0.3db vs 0.6db Noise Ku LNBs
- Thread starter HDTVFanAtic
- Start date
- Latest activity Latest activity:
- Replies 8
- Views 4K
HDTVFanAtic said:
Noise Figure is based a terrestrial ambient temperature reference of 290K, and is defined as how much noise is added by passing thru the amp. So 0.3 dB adds 21 degrees K, 0.6 dB add 43 degrees K. The unknown is the Antenna temperature at your elevation angle above the horizon (the higher, the more you see of the cold of space, and the less of the 290K terrestrial heat. But if were to say it was 30K, then the NF improvement calulation would be 10*log ((30+21)/(30+43)) = 1.55 dB improvement in CNR (Carrier to Noise Ratio). Commercial antennas (as opposed to consumer) usually have a graph of noise temp as a function of elevation above horizon on their data sheet, to facilitate the calculation I made above.
Last edited:
k2ue said:
If I were at sea level (thus not in the cold air) - what % improvement should that 1.55db give me over a 0.6?
HDTVFanAtic said:
It depends entirely on how adequate your signal is now: if poor, 1.5dB might nudge it up to good; if good then perhaps to very good -- but it probably won't make a poor signal very good.
Thanks for the input/
There are several articles that i have found that lead on to believe that the 0.3 db signal spec is just marketing hype - that the real figure needed is the maximum - worse case scenario.
Right now I have a usable 74 from E* 148 with a toroidal T90 and a 0.6 lnb. When I used a .5 meter Dish 500 I was able to get a 55, so the move from a .5 meter to .9 meter gave me about 35% additional signal. I was curious what a move to a 0.3 lnb would yield, but that seems to be trick question if I believe everything I read.
There are several articles that i have found that lead on to believe that the 0.3 db signal spec is just marketing hype - that the real figure needed is the maximum - worse case scenario.
Right now I have a usable 74 from E* 148 with a toroidal T90 and a 0.6 lnb. When I used a .5 meter Dish 500 I was able to get a 55, so the move from a .5 meter to .9 meter gave me about 35% additional signal. I was curious what a move to a 0.3 lnb would yield, but that seems to be trick question if I believe everything I read.
HDTVFanAtic said:
The move from 0.5 to 0.9 meter would have netted about a 5-6 dB improvement in CNR, roughly 4x what the LNB change would yield. Small antennas have a higher noise temp at the same elevation, giving less advantage to a better LNB, so you should max out antenna size before going to lower temp LNB's if size alone is not enough.
Thank you for your knowledgable info on this.
If I could ask you one last thing, how much gain should I net going from a 24" dish to a 30" dish.
Also, how much should I net if I move from my .9 Meter to 1.2 Meter?
Are the increases linear and consistent?
If I could ask you one last thing, how much gain should I net going from a 24" dish to a 30" dish.
Also, how much should I net if I move from my .9 Meter to 1.2 Meter?
Are the increases linear and consistent?
HDTVFanAtic said:
Power gain is directly proportional to capture area for the same efficiency, and efficiencies are all fairly similar, plus the noise temp goes down slightly as dish size goes up, so there is a (very) small improvement there too. 24" to 30" would be 1.9+ dB, 0.9m to 1.2m would be 2.5+ dB. The gain increase is just 10*log(area1/area2), or 10*log((dia1/dia2)squared), if you have a caluculator handy.
Last edited:
Although Ku2 is correct in all of their assessments, the biggest reason for going to a larger dish assy. and a higher grade LNB, is to help eliminate the "Rain Fade" problem, as much as possible... Of course there could be commercial applications that would gain more by this application, as well.
