Guys, I've installed a dish at the end of my garden (only place it can go) which means I'm going to have to run 40 metres of cable to my Humax DCI2000. Will I experience problems with signal loss over this run? Should I go for a particular type of cable?
Thanks
I think you will probably be OK with a 40 m cable run of CT100 / WF100 (or better), without requiring an amplifier. I have a satellite dish at the far end of the garden from the house (the only suitable location) and the cable is 100 m long. This does require an amplifier, about 35 m from the LNB end, but your 40 m cable may not require an amplifier. Fitting an amplifier when it is not needed may actually degrade the overall noise performance of the system.
What matters is not the cable signal loss as such but the degradation in signal to noise ratio at the satellite receiver demodulator input. This degradation is likely to be be less than 0.01 dB for a 40 m CT100 cable (or its equivalent) and very slightly better for CT125 (but the improvement (of CT125 over CT100) for a 40 m cable length would be very marginal).
If we assume:
LNB Noise figure = 0.7 dB
LNB minimum conversion gain = 50 dB
Loss of 40 m of CT100 satellite cable at 2 GHz = 11.6 dB
Noise figure of satellite IF receiver = 10 dB
The Overall Noise Factor = F1 + (F2 - 1) / G1 + (F3 - 1) / G1 G2 + -----
In our case:
F1 = LNB Noise Factor = 1.174898
G1 = LNB conversion gain = 100 000
F2 = Noise factor of 40 m of CT100 cable = 14.45
G2 = Gain of 40 m CT100 cable at 2 GHz = 0.0692
F3 = Noise factor of satellite receiver (IF) = 10
So the overall noise factor with the 40 m cable included:
= 1.174898 + (13.45 / 100 000) + (9 / 6920) = 1.176332
= 0.7053 dB noise figure
So the 40 m cable degrades the noise figure by 0.0053 dB, which should have negligible practical effect.
[If the cable was much longer, say 100 m, then:
the overall noise factor using the 100 m cable is:
= 1.174898 + (793 / 100 000) + (9 / 125.9) = 1.254313
= 0.984 dB noise figure overall (for 100 m CT100 cable), nearly 0.3 dB degradation].
In practice there will be mismatch losses at the cable ends which should be added to the cable loss. On the other hand, the assumed conversion gain for the LNB is probably on the pessimistic side.
Alan