Hi Bill and Robin,

I think I do not need to further explain about my words in my previous memo to 
WSJT-X experts like you but I doublchedked my understanding about “TDM and FDM” 
fundamentals has the validity or not through google search.

You can see several cons for TDM about non-linearity from the analog age.

For example.


As you know, 4G technology introduces Single-carrier FDMA for mobile terminal 
usage (cost of the power amplifier) to reduce lower-to-average power ratio 
(PARR) against OFDMA.


I interpret the principle is unchanged from the analog age to modern 4G and it 
can be sharable for us.




Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10

From: Tsutsumi Takehiko <ja5...@outlook.com>
Sent: Monday, April 9, 2018 11:07:24 AM
To: WSJT software development
Subject: Re: [wsjt-devel] Second Public Test of FT8 DXpedition Mode: April 7, 
1400-1600 UTC

Hi Bill and Robin,

So, we stay at single carrier architecture along with 5x clock for the purpose 
to maintain the encoder and decoder codes.




Hi Take-san,

the output when NSlots >1 is not a simple distribution of the Tx power

between tones, the reason for this is that multiple tones will mix and

some filtering is necessary to minimize undesirable side-bands. The

result for NSlots=5 is a power reduction per signal of ~14dB with

respect to an NSlot=1 transmission using the same radio settings.





for a small number of constant level carriers, such as 5, they should be

considered to add in phase when passed through a clipping amplifier,

rather than according to individual power. Thus the second term in the

formula quoted below would be -20log_10 (5), about -14dB, rather than -7dB.

If these constant carriers are not considered to add in phase, rather

than according to power, then the signal will clip, causing

intermodulation products and worse, depending on the degree of clipping.

Hope this helps,

Robin, G8DQX

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