http://elecraft.85.s1.nabble.com/K3S-SDR-superhet-hybrid-vs-entry-level-direct-sampling-radios-tp7632855p7632863.html
Welcome to Flex's own myth. If the information posted in that paper
amplifiers rated for average power. That is demonstrably not true as
... Joe, W4TV
> 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 <
[hidden email]> 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 <
[hidden email]>
>> Date: 7/30/17 11:14 AM (GMT-06:00) To: Elecraft Reflector <
>>
[hidden email]> 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
>>
>>
>>
>>
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