[Elecraft] Sherwood's receiver performance table updated

Mon Apr 25 20:12:44 EDT 2016

> Firstly, the K3/K3S (without the second receiver) cannot be on more
> than ONE amateur band at a time. So, why create an artificial "test"
> that the typical K3 can't even do?

Because that is *exactly* what Flex (and others) promotes - multiple
"slice receivers" anywhere from 1 to 54 MHz.

> Secondly, I wonder how good the K3/K3S would be if you also pulled
> their front-end filtering?

It's not an issue because the filtering is built in - unlike the Flex
6300 that has *no* preselector/bandpass filters.

 > 14-bit ADCs aren't showing this problem here, even without
 > the HPF.

I have an AM site (two transmitters about 5 miles away) that puts
more than 2 mW into the reverse port of my microHAM SMORF vector
Wattmeter when I use my 160/80/40/30 trapped inverted V during the
daytime.  Even after the K3 T/R switch and KBPF3, I see at least
two signals higher greater than -20 dBm on the P3 and more than a
dozen at -30 dBm or more.

Another individual in rural Colorado reports 15 signals > -30 dBm
on his 160/80 meter Marconi T that makes an unfiltered 14 bit ADC
direct sampling transceiver unusable on 160 and 80 meters.  In his
case it required 22 dB of attenuation plus an ICE 402 1.8 MHz HPF
to "clean up" the broadcast intermod.  Now maybe an MDS of -100 dBm
works on 160 but it certainly isn't going to work on the high bands.

73,

    ... Joe, W4TV

On 4/25/2016 6:17 PM, wb4jfi at knology.net wrote:
> While I don't disagree with the possibility of your first paragraph Joe,
> your third one doesn't make a lot of sense to me.
>
> Firstly, the K3/K3S (without the second receiver) cannot be on more than
> ONE amateur band at a time.  So, why create an artificial "test" that
> the typical K3 can't even do?  I believe that most K3/K3S out there
> don't have the second receiver.  Plus, the K3/K3S cannot listen to three
> (or more) bands at once, which the 6500 and 6700 can.
>
> Secondly, I wonder how good the K3/K3S would be if you also pulled their
> front-end filtering?
>
> I'm still very much an Elecraft fan with both a K3 and a KX3, so I'm not
> disparaging the Elecraft equipment at all.  I LOVE THEM!  I just want
> apples vs apples, please.
>
> BTW, I have an AM station within a couple of miles - directly
> line-of-sight down the river, and I don't see this alleged problem at
> all.  But, I'm only using dipoles, a Steppir vertical, or a 50-ohm
> resistor for antennas. Hi Hi. I do see this problem with several 8- or
> 12-bit SDR designs without high-pass filtering, but with a filter, it
> goes away.  14-bit ADCs aren't showing this problem here, even without
> the HPF.
> 73, Terry, N4TLF
>
>
>
>
> -----Original Message----- From: Joe Subich, W4TV
> Sent: Monday, April 25, 2016 5:30 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] Sherwood's receiver performance table updated
>
>
> On 4/25/2016 4:44 PM, Dave Hachadorian wrote:
>> It's interesting that the 7300's ranking in the table is because of its
>> 94 dB Dynamic Range at 2 KHz spacing.  But the footnotes indicate that
>> this dynamic range is with AP+ turned ON.  With AP+ ON, minimum
>> detectable signal is degraded by 11 dB.
>
> That's true of *every* direct sampling SDR in the list.  That's the
> "dirty little secret" of direct sampling SDRs ... in order to maintain
> that "pristine" IMD DR the "total signal level" or instantaneous peak
> voltage at the ADC must stay below the clipping/overflow level.
>
> Look at the ARRL review of the Flex 6700 and 6300 ... compare their
> MDS with the preamps on and preamps off, then look at the IMD DR
> with the preamps on and off (where the data is available).  Even for
> the Flex, MDS is degraded by 10 to 15 dB in order to maintain the full
> dynamic range (not much different than the 7300).
>
> Direct sampling disciples will claim the MDS reduction is not a problem
> but try running one of their radios within a couple miles of an AM
> station with "slice receivers" on more than one amateur band (so the
> preselector/bandpass filters are bypassed).
>
> 73,
>
>   ... Joe, W4TV
>
>>
>> With AP+ OFF, as generally recommended in the footnotes, 2 KHz dynamic
>> range is only 81 dB, which would place the 7300 considerably lower in
>> the table, but still pretty good.
>>
>> Dave Hachadorian, K6LL
>> Yuma, AZ
>>
>>
>> -----Original Message----- From: Joe Subich, W4TV
>> Sent: Monday, April 25, 2016 11:55 AM
>> To: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] Sherwood's receiver performance table updated
>>
>>
>> Very interesting ... pretty good performance from the IC-7300 for an
>> "entry level radio."  On the other hand, the IC-9100 should be better
>> than "mid pack" given it's recent design and price - it's even *worse*
>> (both IMD and LO Noise) that that paragon of "high performance," the
>> IC-706mkIIg!
>>
>> 73,
>>
>>    ... Joe, W4TV
>>
>> On 4/25/2016 10:55 AM, Wayne Burdick wrote:
>>> Rob has added the IC-7851, IC-7300, and IC-9100 to his table:
>>>
>>>     http://www.sherweng.com/table.html
>>>
>>> 73,
>>> Wayne
>>> N6KR
>>>
>>>
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