[Elecraft] USB sound dongle

Tue Aug 21 14:57:51 EDT 2012

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
>>>> ______________________________________________________________
>>>> Elecraft mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:Elecraft at mailman.qth.net
>>>>
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:Elecraft at mailman.qth.net
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>