Beta Address: http://blish.org/sdrdxdoc/tuning.html
5 - Operations
5.1 - Exiting the Software
When you're done using SdrDx, you must →Left-click or →Left-click or →Left-click 
> and wait at least a couple of seconds before exiting the program. Otherwise, some threads may not be properly terminated, and that can cause problems of a somewhat random nature.
5.2 - Advice for New Users
The one thing you should not do when learning SdrDx is randomly or blindly click on buttons or keys. The way to go about this is to learn what the various controls do by reading this documentation, and then do them. Otherwise, you can get SdrDx into states that may be very difficult to fix, as you won't understand what you did to get there in the first place.
I know it is difficult for many to actually sit down and read a manual, but I hope you'll make an exception here. I've put some effort into trying to get you the information you need, in the order you'll generally need it; you can save a lot of confusion and time by going at this the way I recommend.
5.3 - Basic Tuning Steps
SdrDx is a radio, but it's not a radio with a single tuning knob. It's more of an instrument-class tool than a simple consumer tool. One of the consequences of this is that tuning around in the most effective and informative manner — by which I mean making sure the displays tell you as much as possible and the received signal is of as high a quality as possible — requires that you learn a number of steps to be performed when making significant tuning changes. Here they are, in order:
- (If you have an SDR) Change frequency to different band or spectral region. Make sure that your SDR's bandwidth is reasonably wide (at least 48 KHz.)
- Use the two Span buttons (S- and S+) to ensure that the RF Display is at least 48 KHz wide. Span is not the same as SDR bandwidth; SDR bandwidth controls the amount of data coming into SdrDx, while Span controls how much signal you can see on the RF display, and indirectly, how well you can adjust the demodulator bandwidths. Now, →Left-clickGS to adjust the interval between the spectrum labels. For bandwidths typically used within HF, I suggest a label every 5 KHz; so if your spectrum is 100 KHz wide, you would set the grid spacing to 20.
- Adjust the Max control at the left so the noise level lies within a gridline or two above the numbers that label the signal display area at the bottom — you don't want those numbers obscured.
- (Possibly) adjust the dB/Div control so the signal amplitudes are satisfactory to you. Or perhaps not. I usually leave mine on 7 dB/Div, but this is a choice made because most signal levels I encounter from my magnetic loop are fairly similar as I am located in a rural, radio-station poor area. Very strong signals are rare for me.
- ⇔ I
= (vertical, right next to the S-Meter) so that
the noise level falls into the dark blue color range with only specks of
yellow (this is with the default waterfall palette.) - ⇔ C = (vertical, next to I) so that the
amplitude of the signals result in waterfall colors that are satisfactory. This may require you going back to the previous step and re-adjusting I... they do interact.
- Especially with sideband signals, check reception with the noise
blanker
and
. Good starting settings are ⇔ NBT = 50 and ⇔ NBW = 30. You would be amazed at the degree of assistance the noise blanker can provide under certain types of noise conditions. It can bring the noise floor down by as much as 9 dB, revealing signals you didn't even know were there.
- Listening to SSB or AM signals, adjust the demodulator bandwidth(s) so that you're hearing the desired signal (and not others) the way you want to. Now try the ring reduction and . Again, you may be very surprised at the difference in audio quality.
- AM SW or BCB listening? Many AM mode broadcasts are far too heavy on the bass (I presume they think you have a tinny little transistor radio in your hip pocket.) →Left-click (high pass filter) and ⇔ Hpf = 150...200. This will suck some of the life out of the bass end of the audio spectrum, and make many AM stations considerably easier to listen to.
- AGC adjustment with DCY: With AM SW and BCB stations, you probably want this to be fairly short, say 250...500 ms or so. With s SSB and CW, you'll want it to be longer, perhaps as much as 2500...5000. With RTTY and other fast digital modes, set it to about 100. Of course, if these settings are unsatisfactory, change them!
- Hum? You can →Left-click 60 button, or you can set up a notch filter using
N1, ⇔ F = 60 Hz and ⇔ Q = (leftwards) (or 50 Hz if the station isn't using 60 Hz power.) You might want to adjust the Q as well — leftward results in a wider notch. For instance, as I write this, Radio Havana has been notorious for 60 Hz hum for many months now. I can't listen to it without a 60 Hz notch active, but with it, it sounds like any other station. Heterodyne? Same answer — set up a notch. You'll find the audio waterfall (bottom right scope,
) very handy for working with the notches, as left-dragging the mouse in the audio waterfall or spectrum adjusts the currently selected notch accordingly. Note that the
60 and
50 filters do more than a single notch filter does — they also reduce harmonics at 2f, 3f and so on.
...all of this activity on your part is required because the signal levels in different portions of the RF spectrum, and how they are picked up by various antenna designs, vary enormously. This is even true over time... for instance, signals at 14,200.000 will have a very different noise floor in the afternoon than they do late in the evening; and when conditions are changing rapidly, such as at local sunset and sunrise, you may even find yourself adjusting settings every few minutes.
Learning how to adjust SdrDx for optimum display of these signals is a key skill, and you should work diligently to acquire it.
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