Cooling the LNB

Prodelin · 09-07-2008

Latest Drdish shows dramatic increase of about +2dB C/N when he freeze a LNB down to -34 degrees celsius with a freeze spray.

This is a temporarily procedure of course.

Is there any good permanent freezing solution for resonable money that could cool down a LNB to -40 or around that?

Drdish talked about peltier elements that could be placed on both sides of LNB.

**Topper** · 09-07-2008

Originally Posted by Prodelin

Drdish talked about peltier elements that could be placed on both sides of LNB.

For someone with time and money on their hands it may indeed work but smacks of desperation to me but if you wanted them they are easy enough to get hold of here.

**Turok** · 09-07-2008

maybe we must move to antarctica,then it is cold enough

i think a profesional solution coasts many 1000€++

most lnb i think will fault after a short period of time,try to put your lnb in a freezer 2 hours,then install it rapedly and check the signal!

**divibi** · 03-08-2008

Originally Posted by Prodelin

Latest Drdish shows dramatic increase of about +2dB C/N when he freeze a LNB down to -34 degrees celsius with a freeze spray.

How does an increase of 2dB C/N convert into dish size requirements decrease? Would that make 1,20m dish act like a 1,80m one or better. Could zone 1 sky minidish be used in zone 2 dish zone

? Thanks in advance

**Analoguesat** · 03-08-2008

Theres no substitution for more metal collecting signal - theres never going to be a practical solution for dramatic cooling of lnb in a hobby situation. Water based peltiers can cool things a bit but unless you go for industrial cooling fluids you arent going to get below zero celcius.

Freezy spray might make some dramatic temporary improvements but how are you going to keep the temp at that -30 temp for hours on end without some pretty heavy duty cooling kit??

**Channel Hopper** · 06-08-2008

Originally Posted by Analoguesat

Theres no substitution for more metal collecting signal - theres never going to be a practical solution for dramatic cooling of lnb in a hobby situation. Water based peltiers can cool things a bit but unless you go for industrial cooling fluids you arent going to get below zero celcius.

Freezy spray might make some dramatic temporary improvements but how are you going to keep the temp at that -30 temp for hours on end without some pretty heavy duty cooling kit??

When I was doing tests back in the late 1990's we were using refridgeration components, which are certainly cheap (almost every town has a place where people dump old freezers). This was in the days when there were honest noise figures supplied by most manufacturers.

We were able to get a stable temperature of -32 C within the LNB casing from a standard freon jacket provided by a small tabletop freezer, giving the impression of a 40% gain in dish area (20% gain in dish size)
similar to upgrading from a 1.2 to a 1.5m reflector.

If you want a refined product though and are prepared to modify it for use with your satellite gear, then the following link from Denmark is probably the best one to go for.

_http://www.asetek.com/content/view/51/101/

Reports claim that the cooling can reach -40 C in the area surrounding the microprocessor in a PC cabinet, down from an ambient 15 C on a forced air system, which is quite impressive

The LNB doesn't produce heat like a microprocessor does, however additional shielding should be used deflect heat generated by the dish reflector in warmer climates. It is also adviseable to coat the finished LNB PCB in silicone, to prevent the condensation mucking up your hard work.

**divibi** · 08-08-2008

Originally Posted by Channel Hopper

When I was doing tests back in the
We were able to get a stable temperature of -32 C within the LNB casing from a standard freon jacket provided by a small tabletop freezer, giving the impression of a 40% gain in dish area (20% gain in dish size)
similar to upgrading from a 1.2 to a 1.5m reflector.

Hello,

At what minus temperature point could the impression of DOUBLING the dish size possibly occur???
Would you say that at -100*C, it would be like doubling the dish size?

Could it also be that at -150*C, it's like 3x dish size, at -200*C it's 4x dish size and near absolute zero it'd be 8x dish size???

Who knows (or guesses)? Thanks in advance.

**Channel Hopper** · 09-08-2008

The noise figure of the LNB is only one factor in the total loss of a system, and so there is no direct correlation between dish size and a drop in noise temperature

Noise temperature of an LNB forms only part of the total signal path, and the eventual quality of signal (G/T ) of the system is governed by everything else making up the link. It does not replace or form part of any of the other parameters in the equation.

19-08-2008

I gave this a shot today on a 90cm dish i set the dish up on nilesat then i sprayed the lnb with freeze spray and whats the signal on a nilsat horizontal transponder rise until it lock on

SatSearcher · 19-08-2008

Interesting topic! Is this definately safe to do? Freezing the LNB won't damage it? Also, i presume this means we should get better signals in cold weather than in warm weather?

