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Question re: ATV modulation on Lime


James Dallas
 

Hi everyone,

Has anyone had any success with ATV modulation? I have been trying to generate PAL-M (which should be compatible with NTSC / US standard in black and white) signals, 525 / 30 / PAL525 on 4.4.4 and getting no signal on an NTSC USB TV dongle (or for that matter on a "real" TV.

I have the frequency set to 427.25 MHz and am trying to use VUSB, with the bandwidth set to 1300 kHZ on the lower sideband and 4800 on the right.

(Incidentally, the standard specifies a 1.25 MHz vestigial lower sideband, but the slider switches over to 100 kHZ blocks before I can get a full 6 MHz signal).

Any thoughts?

Thanks and 73s,

AD5NL


Siegfried Jackstien
 

should it not be am modulated for a normal tv set ... and fm modulated if using an analog sat receiver??

dg9bfc sigi

Am 23.02.2019 um 05:17 schrieb James Dallas:

Hi everyone,

Has anyone had any success with ATV modulation? I have been trying to generate PAL-M (which should be compatible with NTSC / US standard in black and white) signals, 525 / 30 / PAL525 on 4.4.4 and getting no signal on an NTSC USB TV dongle (or for that matter on a "real" TV.

I have the frequency set to 427.25 MHz and am trying to use VUSB, with the bandwidth set to 1300 kHZ on the lower sideband and 4800 on the right.

(Incidentally, the standard specifies a 1.25 MHz vestigial lower sideband, but the slider switches over to 100 kHZ blocks before I can get a full 6 MHz signal).

Any thoughts?

Thanks and 73s,

AD5NL


James Dallas
 

AM may/probably works but the traditional 6 MHz NTSC / System M signal has a 4.75 MHz upper sideband and a 1.25 MHz wide lower sideband. The lower sideband is vestigial (although what is labeled as VUSB in sdrangel seems to have the full upper and vestigial lower).

It's basically AM with most of the lower sideband chopped off.

To make it weirder, NTSC uses FM for the audio.

The NTSC committee basically threw in every idea that was cutting edge ca. 1950 when they wrote their standard.

On Sun, Feb 24, 2019, 2:19 PM Siegfried Jackstien <siegfried.jackstien@...> wrote:

should it not be am modulated for a normal tv set ... and fm modulated if using an analog sat receiver??

dg9bfc sigi

Am 23.02.2019 um 05:17 schrieb James Dallas:
Hi everyone,

Has anyone had any success with ATV modulation? I have been trying to generate PAL-M (which should be compatible with NTSC / US standard in black and white) signals, 525 / 30 / PAL525 on 4.4.4 and getting no signal on an NTSC USB TV dongle (or for that matter on a "real" TV.

I have the frequency set to 427.25 MHz and am trying to use VUSB, with the bandwidth set to 1300 kHZ on the lower sideband and 4800 on the right.

(Incidentally, the standard specifies a 1.25 MHz vestigial lower sideband, but the slider switches over to 100 kHZ blocks before I can get a full 6 MHz signal).

Any thoughts?

Thanks and 73s,

AD5NL


James Dallas
 

Updates...

(1) I was able to modify fsphil's hacktv GitHub code to work on LimeSDR (had to add a call to Soapy API to set antenna). It's not perfect... See some jitter... But at least I have a standard reference. HackTV also can generate IQ files but not sure if they are compatible with sdrangel.

(2) in playing with HackTV I discovered the antenna on my TV was not good, so I hooked the LimeSDR transmit out cpax straight to the TV through an sma to F adapter. Working great now (as noted with some jitter..).

(3) This afternoon I will try again with sdrangel now that I have eliminated the hardware/antenna problem. Maybe it will work. If not I have HackTV as a backup (it also transmits color and can hook right into ffmpeg).

On Sun, Feb 24, 2019, 2:29 PM James Dallas via Groups.Io <jim.dallas=gmail.com@groups.io> wrote:
AM may/probably works but the traditional 6 MHz NTSC / System M signal has a 4.75 MHz upper sideband and a 1.25 MHz wide lower sideband. The lower sideband is vestigial (although what is labeled as VUSB in sdrangel seems to have the full upper and vestigial lower).

It's basically AM with most of the lower sideband chopped off.

To make it weirder, NTSC uses FM for the audio.

The NTSC committee basically threw in every idea that was cutting edge ca. 1950 when they wrote their standard.

On Sun, Feb 24, 2019, 2:19 PM Siegfried Jackstien <siegfried.jackstien@...> wrote:

should it not be am modulated for a normal tv set ... and fm modulated if using an analog sat receiver??

dg9bfc sigi

Am 23.02.2019 um 05:17 schrieb James Dallas:
Hi everyone,

Has anyone had any success with ATV modulation? I have been trying to generate PAL-M (which should be compatible with NTSC / US standard in black and white) signals, 525 / 30 / PAL525 on 4.4.4 and getting no signal on an NTSC USB TV dongle (or for that matter on a "real" TV.

I have the frequency set to 427.25 MHz and am trying to use VUSB, with the bandwidth set to 1300 kHZ on the lower sideband and 4800 on the right.

