[A-DX] Shortwave Radiogram, 10-11 March 2018

[Roger]

Am 09.03.2018 um 12:49 schrieb Shortwave Radiogram:
> Hello friends,
>
> As I was typing last week's edition of this email, the lights in my 
> house were flickering because of the high winds on 2 March. I knew I 
> had to work fast: adding new names to the mailing list, then sending 
> the email three times, each with a third of the mailing list, and 
> finally uploading the Shortwave Radiogram audio to Bulgaria and to 
> WRMI. All of that was finished just before the lights went out at 6:00 
> am. (Actually, I was on the UPS.) Power was not restored until about 
> 7:00 pm.
>
> But my internet connection was not restored at that time. The Verizon 
> fiber optic lines were victims of falling trees a few blocks away. 
> Internet did not return until Sunday at about 3:00 pm. Because of 
> this, I was not able to send my usual Twitter reminders and retweets 
> of listeners' images, at least for the Saturday 1600 UTC show.

Is there really no gateway between RF applications of radio amateurs 
(via Packet Radio or similar) and social networks?
Well, the authentication via RF radio could be a problem.



>
> And I was not able to attend the Winter SWL Fest because of poor 
> conditions on I-95 up to Philadelphia. Sorry that I was not able to 
> see some of you at that event.
>
> *MFSK image experiment*
>
> This weekend's Shortwave Radiogram will include an MFSK32 image 
> transmitted at normal speed. It will then be transmitted at half 
> speed, to be recorded then played back at double speed. Is the quality 
> of the latter image better?
>
> You can use Audacit <https://www.audacityteam.org/>y to record and 
> change the speed of the transmitted audio. (Effect > Change Speed > 
> Percent Change: 100.0) Other audio editors 
> <https://www.musicianonamission.com/best-free-audio-editor/> are also 
> available. Sometimes it is tricky to transfer audio from one 
> application to another inside a PC. A virtual audio cable such as VB 
> Cable <https://www.vb-audio.com/Cable/> might help. 


This time, a kind of "re-sampling" was used, half speed at half pitch, 
and: half bandwidth. Perhaps in future experiments "transposing"  would 
also be conceivable, that means:

also half speed, but original pitch (1500 Hz) and original bandwidth. 
Maybe also with Audacity feasible. Or was half the bandwidth a desired 
effect?
Here the reception was so good that no benefits were to be seen.

But double transmission time also carries a certain danger in the case 
of a transmission of "complex structures". If there are dropouts and 
synch problems caused by them, then all the data behind them are also 
affected.
This is like "solid archive formats". Better packing density but at the 
slightest file damage the risk of complete loss.

The simplest possibility  for a maximum redundancy would be a simultan 
second MFSK-32 track with a "backward recording". Then one would have 
the whole show after 15 minutes, theoretically, and the data would have 
a maximum temporal diversity in the case of short-term transmitter failures.

I work with Adobe Audition as a wave editor. Here I process directly 
(narrow) IF-recordings, without going through an SDR program. This works 
only with AM, not with SSB or narrow FM.

http://www.rhci-online.net/radiogram/SW_Radiogram_2018-03-11.htm#SWRG


roger