**Channel Hopper** · 20-08-2008

Originally Posted by SatSearcher

Interesting topic! Is this definately safe to do? Freezing the LNB won't damage it? Also, i presume this means we should get better signals in cold weather than in warm weather?

Freezing the components inside the LNB will not adversly affect them, however condensation should be vented as per my earlier post.

Better signals are achieved in colder weather, but this is not solely down to the LNB temperature. The dish material, feed, air temperature, and even the ground temperature all contribute to the overall noise received at the tuner.

Additionally noise figures are measured in Kelvin, and so the starting point for the calculations is at -273 degrees Celsius, a drop of 50 degrees isn't so much in the great scale of things (but will make a difference).

***pedro2000uk*** · 21-08-2008

Originally Posted by Channel Hopper

Freezing the components inside the LNB will not adversly affect them, however condensation should be vented as per my earlier post.

How do you vent condensation at minus 30C? I think before you said use
silicone to seal it from condensation...... I liked that, or using another sealant material.

Venting would increase condensation and freezing on the LNB ... if it was working at minus 30C then all moisture in passing air would want to condensate on it and then freeze to the point where you should end up with a block of ice where the LNB was (that might be OK if the LNB's PCB is protected from moisture).

If you can get it to minus 30C with a butchered domestic freezer, some of the things we came up with when looking at the practicalities of this were running costs, lagging, strengthening the LNB arms and using a thermostat.

If you lag it and seal it at the same time, the actual moisture available to condensate could be almost completely removed. With good lagging, the actual energy needed could be greatly reduced and the efficiency could be increased and with a stat you could turn it up and down or off depending on the particular satellite (hmm like a super charger) but if it were off, with the lagging it might mean that it actually gets hotter than normal and may need a bit of cooling.

**Channel Hopper** · 21-08-2008

Originally Posted by pedro2000uk

How do you vent condensation at minus 30C? I think before you said use
silicone to seal it from condensation...... I liked that, or using another sealant material.

vent 1 (vnt)
n.
1. A means of escape or release from confinement; an outlet: give vent to one's anger.
2. An opening permitting the escape of fumes, a liquid, a gas, or steam

***pedro2000uk*** · 21-08-2008

Originally Posted by Channel Hopper

vent 1 (vnt)
n.
1. A means of escape or release from confinement; an outlet: give vent to one's anger.
2. An opening permitting the escape of fumes, a liquid, a gas, or steam

-30c water vapour is very quickly a solid... ice, not vapour or liquid.

Ice build's up in freezers or Fridge ice boxes... .. leave the door open (& increase the ventilation(1&2)) and it will increase to the point where you'll just end up with a plug of ice, close the door and you can only freeze the moisture in the air in the fridge/ freezer- if there were no water vapour - no ice would form.

99% of ice that builds up in a freezer or ice box is from your kitchen /house. Every time you open the door of a freezer/ fridge, the cold, dry air drops out and onto the floor of your kitchen and draws the kitchen's warm, moist air in at the top. The moisture then condensates on the elements ....and quickly freezes (and still would with the door open & central heating on). In the case of sub zero temps, ventilation works the opposite way and outside there is rain etc. to deal with. There are plenty of low temp chemical processes that suffer from pipes being covered in ice.

Whether ice build up would effect the LNB is another issue.. it might not adversly effect it anyway once it's sealed as you suggested and then sealed in lagging. Un-compacted ice is a good insulator anyway.

A meal time thought...

.....all the ice in a freezer surrounding your food is made up of ... exhaled breath, evaporated sweat, evaporated bleach and cleaners, x amount of evaporation from your toilet, bath, shower, the dog's little accident, cigarette smoke, any drugs smoke, 1000s of chemicals given off by various products around the house, VOCs from redecorating, all laid down in layers ... it's actually quite full of ####.

**Channel Hopper** · 21-08-2008

Originally Posted by pedro2000uk

-30c water vapour is very quickly a solid... ice, not vapour or liquid.

Ice build's up in freezers or Fridge ice boxes... .. leave the door open (& increase the ventilation(1&2)) and it will increase to the point where you'll just end up with a plug of ice, close the door and you can only freeze the moisture in the air in the fridge/ freezer- if there were no water vapour - no ice would form.

