2021 is dedicated to the user - adding all the features an advanced user needs.

zoom and frequency issue with external radio and tracking

All bug reports here please
iz1fks
Posts: 9
Joined: Sun Mar 14, 2021 1:50 pm

zoom and frequency issue with external radio and tracking

#1

Unread post by iz1fks »

zoom function with external radio doesn't work in the right way, the signal move from the tuned frequency. changing zoom an offset on the sdr tuning about 1 kHz is applied.

In addition moving radio vfo change the zoom on the spectrum.

Tracking in 3.0.27 is not understandable, since Radio=>SDR looks no difference even it's active or not



73 de Phil,iz1fks

jdow
Posts: 315
Joined: Mon Aug 10, 2020 8:17 pm

Re: zoom and frequency issue with external radio and tracking

#2

Unread post by jdow »

This is the correct behavior. The zoom follows the active receiver not the display center frequency. This is one of the key features that keep me coming back to SDRC when I check out SDRSharp's latest.

{^_^}

iz1fks
Posts: 9
Joined: Sun Mar 14, 2021 1:50 pm

Re: zoom and frequency issue with external radio and tracking

#3

Unread post by iz1fks »

jdow wrote:
Sat May 01, 2021 10:15 am
This is the correct behavior. The zoom follows the active receiver not the display center frequency. This is one of the key features that keep me coming back to SDRC when I check out SDRSharp's latest.

{^_^}
thanks for answer.
The actual behaviour is the opposite you described. The zoom function causes the active receiver to loose the signal it was centered to, and it's easy to see that the signal previously decoded moved up to about 1 kHz.

Moving radio vfo the zoom is restored to previous setting, it's not possible to change radio frequency with a different zoom level.
This issue is related to External Radio mode only.
Indeed enabling tracking in both directions the active receiver shall be the same that display center frequency in external radio mode.

If SDR->Radio is disabled frequency in spectrum go out of control and not correlated anymore with the rf spectrum itself, Tracking mode SDR->Radio and Radio->SDR have serious issues at my side. In detail Radio->SDR doesn't work if SDR->Radio is not enabled!

Without external radio the zoom work good, but not in the way you described, in fact the zoom always follows the center displayed frequency (center of the spectrum window), not the receiver cursor frequency.
I have found if there is any setting to modify this behaviour but I was not able to find it out.

73 de Phil, iz1fks

jdow
Posts: 315
Joined: Mon Aug 10, 2020 8:17 pm

Re: zoom and frequency issue with external radio and tracking

#4

Unread post by jdow »

"The actual behaviour is the opposite you described." I know. I was taking a gentle (maybe not so gentle) jab at Simon over it. We've been of different opinion for a long time. I am trying to wear him down. However, some other features he has that other waterfall/spectrum displays lack may make the correct form of Zoom action impractical. He's not said that yet, so Gentle-Jibes-R-Us. I do find this behavior distressing. At least the receive matrices help make up for it. The matrix receiver windows do not have a zoom control as the main display has. It has a set of discrete steps of zoom and does stay centered.

{^_-}

iz1fks
Posts: 9
Joined: Sun Mar 14, 2021 1:50 pm

Re: zoom and frequency issue with external radio and tracking

#5

Unread post by iz1fks »

jdow wrote:
Sun May 02, 2021 7:31 am
"The actual behaviour is the opposite you described." I know. I was taking a gentle (maybe not so gentle) jab at Simon over it. We've been of different opinion for a long time. I am trying to wear him down. However, some other features he has that other waterfall/spectrum displays lack may make the correct form of Zoom action impractical. He's not said that yet, so Gentle-Jibes-R-Us. I do find this behavior distressing. At least the receive matrices help make up for it. The matrix receiver windows do not have a zoom control as the main display has. It has a set of discrete steps of zoom and does stay centered.

{^_-}


In this video several issues related to external radio are visible. The tuned signal move up to 1 kHz after zoom in. Moving radio vfo zoom resets, while the spectrum refresh is not fluid.

Hope it can help to solve panadapter functions of this wonderful software.
73 de Phil,iz1fks

jdow
Posts: 315
Joined: Mon Aug 10, 2020 8:17 pm

Re: zoom and frequency issue with external radio and tracking

#6

Unread post by jdow »

rtlsdr dongle on HF? I have religiously stayed away from that. I hear no audio so I cannot tell what is happening. I do not even know which receiver you are thinking is displaying wrong.

