[Elecraft] USB sound dongle

[Barry LaZar]

I concede that a lot of 24 bit cards are no better than 16 bits. 
However, I stand by what I said that it is better to use a 24 bit A/D.

It is also true that most receivers are externally noise limited up 
through around 15 meters. And, that gets to a design subtlety known as 
proper gain distribution in the receive chain and proper noise figure 
design, It sure makes little sense to design a radio that has a 15db 
noise figure for say 80 meters where excess external noise might be 
around 80db; I suggest CCIR-322 as a reference. But that doesn't mean 
one should run his radio at wide open gain from 160-10 meters. Yet, we 
hams do that most of the time. It would be a surprise to me if more of 
us didn't complain about overload.

Having said all of that and possibly adding to the fog of this 
discussion, I would suggest that 80-90 db would probably satisfy most, 
most of the time. The exceptions might be contests and 40 meters in the 
evening when the international BC gets going full bore.  But, that 
should be based on a 10log function and not a 20log function. A good 
sound card would be my recommendation if you are doing what I do, run 
the KX3 as SDR ala FlexRadio. If all you plan to do is use SDR software 
for panadapter purposes, It probably doesn't make  a lot of difference.

The technology is here today to go first class, or nearly so, so why 
not. If you have a KX3, you are right up there, so why not get a good 
card and finish the job for another $100-$150. The software is free.

73,
Barry
K3NDM

On 8/21/2012 11:18 AM, Jim Brown wrote:
> On 8/21/2012 7:48 AM, Barry LaZar wrote:
>> However, 24 bits of
>> quantization will get you a better dynamic range.
> Not if the dynamic range of the analog electronics limits it, which is
> what Joe has pointed out. Often those extra bits are "advertising bits"
> -- they fool those who don't know any better into believing that more
> bits is better.  Actually, it's far more important to optimize the
> signal level that the A/D converter sees. That's why I like the Tascam
> USB interface better than the Numark -- it has a much greater range of
> gain adjustment and a clip light on the front panel. That allows me to
> easily optimize the 90 dB or so of dynamic range that its 16 bits provides.
>
> Besides -- the 90 dB dynamic range provided by a decent 16-bit A/D is
> probably more than most hams will ever see at the audio output of their
> radios.  While the radio itself has much greater dynamic range, the
> WORKING dynamic range is limited by noise received by the antenna that
> is often 30-50 dB greater than the electrical noise levels inside the
> radio.
>
> 73, Jim K9YC
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