Off the shelf A/D converters (mostly single chip) have come on in leaps and
bounds in recent years, thanks to (dictated by ?) the mobile phone industry.
I think most cell phone base stations just downconvert and digitise the whole
band in one go. So, with forward power control implemented, 14 bit (16 bit
now) resolution is adequate. The GSM band is 25MHz wide so 65MHz sampling is
adequate. This is just about suitable for entire HF band digitisation. At
least, on a good day provided there are no mega-strong signals present such as
on-board transmitters - there often will be!
A/D converters got to this point over a very short period, a few years ago. In
1994, such 14 bit devices cost 10000 pounds each (from Analog Devices), now
they cost a few tens of pounds.
Now, I have heard of 100MHz devices - which are needed for 3G phones - but
things seem to be moving more slowly now, so it looks as if technology is the
limiting factor, or more likely the money that the mob. phone industry is
prepared to throw at development of better A/D converters.
However, the product I mentioned, was produced, by Hewlett Packard I believe,
some time ago specifically for intercept equipment for communications and
radar. It was in the HP catalogue at one time, but going back a few years.
Don't have the exact hardware details to hand, but vaguely remember it was
made up of discrete components, and was almost certainly a sigma delta type of
A/D ( one or two bit sampling very, very fast, ie. several GHz, followed by
processing, Same idea as in Codecs on soundcards) and cost an awful lot of
money. I would have cost tens or hundreds of thousands of dollars for the
complete system.
While it may have been enhanced a bit by now , more likely its been forgotton.
Contrasting the massive leap forward in technology in the commercial, and
particularly mobile phone industries, with the slow down / stagnating of purely
military research since the end of the Cold War, I guess much comint (and
software defined radio) hardware just uses off the shelf devices now.
On a totally different matter :
Have just read that the Zepp antenna is so named as it was once used as the
antenna towed behind Zeppelin airships. Does anyone know if this is so? I've
certainly never come across any other derivation of its name.
Andy G4JNT
for [the modern day equivalent equivalent of WW2 monitoring
>stations] that digitises the entire HF spectrum in one go.
>
Do really exist A/D converters capable of 24-bit resolution at 30 MHz
bandwidth ?
If the answer is yes, then recently I haven't paid too much attention to
what was
happening in the technology field...
73 Alberto I2PHD
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