Что то не нравится мне работа приемников прямых.. шум какой то противный со смесителя и вообще, мне похоже без DDS в передатчике не обойтись, так что вопрос смещения TCXO снимается. Короче разброд и шатание в голове. Мне вот интересно, трансиверы Si4463 могут работать как с низкой 500 кГц ПЧ, так и с нулевой, но на нулевой чутье указано на аж 10 дБ хуже. Неспроста
is possible to operate the RX chain in different architecture configurations: fixed-IF, zero-IF, scaled-IF, and
modulated IF. There are trade-offs between the architectures in terms of sensitivity, selectivity, and image rejection.
Fixed-IF is the default configuration and is recommended for most applications. With 35 dB native image rejection
and autonomous image calibration to achieve 55 dB, the fixed-IF solution gives the best performance for most
applications. Fixed-IF obtains the best sensitivity, but it has the effect of degraded selectivity at the image frequency.
An autonomous image rejection calibration is included in Si446x devices and described in more detail in "5.2.3.
Image Rejection and Calibration" on page 31. For fixed-IF and zero-IF, the sensitivity is degraded for data rates less
than 100 kbps or bandwidths less than 200 kHz. The
reduction in sensitivity is caused by increased flicker noise as
dc is approached. The benefit of zero-IF is that there is no image frequency; so, there is no degradation in the
selectivity curve, but it has the worst sensitivity. Scaled-IF is a trade-off between fixed-IF and zero-IF. In the
scaled-IF architecture, the image frequency is placed or hidden in the adjacent channel where it only slightly
degrades the typical adjacent channel selectivity. The scaled-IF approach has better sensitivity than zero-IF but still
some degradation in selectivity due to the image. In scaled-IF mode, the image frequency is directly proportional to
the channel bandwidth selected. Figure 9 demonstrates the trade-off in sensitivity between the different architecture
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Причем чем ниже битрейт тем все печальнее, что логично. А у меня битрейт условно можно считать 10 бит сек считать, так что попа.