[Elecraft] Sherwood's receiver performance table updated

Mon Apr 25 18:17:48 EDT 2016

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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