Re: LF: Slow Voice - testing on 137.0 kHz

[M0FMT <m0fmt@yahoo.co.uk>]

Well done Marcus and co.

 

Thank you for your innovative contributions to Ham Radio. Proving that even with current technology the limits can be pushed further.

 

In the UK (and I am sure elsewhere) there is a single channel VHF Parrot type repeater which is operated in a similar way where you speak, drop carrier, hear your own transmission rebroadcast and then wait for a reply which some times can be heard directly on the channel and is then re-enforced by the Parrot in the following transmission. It is slow and laborious but many stations use it.

 

I guess the difference is that you have an added element of delay each way for audio frequency com/decompression which amounts to the Parrot in the above case rebroadcasting each transmission only longer by a factor..

 

Like to hear an audo file?

73 es GL Pete M0FMT IO91UX

From: Markus Vester <markusvester@aol.com>
To: rsgb_lf_group@blacksheep.org
Sent: Saturday, 12 January 2013, 14:03
Subject: LF: Slow Voice - testing on 137.0 kHz



Yesterday morning I have uploaded a new version SlowVoice v0.2 to

http://www.df6nm.bplaced.net/slowvoice/SlowVoice.zip

I have reworked some details of the timing, and added simplified scripts for receive-only and transmit-only in mono mode. The serial port PTT control utility has also been modified to function under WinXP.

 

This afternoon I am sending a few slow voice tests with 3 times deceleration in 1-minute frames. The 800 Hz wide passband is centered on 137.0 kHz, thus 136.6 to 137.4 kHz corresponds to 0.3 to 2.7 kHz audio. Attached screenshot shows the narrow SSB signal on the Twente WebSDR tuned to 135.5 kHz USB. I used a narrow passband to improve rejection for DCF and HGA. This audio around fc=1500 Hz was fed to the receive-only utility, which then produced clear speech during 20 seconds of each minute. 

 

I intend to run some more test transmissions this afternoon, starting now 14 UT. Any reports would be much appriciated!

 

Best 73,

Markus (DF6NM)  

 

 

 

----- Original Message -----

From: Markus Vester

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, January 08, 2013 11:31 PM

Subject: LF: Slow Voice utility

A few minutes ago I have uploaded an experimental SlowVoice script to

http://www.df6nm.bplaced.net/slowvoice/SlowVoice.zip

 

The main purpose is to be able to convey high quality speech in less than 800 Hz on the RF side, as prescribed by German LF and MF regulations. By default, an audio band of 300 to 2700 Hz is slowed by a factor of 3 and upconverted to 1500 Hz center frequency. Thus a range of 1200 to 2000 Hz is fed to the SSB transmitter. As an aside benefit we get a very much welcome 5 dB improvement in SNR.

 

Like JT9-1, the procedure is clock-synchronized in fixed one-minute time slots. At the beginning of the minute, the transmitting station is asked to speak for 20 seconds. It feels a bit like to speaking to a telephone answering machine ;-) The slow converted output of the growing audio buffer begins to play immediately, and will go on during the whole minute. On the receive side, fast replay begins at second number 40, and the shrinking buffer will finally be used up by the end of the minute.

 

The SlowVoice.bat script is set up for full duplex operation. One channel is supposed to handle the transmit side (eg. mic connected to left input, transmitter to left output), while the other channel has the receiver fed to the input and phones on the output. This is symmetrical, and there is no further need to switch audio pathways between TX and RX. It is also possible to monitor the result of one's own transmission, eg. by physically connecting left line out to right in. If you want you can use SpecLab in conjunction with Virtual Audio Cable to preprocess both the mic and receiver audio inputs. In this case VAC will have to be selected as the standard audio input device before the running the script.

 

Whether a slots is used for TX or RX is not controlled by the software but only by the user's PTT. I have included two extra scripts which are supposed to activate the serial handshake lines (RTS and DTR) on either even or odd minutes. Unfortunately the port control does not seem to work on my XP machine with an external USB to serial converter, so for the time being you may have to do with either vox control or manual switching.

 

I haven't gotten around writing more detailed instructions, but some basic hints have been included in the SlowVoice script. Similar to the first slow WSPR experiments, the whole deceleration / acceleration process is based on Wolf's sound utilities which you will need to download from the DL4YHF web site. You will have to run the included patch utility once to duplicate SndInput and SndOutpt instances.

 

Have fun! And please report bugs and other troubles.

 

73, Markus (DF6NM)

 

 

 

 

----- Original Message -----

From: Markus Vester

To: rsgb_lf_group@blacksheep.org

Sent: Sunday, January 06, 2013 1:50 PM

Subject: LF: Bandlimited SSB test on 136 kHz

...

 

Slow voice transmission (ie the audio deceleration/acceleration method originally used by DK8KW and myself) would be nicer as it can fit a full SSB channel into 800 Hz. I have been working on a semi-automatic control, with a fixed one minute raster similar to JT9-1. This will hopefully allow us to comfortably exchange one 20 second voice message per time slot (speak during seconds 0 to 20, concurrent transmit and receive at 1/3 speed from 0 to 60, replay starting 40 to 60). Anyone interested?

 

...

 carr