FreeDV

[fgentges at mindspring.com]

The transmitted signal of FreeDV is 14 tones.  Each time you double the 
number of tones you double the peak to average ratio of the transmitted 
signal.  The result is that this type of multitone signal with its high 
peaks will overload the RF linear amplifier.

Some years ago we found that with a 1 KW amplifier we needed to run 
about 110 watts average power.  That value still had some clipping but 
gained enough on the signal to noise such that it worked better.  When 
you start with a 5 watt radio you will have to run at a really low level 
and not much of anyone will hear  you.  We searched for some way to 
improve on that and short of building an amplifier good for huge peaks, 
there is not much you can do.

One fellow worked to improve the phase angles of the tones but nothing 
much came out of that effort.

Frank K0BRA

On 1/27/2013 7:33 PM, A. Maitland Bottoms wrote:
> Alex Fraser <beatnic at comcast.net> writes:
>>          I  heard my first freeDV stations on
>>        14236 (Saturday 4:20pm East Coast United Snakes).
>
> I wasn't active Saturday, but this (Sunday) afternoon there
> was more FreeDV there. I heard N9NJY's first few DV contacts.
>
> The people I am hearing have better antennas and more power
> than I do. The good signals come from 20m Yagis atop towers
> and 35 to 80 W RF power.
>
> My little Yeasu 817 and non-resonant dipole do not seem
> to attract attention. I took the opportunity today to
> swap out the CW mechanical filter for the SSB filter, but
> so far other than darker edges on the waterfall I don't
> notice a difference in decoding ability. I'm guessing
> my power out is about 2W (I've backed down the drive
> a bit in search of linearity, CW is about 5W on the rig.)
> How much power actually radiates is anyone's guess.
>
> I do have a good start in my PTT software mod...
> The interface I am using is a DMK engineering USB
> radio interface. Like other C-Media sound fobs, it
> handles the audio as a USB audio device and has
> GPIO pins that can be toggled with the USB HID
> interface. The cable from the interface plugs into
> the PS2-like Data connector on the 817 for a neat hookup.
>
> Good Luck!
>
> 73 de aa4hs,
> -Maitland
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