Sound Card Check:

During the low sunspot years, digital modes became more and more of interrest for hams,
JT65 and now FT8. Report statistics on pskreporter.info tells us: "Modes used over the last
two hours": For FT8 we have 807.122 entries. Enough said ;-)

Yes, there is a basic rule in HamRadio: 'anything goes', but did you ever check one of the
important parts in the chain of your digital mode: the sound card?

There is a free and very powerful tool available, written by DL4YHF,
it is the
DL4YHF's Audio Spectrum Analyser

Spectrum Lab in action, connected to the output of an microphone amplifier:


You will find the download link on the web page (roll down) DL4YHF's Audio Spectrum Analyser
Newest version of November 2018
is the version 2.93. Don't let yourself be drowned by the immense options and
functions of the software. We want to check the basic noise floor of
our sound card, to compare and making decissions.

Go to your windows sound card settings, check that there is no extra amplfication activated, click on the speaker
symbol with your right mouse button, select 'db' instead of steps (?) and set the level to '0db' level.
Most sound cards
offer all kind of options, like 'surround' and Dolby etc.
For digital modes in HamRadio - this has to be set to 'OFF'!

Download and install 'DL4YHF's Audio Spectrum Analyser'. Start it and go to 'File', click on 'Load Settings From...'
and load the
unzipped 'noisefloor.usr'. This file can be downloaded here:: noisefloor.zip. It is just a ready made
settings file for Spectrum Lab.


IMPORTANT: the sound card to be checked must be connected to your PC before you start Spectrum Lab, either
without cables or 
absolute no signal input from  your RX. You can check this in two different ways: sound card
connected,  RX muted, or sound card
connected, RX without any antenna connected.

Just in case, you want to check the settings in Spectrum Lab:

Go to (top menu) 'Options', [1] 'Audio Settings I/O device selection' and select your sound card and sampling rate [2]
Go to (top menu) 'Options', click on the down arrow [2] and select your sound card to be tested and set the sampling rate.
Go to (top menu) 'Options', select '...part 2: Ampl-Range...' [3] click on it and in [4] set your desired range to be displayed.




To give you some info and see what I discovered:

The famous 'SignaLink USB' sound card. Does not need any power supply, power is retrieved by the USB port.
And this could be disastrous. Did you ever check your +5Volt about hum? Look what I saw on my Signalink:



A perfect 50 Hz hum and the basic noise level is around -70db. OK, OK, SignaLink design is of 2001, so in fact it is
a very old design. Several web pages giving you infos how to 'mod' the SignaLink for surpressing  the 50Hz / 60Hz
hum of the +5V. Apparently at my setup, my 7 port USB hub works perfect for all kind of sticks and devices, but the

50Hz of the +5 Volt is creeping into the SignaLink.


Next, I pulled out several 'USB sound card dongles of my junk box, collected over the years.:


Well, a little bit better, basic noise floor is around -90db.

And then I grabbed my, not so cheap, 'Audiophile Performance' Sound Blaster X-Fi HD SB1240 USB sound card:


Wow, a -125db at 1500Hz basic noise level. What a difference! At least 60db improvement (!) over the worst and
40db better than
the USB Dongle Sound Cards.

But, I have a sound card in my TS-990, an expensive toy, let's see what we got. Settings: USB-D1 (upper sideband,
data), no antenna connected, audio 'MUTE' is 'ON', input from internal TS-990 sound card via USB:


Not bad, but not amazing either. Just ~7db better than one of the 'no-name' USB Sound Card Dongle?
There is a constant 'hump' 
at 1700Hz, could not find out, why this can be seen all the time. Not nice at all :-(


So, with some mixed feelings I selected my new 'micro KEYER III'. Let's see what we have on a Kenwood TS-990.
Settings: USB-D1 (upper sideband, data), no antenna connected, audio 'MUTE' is 'ON', input at ACC2:



Not bad, what the guys at microHAM have developed in the micro KEYER III
The MKIII is even a tick better and more linear than the highly praised Sound Blaster SB1240
:-)

Next settings: USB-D1 (upper sideband, data), no antenna connected, audio in 'MUTE' is 'OFF', micro KEYER III
input at ACC2. 
In this case we have the receiver noise at the input of the MKIII, but no antenna connected:


So we realize, the TS-990 will lift the noise level to - 100db, we loose 25db due to mixer and audio in the TS-990

The next step I tried: USB-D1 (upper sideband, data), antenna connected, micro KEYER III input at ACC2. and tuned
to the 
FT8 QRG on 20m on a late afternoon in November 2018, QTH located in the urban area of Vienna / Austria.



The conclusion: check your sound card, you will be surprised!

2018-12-01, Wolfgang Meister, OE1MWW, email: oe1mww (at) gmail.com





PflegedienstVergleichen.de