define ht length

[ik1xpv]

#define HTLEN in fft_mt_r2iq.cpp allows manual test other lenght

[ik1xpv]

#define _SOFT_TONE_DEBUG in config.h
enables the generation of soft tone close to 1MHz with ADC clk 64MHz,
the tone period is an integer factor of transferSamples.
GUI Rand CheckBox activates the software generated tone.

[ik1xpv]

Here the comparison of some ht lengths with real signal stream input bandwidth 2 MHz.

The distortion increases when length increases toward N/2+1.
The difference does non shows when the _SOFT_TONE_DEBUG is selected instead of the real one.
? maybe related to the transferSamples burst length used by _SOFT_TONE ?

[ik1xpv]

If we use a large FFTN_R_ADC (32768) // FFTN used for ADC real stream DDC tested at 2048, 8192, 32768, 131072
in config.h the ht length increases to HTLEN ( HALF_FFT / 4 + 1) => 8193 or even HTLEN ( HALF_FFT * 3 / 8 + 1 ) => 12289.
HTLEN ( HALF_FFT / 2 + 1 ) shows always distortion...