Ice Pack

[cyberham]

I may have asked this long ago but I forget. With the high temperatures we are now experiencing (about 88F yesterday), I'm wondering if enclosing an LNB in an ice pack would improve its performance. I find that reception on my C-band dish is better at night in particular on the occasional transponder that is at or slightly below C/N lock value during the day.

Or maybe it's the fact that the Sun is behind the dish in the evening that contributes to improved performance.

 

[comfortably_numb]

Buying a Bullseye LNB eliminated temperature issues for us, here in New Mexico. Signals that would fade as the day got hot now stay steady 24/7.

I think it's worth the investment.

 

[cyberham]

I don't really have a problem on Ku. It's on C-band where I could use improvement in a few situations likely due to my dish only being 7 1/2'.

 

[ZetaMale]

I use a regular LNBF with no problems even on 100+ days. I'm using a much bigger dish than you are though (12 footer).

 

[cyberham]

I use a regular LNBF with no problems even on 100+ days. I'm using a much bigger dish than you are though (12 footer).

Your larger dish would likely compensate. In your case, you would need to graph your C/N values over several days/nights against measured temperature to see if there's any correlation. It's easier in my case since it's more noticeable. I lose a solid lock during the day but right now at 9 pm it's locked solidly.

 

[clucas]

I'm probably far off base so maybe someone with more knowledge could give a correct answer.

I started thinking (bad thing) and wondered if air density is a factor due to the air temperature not just the temperature of the LNB(F) itself (i.e. cooler, more dense air at night). A short search came up with this AI generated answer for RF waves:

Yes, air density is a factor that can affect radio frequency (RF) power, particularly in terms of signal propagation. Here's how air density plays a role:

• Refraction and Bending of RF Waves: Changes in atmospheric density, caused by variations in temperature, moisture, and pressure, lead to changes in the speed of electromagnetic (EM) waves, including RF waves. This variation in speed causes the waves to bend, or refract, as they pass through the atmosphere. Refraction can lead to changes in the propagation direction of RF signals.
• Impact on Signal Range and Strength:
  
  • High atmospheric pressure (denser air) can potentially increase signal range by providing a denser medium for the waves to travel through.
  • Conversely, low atmospheric pressure (less dense air) can reduce range by decreasing air density.
  • High humidity levels and rain can scatter and absorb radio waves, leading to signal degradation and attenuation, impacting signal strength and clarity.

A search for "is air density a factor in wave propagation" came up with this:

Electromagnetic waves (including light and radio waves)

• Density fluctuations and distortion: Random fluctuations in air density can distort electromagnetic waves, particularly at higher frequencies (shorter wavelengths) like those in the millimeter, infrared, and optical ranges. This is the reason for the twinkling of stars.
• Density and absorption/radiation: Denser air at lower elevations absorbs and radiates more energy, while air density decreases with elevation, leading to less energy absorption and radiation at higher altitudes, according to www.vaia.com.
• Refraction: The index of refraction, which depends on air density, can cause electromagnetic waves (including light and radio waves) to bend as they pass through layers of air with different densities. This bending is known as refraction.

In summary: Air density is a significant factor in the propagation of sound waves, directly impacting their speed and intensity. For electromagnetic waves, air density primarily influences propagation through phenomena like distortion and refraction, which can affect the overall power or clarity of the signal.

 

[a33]

I'm wondering if enclosing an LNB in an ice pack would improve its performance.

Yes it would, it causes less noise in the LNB, so the S/N ratio improves.

There was a (german) DrDish TV video on it, with Klaus Schumacher in Brasil receiving Astra1 (19.2E) in the analog days. Alas, I can only find the first video with him on the internet, not the second video where they tested the ice spray.

Greetz,
A33

 

[a33]

I may have asked this long ago but I forget.

Google doesn't forget.

Thread 'LNB Performance vs Temperature'

Oct 24, 2021

Today the temperature is 48 F. My C-band LNBF hasn't performed as well as it this since last autumn.

