Playing around with these commercial RXs of the 1970s,
the Racal 1772 and the Eddystone 1837/2, you relaise how much
of the size of the beasts in the 19" rack was dedicated to
providing very stable HF VFOs, something that today can be
supplied by something no larger than the small finger's
fingernail, the si570 et al chips.

Now, although well versed in the theory of DSP, I've
no practical experience of it which raises a couple
of questions ...

1. When listening to CW through a narrow 300 Hz BW filter
do the DSP versions ring in the same manner as analogue filters,
the ringing of the analogue filters rendering it nigh impossible
to read Morse at much greater than 20WPM?

2. In a DSP where the whole of the spectrum from the aerial or
antenna is sampled presumably there is no problem with blocking,
cross or inter modulation or reciprocal mixing? ie. Strong
signal handling is excellent?

3. Therefore, do the frequency stability, selectivity and strong
signal handling of DSPs make all previous technologies of radio
engineering seem to be escapees from the age of the dinosaurs,
despite that DSP requires many zillions of active devices as against
the typically less than 50 active devices in the signal path as
implemented in analogue designs?

4. Does the integration of facilities into the DSP rigs now mean
that traditional amateur radio in terms of the understanding
and construction of basics of TX and RX is now a thing of the past and
that technological advancement by radio amateurs becomes an aspect
of application software such as the recently vaunted FT8Call?

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42. What is the meaning of life, the universe and everything? :-)

Gareth's Downstairs Computer
wrote:

Playing around with these commercial RXs of the 1970s,
the Racal 1772 and the Eddystone 1837/2, you relaise how much
of the size of the beasts in the 19" rack was dedicated to
providing very stable HF VFOs, something that today can be
supplied by something no larger than the small finger's
fingernail, the si570 et al chips.

Now, although well versed in the theory of DSP, I've
no practical experience of it which raises a couple
of questions ...

1. When listening to CW through a narrow 300 Hz BW filter
do the DSP versions ring in the same manner as analogue filters,
the ringing of the analogue filters rendering it nigh impossible
to read Morse at much greater than 20WPM?

2. In a DSP where the whole of the spectrum from the aerial or
antenna is sampled presumably there is no problem with blocking,
cross or inter modulation or reciprocal mixing? ie. Strong
signal handling is excellent?

I have no experience of how much strong signals degrade weak signals
within the dynamic range of an ADC, but it is obvious that ADCs have a
finite dynamic range related to the number of bits. So a strong local
signal still has to be filtered out to avoid overloading the ADC (so you
get a square wave of all noughts to all ones at the interfering
freqency) when at the wanted frequency sufficient sensitivity is used to
receive small signals. So RF preselectors, and amplifiers at
frequencies where received noise is not limiting, are still needed.





3. Therefore, do the frequency stability, selectivity and strong
signal handling of DSPs make all previous technologies of radio
engineering seem to be escapees from the age of the dinosaurs,
despite that DSP requires many zillions of active devices as against
the typically less than 50 active devices in the signal path as
implemented in analogue designs?

4. Does the integration of facilities into the DSP rigs now mean
that traditional amateur radio in terms of the understanding
and construction of basics of TX and RX is now a thing of the past and
that technological advancement by radio amateurs becomes an aspect
of application software such as the recently vaunted FT8Call?

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42. What is the meaning of life, the universe and everything? :-)


--

Roger Hayter