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5.17 - Band-stacking VFO/Bands

ARO Presets

BCB Presets

Custom Mixed Presets

5.17.1 - Basic use of the VFO bands

SdrDx offers 14 customizable, bandstacking, band-specialized VFOs.

They are shown above; what they do is, when you are within the band limits each VFO is set for, they will keep track of your tuning, bandwidth, intercept and so on so that if you switch to another band, you can come back to that one and be right where you left off.

So you can click on 20m, tune around the 14 MHz amateur band, click on 40m, tune around the 7 MHz band, then click again on 20m, and you'll be right back where you were when you last were using that VFO.

Each VFO knows its band limits, so if you tune outside them, it won't track your tuning there. - Bandstacking

Each VFO can store a single tuned circumstance, or up to eight. This is called "bandstacking". What this means is that when you select a VFO, there can be multiple separate memories for each one. If you have Bandstack Registers set to 3 in the Band Setup dialog, for instance, the first time you click, the button is 20m. Now, click again, and it is 20m; you can now tune around again. It will keep track. Now click again, and it's 20m, and yet again, it will keep track. That's all three in the stack. Now click once more, and it turns green again — and you're back where you were when you were tuning around each time. Keep clicking, and you'll see that all three sessions were stored in a different instance of that same VFO.

Each stacking register records center frequency, demodulator frequency, demodulator mode, and demodulator high and low bandpass limits, as well as a large set of other settings you can choose from.

There's a different color for each of the eight possible stacking registers:

20m 20m 20m 20m 20m 20m 20m 20m - Bandstack Registers - Multiple Bandstacking Registers per VFO

Set Bandstack Registers to a number from 1-8. To start with, 3 is suggested; Eight is a lot! Once you get a feel for how all this works, you'll have a better idea what you like. You can change this at any time.


Band Setup Dialog configured for 3 Bandstack Registers

Above is the Band Setup dialog along with the actual VFO / band buttons, just above it. You access this dialog by Right-click on any of the VFO buttons, shown above the dialog here.

The top left three edit boxes are where you set the band limits and button legend for the selected VFO.

The buttons at the left vertical center of the dialog let you quickly set the VFOs to pre-programmed, commonly-used bands, and also save and load your own custom setups.

The buttons numbered 1-14 at the bottom of the dialog correspond to the VFO buttons by position. #1 is the top left VFO / band button, and #14 is the bottom right VFO / band button. The 1-14 buttons are used to control   Edit ,   Copy To ,   Paste From , and   Swap With  operations.

Under Settings and Tracking are global settings that affect how the VFOs operate overall. The left column of checkmarks control whether the VFO being edited carries the named settings with it; the right set of checkmarks determines if those settings are independent with each bandstacked instance of the VFO, or if a change in the setting to the left of the checkmark will be immediately applied to all of the bandstacks within this VFO.

At the far right under Bandstacks, each of the eight stacking register's center and demodulator frequencies are displayed. If the bandstack is available (controlled by the Bandstack Registers setting), the values will be green. Otherwise, they will be red.


If you Shift- Left-click any VFO button, it will change to VFO, the first of the bandstacks.
This is how it works:

Shift- Left-click VFO = VFO

Shift- Left-click VFO = VFO

Shift- Left-click VFO = VFO

Shift- Left-click VFO = VFO

Shift- Left-click VFO = VFO

Shift- Left-click VFO = VFO

Shift- Left-click VFO = VFO

Shift- Left-click VFO = VFO

Here's one way I use this. I generally have my SDR set for 240 KHz bandwidth when DXing from ELF to HF. This gives me a comfortable viewing width for signals with good resolution. In the AM BCB band, This lets me see a little less than 1/5th of the band at a time with 10 KHz overlap at either end of each segment. So with six bandstacks active, I set the center frequency of each VFO stack to 650.000, 870.000, 1,090.000, 1,310.000, 1,530.000 and 1,590.000

So as I move from the BCB bandstack to the BCB bandstack, I'm panning across the AM BCB band. I change the demod frequency as it strikes my fancy, but leave the center alone. It's a very nice DXing setup.

Shift- Left-click at any point takes me back to the 650.000 center frequency, and I can start at the beginning regardless of where I left off last.


But wait! There's more! If you Opt- Left-click a VFO, it will step to the previous bandstack.

