Gerald, I think we have to start over. My concern with noise figure had to do only with 2 meter DX. I had no question about any performance on the HF bands or 6 meters. And I certainly know about putting the low noise preamp at the feed point of the antenna and I know about the switching associated with a practical system and I do have a sequencer.
Now, I insist that we go back some 50 years to find me growing up in northern Wisconsin where there were a total of some four teenagers routinely on the cutting edge of ham radio: two meters. And this is over nearly one half of the state. Finding someone to talk to was a very big deal. And I think I can still find low noise preamps using the Western Electric 416b and 417a tubes in my shed that I built at that time. Moonbounce was only on 1296 and there was a lot of discussion on what was involved in calculating total system performance. Now let's go back a few days. I don't think I ever mentioned it to you but I do have the V/U upgrade and sitting on top of my 5000A are the Elecraft 144 and 432 transverters. I feed those into the RX2. If I can believe my 5000A my local noise floor a few days ago was a little better than -140 dBm. I would think most folks would expect that I would be interested in comparing the performance of the Elecraft and Flex front ends. And I do this frequently and I can safely say that with the Flex I can hear weaker signals and that never surprised me because the specs of my several year old Elecraft. I sincerely regret having commented on what I'm fairly sure is still an encouragement of mediocrity and I will not do that again. But I appreciate your taking the time to write me. 73 Lee K9WRU ----- Original Message ----- From: Gerald Youngblood To: Lee Mushel Cc: Brian Lloyd ; Ron Stockton ; [email protected] Sent: Thursday, May 24, 2012 3:49 PM Subject: Re: [FlexEdge] Flex 6000 MDS Lee, It is a very common misconception that lower noise figure is always better. A good article on the subject was in the June 2010 issue of QST. The article written by Joel Hallis is titled, "Receiver Sensitivity - Can you have too much?" The answer is yes. All you get is more noise and lower total dynamic range. What you want is for the gain to be set optimally for the band noise floor at your specific location. In fact a low noise figure may actually reduce total dynamic range for a given band and conditions. We could easily have put a <1 dB preamp for the same cost in the radio but that would have degraded total total IMD dynamic range. If you really care about a 0.1 dB NF preamp, it would be a total waste to put that inside the radio because it would ruin gain distribution and it would be swamped by the coax loss. The FLEX-6700 can give you a 4 dB NF on 20m but that would would ridiculous since the atmospheric noise figure equivalent in a rural area is probably greater than 35 dB above kTb. All you would be doing is to reduce the total dynamic range because you have too much gain. MDS of around -120 dBm is probably appropriate for most locations on 20m On 10m you probably need an MDS of around -130 dBm in rural areas and -122 dBm in residential areas. On 10m you can probably use -137 dBm (10 dB NF) only if you are in the quietest rural areas. The bottom line is if you want lowest noise figure on 2m, put the low noise preamp at the antenna and turn off the preamp in the radio. That will give you better gain distribution and will overcome the coaxial line loss. Regards, Gerald Gerald Youngblood, K5SDR President and CEO FlexRadio Systems(TM) Email: [email protected] Web: www.flexradio.com Tune In Excitement (TM) PowerSDR(TM) is a trademark of FlexRadio Systems On Wed, May 23, 2012 at 9:39 AM, Lee Mushel <[email protected]> wrote: I sure hope you are wrong about that number. You know, in 1958 I had a Techraft Converter that had a noise figure of 7dB and my quite excellent V/U upgrade is somewhere around 1 dB and my dedicated pre-amp is somewhere close to 0.4 dB. A noise figure of 4 in 2012 would rate somewhere between wretched and miserable! Lee K9WRU ----- Original Message ----- From: "Brian Lloyd" <[email protected]> To: "Ron Stockton" <[email protected]> Cc: <[email protected]> Sent: Tuesday, May 22, 2012 11:23 PM Subject: Re: [FlexEdge] Flex 6000 MDS On Tue, May 22, 2012 at 8:19 PM, Ron Stockton <[email protected]> wrote: Before I jump in and place a pre-order, can you provide a hint of the Minimum Discernible Signal (MDS) level on 30 MHz? This was a conspicuous TBD on the preliminary spec sheet. Gerald mentioned in a posting that the performance on 2m will be about 4dB NF. Since it is the same receiver, I would suspect that 10m performance will be at least as good. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 [email protected] +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software. _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software. _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software.
