BATC Forum

I wonder what typical sensitivities people are getting on 24cm for the various data rates and FEC ?

At 4Mbps and an FEC of 3/4 I get a signal threshold of -100dBm

Not sure if this is good / bad or average.

This is after going thru' a duplexer with about 0.7dB of loss into a PGA103 LNA (about 1dF NF and 13dB gain) followed by a 7 pole interdigital with a loss of 2dB into a Comag SL30/12.

Not knowing the NF and bandwidth of the comag makes it hard to calculate the overall system performance.

73 Tim

Hi Tim,

That sounds about right - I do all the coverage plots for -95dBm and have seen up to -100 dBm for 4 Ms on rxrs I've tested.

In practice you will find you will need more gain to drive a sat rx - a typical LNB has 55 dB end to end gain so most of us use a 20 dB sat line amp on the input to the receiver.

73

Noel - G8GTZ

It is not easy to give an exact answer:
all NIMs we can find inside SetTopBox or used with a MiniTiouner have an already built in LNA before the zero IF tuner.
gain and noise factor are different for each kind of NIM ( Eardatek NIM uses a BFP450 Gain 15.5dB NF=1.7 dB, LG NIM uses BFP420 gain 21 dB NF=1.1 dB, Sharp uses a 2SC5751....)
so we measure the sensitivity of the whole structure inside the NIM: LNA+ zeroIF + demod.

TT S2-1600 has not LNA between the F plug input and the zero IF.

(So as the level value given by Tutioune/Minitioune is taken from the AGC value given by the DVB demod, you will see a difference of value between the 2 software)

Jean-Pierre F6DZP

Hi Guys,

thanks for the replies.

Looks as though I'm in the right ballpark and making some best case assumptions for noise figure, BW and qpsk demodulation threshold for a given data rate leads me to conclude that the very best theoretical sensitivity in my case would be about -104dBm.

I'm currently measuring -100.8dBm on a repeatable basis.

So taking into account connector, duplexer and cable losses I'm probably only about 2dB off and part of that could be down to my LNA NF.

I do find that for a given signal level the Comag SL30/12 captures the signal about 1-2dB before the TT3200 I also run. But both drop out at similar levels.

I'm not trying to measure absolute RF signal levels with the rx - just wanting to make sure the rx threshold is where it should be.

73 Tim