[Elecraft] USB sound dongle

Barry LaZar k3ndm at comcast.net
Tue Aug 21 18:17:05 EDT 2012 

Joe,
     I think I just figured out we are not necessarily comparing apples 
to apples. I just responded to a note you wrote on this reflector that 
caused me to review what we are saying. You are correct of course if we 
allow our basic radios to do their thing without our involvement and 
then we do an A/D afterward.

     You are also correct in pointing out that all of our radios are 
externally noise limited today. However, the issue of USEFUL dynamic 
range is only eluded to by you. Antenna noise is the vector sum of all 
of the noise in the environment, regardless of how it got there. It's 
true living where I do, in an urban environment with power lines and 
gasoline engines, I'll never see antenna noise that looks like the 
atmospheric noise that can be seen down on the farm. And yes, I'm a 
little idealistic in my designs, but during a contest or near the BC 
stations your electronics and software are going to be tested. And 
remember that the international BC guys design to hit urban 
environments, meaning lots pf power that will assure high S/N ratios on 
you communications receiver, not necessarily that cheapy SWL radio from 
Radio Shack.

     I am not using demoded line out audio from my KX3. I use the raw I 
& Q data. I think that is what we missed in our past exchanges. That 
means I can really use the dynamic range of a 24 bit card because I set 
things so that noise doesn't control my A/D any more than a few bits. I 
believe you need to so it this way just so you don't miss anything. But, 
we can discuss that in the future.

73,
Barry
K3NDM

On 8/21/2012 2:57 PM, Joe Subich, W4TV wrote:
> Barry,
>
>> The issue is really when will all those bits go to a logic 1. With 16
>> bits, it will be ~96 db where db=20log V2/V1. I know this is not
>> what most perceive, but it's true the A/D convertor is a voltage
>> sensitive and not a power sensitive device.
> The issue with dynamic range is just as much the ability of all those
> bits to go to logic 0.  If the receiver has so much noise - whether
> atmospheric noise at the antenna, thermal noise in the IF, masking
> due to A/D/A conversions in the demodulator, or thermal noise/hum in
> the audio output stages, the sound card will never achieve even the
> theoretical 96 dB dynamic range for 16 bit A/D.
>
> Add to that, switching noise on the typical USB power line, the lack of
> secondary regulation in inexpensive USB sound "dongles", the failure
> to provide a separate *regulated* reference for the ADC, failures to
> provide *regulated* references for op-amp preamps, lack of attention
> to grounding and bypassing, etc. and the noise floor in commodity USB
> sound devices (and "inexpensive" amateur products) further limits the
> achievable dynamic range.
>
> With external noise sources, it doesn't matter if one has a 16 or 24
> bit ADC, the achievable dynamic range will be limited to the area
> between *all* of the noise contributors and the maximum voltage
> handling capability (typically < 5.0V) of the ADC ... or between
> 65 and 70 dB in many of the commodity and inexpensive amateur
> devices.
>
> 73,
>
>      ... Joe, W4TV
>
>
> On 8/21/2012 10:48 AM, Barry LaZar wrote:
>> Joe,
>>         I agree with your comment on internal noise. However, 24 bits of
>> quantization will get you a better dynamic range. But, It becomes an
>> interesting point when the effects of receiver AGC gets into the
>> discussion on this point. Someone in a much earlier post said that the
>> receiver's AGC would keep things within bounds for a 16 bit card; he may
>> be correct. But, if you run without AGC on the receiver and use AGC
>> developed by the SDR software, having those extra bits will make a
>> difference, particularly during noisy periods or contests.
>>
>>        The issue is really when will all those bits go to a logic 1. With
>> 16 bits, it will be ~96 db where db=20log V2/V1. I know this is not what
>> most perceive, but it's true the A/D convertor is a voltage sensitive
>> and not a power sensitive device. There are some other interesting
>> subtleties like how much dynamic range do you really need, etc. Since I
>> haven't had my first cup of coffee yet, I think I would not like to get
>> in to those at this time.
>>
>> 73,
>> Barry
>> K3NDM
>>
>> On 8/21/2012 10:13 AM, Joe Subich, W4TV wrote:
>>>> However, this card is not current; I think the 0404 replaces it.
>>>> Someone can address this for you.
>>> The current version is eMU 0204 - approximately $125 at places
>>> like B&H Photo Video.
>>>
>>>> You really do want a 24 bit card and not 16 bit one.
>>> Unless you need the high sample frequency for wide panadapter service,
>>> any well designed 16 bit/48 KHz USB sound device will provide all the
>>> performance you need at less than 1/4 the price of something like the
>>> eMU 0204.
>>>
>>>     > The other thing is that that card should have low internal noise;
>>>
>>> This is *the most important* determinant of performance.  Internal
>>> noise dramatically reduces the effective dynamic range of the sound
>>> card.
>>>
>>> 73,
>>>
>>>        ... Joe, W4TV
>>>
>>>
>>> On 8/20/2012 4:40 PM, Barry LaZar wrote:
>>>> Howie,
>>>>          The dongles I have seen are not spectacular. They are about on par
>>>> with your average stereo laptop soundcard, OK but not great. I use a
>>>> E-MU0202 from Creative Labs. This card is a 24 bit card that can sample
>>>> beyond what Elecraft recommends. However, this card is not current; I
>>>> think the 0404 replaces it. Someone can address this for you. You really
>>>> do want a 24 bit card and not 16 bit one. The other thing is that that
>>>> card should have low internal noise; the high end Creative Labs card
>>>> meet this as does several others.
>>>>
>>>>          There are a number of software packages around that you can use. I
>>>> use NaP3 because it can control the KX3 and allows me to use VAC so that
>>>> I can pipe the output to FLDIGI for reading the digial modes. I have
>>>> essentially a full up computer controlled SDR that I can take out for
>>>> Field Day and operate portable with knobs and a battery. It's the craziest!.
>>>>
>>>>          I think, once you have it all lashed up, you will really have some
>>>> fun. Good luck and do use a good card with ASIO drivers for best
>>>> performance.
>>>>
>>>> 73,
>>>> Barry
>>>> K3NDM
>>>>
>>>>
>>>> On 8/20/2012 12:37 AM, Howard Hoyt wrote:
>>>>> Hi,
>>>>>
>>>>> I have been following the fun on this reflector while awaiting my KX3
>>>>> (next Friday!).  I am very interested in using the I&Q outs to interface
>>>>> with my laptop, and as many have noted, you need a good, compatible
>>>>> sound device to have a usable panadapter display. Does any one have
>>>>> experience with a 192k sampling USB sound dongle for their laptop?
>>>>>
>>>>> TIA!
>>>>>
>>>>> Howie
>>>>>
>>>>> Howard Hoyt - WA4PSC
>>>>> CE - WXYC-FM 89.3
>>>>> UNC Chapel Hill, NC
>>>>> www.wxyc.org
>>>>> 1st on the internet
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