Perhaps the improvement is due at least partially to the LNBF being colder which therefore might lower the thermal noise in its electronics. If this were true, would it be possible to have a refrigerated LNBF? You could literally plug the LNBF into AC power like a fridge or a freezer.

"Crazy ideas can turn into modern inventions". Red Green

Sent from my SM-G950W using Tapatalk

• cyberham
• Replies: 33
• Forum: Free To Air (FTA) Discussion

• 

 

[cyberham]

I re-read the comments from that old posting. Educational. Maybe I can fill my C-band dish nose cone with ice.

Added: This morning the temperature outdoors is 66 F at 8am local time. C/N of the transponder in question is a solid 74%. This means the tp is locked solid. Typically later in the day it will become 71% or lower and this will result in loss of lock.

 

[a33]

By the way. I've had an LNB with temperature-dependent (unstable!) LOFs, for which I had to change the LOFs with about 5 MHz twice a year, for summer and winter.
But if I remember correctly, that had only effect on if the receiver could lock, or not (depending on the range of the AFC automatic frequence control). Once I had a lock, reception was good again (if I recall correctly).

It looks like you have a lock, but unstable reception. That would be a different problem?

Greetz,
A33

 

[cyberham]

By the way. I've had an LNB with temperature-dependent (unstable!) LOFs, for which I had to change the LOFs with about 5 MHz twice a year, for summer and winter....

It looks like you have a lock, but unstable reception. That would be a different problem?

How did you change your LNB LO frequency setting by 5 MHz? My receiver has fixed choices only for LO frequency for C-band.

When locked, reception is stable. I'm using a C1-PLL. As the signal C/N drops, then the lock fails once below minimum C/N. This is normal operation.

 

[a33]

How did you change your LNB LO frequency setting by 5 MHz?

I have experience only with Ku-LNBs.
Normal LOFs for universal LNB are 9750/10600
I could set these at "manual", and then input 9745/10595 or 9755/10605.

Standard LOF for C-band is 5150 or so? No possibility for manual setting?

But with me, C/N levels were never the problem, only getting the (initial) lock.
And I must confess, this was more than 10 years ago. So my memory is not very detailed anymore.

Greetz,
A33

 

[cyberham]

On my GT Media receiver I can't manually select an LOF. But on my Edision Mio+ I can. I tried it and the manual selection seemed to work on the Edision.

It sounds like you had a different issue. I have no trouble locking tps as long as the C/N reaches minimum lock value.

I've just learned it's all a moot point in this case. I understand this mux in question will end by next week at the latest. I don't have this issue on too many other tps since in most cases the signal is strong enough to lock. The exception is network feeds on 99W C like CBS or ABC with 4.2.2 coding and maybe 16APSK.

 

[mountaineer2]

Edit tp to 5 below ...
Also I had an lnb like that on an 8.5 footer .. I had some type of tape that looked like the size of duct tape ... but had a quarter inch of stick foam on one side and like an aluminum foil on the outer side .... wrapped my lnb in that and it helped a lot ...

 

[cyberham]

...I had an lnb like that on an 8.5 footer .. I had some type of tape that looked like the size of duct tape ... but had a quarter inch of stick foam on one side and like an aluminum foil on the outer side .... wrapped my lnb in that and it helped a lot ...

I'd rather do that to the LNBF feed cover. Insulation plus reflective tape. Then I could lift it off and reinstall to access the LNBF for adjusting skew when I change satellites.

 

[Brct203]

I may have asked this long ago but I forget. With the high temperatures we are now experiencing (about 88F yesterday), I'm wondering if enclosing an LNB in an ice pack would improve its performance. I find that reception on my C-band dish is better at night in particular on the occasional transponder that is at or slightly below C/N lock value during the day.

Or maybe it's the fact that the Sun is behind the dish in the evening that contributes to improved performance.

I would expect that lower temp of the LNB means lower noise so would improve the C/N ratio..

my experience is that I have poor view of the western end of the arc (127W and beyond), bacause they are low on the horizon and my neighbor has trees there. Even in winter when the trees are bare, I can get only a few TPs on 131 and 133 and nothing on 135W. However the few nights when it gets really cold I can get all of them. By really cold I mean bellow 5 F/-15C.

