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Static desiccator

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Apek
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Jan 29th, 2019 at 5:26am  
Hi all,

Just want ask the necessity of having this static desiccator to be installed at 1.2m antennas equipped with 25W BUC..?

As we know, this device would help to eliminates moisture in small transmission line/ antenna systems. But I'm not sure is it worth to install this device for such small antenna.

Any comment/feedbacks are most welcome.

Apek
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Reply #1 - Jan 30th, 2019 at 1:57pm  
I've not seen any 'static desiccator' device for VSAT.  What does it look like ?   Maybe it is a short length of waveguide with a cavity on the side with the desiccator (silica- gel) inside, coupled to the waveguide with a small hole on the centre line of the broad face of the waveguide.  Sounds like an interesting idea. Is it possible to remove and heat (refresh) the dessicant every month or so ?

In a large earth station I have come across static desiccators that involve a large canister of dessicant and a dried air tube to the waveguide/feed system, plus a compressor. This relies on a very small calibrated leak on the far end of the waveguides so there is a slight air flow.  Someone needs to check the dessicant regularly and refresh as required. The danger is that it will inject damp air/water into the system.  Most large earth stations use automated twin desiccators canisters, one in use while the other is heated.  Your need a calibrated leak, air flow, humidity and pressure monitoring.

For VSAT systems I've not seen any dehydator systems in use. I've seen mostly completely sealed systems where the feed has plastic windows at both ends. LNBs and BUCs have plastic windows or extremely small air volumes at the waveguide connection.

In some cases there are two air holes, one at the top and one at the bottom of the system. This makes the air inside flow very slowly and I've not seen it fail. Example: holes at the top and bottom of the feed window with 'shades' to stop rain directly entering. It works OK if the feed window in tilted downwards so that rain/snow does not land on it.

If there is only one hole or only one slightest single leak then the feed will accumulate water. At night cold damp air is sucked in and condenses and is not expelled in the warm day. It gets gradually worse each day untill the feed is partially filled with water at which point it is noticed by system failure.

If you have a long flexible waveguide I would be tempted to try a pinhole at the extreme lower end and a similar pinhole at the top edge of the feed window, in both cases so that rain/snow is stopped.

I suspect that most 25W BUCs by design have sealed lids with a packet of dessicant included inside. This is intended for life and there will be a waveguide window at the flange.

What does your static device look like ?

Best regards, Eric
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Apek
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Reply #2 - Feb 3rd, 2019 at 12:27pm  
Hi Eric - thanks for your reply..i have a plan to install this model SD-003UV from CommScope for my 1.2m uplink chain.. Does it worth to have this on-board?
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Reply #3 - Feb 4th, 2019 at 10:19am  
If you have a flexible waveguide between the BUC and the feed system then a device like this makes sense.
In addition to the desiccator bottle you will need a length of the correct type tubing and a matching gas port at the waveguide/feed/BUC.  If the BUC is mounted low down below the feed arm I would suggest connecting the tube near the flex-waveguide BUC connection.

The only gas ports I have come across have been the ones incorporated in the flanges at the ends of elliptiguide waveguide.  See my pictures http://www.satsig.net/cgi-bin/yabb/YaBB.pl?num=1534530882

Looking on the internet the only device I can find that might apply to you is here: https://www.also.com/pub/assets/1bc08f2c-f5c3-4b2e-a9fe-bdce47bbf667.pdf
Find out how much it costs.

If your BUC has an air port, see if it applies just to the internals of the BUC or if it includes the waveguide flange. Normally BUCs have a window at the waveguide flange and the internal air is completely sealed with several bags of silica gel desiccant inside. 

I note that the SD-003UV from CommScope uses a new Cobalt Chloride desiccator which is safer than the traditional Silica Gel which is toxic (but which can be simply heated and reused many times).  The SD-003UV from CommScope also needs replacing approx annually. Read the instructions: https://www.commscope.com/catalog/doc/pdf/6305/SD-003_Static_Desiccator_with_UV_...

Eric

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Apek
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Reply #4 - Feb 13th, 2019 at 7:14am  
It is well explained and thank Eric!
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