Venting of any cold surface is one of the key methods to prevent ice formation, your icebox example is incorrect as it is one of confinement, interspersed with exposure to humid air, and then confinement again.

Do a search on ice dam prevention, and you will see that with correct venting of any cold location will prolong a dry environment regardless of size, or temperature extreme.

***pedro2000uk*** · 21-08-2008

Originally Posted by Channel Hopper

Venting of any cold surface is one of the key methods to prevent ice formation, your icebox example is incorrect as it is one of confinement, interspersed with exposure to humid air, and then confinement again.
Do a search on ice dam prevention, and you will see that with correct venting of any cold location will prolong a dry environment regardless of size, or temperature extreme.

I actually did look for ice dams... it's nothing to do with it.. the freezing is general cold/ freezing weather, snow fall and rain or a temperature differential that melts then freezes the rain or melt water into an ice dam.

That is not the same as an isolated cooling element at minus 30c from a butchered freezer or peltier that air born moisture condensates and freezes on -30c (and you want it to be -30c). If you leave a freezer door open it will just carry on freezing until it goes beyond the door, as I said- even if the central heating is on. If you fire up a peltier on its own but with an appropriate cooler on the hot side- ice will form on the cold side. You routinely see gas bottles with ice build up in the middle of summer.

This is very basic and not really worthy of too much other than if it causes too much of a problem then it needs dealing with. It's getting it to work and at low cost/ running cost that should be the focus.

Also, if you vent it, you lose a lot of the efficiency - you need to do the opposite and lag it keeping the cold in.

**Channel Hopper** · 22-08-2008

Originally Posted by pedro2000uk

I actually did look for ice dams... it's nothing to do with it.. the freezing is general cold/ freezing weather, snow fall and rain or a temperature differential that melts then freezes the rain or melt water into an ice dam.

But prior to that the liquid water forms as a result of precipitation of humid air that can no longer hold the mass within it, often as a result of a pressure, or temperature drop.

Originally Posted by pedro2000uk

That is not the same as an isolated cooling element at minus 30c from a butchered freezer or peltier that air born moisture condensates and freezes on -30c (and you want it to be -30c)

If the air can be kept circulating past any cooled component (taking into account the resultant rise in temperature by further cooling) then the chance of water precipitating out as ice is reduced.

I do prefer to keep the box of tricks completely isolated from the atmosphere, but hermetically sealing the feed/LNB from water vapour is virtually impossible once cooling elements have been fitted, as other technologies have discovered (optics in astronomy for example) . Adding non replaceable drying compounds into the mix is a no go area owing to their drop off in performance after a couple of weeks, which is why the commercial users in this industry use forced air switching dehydrator systems, often beyond standard atmospheric pressure, to keep the dewpoint and resultant moisture from affecting components, lowering the efficiency of the feed system and/or damage through corrosion.

http://www.physicsforums.com/archive.../t-102760.html

There is no need to dismiss a forced air operation in a subzero cooling system, except for the initial costs and constant energy requirement, as it is proven technology.

http://www.etitelecom.com/17980.htm

**divibi** · 22-08-2008

Hello,

At -273 degrees Celcius inside an LNB;

would a 1 metre dish act like a 5 metre and 10m like a 50 m???
If not that much , then how much better? You guys know your physics and how to calculate G/T and C/N and dB's...

Thank you in advance.

**Channel Hopper** · 22-08-2008

Originally Posted by divibi

Hello,

At -273 degrees Celcius inside an LNB;

would a 1 metre dish act like a 5 metre and 10m like a 50 m???
If not that much , then how much better? You guys know your physics and how to calculate G/T and C/N and dB's...

Thank you in advance.

Cooling the LNB

***pedro2000uk*** · 22-08-2008

Originally Posted by Channel Hopper

If the air can be kept circulating past any cooled component (taking into account the resultant rise in temperature by further cooling) then the chance of water precipitating out as ice is reduced.

