Message-ID: <53EE894B.8050502@gmx.net>
Date: Sat, 16 Aug 2014 00:27:23 +0200
From: Tobias DG3LV <DG3LV@gmx.net>
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <CAMFjj73P4GEnkpJjQ1LLHBsY3zpbRSCn+FQBXVKeDye2UerPbA@mail.gmail.com> <CAMFjj71p3xTzFoa_aYrYmYD-=jxAD=VKg2-VHYLovS2iyRPsRg@mail.gmail.com> <53EE5E74.4030405@tiscali.co.uk> <02fc01cfb8c5$542235f0$fc66a1d0$@comcast.net>
In-Reply-To: <02fc01cfb8c5$542235f0$fc66a1d0$@comcast.net>
Subject: Re: LF: USB Sound Card?
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

Hi Jim, Gary !

Experiences with Software Defined Radios ("Softrock" type) over years 
showed me the highs and lows of using a soundcard as an A/D-converter 
for HamRadio use. The situation improved from using the onboard-devices 
to professional external Firewire- or USB-2.0 soundcards as they became 
available at reasonable prices.

to A) it's true, the windows type drivers support up to 16 Bit only. 
There are some issues to sampling rate stability under windows, too. 
That's why SDR-programs like Winrad, HDSDR etc. use the alternative 
"ASIO" driver model, where 24 Bits are supported natively and where the 
latency is smallest. ASIO drivers typically are bundled with 
(professional) soundcards for studio-recording. I had the usual 
"EMU-0202-USB" card, which was sampling at 192kHz/24 Bit. As this is 
available no longer, today I use an "Icon Cube" and "Icon Cube pro" (2/4 
Channel,192kHz,24Bit,USB-2.0) for my softrock SDR. They are not too 
expensive and do a good job!

to B) Windows has different properties for the hardware sampling rate 
and the offered (simulated) sampling rate. If these are not identical, 
there is a software up/down-resampling done by windows. You have to set 
the correct sampling rate at the hardware-settings (!) of the chosen 
soundcard input/output. (sometimes Win7 resets this to 44.1 kHz/16Bit at 
another booting, so you have to check this first after booting up the PC.)
e.g. Even if the soundcard is just sampling at 48kHz, the windows 
drivers offer 96 and 192 kHz as well, but actual audio-data is still not 
more than 48kHz, the rest of the spectrum is filled with "blanks".

to C) Typically the anti-aliasing filters of a soundcard are bound to 
the current (hardware-) sampling rate (=Nyquist) and not be static. 
Those filters are digital ones and part of the A/D converter chips. But 
the datasheets of soundcards shows the filters of the 44.1/48 kHz 
sampling rate only (0-20 kHz), as this is the standard where the 
"dB-"measurements are done.

73 kHz Rx :
In Europe you can receive the DCF77 signals (77.5 kHz) very well by a 
length of wire (or better a PA0RDT) and directly attaching it to an 
input of a 192 kHz soundcard. (Here 55dB above noise at 600km distance, 
software time-decoding by "SoDiRa" SDR-software). It is the same setup 
as used for SAQ-listening at 17.2 kHz (using HDSDR).

For decoding digimodes (WSPR,JT65,WSQ...) a simple USB-micro-soundcard 
($5) or onboard is ok, the programs just use "mono" and 48kHz at most, 
even the cheapest (for headset use) do well.

73 de dg3lv Tobias

Am 15.08.2014 22:12, schrieb hvanesce@comcast.net:
> Gary,
>
> I use a number of expensive and inexpensive external (USB) audio
> interfaces, and I like them all (good sensitivity, good dynamic range);
> but I experience the following limitations:
>
> A)
>
> I have not been able to persuade Windows and/or Speclab to process 24
> bits (I have been successful in applying 24-bit settings in
> Windows>ControlPanel>Sound  and Speclab, but have not acquired valid
> data after doing so; and accordingly have always used 16-bit settings
> with 24-bit external audio interfaces, even though I need at least 24
> bits for dynamic range considering VLF and LF environmental noise in
> some of my locations)
>
> B)
>
> Similarly to the above, I have been able to set up Windows and Speclab
> for 192kHz sample rates, but have not been able to view past 48kHz
> without aliasing (and accordingly I settle for 96kHz settings and
> interfaces in most cases)
>
> C)
>
> All of my external audio interfaces have steep low-pass filters at or
> near 22kHz pole frequency, so SNR is compromised for signals at 20kHz
> and above. I’ve disassembled some of these interfaces in attempts to
> modify the low-pass filter cutoff frequencies, but without a schematic
> could not be certain regarding changes.
>
> Have you seen any of the above issues with internal or external audio
> interfaces that you have used?
>
> 73,  Jim AA5BW
>
> *From:*owner-rsgb_lf_group@blacksheep.org
> [mailto:owner-rsgb_lf_group@blacksheep.org] *On Behalf Of *Gary - G4WGT
> *Sent:* Friday, August 15, 2014 3:25 PM
> *To:* rsgb_lf_group@blacksheep.org
> *Subject:* Re: LF: USB Sound Card?
>
> Hi Warren,
>
> Yes, I had an internal (on main board) & used it for a while for my
> grabber when 73kHz was first allocated to USA.
> It was good to about 94kHz.
>
> The SB0490 I suggested is only 96kHz :-((
>
> *73, de Gary - G4WGT*
>
> *                             *
>
> *MF-LF-VLF Grabber :http://myweb.tiscali.co.uk/wgtaylor/grabber2.html*
>
> *Web :http://myweb.tiscali.co.uk/wgtaylor/index.html*
>
>
>
> .
>
> On 15/08/2014 20:09, Warren Ziegler wrote:
>
>     I guess I should have been more specific .
>
>     What I am seeking is are some sound cards more stable with respect
>     to sampling rate and calibration? Also, any advantage to 24bit A/D
>       for LF data modes?
>
>       I wonder if anyone has tried 192kHz sample rate for direct
>     reception of 73kHz?
>
>     73 & Tnx Warren
>
>     On Fri, Aug 15, 2014 at 2:27 PM, Warren Ziegler <wd2xgj@gmail.com
>     <mailto:wd2xgj@gmail.com>> wrote:
>
>
>     I just acquired a Windows Vista tower computer - the price was right
>     it was free!
>
>     Seems that there is a problem with the internal sound card, but
>     everything else checks out FB.
>
>     I plan on using it with WSPR and other digital modes, am thinking of
>     an external USB sound card - will any old sound card do ? Or do I
>     need one with a calibrated sampling rate? I suspect that I will need
>     something really good for Spectrum Laboratory if I want to sample at
>     microHertz rates.
>
>     73 & Tnx Warren K2ORS
>
>
>
>     --
>     73 Warren K2ORS
>                      WD2XGJ
>                      WD2XSH/23
>                      WE2XEB/2
>                      WE2XGR/1
>