Cooling the LNB

[Channel Hopper]

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.

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)

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.

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 ?

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.

.... 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 ?

 

[guest poster]

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]

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.

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

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 then the methods of cooling would have to be modified)

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

Yes it does/ or can ...

not in a house though ...

if a house ...snip ..... all produce litres of water that have to be..... vented away***.

but a sealed LNB doesn't produce any moisture .

It is not sealed, the air around it is able to permeate through the feed/cooling pipes, or lack of sealing between the feed and LNB.

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..

But the refrigeration part is also inside any potential lagging, and moisture will be present either side of the lagging, ready to freeze once the temperature is reduced.

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..

You cannot leave dessicated silica gel on its own, it will spoil within a week of freezing and then you will need to dismatle all your work

**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).
.

No need if you vent it

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

We know

 

[guest poster]

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.

I agree but it's not what you said... earlier re use of extra heat to reduce condensation... ... but lets move on... the above is almost exactly one solution I came to.


The feed is not sealed in the systems I have used for testing (are you talking about integral feed/LNBs , if so then the methods of cooling would have to be modified)

I had pictured mostly using a metal case lnbf - it's already sealed and self contained and ideal to seal in a lagging block. ... but once a c120 is made up with a feed horn as a sealed unit and made up in an ultra dry environment then treat them the same.

It is not sealed, the air around it is able to permeate through the feed/cooling pipes, or lack of sealing between the feed and LNB.

What about the seal (gasket or O ring) between the feed horn and the C120? anyway if that is a problem... increase the sealing ... use gasket compound and make it up in an ultra dry environment.


But the refrigeration part is also inside any potential lagging, and moisture will be present either side of the lagging, ready to freeze once the temperature is reduced.

Not if it's sealed from the outside air and it's been done in an ultra dry environment... where is the moisture going to come from inside the sealed lagging block with the cooling pipes/ cooling manifold (or whatever proves effective as a design)... inside it will be very cold ..but dry.. outside the lagging it will be .... not as cold, it may get some condensation or even ice build up ... but it doesn't matter.

You cannot leave dessicated silica gel on its own, it will spoil within a week of freezing and then you will need to dismatle all your work

I was thinking of a Silica gel pack... or perhaps the gadget they use in double glazing sealed units.. If Silica spoils on freezing then that's out..


No need if you vent it

The face of the feed horn.... yes ... that's different ... but it is very likely to suffer from excessive condensation and ice build up if millimetres away it's -30c... and natural ventilation and any heat off the dish focus is doubtful to be capable of dealing with it (it might) ... so if it doesn't, vent a bit of warm air off the hot side via a small pipe back to the face of the feed horn .. like warm air on a misted up windscreen ...

We know... but they didn't

You do realise this thing is getting designed as we go...




Other issues..

* The pipes to and from the LNB need to be lagged too. * A stat control at the stb is needed. * The heat at the back of the dish would double up as a dish face defrost in snowy weather, * but heat concentrated in one area of the dish could distort it and should be avoided. * what temp drop could you expect off a small freezer .. bearing in mind the area to super cool is a fraction of the area of a mini freezer and sealed in a lagging block and * would that cause other problems with the butchered freezer. * Power consumption should also be very low. * Needs shading from the sun. * Flexible cooling pipes ...? * Test a mock up on a ground based fixed dish first *.

 

[divibi]

Hi all,

I've been reading archive posts in this forum ... and one member, ralphmagno wrote, maybe jokingly, that 'if you freeze it (LN to -470*F noise figure is 0.00 dB'!!! Could LNB noise figure decrease that much, or let's say to 0.02 dB??? And would we then have a typical LNB NF of 0.02 dB? We're talking THEORETICALLY here (not that it's practically possible)?

 

[guest poster]

It sounds off the scale, but liquid nitrogen can be used at about -200c (-345F) to cool radio electronics commercially to drastically improve signal to noise ratios, it's not new, just making it practical for DTH and build & running cost issues (hmm). The German guy in Brazil could possibly consider it considering the lengths he's already gone to.... I think we'll stick with a butchered freezer for now.....

 

[divibi]

It sounds off the scale, but liquid nitrogen can be used at about -200c (-345F) to cool radio electronics commercially to drastically improve signal to noise ratios, it's not new, just making it practical for DTH and build & running cost issues (hmm). The German guy in Brazil could possibly consider it considering the lengths he's already gone to.... I think we'll stick with a butchered freezer for now.....

Hello,


I was thinking about Klaus in southern Brazil with that. He may be abt 84 years old now.

From what I read, it is possible to 'stack' or 'daisy chain' kind of connect many peltier plates together to get ever lower temperatures (same is with phase change cooling) You can go lower and lower and lower. Good, b/c liquid nitrogen is too dangerous to test with, I think?

 

[guest poster]

How much does it cost to run per watt/ yr including the gear to remove the heat off the peltier's hot side but allowing for good lagging on the cold lnb side and the fact that the lnb doesn't need anywhere near as much as a CPU to cool per degree drop?

& What's phase change cooling?

 

[baxter_norway]

I think he refers to the fact that if you attach a peltier on the warm side of another peltier, you can force the temperature of the first peltier down since they mainly deal with difference from hot to cold.

I.e if I have a peltier that can produce 60degrees difference, so the hot side is +40 and the cold side is -20, but then I attach another peltier to the hot side, so it gets cooled down say 20degrees, then the result is -40 next to the lnb, and +80 outside the second peltier. In theory you can do this several times, but there is a limit with regards to solder temp etc.

