Brian, Thank you for the quick response. I have been researching the Heros SCR-cat, reading reviews, watched the YouTube videos and decided that is what I want for the Flex, especially when I use the Flex as a general coverage receiver outside of the ham bands. I just cannot get past the 910.00 US sticker shock price.
I hate intermods and broadband noise so a pre-selector seems like a nice item to have. I have a classic Collins also and yes, the pre-selector is nice. Those were the days of tuned circuitry on the input. 73, Robert KB6QXM "Ham Radio Open Conversation" Yahoo group owner/moderator ----- Reply message ----- From: "Brian Lloyd" <brian-wb6...@lloyd.com> To: "Robert Costa, KB6QXM" <kb6...@yahoo.com> Cc: "Lee Mushel" <herbe...@centurytel.net>, "FlexRadio" <FlexRadio@flex-radio.biz> Subject: [Flexradio] education/information Date: Sun, Feb 3, 2013 9:35 am On Sun, Feb 3, 2013 at 9:26 AM, Robert Costa, KB6QXM <kb6...@yahoo.com> wrote: Brian, So what you just said, the introduction of a pre-selector to the Flex would have negative effects? Not the 6000, but the non-stratosphere Flex radios. No, Any time you can eliminate an unwanted signal you eliminate its ability to intermodulate with other signals. Therefore a preselector early on in the receiving chain is very useful, especially if the rest of the radio is prone to IMD. (I have been thinking that the narrow-tuned preselector is one of the reasons that older tube rigs from the likes of Collins performed pretty well. Remember those went away with the High-IF-General-Coverage receiver that showed up in the late '70s. Remember how RX performance went to hell around the same time? Hmm?) >*BUT*< If you can eliminate nonlinearity and nonlinearity-causing components before you get to the A:D, i.e. connect your A:D directly to the antenna, and as long as that A:D does not saturate (clip), you have the (almost) perfect receiver with no IMD, modulo operating within its dynamic range. Remember those two 0dBm peaks standing alone in the spec-A display in Gerald's latest missive? That's what I am talking about. 73, Robert KB6QXM "Ham Radio Open Conversation" Yahoo group owner/moderator ----- Reply message ----- From: "Brian Lloyd" <brian-wb6...@lloyd.com> To: "Lee Mushel" <herbe...@centurytel.net> Cc: "FlexRadio" <FlexRadio@flex-radio.biz> Subject: [Flexradio] education/information Date: Sun, Feb 3, 2013 9:14 am On Sat, Feb 2, 2013 at 7:45 PM, Lee Mushel <herbe...@centurytel.net> wrote: > Has anyone put together a presentation on the "nature of SDR" specifically > for use as a club program where no one is familiar with the topic and all > that is known is vanilla "knob and button audio?" I know how difficult > this can be and can claim no success. Has anyone discovered techniques > that you can honestly say were successful! My own experience has detected > downright hostility but then asking for a mental transition from mechanical > activity and only audio input is a far cry from asking someone for > considerable dependence on video display. > Well, I am producing just such a presentation to give to a ham club. The thrust of my talk has nothing to do with knobs and computer screens. In fact, one of my main assertions is that SDR does not have anything to do with knobs or computer screens. My thrust is on the problems that face the receiver designer and how the components in an analog radio combine to create problems and how SDR makes it possible to reduce or eliminate those problems and produce a markedly better receiver. Here is the general thrust: - every component is non-linear to some extent. Some components, e.g. active devices, are more non-linear than others. All non-linearity produces intermodulation. And intermodulation products intermodulate with all real signals and other IM products producing crud everywhere. The fewer components you have between the antenna and the first point of demodulation, the better the receiver is going to be. In fact, if we could effectively detect the signal right at the antenna without having to pass it through a bunch of IM causing active components (and these can be tubes, transistors, diodes, FETs, etc.) then the receiver is going to be a LOT better. >POOF< Enter the Flex 6000 series. - Crystal filters are evil. Yes, they filter out unwanted signals but what they do to desired signals is un-pretty, e.g. ringing, phase shift, amplitude ripple, group delay, IM, etc. So anyone who touts the use of crystal roofing filters as a good thing doesn't really understand what is happening. Mostly crystal roofing filters are there to make the specs look better for signals outside the passband as opposed to actually making the radio work better. Regardless, the problem is still there. (See my first argument about IMD.) - Early on in the presentation work in discussion about how any analog signal may be represented in digital form and that once in digital form, it may be processed with no increase in IM products as long as you can avoid non-integer ratio resampling and make sure that there is no power above the Nyquist frequency. Oh, you may have to explain resampling and Nyquist frequency. And while you are at it, you might want to explain how filtering and decimation can increase dynamic range. This is where you are likely to lose the stragglers. :-) - And when someone calls you on this, inject the Albert Einstein reference. (See below.) > > Maybe the use of a "demo only" even with the assist of Powerpoint is > asking for too much. It seems that suggesting that software extensions > be considered something other than "soundcard modes." Doing so seems to > break off teeth in the mental gears. > To paraphrase Albert Einstein -- "Things should be made as simple as possible ... but no simpler." This means that you may have to tell people that they are going to have to THINK about what you are saying for awhile until the light bulb comes on. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
