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?
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. Sabrent-au-emac (picture above) is even better, basic
noise floor is around -120db. And it costs only 8,- Euro!
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