(Incidentally, the standard specifies a 1.25 MHz vestigial lower sideband, but the slider switches over to 100 kHZ blocks before I can get a full 6 MHz signal).

Any thoughts?

Thanks and 73s,

AD5NL


Siegfried Jackstien
 

ah ok ... i didnt know that

thanks for clarification

greetz

sigi dg9bfc

ps it would be nice if we would have FULL analof tv support with colour and subcarrier(s) selectable

in rx and tx

Am 24.02.2019 um 20:28 schrieb James Dallas:

AM may/probably works but the traditional 6 MHz NTSC / System M signal has a 4.75 MHz upper sideband and a 1.25 MHz wide lower sideband. The lower sideband is vestigial (although what is labeled as VUSB in sdrangel seems to have the full upper and vestigial lower).

It's basically AM with most of the lower sideband chopped off.

To make it weirder, NTSC uses FM for the audio.

The NTSC committee basically threw in every idea that was cutting edge ca. 1950 when they wrote their standard.

On Sun, Feb 24, 2019, 2:19 PM Siegfried Jackstien <siegfried.jackstien@...> wrote:

should it not be am modulated for a normal tv set ... and fm modulated if using an analog sat receiver??

dg9bfc sigi

Am 23.02.2019 um 05:17 schrieb James Dallas:
Hi everyone,

Has anyone had any success with ATV modulation? I have been trying to generate PAL-M (which should be compatible with NTSC / US standard in black and white) signals, 525 / 30 / PAL525 on 4.4.4 and getting no signal on an NTSC USB TV dongle (or for that matter on a "real" TV.

I have the frequency set to 427.25 MHz and am trying to use VUSB, with the bandwidth set to 1300 kHZ on the lower sideband and 4800 on the right.

(Incidentally, the standard specifies a 1.25 MHz vestigial lower sideband, but the slider switches over to 100 kHZ blocks before I can get a full 6 MHz signal).

Any thoughts?

Thanks and 73s,

AD5NL


James Dallas
 

Update #2 I was able to get PAL-M / quasi-NTSC working in sdrangel. See photos attached comparing sdrangel and HackTV (as modified by me) outputs.

I noticed that sdrangel seemed really unstable and sometimes unresponsive when under this load. The start/stop transmit button would often get unresponsive.

In addition to color HackTV also supports sound, at least in theory. In practice I will have to do some ffmpeg magic to make a combination video/audio stream with my webcam. I was able to get audio just fine though when playing a video file rather than /dev/video0 (Big Buck Bunny mp4).

The key settings for sdrangel:

Frequency 55.250 MHz (my is tuned to channel 2). This is not critical and be changed, I just used this because I didn't want to wait for my TV to scan all the way to 421 MHz for cable channel 57.

SR 10 MHz. h 8 s 1.

Open up the lpf, make this at least 10 MHz.

ATV modulator settings:

Rational decimation on.

VUSB 1200k/4800k

525 lines, 25 or 30 fps (25 has smoother video but flashes periodically, 30 has jerky video but I believe that is an issue with my aging computer not being able to walk and chew gum at the same time.
). Make sure Inv is checked .. this is critical!! Set luminance to 90.

Use camera and perhaps set manual fps lower.

You should then be able to look like you are starring in a fake Apollo moon landing (with the jerky b/w video) hihi.








On Sun, Feb 24, 2019, 2:42 PM Siegfried Jackstien <siegfried.jackstien@...> wrote:

ah ok ... i didnt know that

thanks for clarification

greetz

sigi dg9bfc

ps it would be nice if we would have FULL analof tv support with colour and subcarrier(s) selectable

in rx and tx

Am 24.02.2019 um 20:28 schrieb James Dallas:
AM may/probably works but the traditional 6 MHz NTSC / System M signal has a 4.75 MHz upper sideband and a 1.25 MHz wide lower sideband. The lower sideband is vestigial (although what is labeled as VUSB in sdrangel seems to have the full upper and vestigial lower).

It's basically AM with most of the lower sideband chopped off.

To make it weirder, NTSC uses FM for the audio.

The NTSC committee basically threw in every idea that was cutting edge ca. 1950 when they wrote their standard.

On Sun, Feb 24, 2019, 2:19 PM Siegfried Jackstien <siegfried.jackstien@...> wrote:

should it not be am modulated for a normal tv set ... and fm modulated if using an analog sat receiver??

dg9bfc sigi

Am 23.02.2019 um 05:17 schrieb James Dallas:
Hi everyone,

Has anyone had any success with ATV modulation? I have been trying to generate PAL-M (which should be compatible with NTSC / US standard in black and white) signals, 525 / 30 / PAL525 on 4.4.4 and getting no signal on an NTSC USB TV dongle (or for that matter on a "real" TV.

I have the frequency set to 427.25 MHz and am trying to use VUSB, with the bandwidth set to 1300 kHZ on the lower sideband and 4800 on the right.

(Incidentally, the standard specifies a 1.25 MHz vestigial lower sideband, but the slider switches over to 100 kHZ blocks before I can get a full 6 MHz signal).

Any thoughts?

Thanks and 73s,

AD5NL