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*Subject*: FT736 Noise Figure ?*From*: Chris Hill <CRH_Telnet@xxxxxxxxxxx>*Date*: Tue, 12 May 1998 23:55:51 +0800

Hello, Sometime ago, there was a message via this list on the improvements which could be realised on the FT-736 by fitting the MuTek front-end kit. I seem to remember there being an analysis of the original 736's noise figure, mostly blaming the helical filters and PIN-diode switch. A very vague memory of 3.5dB comes to mind? Does anybody have a copy of that information? I'm trying to do a 'proper' analysis of what signal strength is required to maintain a given BER on the 9600bps downlinks from UO-22 etc. If a BER of 1 x 10E-4 is acceptable, and is available when Eb/N0 is 12.1dB (from BER graph available at http://www.ee.surrey.ac.uk/EE/CSER/UOSAT/papers/icdsc_ws/icdsc_ws.html), then this converts to a required C/N of 8.9dB for a bit rate of 9600bps and receiver bandwidth of 20kHz. If the FT736 *does* have a Noise Figure of 3.5dB, then this converts to an excess noise temperature of 359K (using Te = (F-1)T0) The required signal strength ('C') required to provide a C/N of 8.9dB is able to be derived from; C = C/N + k + T + B (all in dB) where k is Boltzmann's constant, T is noise temperature and B is bandwidth. T(sys) = T(ant) + T(receiver) (assuming no feedline loss) and at 430MHz, the effective sky noise temperature at low elevations is the same as the warm earth : 290K. We can then use a figure of 290K for system antenna temperature. thus T(sys) = 290K + 359K = 649K Plugging all this into our C = C/N + k + T + B (all in dB) formula gives; C = 8.9dB + (-228.6dBJ/K) + 28.12dBK + 43.01dBHz therefore C = -148.57dBW = -118.57dBm in other words, maintaining a received signal strength into the receiver of -118.57dBm will give a BER of 1x10E-4. If a low-noise pre-amp (NF = 0.9dB, gain = 10dB) is used, then Tsys can be expressed as; T(sys) = T(ant) + T(preamp) + T(receiver)/G(preamp) (assuming no feedline loss) therefore; T(sys) = 290K + (1 - 10^(0.9/10)) * 290 + 359K/10 T(sys) = 290K + 66.8K + 35.9K = 392.7K = 25.94dBK therefore when using the preamp, the required signal strength is -120.75dBm to give a BER of 1x10E-4 So, if the NF of the 736 is 3.5dB, then the use of a (typical) mast-head preamp delivers a 2dB benefit... you could almost use an antenna which was half the size. Anyway, back to the original question; does anyone have the measured noise figure for the FT-736 on 70cm? Many Thanks, Chris Hill VK6KCH

**Follow-Ups**:**Re: FT736 Noise Figure ?***From:*Dean Shutt

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