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Shortwave Radiogram, 11 Mar 2018

Ron
 

Hi Kim,

Good experiment with the image sent normal and half speed.  The second show at 2330 UTC reception, S30 was much better than at 2030 UTC show S5 here near Philadelphia.  Here are the two images.  I used audacity to record the show and then increased the speed to decode the 2nd image.  While receiving the second image at 1/2 the speed I noticed the signal was down at 750 Hz from 1500 Hz on the waterfall.  I think this is because the speed of the transmission was cut in half and that changed the frequency of the audio 1/2.


 

Image sent normal speed         Image sent 1/2 speed

So the image seemed to improve with the reduction in speed.  Thanks that was fun.

73, Ron NY3J

Dave
 

How to play back a recorded audio file at high speed:
  1. record the audio signal using fldigi's built in wav recorder, "File / Audio / RX capture".  The saved file will be a "wav" format.
  2. set up a Macro with one of the following undocumented macro tags:
    <HS:toggle>  - toggles the wave file play back between normal and maximum playback speed (cpu will hit 100%)
    <HS:on>      - high speed playback on
    <HS:off>     - high speed playback off
  3. play back the wav file and then shift to high speed playback using the new macro key.

This is used by developers during new modem development.  The playback speed can be as much as x10 depending on computer hardware.

If you have a previously recorded audio file you can convert it to a monophonic wav file, preferably at a 8000 samples / second.  fldigi will only play back wav files.  The sample rate is not constrained to 8000 sps.

Dave


On 03/11/2018 07:37 PM, Ron wrote:
Hi Kim,

Good experiment with the image sent normal and half speed.  The second show at 2330 UTC reception, S30 was much better than at 2030 UTC show S5 here near Philadelphia.  Here are the two images.  I used audacity to record the show and then increased the speed to decode the 2nd image.  While receiving the second image at 1/2 the speed I noticed the signal was down at 750 Hz from 1500 Hz on the waterfall.  I think this is because the speed of the transmission was cut in half and that changed the frequency of the audio 1/2.


 

Image sent normal speed         Image sent 1/2 speed

So the image seemed to improve with the reduction in speed.  Thanks that was fun.

73, Ron NY3J


Ron
 

Hi Dave,

Thanks for that information.  It's fun to speed up the mode while decoding the recording with the Macro.  I tried to decode the 1/2 speed recording from the radiogram show even using the RX capture feature and couldn't get it to work when it switched to 1/2 speed.  I'll have to try it again next time making the recording with Fldigi.

73, Ron NY3J

On 3/11/2018 10:57 PM, Dave wrote:
How to play back a recorded audio file at high speed:
  1. record the audio signal using fldigi's built in wav recorder, "File / Audio / RX capture".  The saved file will be a "wav" format.
  2. set up a Macro with one of the following undocumented macro tags:
    <HS:toggle>  - toggles the wave file play back between normal and maximum playback speed (cpu will hit 100%)
    <HS:on>      - high speed playback on
    <HS:off>     - high speed playback off
  3. play back the wav file and then shift to high speed playback using the new macro key.

This is used by developers during new modem development.  The playback speed can be as much as x10 depending on computer hardware.

If you have a previously recorded audio file you can convert it to a monophonic wav file, preferably at a 8000 samples / second.  fldigi will only play back wav files.  The sample rate is not constrained to 8000 sps.

Dave


On 03/11/2018 07:37 PM, Ron wrote:
Hi Kim,

Good experiment with the image sent normal and half speed.  The second show at 2330 UTC reception, S30 was much better than at 2030 UTC show S5 here near Philadelphia.  Here are the two images.  I used audacity to record the show and then increased the speed to decode the 2nd image.  While receiving the second image at 1/2 the speed I noticed the signal was down at 750 Hz from 1500 Hz on the waterfall.  I think this is because the speed of the transmission was cut in half and that changed the frequency of the audio 1/2.


 

Image sent normal speed         Image sent 1/2 speed

So the image seemed to improve with the reduction in speed.  Thanks that was fun.

73, Ron NY3J