Marconi Digital I.F. interface.
The digital I.F. stage could be at 100 KHz, here were all the signal modulation and de-modulation is achieved. The output of the TX or RX I.F. stage could then be digitised using an AD7357 device which is a dual 14 bit A/D successive approximation convertor. This output could then be framed into an Ethernet link data structure for broadcast over an Ethernet link through an Ethernet switch to a remote TX/RX unit. This unit could be the VHF, UHF, or 23cm etc. radio modules. The 100 KHz I.F. could come from the HF Radio set, be it a RX or a RX/TX radio set used for Ham Radio or other uses.
By using a 100 KHz I.F. to provide the carrier modulation and demodulation, the overhead requirements of the computer system on board the radio are of a lesser demand. Less specialised components are then needed, the cost of the computer then less in terms of the manufacture of the radio and also of a replacement part in case of system failure. The cost of DSP radios such perhaps as the Flex radio system, the customer base to my pocket is of a smaller level.
The digitising of the 100KHz I.F. means that once it is recompiled back into an analogue signal, the signal can then be passed through a I.F. filter to remove any distortion of the I.F. carrier signal from the A/D then D/A processing, in other words the quantisation noise.
The signal presented by the I.F. before A/D conversion would have to be presented after an effective AGC circuit to prevent any boundary voltage signal clipping. An analogue circuit has a compression point and a 3rd harmonic signal IMD performance, here the signal is still preserved but distorted but readable. However a digitising system would signal clip, and thus produce square voltage converted signal at the D/A signal end, which would provide very little message content from an “AM” carrier signal modulation format.
A computer could also be used to provide the D/A conversion for a remote receive and control of the radio set.