Read this if you are so determined
I do.
Firstly, it is just as important as gain in determining if a satisfactory C/N ratio can be achieved. Secondly, I can't get the Swedish Microwave 'smwlink' program to calculate a meaningful C/N figure unless I can input the antenna noise temperature.
Unfortunately, calculating an antenna noise temperature "properly" is a bit (a lot) too complicated for me. Ideally, this should be provided by the antenna manufacturer, but we are lucky to find any data at all for most dishes that are readily available. So the approximation formula from Tony's article really comes in handy, I just have to figure out if it should also have a frequency/wavelength term.
BTW, I did find some antenna noise temperature data here : Note however, that some figures appear wrong, eg. Channelmaster model 243 @ Ku 30 deg.
Joe.
Read this if you are so determined
DM800 DM800se Vu+Duo ET9000
j_ds_au (11-03-12)
Thanks Vic,
This one says that for elevations above 10 degrees :
andFor a large (≈5m) Cassegraine antenna Tearth ≈ 10K
For a small (≈ 0.5m) antenna Tearth ≈ 100K
So, although this is a rougher approximation than previously (because elevation is not an explicit term), the fact that frequency is not a term here, suggests that it really isn't a term in the previous equation either. In other words, this gives some confidence that the previous equation can be applied from S band through Ku band, at least. Of course, actual noise data for the particular antenna model is preferable, if available.For E ≥ 10° and f ≤ 15GHz Tsky ≤ 40K
Joe.
Back to the dish topic. It comes down to the Optics and wave length.
Optics refers to how accurate the manufacturer has manged to get the parabolic curve ( Radios Square divided by 4 times the focal length ) to the stage where the dish has been assembled and installed. This translates to the dish efficiency. Many Asian manufactures didn't have a clue, they copy'd some US brand and got it sort of right but lower efficiency which translated to less gain.
The Wave length of C band microwave is between 20 to 25mm and Ku 4 to 5mm and so the bottom line for the domestic user:
For Ku band it should be a solid dish most are under 90cm and are affordable.
For C band a mesh dish will do the job. Most common are the 2.3m, depends on the brand some are more efficient then others.
The above refers to what is readily available and affordable. Large solid dishes especially new once can be expensive. Jonsa once produced a solid 1.8m single piece which was fixed to an outer ring, it had excellent gain. unfortunately mine completely rusted away.
IF EVOLUTION WORKS, WHY SO MANY IDIOTS?
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