Tip: You can have a full ELF through HF VFO by simply setting the band limits to 0 and 30000. Once you do that, the VFO will act as a multiple-bandstacking VFO that tracks everything you do in the entire range. If you have a wider range SDR, you can extend that beyond HF if you like. If you do this, you should check   Ind.  for any of the settings (at the left of the dialog) that you select for tracking, as this will allow each bandstacked VFO instance to deal with its own set of challenges.

5.17.2 - How Independence Works

As an example, we'll go over   Spectrum , which tracks the settings of both I and C.

When   Spectrum  and the adjacent   Ind.  are both checked for a particular VFO, adjustments of I and C are tracked by each VFO stacking register independently.

When   Spectrum  is checked, but   Ind.  is not checked, adjustments of I and C set all stacking registers within a single VFO at the same time.

If   Spectrum  is not checked, the VFOs will not set I or C, and the setting of   Ind. .

Both   Spectrum  and   Ind.  settings apply only to the VFO that is being edited; generally speaking, for normal bands that are a small section of the spectrum such as the 49 meter shortwave band, setting all stacking registers at once for that VFO makes more sense (in other words, don't check the associated Ind. to the right of these settings.) But with a wide frequency range applied to a VFO,   Ind.  for   Spectrum  becomes important, because the various stacking registers can be widely separated in frequency, and therefore in base noise level.

For instance, if you set up a VFO for all of your SDR's range which might be 0 KHz to 30 MHz (30,000 KHz), one stacking register might be set to the AM broadcast band, where the noise levels are very high, and so I is at a lowish setting; whereas another stacking register for that same VFO might be set to the 10 meter ham band, where the noise level is very low, and so I is at a fairly high setting. When the two sliders are tracked independently, the stacking registers within each individual VFO remember your adjustments specific to the location you've got them set to.

On the other hand, if you have a VFO set up for a relatively small amount of spectrum, such as 5800 KHz to 6200 KHz for the 49 meter shortwave band, the noise level across the band is likely to be almost exactly the same. If this is how you tend to use the VFOs, you might prefer not to have independent I and C tracking, so that any adjustment of either one is saved in all of the stacking registers at once.

Looking at the dialog, you can see that every trackable setting has an associated   Ind.  setting; so you can treat each setting as you wish without affecting how the others work. Each VFO has its own group of settings.

Here's another quick example. I have a BCB preset, 530 to 1710 KHz. Generally speaking, the band is consistent, and so almost all of the   Ind.  boxes are unchecked. This means that whatever I do in one stack is immediately reflected in the others. RF Gain, etc. But I do have a problem with power-line noise in several portions of the band, particularly around 1 MHz. So I have checked   Ind.  for NBL; that means I can turn it on in one stack, while the other bandstacked NBL settings stay on or off, however they have been previously set.

5.17.3 - Bandstack FIFOs

Each bandstack in a VFO provides a FIFO, which is a set of First-In, First-Out memories of the most recent places you have tuned within each VFO's bandstack.

In the VFO dialog, the time it takes to memorize a new tuning is variable (using the FIFO time edit box) from 1 to 60 seconds and the number of FIFO memories (using the FIFOs edit box) is variable from 2 to 16. You can access the next and previous FIFO memories from the main control panel with Left-clickF > and Left-click< F respectively, or key functions 398 (Next FIFO) and 397 (Previous FIFO) respectively. These are session-local; this means they are not saved when you exit the program.

Key function 399 (Clear FIFOs), Right-click< F, or Right-clickF > will clear the active VFO's FIFOs. At this point, the timer starts again, and if the tuned frequency remains stable for the number of seconds specified in the VFO dialog's FIFO time edit box, this will be the first entry in the FIFO.

5.17.4 - Customizing a VFO

If you Right-click on any one of the VFOs, you can completely customize the band it sets up for. You set the band start and band end, and the label for the button (you should use 3 characters for the label if possible.) If you click OK, the button will be updated, and now you have a bandstacking-capable VFO for your own customized band limits!

When you customize a VFO, setting the start and end limits, all of the stacking registers will be set to about the middle of the band span, on a 10 KHz frequency interval at, or below, the middle of the band limits you have chosen. In addition, the first (green) stacking register will be selected.

5.17.5 - Edit operation

When the dialog opens, you are in   Edit  mode for the VFO you right-clicked over, as indicated by the text to the right of the Button Label: edit box. You can change the contents of any or all of the three edit boxes, then hit Apply or OK and the changes will be applied. If you hit Cancel, your changes will be discarded.

