[Lowfer] SDR-IQ Preamp Info

[Douglas D. Williams]

Bill,

I've heard good things about the SDR-IQ, though I don't own one personally.

You will find that most LF operators, either part 5 experimental
licensees (MF and LF) or part 15 "lowfer" (160-190 kHz) operators are now
transmitting in QRSS (VERY slow CW) or some "digital" mode, with WSPR being
the most common. A few are still transmitting plain old CW.

Your best bet for your first reception is trying for one of the "big boys"
running QRSS around 137.780 kHz. Tune your receiver to that frequency,
start Argo, and set it for QRSS30, "slow". Look at the green bar on the
left side of Argo, and adjust your receiver AF gain so the green bar stays
around the middle, and stays green, not red.

But, even before that, you need to calibrate Argo so that your
receiver/computer displays the correct frequency on the Argo screen. Do
this by letting your SDR-IQ warm up for an hour, then tune to WWVB on 60
kHz. If you don't hear WWVB *very* loudly, you have little hope of hearing
anything else, and need to improve your antenna. I'm not familiar with the
SDR-IQ, but do whatever you have to do to set it to CW mode and a sidetone
of whatever you normally like to listen to (I use 700 Hz). Now to
calibrate Argo, set it on QRSS-10 "normal", horizontal scrolling, and make
whatever sidetone you selected on your SDR-IQ (700 Hz or whatever) the
center frequency on the right of your Argo screen. You should see a thick
white line on the display, scrolling slowly to the left of the Argo screen.
That's WWVB.

Note the frequency you see the "line" on. Let's say you see it at 710 Hz.
Now, up on Argo's menu bar, click on Setup, then scroll down to
Calibration, and click on that. Now (assuming you are using a 700 Hz
sidetone), type in 700 in the Measured Frequency box, and (continuing my
example) 710 in the Displayed Frequency box, then click OK. You should now
see the thick line of WWVB move down to 700 Hz (or whatever sidetone you
selected) on the Argo display. Ignore the Offset box for now. You are now
calibrated "close enough" to receive most QRSS signals.

Put Argo back on QRSS30 "slow" and monitor 137.780 and see if you receive
any QRSS signals. QRSS is just super slow CW, so you will see CW "dahs and
dits" form on the Argo display, if anybody is transmitting. QRSS30 means
thirty second long "dits". Yep, it takes a while to communicate anything in
QRSS. :-)

As you noted to me earlier, Argo has a very narrow passband. The slower the
QRSS mode, the narrower the passband. It is extremely important for both
the transmitting and receiving stations to be very precise, and very
stable, in their frequency.

Have fun, and I hope I made some sense.

73, Doug KB4OER









On Fri, Feb 1, 2013 at 3:08 PM, WD8ARZ <wd8arz at comcast.net> wrote:

> More about a preamp.
>
> The SDR-IQ has a built pre-amp, and is so hot now on frequencies below 53
> 0khz that I have to turn down the rf gain. RF gain control panel has +10
> dB, -10dB, 0 dB, and -20dB options. Then there is the IF Gain panel that
> allows for +24 dB, +18 dB, +12 dB, +6 dB, and 0 dB options. Seems to be ok
> with -10 dB setting for RF Gain, and +24 dB for the IF gain.
>
> Now to start recording a couple hundred kilo hertz band width to the hard
> drive today and tonight and go through the file and see who I can hear.
>
> Thanks for all the feedback from everybody.
>
> 73 from Bill - WD8ARZ
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