The idea is to freeze the LNB and lose the heat elsewhere, if there was enough heat at the cooling site to actually effect condensation (and therefore freezing) then it would be really inefficient and you wouldn't want that either. The peltier suffers from that (hot right next to cold) and it is more difficult to rip the heat away and lose it with a remote heat exchanger without heating the air near the LNB to a degree. I think butchering a small freezer or fridge / ice box could be the most practical for this.
BTW.. The thread post 2 http://www.physicsforums.com/showpost.php?p=846711&postcount=2 describes the ‘use’ of freezing onto an element to trap vapour in another dehydration process demonstrating what I have said about condensation/ freezing- that is it is that good at extracting moisture out of the air. The process that is the main thread demonstrates the same problems and the air flow to a dryer element. That is that ventilation (in open air) is not anything you would want to do (unlike ventilation in a house for example) but a drying system in an enclosed environment is as I said earlier, if there is no vapour in the air it will not result in ice build up (or condensation). It doesn’t say if they are using a cooler at the uplink or this is a passive system for general dry air/ minimal condensation. I have been involved in engineering/ chemical projects that, although not directly radio electronic cooling related, give you the experience of the kind of other problems that will arise trying to cool any object like that.
The worst issue may be condensation and ice in the feed horn/ wave guide and on the antennae (and down the connected coax). Until you try it you don’t know, the gains may out way the problems or have to be dealt with.

Lagging:
Dr Dish & RD100‘s.… cooling with freezer spray.. A far better test and result is to use lagging… when you use freezer spray to freeze a water pipe, you lag the pipe- you can’t do it without lagging - the lagging increases the freezing massively and retains it. If Dr Dish had lagged the LNB and pushed the freezer spray through a small hole instead, the temperature would have been far lower. The same goes for a proper setup and lagging will reduce condensation and freezing air bourn vapour as well as make it far more efficient.

Divibi
The noise reduction gains we are after are in the order of the equivalent of 10-20-30% (40-50% would be fantastic but doubtful and certainly not those massive gains you have mentioned- we wish)… say a 1m acting like a 1.2- 1.3m or a 1.2 like a 1.5 to be realistic (in actual signal to unwanted noise wise- not signal strength- that shouldn’t alter with this). From our point of view in the UK there is a planning limit of 1 x 1m & 1 x 60cm dish per property now, so maximising a 1m rather than just getting bigger ugly dishes is attractive for a lot of people as well as bigger enthusiast’s ground based dishes gaining. Bigger dishes also have their problems too, weight, wind effect increases and needing 36v and far stronger gear all round etc.. this can help avoid some of this so it might be worth a bit of trouble.

**Channel Hopper** · 23-08-2008

Originally Posted by pedro2000uk

The idea is to freeze the LNB and lose the heat elsewhere, if there was enough heat at the cooling site to actually effect condensation (and therefore freezing) then it would be really inefficient and you wouldn't want that either. .

Venting the LNB circuitry directly to the air ( or a bespoke dehydrator system) achieves this without the need to tranfer the heat elsewhere.

Originally Posted by pedro2000uk

I think butchering a small freezer or fridge / ice box could be the most practical for this.

That was what I was doing a decade ago, (working on a minimum cost also had its own advantages)

Originally Posted by pedro2000uk

BTW the thread 2 ...... snip .....describes the ‘use’ of freezing onto an element to trap vapour in another dehydration process demonstrating what I have said about condensation/ freezing- that is it is that good at extracting moisture out of the air. The process that is the main thread demonstrates the same problems and the air flow to a dryer element. That is that ventilation (in open air) is not anything you would want to do (unlike ventilation in a house for example) but a drying system in an enclosed environment is as I said earlier, if there is no vapour in the air it will not result in ice build up (or condensation).

Which comes back to the almost impossible task of removal of the humidity out of the air.

Optics (binoculars/telescopes) use a nitrogen or other inert atmosphere, but again this requires hermetical sealing, almost impossible where a microwave transparent feedhorn is a neccessity.

When carrying out tests, it was found that cooling of the air inside the feedhorn (and the feedhorn itself) also improved the C/N ratio, however the advantages were only 5%-10% that of freezing the LNB directly.

Originally Posted by pedro2000uk

It doesn’t say if they are using a cooler at the uplink or this is a passive system for general dry air/ minimal condensation. I have been involved in engineering/ chemical projects that, although not directly radio electronic cooling related, give you the experience of the kind of other problems that will arise trying to cool any object like that.
The worst issue may be condensation and ice in the feed horn/ wave guide and on the antennae (and down the connected coax). Until you try it you don’t know, the gains may out way the problems or have to be dealt with..

See above, but since the feed is in outside air, venting occurs naturally and the natural focus of the dish provides additional heat to stave off any permanent buildup of ice (in the UK anyway).
Did I mention that I sold dehydrators and Ice heaters for quite a few years in the commercial sector ?

