[Premium-Rx] bandscope frequency conversion question

[Brooke Clarke]

Hi Jack:

The connection between RBW and sweep speed comes about because of the physical 
nature of the band width filters.   Those restrictions are not present when 
using a digital system.  For example the HP/Agilent 4395A combo box when used 
as a spectrum analyzer can sweep a 100 kHz span with a 100 Hz RBW in 0.3 
seconds whereas an analog SA will need 30.0 seconds to make the same sweep.
http://www.prc68.com/I/4395A.shtml#SA

This kind of thing is great for doing a spectrum survey.  The narrow RBW puts 
the noise floor way down.  Peak capture remembers any transmissions.  Come back 
after a day or so to see where the action is.

The thing I really like is that the RBW (as well as but different than VBW) can 
be set to 1 Hz, much too narrow for an analog filter.  But now I wonder what it 
would be like to have sub 1 Hz RBW capability.

I think this is one of the reasons why the SDR-IQ and other SDRs are popular.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com



Jack Smith wrote:
> You might find my article on  the Z90 digital panadapter of some 
> interest, as it discusses span versus resolution and sweep time. A copy 
> is available at the ARRL's QEX site.
> http://www.arrl.org/qex/2007/03/smith.pdf.
> 
> You might also find some useful things if you poke around my web site a 
> bit. www.cliftonlaboratories.com. It shows some typical spectrum 
> displays of different modulation types among many other things.
> 
> 
> Jack K8ZOA
> 
> H. L. wrote:
> 
>> Just discovered the premium-RX group and am enjoying the archive very, 
>> very much.  Quick question. Has a circuit been published for an 
>> outboard mixer/oscillator that will convert a premium receiver's 455 
>> kHz IF output to 21.4 MHz for connecting to a WJ (or other) panoramic 
>> bandscope spectrum analyzer. I understand that the display frequency 
>> range will be highly limited (or compressed) and that a lower quality 
>> Heathkit SB620 bandscope will give a better, higher resolution display 
>> than an expensive WJ scope because it is designed for a 455 kHz 
>> input.  I don't understand the mathematics of this issue and would 
>> appreciate an article reference if available.  Regards, Hal, KK6HY 
>> (main premium receiver: Stoddart NM-26T -- with a 455 kHz IF output 
>> jack). My Stoddart radio history website: 
>> http://online.sfsu.edu/~hl/src.html
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>>
>>
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