Six meters at the boundary of HF to VHF characteristics. Sky noise still dominates on 6m with approx. 2000K noise temperature. The PR6 noise figure reduces K3 sensitivity to -148 dBm (approx. NF of 2 dB). That is a noise temp of 178K.
So if we add Tsky=2000K to Tr=178K and assume Tant=100K, the overall system noise temperature is 2378K. With a bw of 500-Hz this is a system sensitivity of -138.0 dBm. If we add 1-dB coax loss from antenna to preamp, the sensitivity drops to -137.8 dBm. Not very significant change in sensitivity for placing the preamp at the antenna. I am installing a 6m eme station with 0.85 dB coax loss. My preamp is attached to the back of the K3. http://www.kl7uw.com/K3-ARR-6mPreamp.jpg http://www.kl7uw.com/6m.htm 73, Ed - KL7UW ------------------------------ Message: 12 Date: Sun, 03 Jul 2011 11:28:31 -0700 From: Alan Bloom <n...@sonic.net> Subject: Re: [Elecraft] New to list; My first question To: "Larry, KB5HMU" <kb5...@starlightsolar.com> Cc: elecraft@mailman.qth.net Message-ID: <1309717711.1754.27.camel@ulinux-desktop> Content-Type: text/plain; charset="UTF-8" On Sun, 2011-07-03 at 11:02 -0700, Larry, KB5HMU wrote: > Here's my first question to the group: > I enjoy 6 meters immensely and someone recommended that I buy the > pre-amp. My understanding about the effectiveness of a VHF preamp is > to amplify the highest signal, i.e. at the antenna, to give the lowest > noise increase. The PR6 mounts at the radio. Wouldn't that be > amplifying noise in a weak signal more than if it were mounted at the > antenna? Yes, theoretically it is always better to put the preamp at the antenna end of the feedline so that the noise figure is not degraded by the feedline loss. However, that is less of an issue on 6 meters than on the higher VHF/UHF bands because: (1) Coax cable loss is less at the lower frequency and (2) Background noise is higher on 6 meters so that a super-low noise figure is not as necessary. It depends on what you're doing. If you are into 6 meter moonbounce or you have a long and/or lossy feedline then a remote preamp would be worthwhile. Alan N1AL 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-? DUBUS Magazine USA Rep dubus...@gmail.com ====================================== ______________________________________________________________ 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
