[Elecraft] Sherwood's receiver performance table updated

Wed Apr 27 03:52:00 EDT 2016

The IC-7300 uses a 14-bit ADC.

My ANAN-100D uses 16-bit ADC and overload of ADC occurs at a signal level
of -10dBm, which I never see in my single transmitter environment.  I do
prefer the K3s for contesting, but not for lack of front-end robustness on
the part of the ANAN.

73, Barry N1EU

On Wed, Apr 27, 2016 at 3:48 AM, Barry LaZar <k3ndm at comcast.net> wrote:

> Joe,
>     I agree with you basically. I think it's just the manor in which you
> state the problem.
>
>     You touch on the real problem 14-16 bits of sampling vice having more
> bits in the sample. It's not specifically the direct sampling architecture.
> I think the radio companies just can't get 24 bit ADCs fast enough to do
> direct sampling at commodity pricing which would allow direct sampling with
> out the baggage. If I can do 24 bit sampling and high and low pass
> filtering, I can simplify receiver design AND have a an acceptable dynamic
> range. Multiple instances of DSP processing of the 24 bit samples will
> allow as many virtual receivers, slices, as processor power will allow. My
> guess is we are on the verge of getting to where we would like to be.
>
>     Flex is using a 16 bit ADC and I'm not sure what the 7300 is using,
> but I infer it, too, is 16 bit. I do believe that the Elecraft
> architectures are all based on 24 bit sampling. The Elecraft designs should
> be tolerant to serious environmental abuse short of a local thunderstorm.
>
>     Our comments reflect a rigorous tech discussion. But, there is another
> issue that has not been discussed in anything I've read so far, ultimate
> filter rejection. Flex, Kenwood, and Elecraft have filtering that runs in
> the 100 db region, or a little better. I saw that the IC-7300 is about 20
> db worse. What that means if you are a CW operator, serious or otherwise,
> and there is a pile up on a DX station, a contest, or just a really busy
> weekend, you may have problems from strong stations not too far away while
> you are trying to work an S1-3 station. SSB operators have other problems
> like splatter and no amount of superb design will fix that.
>
>     I'm pleased there is a vigorous discussion on the new radios. It helps
> push the designers and the technology.
>
> 73,
> Barry
> K3NDM
>
>
> ------ Original Message ------
> From: "Joe Subich, W4TV" <lists at subich.com>
> To: elecraft at mailman.qth.net
> Sent: 4/26/2016 10:10:32 PM an
> Subject: Re: [Elecraft] Sherwood's receiver performance table updated
>
> On 4/26/2016 8:08 PM, Kevin Stover wrote:
>>
>>> Everybody is ignoring W4TV's 800lb Gorilla, ADC overload.
>>>
>>
>> I can't take credit for that ... the warning comes from some of the
>> best RF designers in the world.  Direct sampling receivers are very
>> good in controlled situations.  Unfortunately, those who are used to
>> analog superhetrodyne receivers do not recognize the symptoms of ADC
>> overload/overflow in many cases.
>>
>> The overflow can show up as an occasional click or pop if the number
>> and strength of signals continues to increase conditions go down hill
>> very rapidly.  The best 16 bit ADC based SDRs can and do show very
>> significant overload issues when run without effective front end
>> bandpass filtering in high RF environments (160 meters near AM BC
>> stations, 40 meters in Europe, 160 meters in New England during a
>> contest, etc.).
>>
>> One can apply filtering (which Icom seems to have done in the 7300),
>> apply attenuation (which Flex seems to have done in the 6000 series)
>> or both.  Filtering limits the number and width of "slice receivers"
>> while attenuation kills weak signal performance.
>>
>> I find Icom's implementation interesting in that they are using the
>> technology as a single band, single channel receiver (they could have
>> added Dual RX within the same band at practically no hardware cost) - an
>> application where, with tight bandpass filtering, direct sampling
>> may be ready to compete as indicated by the fact that Sherwood's tests
>> place the 7300's above some "good" conventional rigs like the Ten-Tec
>> Eagle, Kenwood TS-590SG and TS-990 in MDS, LO Phase noise and IMD DR.
>>
>> However, for the ultimate multi-channel receiver, ADC technology is
>> still 4 to 6 bits short as witnessed by the need for 12 to 20 dB of
>> attenuation in the Flex 6000 or the 0 to 30 dB electronically stepped
>> attenuators in some of the other products like the Anan, Hermes, etc.
>> Sherwood's results hint at this when comparing the MDS with the
>> preamp on and preamp off ... even with its preamp on the Flex 6700
>> MDS is the same as the K3S with *no preamp*!
>>
>> 73,
>>
>>    ... Joe, W4TV
>>
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