Concerning Flex, one of the engineers posted a pretty detailed explanation of how they handle strong signals in a wide band environment. This stuff is still a bit over my head but owning both the KX3 and the Flex-6500 I can say, I am never disappointed with either receiver in any environment. I kind of feel like the luckiest dog in the world to have both.
I hope it is OK to post the link: https://community.flexradio.com/flexradio/topics/adc-overload-myths-debunked 73, Kev K4VD On Sun, Jul 30, 2017 at 12:27 PM, GaryK9GS <[email protected]> wrote: > Thanks for sending Wayne. To take this discussion a step further, is > the Flex series of radios in the same category as the 7300? > > > 73, > Gary K9GS > -------- Original message --------From: Wayne Burdick <[email protected]> > Date: 7/30/17 11:14 AM (GMT-06:00) To: Elecraft Reflector < > [email protected]> Subject: [Elecraft] K3S (SDR/superhet hybrid) > vs. entry-level > direct-sampling radios > Hi all, > > Over the past two days I’ve been deluged with requests for our K3S vs. > IC7300 comparison chart. This stems from a posting that mentioned the > latter rig, and my subsequent offer to send out the chart, which we > normally use for in-house training purposes. > > What’s become clear from all the questions and comments is that there’s a > need for clarification on receiver architecture. > > The K3S, an SDR/superhet hybrid, includes narrowband protection of its > A-to-D converters in the form of roofing filters (crystal filters). This is > fundamentally different from the approach taken by direct-sampling radios, > which have only very broadband filtering ahead of their ADCs. Typically, > front-end band-pass filters are 0.5 to 4 MHz wide. Their ADCs will be > impacted by all strong signals in this range, alone and in summation. > > When the ADC over-ranges in this “pure” SDR architecture, the radio > usually reduces its gain automatically by either turning off preamps or > adding attenuation. This increases the noise figure, often resulting in the > loss of weak signals, both audibly and in the panadapter. Another word for > it is “desense.” You might hear a pulsing sound as the noise floor goes up > and down in response to a particular signal, or the sensitivity may degrade > for many seconds at a time while the firmware waits for levels to drop at > the input to the ADC. > > Such over-ranging is almost unheard of in the K3S, for multiple reasons. > First, we use very strong mixers and gain stages. Second, in many cases > there’s no need to turn the preamp on at all. (Example: the K3S’s > preamp-off sensitivity is typically -135 dB, while the preamp-off > sensitivity on a typical direct-sampling SDR is -115 to -125 dB.) The third > reason for the K3S’s strong-signal performance is its crystal roofing > filters. These protect the ADC from not only wide-spaced signals, but also > from signals very close by. As K3 and K3S owners will attest, you can have > a huge signal just a few hundred Hz away and not even know it’s there -- > unless that station’s transmit phase noise is blanketing the band anyway. > (There’s no defense against an unclean or clicky transmit signal.) > > I’ve updated the referenced comparison chart to clarify this important > difference. Our webmaster will put it up next week. > > Meanwhile, I’ll continue to send it on request (email me directly). Feel > free to share the information with anyone interested in the topic. > > 73, > Wayne > N6KR > > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