Originally Posted by pedro2000uk

Lagging:
Dr Dish & RD100‘s.… cooling with freezer spray.. A far better test and result is to use lagging… when you use freezer spray to freeze a water pipe, you lag the pipe- you can’t do it without lagging - the lagging increases the freezing massively and retains it. If Dr Dish had lagged the LNB and pushed the freezer spray through a small hole instead, the temperature would have been far lower. The same goes for a proper setup and lagging will reduce condensation and freezing air bourn vapour as well as make it far more efficient.

Lagging does not reduce condensation, this is at the crux for correcting your responses.

Originally Posted by pedro2000uk

.... maximising a 1m rather than just getting bigger ugly dishes is attractive for a lot of people as well as bigger enthusiast’s ground based dishes gaining. Bigger dishes also have their problems too, weight, wind effect increases and needing 36v and far stronger gear all round etc.. this can help avoid some of this so it might be worth a bit of trouble.

Ugly dishes ?

***pedro2000uk*** · 23-08-2008

Originally Posted by Channel Hopper

Venting the LNB circuitry directly to the air ( or a bespoke dehydrator system) achieves this without the need to tranfer the heat elsewhere.

Have you forgotten what it is we is supposed to b doin .... and your previous post... ... we is freezing an LNB... you said .. the extra heat produced (through the freezing process wot always produces heat as a by product I presumed you meant.. correct?) will help with condensation**.. but I said... we don't want that heat near it.. that would be counter productive (OWTTE).. we want the heat exchanger etc.. that gets rid of the by product heat.. some distance away... and the LNB as cold as possible. (but see below re feed horn cover face defrosting**).

but since the feed is in 'outside' air, venting occurs naturally ...

feed? by this you mean the feed horn/ (& wave guide etc)? .. it's sealed or it should be.

Lagging does not reduce condensation...... hmmm.

Yes it does/ or can ...

not in a house though ...

if a house was lagged and sealed it would produce masses of condensation .. because people (us) produce massive anounts of water .. sweat (eeer) / exhaled breath/ cooking/ laundry/ bathing/ open gas appliances.. all produce litres of water that have to be..... vented away***.

but a sealed LNB doesn't produce any moisture..

if you super cool it without any lagging, passing moisture in open air will condensate on it like crazy and freeze...
lag it and use the lagging to also seal it in and the lagging will drastically reduce the extreme cold coming in contact with the outside air... on the outer surface of the lagging it will be cold but nothing like the -30c inside... so condensation will be drastically reduced and limited to the outer surface of the lagging and if it (the lagging) is also sealed, then this will limit normal moist air getting in and giving up it's moisture to the -30c surfaces inside.

So lagging can drastically reduce condensation... in this case.

Absolute sealing is a problem.. I thought of sealing the LNB in a lagging block in a super dry environment and including a dry pack in a place that wouldn't cause a problem to at least limit it.... It's the feed horn cover face that is the most vulnerable- can't lag it and most plastic is x% porous. You can only limit it as you say... but most engineering process battle against the laws of physics and rarely win 100% - you just limit it, accept it.. and move on.

**Now... if you used some of the excess heat just on the face of the feed horn cover to keep ice from building up there... that might be a worth while compromise.... which is in part what you said.. (I think).

***- the building regs got that one really wrong in the eighties.

**Channel Hopper** · 23-08-2008

Originally Posted by pedro2000uk

Have you forgotten what it is we is supposed to b doin .... and your previous post... ... we is freezing an LNB... you said .. the extra heat produced (through the freezing process wot always produces heat as a by product I presumed you meant.. correct?) will help with condensation**.. .

No - the idea is to keep the heat components (the radiator or low pressure side of the fridge) away from the LNB, which is why the use of a refrigeration plant has so many advantages over the Peltier units.

The heat transfer components are kept well away from the LNB, best place is strapped to the back of the reflector, but in front of the mount/motor, and then the pipes carrying the freon/halide can be of rigid construction.

Originally Posted by pedro2000uk

but I said... we don't want that heat near it.. that would be counter productive (OWTTE).. we want the heat exchanger etc.. that gets rid of the by product heat.. some distance away... and the LNB as cold as possible. (but see below re feed horn cover face defrosting**)..

As above

Originally Posted by pedro2000uk

feed? by this you mean the feed horn/ (& wave guide etc)? .. it's sealed or it should be..

The feed is not sealed in the systems I have used for testing (are you talking about integral feed/LNBs , if so