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Receiver bandwidth center frequency?

Mike Burns
 

How do I tell what frequency the selected radio bandwidth in SDRConsole is centered at and how is it set?
 
For example, I'm connected to an Elad S3 and if I choose the 3.072 MHz bandwidth option I can tune an SDRC receiver to any freq in the HF range and it will work, so clearly the radio bandwidth center is dynamically moving as my receiver frequency changes.
 
My problem comes when I have multiple receivers operating simultaneously. Obviously the receivers all need to be within the selected radio bandwidth to operate together, but even when I have a radio bandwidth chosen which is wider than the maximum receiver frequency difference, I often cannot get all the receivers working at the same time. Either a receiver or two at the high frequency end are not receiving, or else some at the low end are not. (I can tell because I have each receiver line set to a different VAC channel which monitors activity on each receiver).
 
I'm assuming that's because SDRC is setting the bandwidth center frequency in a way that can never encompass my receivers, hence my question as to just how it does set the actual receiving band. It would be ideal if I could specify the center frequency but I realize that may not be possible due to constraints from the radio.
 
Or maybe something else is going on. I'd appreciate any insights into my problem.

Thanks,
Mike Burns, AB1LD
jdow
 

In general for NFM on a 3.072 Msps radio figure the "clean" bandwidth is about 2.5 to 2.7 MHz. For FM back that off at least another 100 kHz to give room for the full signal. Of course, a full size (attached not inline) screen shot showing what you mean would help clarify if my wild guess at your issue is on the mark. All stations you want to receive must be within about half of 85% of the sample rate less half the signal bandwidth of the center frequency.

{^_^}

On 20221125 16:21:23, Mike Burns wrote:

How do I tell what frequency the selected radio bandwidth in SDRConsole is centered at and how is it set?
 
For example, I'm connected to an Elad S3 and if I choose the 3.072 MHz bandwidth option I can tune an SDRC receiver to any freq in the HF range and it will work, so clearly the radio bandwidth center is dynamically moving as my receiver frequency changes.
 
My problem comes when I have multiple receivers operating simultaneously. Obviously the receivers all need to be within the selected radio bandwidth to operate together, but even when I have a radio bandwidth chosen which is wider than the maximum receiver frequency difference, I often cannot get all the receivers working at the same time. Either a receiver or two at the high frequency end are not receiving, or else some at the low end are not. (I can tell because I have each receiver line set to a different VAC channel which monitors activity on each receiver).
 
I'm assuming that's because SDRC is setting the bandwidth center frequency in a way that can never encompass my receivers, hence my question as to just how it does set the actual receiving band. It would be ideal if I could specify the center frequency but I realize that may not be possible due to constraints from the radio.
 
Or maybe something else is going on. I'd appreciate any insights into my problem.

Thanks,
Mike Burns, AB1LD
Max
 

On Sat, Nov 26, 2022 at 05:22 AM, Mike Burns wrote:
How do I tell what frequency the selected radio bandwidth in SDRConsole is centered at and how is it set?

Mike, to the best of my knowledge the centre of the bandwidth is always set by the "main" SDRC display and the centre frequency of the hardware receiver re-centres if you type in a frequency value. I don't believe there is the ability to lock it to any other frequency. Simon may say it's possible?

To prove this, set your hardware bandwidth (in the ribbon bar top left) to the smallest number you can. Then, looking at the transparent bandwidth "window" at the very bottom of the screen, drag the handles out wide on each side. Now you should see the operative bandwidth of the hardware clearly visible in the spectrum, with zero signal either side of it (as expected). I've attached a screenshot to illustrate what I expect you to see. In this case I've set my hardware bandwidth to just 48kHz just to make it easy to demonstrate. This is the lowest bandwidth setting on my Hermes Lite 2 SDR

Now make it so that you have two SDRC receivers and, with the main screen still zoomed out as above, you can position (by dragging, don't type in the frequency) those receivers anywhere inside or outside of the "active" spectrum and hear that they either are either live, or dead. Place one receiver on each side of the active spectrum part, so both receivers are dead. Now you can get hold of the centre of the transparent bandwidth "window" at the bottom of the main waterfall display and drag it around to either be on top of one of the receivers or the other. I think this helps to illustrate what is actually going on even when the spectrum is set to not display outside the active "slice". 

Typing in a frequency on either receiver re-centres the actual bandwidth centre frequency, and you can do this to with the display set in the above state to see what is actually going on. I've attached a screengrab of the above setup by way of illustration.

Hope it helps.

Max
jdow
 


The red ellipse shows the tuned frequency for the front end. (Its center frequency.)


{^_^}

On 20221127 03:39:30, Max wrote:

On Sat, Nov 26, 2022 at 05:22 AM, Mike Burns wrote:
How do I tell what frequency the selected radio bandwidth in SDRConsole is centered at and how is it set?

Mike, to the best of my knowledge the centre of the bandwidth is always set by the "main" SDRC display and the centre frequency of the hardware receiver re-centres if you type in a frequency value. I don't believe there is the ability to lock it to any other frequency. Simon may say it's possible?

To prove this, set your hardware bandwidth (in the ribbon bar top left) to the smallest number you can. Then, looking at the transparent bandwidth "window" at the very bottom of the screen, drag the handles out wide on each side. Now you should see the operative bandwidth of the hardware clearly visible in the spectrum, with zero signal either side of it (as expected). I've attached a screenshot to illustrate what I expect you to see. In this case I've set my hardware bandwidth to just 48kHz just to make it easy to demonstrate. This is the lowest bandwidth setting on my Hermes Lite 2 SDR

Now make it so that you have two SDRC receivers and, with the main screen still zoomed out as above, you can position (by dragging, don't type in the frequency) those receivers anywhere inside or outside of the "active" spectrum and hear that they either are either live, or dead. Place one receiver on each side of the active spectrum part, so both receivers are dead. Now you can get hold of the centre of the transparent bandwidth "window" at the bottom of the main waterfall display and drag it around to either be on top of one of the receivers or the other. I think this helps to illustrate what is actually going on even when the spectrum is set to not display outside the active "slice". 

Typing in a frequency on either receiver re-centres the actual bandwidth centre frequency, and you can do this to with the display set in the above state to see what is actually going on. I've attached a screengrab of the above setup by way of illustration.

Hope it helps.

Max
Bandwidth.jpg

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