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.