I just tried it with an AirSpy Discovery and it behaved exactly as expected on WWV received USB.

{^_^}

jdow
Posts: 315
Joined: Mon Aug 10, 2020 8:17 pm

Re: zoom and frequency issue with external radio and tracking

#7

Unread post by jdow »

It just crossed my mind that you are running VERY close to the Nyquist frequency, 14.4 MHz. It is not at all unlikely for you to experience aliasing responses. That might be related to what you are seeing.

{^_^}

iz1fks
Posts: 9
Joined: Sun Mar 14, 2021 1:50 pm

Re: zoom and frequency issue with external radio and tracking

#8

Unread post by iz1fks »

jdow wrote:
Fri May 07, 2021 12:18 am
It just crossed my mind that you are running VERY close to the Nyquist frequency, 14.4 MHz. It is not at all unlikely for you to experience aliasing responses. That might be related to what you are seeing.

{^_^}
RTL-SDR is tuned to the IF frequency 64.455 (14MHz is the radio vfo frequency). I know the limits of RTL-SDR but I looks like issue related with panadapter and external radio. I don't see any relationship with tracking issue, zoom issue and not fluid spectrum refresh with RTl-SDR, hope to be wrong anyway.

73 de Phil,iz1fks

jdow
Posts: 315
Joined: Mon Aug 10, 2020 8:17 pm

Re: zoom and frequency issue with external radio and tracking

#9

Unread post by jdow »

Ah, with that IF panadapter configuration you will very likely have to violate what I ever so arrogantly presume is correct practice and stay off the center frequency. You will have to fiddle and play to find the radio's ACTUAL IF center frequency. Tune a signal on your radio, WWV is probably good. For starters, using DSB tune it to zero beat with the BFO in the radio on. Then tune rtlsdr to that frequency the hard way. Tune a receiver to zero beat. Then go up to the zoom corner and click the >|< button. Hopefully the RX frequency and the spectrum center frequency can be made the same. Note that frequency and the radio's frequency. Do some arithmetic so you can correct the conversion frequency listed in the front end's definition. With some fiddling dongle tuned frequency, SDR receiver, and transceiver frequency can all three be lined up. Then MAYBE when you zoom you will get predictable behavior. There is no way, at present, to make the zoom expand around an SDRC "RX" receiver frequency rather than the center of the spectrum display.

If you have a modern rtlsdr dongle then to about a 150 Hz level the numbers derived will be good for quite awhile and quite a room temperature variance, presuming your transceiver has a 1ppm oscillator. If you have an old dongle, may I suggest acquiring a new one and saving your mind from terminal insanity trying to get it all to work? Getting two (maybe three depending on transceiver) oscillators to all line up and give you good results is bad enough. When one or more of them drift it can drive you mad.

As for the "not fluid spectrum refresh", the RTLSDR dongles are, as more recent front ends go, rather light CPU loads. Temporarily ditch the panadapter configuration and use the dongle for aircraft up around 120-130 MHz, utility radio (police/fire/taxis), or simply ham radio. If the tuning still feels ragged to you then the problem lives within the heart of your CPU. Take some load off of it. Going back to the panadapter configuration the communications between the radio and SDRC are not instantaneous. That, too, can make your tuning feel ragged or laggy.

Finally, depending on how your transceiver works it can also introduce significant tuning errors. In your transceiver you have two frequency synthesizers of particular interest, at least. One, the first one, or both can have step size issues that can give problems. There is no law on the books that requires the first conversion converts from the precise receiver frequency to a precise 64,500,000 Hz with the second oscillator fixed tune from 64,500,000 down to the rest of the radio at a fixed frequency. The first oscillator could have a step size of 1 kHz with the smaller steps being made up in the second oscillator's synthesizer. Worse yet the first oscillator's step size does not have to be constant. (The rtlsdr dongle itself does this. The first LO in the tuner is large steps that are not constant size. There is another synthesizer in the realtek chip that give you approximately a 7 Hz step size. In good rtlsdr.dll implementations this arithmetic is taken care of in the DLL. Also note that if you make the rtlsdr dongle change frequency it WILL be ragged. The synthesizers take what I, at least, consider to be a long long time.)

In short, you may be asking for the system you have lashed together to deliver more than it can.

{^_^}

Post Reply