could hook other receivers up to those dual LNBs. Not sure how that would work exactly.

I was wondering if something like an old DN Dp34 or 44 (which I just happen to have laying around) would work?

Temperature It doesn't get too cold here (not freezing at night) and not too hot during the day maybe a 20° - 30° swing

Moisture Unless the coax has a break or somehow water intrusion along the way it looks good. Running a jumper (substitute piece) was to be the next experiment. I visually inspected the ends and hosed them with canned air and they look good.

Corrosion New compression ends on the coax

 

[Greg Mueller]

Hmm

Now the Cal Amp is doing it, so it's not the LNB I guess.

Guess I will dig up another piece of coax and substitute that.

 

[Anole]

future with dualing LNBs?

Since I am going to go to a dual LNB feedhorn (in the future) I was wondering about having a switch that would insert power to the LNBs and would have multiple outputs so I could hook other receivers up to those dual LNBs.
Not sure how that would work exactly.

Dual C-band LNBs on a feedhorn?
Here ya go. See Pendragon's multi-switch mod.
It supplies 18 volts to each LNB, and drives up to 8 receivers.
Beat that with a stick! -
edit: I prefer his WNC switch mod above, but also see his Zinwell mod, too. (still same number of inputs/outputs)

I was wondering if something like an old DN Dp34 or 44 (which I just happen to have laying around) would work?

Well, if you stay with a single LNB, and a polarity servo, the DN switch might be used as big diseqc multi-output switch.
However, the 922 couldn't select which input it wanted (can't do diseqc commands), so I don't immediately see a hookup where that'd be suitable...

 

[Greg Mueller]

Dual C-band LNBs on a feedhorn?

one for V and one for H using the Chaparral 11-1329-1 Dual C-Band Feed Horn that I got from Ricks

 

[mick d]

I also have the dual feed c band, and read anole's threads on multiswitch mods and have not had a chance to try it yet mainly because I can't find a powered multiswitch fairly cheap. I am having pretty good luck with just a cheap zinwell non powered multiswitch. Look inside your cap and make sure water hasn't collected inside, I had that happen a while back.

 

[Cadsulfide]

A dp34 and an 18V power supply connected to port1 should work fine. This will take the dc power load off your receiver, as well as keep the lnb's warmed up.