Re: Checking a LNB


J.W. Davies
 

You could try a technique that has been used since the early days of satellite TV.


Put a satellite signal strength meter in the coax feed to the LNB. The LNB being powered up.

Point the LNB straight up and note the reading.

Repeat but this point the LNB straight down at the ground and compare the reading with the sky pointing one.

There should be a large difference.


The reason this works is that at around 10-12GHz the sky has a noise temperature of a few degrees Kelvin and the ground has a noise temperature of around 280 degrees Kelvin.

Compare with a known good LNB, if you have one, to compare the amount of change.


The effect is surprisingly strong. I've used the effect on many occasions to test LNBs and on old analogue satellite TV receivers the AGC rail would go from one extreme to the other during the test.

How powerful a radio emitter the ground beneath a dish is often forgotten by satellite dish installers and a poorly mount or incompatible LNB feed horn/ dish assembly can result in the LNB seeing the "hot" ground and they being baffled by not being able to achieve a low noise figure even with a large dish.


I hope that is of some help


Regards

James





On 04/12/20 14:33, diogenes1 via groups.io wrote:
Hello All, I am assuming, because of the lack of replies, that the only way to check a LNB is to install it on a dish and check for a signal or not. This seems quite odd to me in this technological age that suck it and see is the only option!
Regards, Peter

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