identification of bandscope markers

KE3C
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Joined: Tue Nov 21, 2017 1:51 am

identification of bandscope markers

Postby KE3C » Wed Jul 31, 2019 6:47 pm

I am curious if anyone can tell me what all the markers on the bandscope are. I believe that the red line marks the current receive frequency and the highlighted area is the bandwidth filter. What are the yellow markers?

BandscopeUSB.PNG
BandscopeUSB.PNG (36.78 KiB) Viewed 867 times


Also, I notice that if I switch from USB to CWU:

-- the frequency goes up by 600 hz but the red line stays at the original frequency, The frequency in the display appears to be at the center of the CW bandwidth. Why does the frequency change and why does the red line no longer represent the receive receive frequency?
-- The bandscope grid has frequency indicators at the bottom and the top on the grid and they are offset from each other. Does the bottom represent the receive frequency and the top the transmit frequency?

BandscopeCW.PNG
BandscopeCW.PNG (33.9 KiB) Viewed 867 times
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w-u-2-o
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Re: identification of bandscope markers

Postby w-u-2-o » Wed Jul 31, 2019 8:41 pm

KE3C wrote:I am curious if anyone can tell me what all the markers on the bandscope are. I believe that the red line marks the current receive frequency and the highlighted area is the bandwidth filter.
Correct on both counts.
What are the yellow markers?
If you have the TX FL option turned on they appear and show the limits of the transmit passband.
BandscopeUSB.PNG
Also, I notice that if I switch from USB to CWU:

-- the frequency goes up by 600 hz but the red line stays at the original frequency, The frequency in the display appears to be at the center of the CW bandwidth. Why does the frequency change and why does the red line no longer represent the receive receive frequency?
The frequency in the display is your true receive and transmit frequency. But the passband will be shifted by the amount specified in the CW offset setting such that any signal that is exactly on frequency will be heard with a tone that is equal to that offset.
-- The bandscope grid has frequency indicators at the bottom and the top on the grid and they are offset from each other. Does the bottom represent the receive frequency and the top the transmit frequency?
Not sure about that one!
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ramdor
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Re: identification of bandscope markers

Postby ramdor » Thu Aug 01, 2019 4:30 am

Ok I thought I would post because I have been working on this code last couple of days.

I have been slowly adding panafall views to RX1 and RX2 I have done a load of tidying of this code, related to the waterfall and the panaadptor. They both now use a single function to draw the grid/frequency labels/band edges etc. Having duplication of code to do the same thing was causing all sorts of problems in keeping them both aligned, and now just a simple flag to draw pana/waterfall. I have also reworked the code that calculated bandedges and simplified it somewhat.

Also, the step nature of the code that displays the frequency labels will sometimes miss a band edge text. There is some code to force draw lines so you will always see the edge. One day it will need a rework.

Also have changed draw order of waterfall so filter is shown etc.

I am still working on it, it is slowly getting there. I should be able to submit the source in a few days (fingers crossed/wind in right direction). Doing a github submit/change might be an issue, but will cross that bridge when I come to it.

73 for now, Richie - MW0LGE.

progress.JPG
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KE3C
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Joined: Tue Nov 21, 2017 1:51 am

Re: identification of bandscope markers

Postby KE3C » Thu Aug 01, 2019 8:42 pm

Thanks to both Scott and Ramdor for the replies.

I have to admit I had a bit of an side motive when asking these questions.

A couple years ago when I first purchased my 200D, I tried to make sense of the C# code for PowerSDR. Even though I have been coding professionally in C# for years I had trouble understanding the code because it was a bit of a mess back then. (I have noticed it is getting much more structured) I wanted to understand a bit more about how a software defined radio worked under the covers.

Fast forward to today. I am in the middle of coding an old school quadrature sampling SDR using the Teensy 3.6 (Arduino) and the Teensy sound card. I have coded much of the interface and I needed a reference as to how band pass filters are set up. I remembered that the Thetis display pretty clearly delineated the filters.....that is until I started looking at them more closely. The filters in some code I have been using for reference have the USB and LSB band pass filters offset +/-300 hz from the receive frequency and extend 2400 hz above or below the offset. I see that Thetis has them offset by 100 hz and the filters extend by the filter width above or below. For CW it seems a little less clear. The bandpass seems to stay centered on the receive frequency, but changing modes from USB to CWU seems to shift the receive frequency up 600 hz (if I have my tone frequency set to 600 hz). I assume that is just trying to maintain the signal in the pass band if the user is listening to it in USB and wants to switch to CW to work it,

I am hoping those that have been through this before can help me get it straight in my head.
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W1JA
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Re: identification of bandscope markers

Postby W1JA » Sat Aug 03, 2019 1:18 pm

@K3EC
I don't have the skills to examine the code as you are doing, but it sounds like you are describing what I see when I examine the visible receive bandwidth shading (receive filter) in the panadapter display. This receive filter indication has always seemed to accurately show the actual filter when I have looked at it closely. The filter is set up with the selectivity controls in the lower right corner of the PowerSDR/Thetis UI.
The filters in some code I have been using for reference have the USB and LSB band pass filters offset +/-300 hz from the receive frequency and extend 2400 hz above or below the offset.
Then if you look at the Low and High textboxes in the UI selectivity controls, you should see 300 in one of them and 2400 in the other, which would result in demodulated SSB audio from 300 Hz to 2400 Hz. If you see 300 and 2400 in the code, I would think they were passed there from the user's UI settings. The filters are highly modifiable in the UI. The different values you report in Thetis must be because the selectivity settings happen to be set differently in Thetis. And 600-Hz shift you see in CW mode is necessary so we humans can hear it. It's often called 'CW offset.' The UI calls it 'Pitch Freq.'

No one else replied so I thought I'd jump in. Hope I didn't misunderstand your question.

73, John

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