Now, is that because of the low temp effect on the electronics of the LNBF - it might be part of the equation but i doubt that it. Most likely it's the thermal noise of the trees that is much lower

My expectation, as explained above, is that the signal remains the same but the noise is lower, thus increasing the signal-to-noise ratio. But I wanted to verify that theory, so I plugged in my SDR and took some screenshots of the spectrum of a transponder and the adjacent noise floor when it was very cold and when it was back to normal temps later in the day. To my surprise, it was the opposite - the floor was the same and the signal was higher. As far as I know there was no automatic gain control involved (unless there's one in the LNBF itself?), so I'm very puzzled by it. Still, the bottom line was that it worked much better in very cold weather.

It woudl be interesting to see if ice packs make a difference in your case. I guess it's easy enough to try if you can easily reach the LNBF.

Please keep us posted if you try it

 

[mikekohl]

I would expect that lower temp of the LNB means lower noise so would improve the C/N ratio..

my experience is that I have poor view of the western end of the arc (127W and beyond), bacause they are low on the horizon and my neighbor has trees there. Even in winter when the trees are bare, I can get only a few TPs on 131 and 133 and nothing on 135W. However the few nights when it gets really cold I can get all of them. By really cold I mean bellow 5 F/-15C.

Now, is that because of the low temp effect on the electronics of the LNBF - it might be part of the equation but i doubt that it. Most likely it's the thermal noise of the trees that is much lower

My expectation, as explained above, is that the signal remains the same but the noise is lower, thus increasing the signal-to-noise ratio. But I wanted to verify that theory, so I plugged in my SDR and took some screenshots of the spectrum of a transponder and the adjacent noise floor when it was very cold and when it was back to normal temps later in the day. To my surprise, it was the opposite - the floor was the same and the signal was higher. As far as I know there was no automatic gain control involved (unless there's one in the LNBF itself?), so I'm very puzzled by it. Still, the bottom line was that it worked much better in very cold weather.

It woudl be interesting to see if ice packs make a difference in your case. I guess it's easy enough to try if you can easily reach the LNBF.

Please keep us posted if you try it

My experiences with dealing with thermal instabilities on LNBs and LNBFs go back several decades. I referred a friend to an oil company that was installing a 24 foot Orbitron antenna on an offshore drilling platform off Indonesia, and he provided valuable information. Without a weather cover, even using commercial LNBs (Norsat) of the best stability found in the mid 1990s, there was substantial drifting in Local Oscillator frequency from the intense daytime heat and solar radiation found at the equator. Orbitron supplied a weather cover (black plastic), so they installed it to cover the LNBs, and painted the weather cover WHITE. That was enough to physically eliminate a lot of the source of drifting (the sun beating down on bare metal). A second step was to cut an extra hole in the bottom of the weather cover, which allowed the muffin fan that was put inside the housing, to vent outwards. That further improved the system reliability.

Cold weather helps too. A friend at Prudhoe Bay in Alaska during the 1980s left a not-so-state of the art LNB out in the weather overnight (no cover, and at least 40 degrees below zero).
It ran flawlessly all night, but gave the user a sense of comfort that it would operate in conditions that cold. He ended up putting a weather cover over it, to avoid other weather issues such as wind and rain (and snow many months of the year).

Both of these situations physically confirm the correctness of everything that has been said in this thread, and when you connect such reality with complicated mathematical calculations, it should be considered a sure thing.

 

[cyberham]

...Even in winter when the trees are bare, I can get only a few TPs on 131 and 133 and nothing on 135W. However the few nights when it gets really cold I can get all of them. By really cold I mean bellow 5 F/-15C.
...

It would be interesting to see if ice packs make a difference in your case. I guess it's easy enough to try if you can easily reach the LNBF....

I remembered I have some "fake" ice packs. These are plastic containers that contain liquid which you can put in the freezer to freeze. They keep something cold until they melt then you put them back in the freezer to refreeze. I can easily duct tape a couple to my LNBF, replace the feed cover if it fits and see if I get any interesting results.