In edit mode, if you Left-click one of the buttons  1 ...14 then you will be in edit mode on that button. This allows you to keep the dialog open and edit different buttons.

5.17.6 - Copy To operation

  Copy To  mode works like this: Click on   Copy To , then click on the numbered button that physically corresponds with the button you want the information in the current button copied to; this occurs immediately, and the dialog is returned to   Edit  mode without changing the button that is being edited.

5.17.7 - Paste From operation

  Paste From  mode works like this: Click on   Paste From , then click on the button you want the information in the selected button copied from; this occurs immediately, and the dialog is returned to   Edit  mode without changing the button that is being edited, but with the new information for that button set up.

5.17.8 - Swap With operation

  Swap With  mode works like this: Click on   Swap With , then click on the button you want the information in the selected button swapped with; this occurs immediately, and the dialog is returned to   Edit  mode without changing the button that is being edited, but with the new information for that button set up, and the button chosen for the swap now set to the information that was previously in the currently selected button.

5.17.9 - Reset

Reset discards all your changes to VFOs and places you in the same state you were in when you first opened the dialog.

5.17.10 - Presets

There are two sets of built-in presets. One for amateur radio bands, and one for broadcasting bands. - For one VFO

If you click Set ARO Default just this one button will be set to its amateur band default settings.

If you click Set BCB Default just this one button will be set to its broadcast band default settings. - For all VFOs

If you click Set All ARO Defaults, all of the VFO buttons will be set to the amateur band default settings.

If you click Set All BCB Defaults, all of the VFO buttons will be set to the broadcast band default settings.

5.17.11 - Bandsets

Each full set of 14 VFO / band settings is considered a "bandset." - Saving a bandset

Once you have a set of bands configured such that you like the whole group of them, you can use Save Band Set to save them under a custom name.


Don't change the file extension set in the save (or load) file dialog. This helps SdrDx locate just the files you are interested in. You can change it, I just strongly suggest you avoid doing that. - Loading a bandset

Once you have saved a bandset, you can re-load it at any time using Load Band Set — after a load, the stacking register for each VFO is set to green (the first stacking register.)

5.17.12 - Cancel Dialog

Clicking Cancel or the window close button () restores all VFOs to the state they were in when you opened the Band Setup dialog. However, if you saved a bandset file while the dialog was open, that file remains in the filesystem as doing so has no effect on SdrDx's subsequent operation.

5.17.13 - Error Correction

If for any reason any of the data or files associated with a VFO or its various stacks become corrupt, internal checking procedures are in place that are intended to return the VFO to a "sane" state.

5.17.14 - Tracked and Trackable Settings

Setting Item(s) Tracked VFO
  • Number of bandstacks for this VFO.
    May be from 1 (no stacking) to 8.
  • Number of FIFOs for all VFOs.
    May be from 2 to 16.
FIFO time
  • How long a frequency must be tuned in before it is added to the current bandstack's FIFO. Set for all VFOs.
    May be from 1 to 60.
FIFO detailsYesYes
  • 9,580.000 Demodulator Frequency
  • 9,500.000 Center Frequency
Low pass filterOptionalOptional
High pass filterOptionalOptional
Noise blankerOptionalOptional
Dynamic Noise ReductionOptionalOptional
RF GainOptionalOptional
CW OffsetOptionalOptional
WFM MonophonicOptionalOptional
WFM High BlendOptionalOptional
dB / Div
  • - Db / Div
Max dB
  • - Max dB
  • NOT
  • RFN
  • F (for all ten notches)
  • Q (for all ten notches)
  • Nx (for all ten notches)
  • Antenna One Gain
  • Antenna Two Gain
  • Antenna Phasing Relationship
  • Span Setting**
  • Grid Setting

* Antenna gains and antenna phasing are only obeyed by SdrDx when DUL is on and an SDR is connected that has dual-channel support such as the AFEDRI AFE822. This is set in the PHA dialog.

** Span settings saved in a VFO will be modified if the SDR's sample rate is less than the specified span. For instance, say you had your SDR sampling at 500 KHz, and a span of 400 KHz was saved in a VFO. Later, you change the SDR to a 200 KHz sample rate, and subsequently select that VFO. The span set by that VFO will now be modified downwards to 200 KHz, and so will the saved value in the VFO — the 400 KHz setting is lost. Remember: VFOs are always adjusting themselves to the current circumstances.

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