It has been said by many hams over the years that if you connect an antenna to a receiver and you can hear the noise level increase, then you don't need a preamp, as it will simply amplify the noise and the signal equally. In general, I've found that to be true. HOWEVER...
Let's say that the noise figure of the receiver's internal preamp is 1.5 dB, and the noise figure of the external preamp is 0.5 dB. Each preamp will give you about 10 dB of gain. It seems clear that using the external preamp instead of the internal one would give you another dB of signal+noise to noise. Is my reasoning accurate on that score? If so, then it would be useful to know the noise figure of the K3's internal preamp at 50 MHz. I don't know what it is.>>>> I don't know the figures of the K3, but here is how it would work out for some arbitrary numbers: .5 dB NF preamp 10 dB gain to 1.5 dB amp 10 dB gain to 8 dB NF 8 db gain mixer. = 0.85 dB NF 1.5 dB NF 10 dB gain RF amp to 8 dB NF 8dB gain mixer = 2.89 dB composite NF There can be a larger NF increase than the difference in NF between the preamps. I doubt any of us would actually need a 0.5 db NF with a terrestrial aimed antenna of normal beamwidth and gain on six meters. I certainly don't and I'm in a quiet rural location on a dirt road. A few dB NF is enough here. What noise figure do other people **really** find they need?? Anyone know exact figures? 73 Tom ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