 

[divibi]

How much does it cost to run per watt/ yr including the gear to remove the heat off the peltier's hot side but allowing for good lagging on the cold lnb side and the fact that the lnb doesn't need anywhere near as much as a CPU to cool per degree drop?

& What's phase change cooling?

Phase change cooling is a form of refridgeration, used also for cooling CPU's. For example Prometeia or asetek sell cooling kits/computer cases. 2 units joined together go to - 130*C IIRC from reading custompc mag or pcformat.

I don't know the answer to your first Q. I would first need to learn abt peltir cooling re; CPU's etc.

 

[divibi]

I think he refers to the fact that if you attach a peltier on the warm side of another peltier, you can force the temperature of the first peltier down since they mainly deal with difference from hot to cold.

I.e if I have a peltier that can produce 60degrees difference, so the hot side is +40 and the cold side is -20, but then I attach another peltier to the hot side, so it gets cooled down say 20degrees, then the result is -40 next to the lnb, and +80 outside the second peltier. In theory you can do this several times, but there is a limit with regards to solder temp etc.

Thanks Baxter, that's what I meant.



Is liquid helium more or less dangerous than liquid nitrogen? Just asking ...

 

[guest poster]

Thanks... I ask about the running costs because it can get impractical very quickly - 400 watts used on one or more peltiers and the cost of finally shifting the heat away can cost £500 a year or more, so one has to keep an eye on running costs.

 

[divibi]

Thanks... I ask about the running costs because it can get impractical very quickly - 400 watts used on one or more peltiers and the cost of finally shifting the heat away can cost £500 a year or more, so one has to keep an eye on running costs.

I know, you are quite right. BTW, I like your posts about the importance of a correctly set up LNB wherever and whenever I read them.

 

[guest poster]

I know, you are quite right. BTW, I like your posts about the importance of a correctly set up LNB wherever and whenever I read them.

Thanks !

 

[BombedOne]

Guys. There's one country, which has stable -40C in winter, and has not so bad satellite coverage. Guess which one is that? - It's Russia. I've browsed trough tens of russian forums, reading posts about LNB performance in extreme cold. No results exceed gain in more than 5% of quality, and there's no data on ability to receive such signals, that are unreceivable under normal conditions. So I won't hardly rely on LNB cooling. It can lower only INTERNAL noise, which is actual only for dirt cheap LNBs. For any serious product, this should not be an issue.

 

[divibi]

So I won't hardly rely on LNB cooling. It can lower only INTERNAL noise, which is actual only for dirt cheap LNBs. For any serious product, this should not be an issue.

I am taking your point onboard, but I still think that at minus 80, 120, 180, 220, 260 deg. C THE MAGIC (that is, science) HAPPENS.

We simply don't know.

How do you make a 0.05 dB Noise Figure LNB (downconverter?)? Recreate the outer space temperature?
Someone once mentioned something called a MASER.

 

[BombedOne]

Yes, of course - many interesting things happen at low temperatures. But I suggest you an experiment - just take plain soldering wire (made of tin and plumbum mix), and put it into liquid nitrogen. When back to normal temperature, it will simply convert into fine dust. There's certain negative temperature, after reaching which, tin changes it's molecular grid structure, and can't return to normal one. This means - you can't simply chill down plain LNB to some amazing 50K or so on it will stop working. In fact, I can try to pour liquid nitrogen onto working LNB, but I'm 100% sure, it won't give any impressive results, so it doesn't worths spending money on liquid nitrogen. Of course - this is MY OPINION, if anyone else is willing to try - I'd like to see results.

 

[guest poster]

The cooling of the lnb to -30c / -40c has been proven to give gains just using freeze spray like you use to freeze a water pipe or even just cooling with water on a hot day can show gains.
It works... to a degree (sic). We are far too busy or we would have a system running... it is more doing it to a budget, especially running costs.

 

[BombedOne]

Well, I just watched youtube video, showing an 60cm offset dish fitted with generic (cheap) lnb being cooled and showing great results. But there are two vital facts being ommited during this test.

1. Dish size. Smaller dish picks up less noise from space, so if say, total noise level is 100%, and in case of small dish the noise distribution across dish(air) and lnb can be 50/50%, in case of bigger dish, it'll be maybe 80% dish(air) and only 20% LNB noise.

2. Used LNB was cheap type. If anyone have access to spectrum analyzer, he can try to put cheap LNB into radioelectrically shielded box, apply voltage and measure noise. And compare that noise level to some top level LNB noise.

The yearly temperature change where I live now, is up to 35C in summer, and to -18C in winter. I checked various LNB performance at different temperatures, no noticeable difference in Ku band. Only reasonable difference (signal Q improvement by 20-30%) can be detected in C band, but this is related to another factor - due to less time exposure to sun in winter, stratosphere ionises less in winter, which greatly helps C band receiving.

Anyways, as noname LNB's are dirt cheap here (3 bucks), I'll try once to repeat the experiment, just will get price of liquid nitrogen (such coolant sprays as in video, are not available here), if it's not too high, and what is MOQ.

 

[guest poster]

Cooling (including with liquid nitrogen) has been used for years for tx rx commercially....
A poor lnb might show a better gain or no more % wise than a good one... or worse..

what is a good lnb to you and price?