[hpsdr] Atlas slot positions

[Graham / KE9H]

Hi Murray:

Good thoughts and ideas.  I have run some experiments with adding bus 
terminations on extra
cards at the end of the bus.  It helps a little bit, but does not solve 
the root problem, which is
not reflections on the bus. 

Phil and Kirk and others are working hard to fix this position 
sensitivity issue.

--- Graham / KE9H

==

Murray Lang wrote:
> Hi all,
>
> I'm stepping outside of my comfort zone here, but it's bugging me 
> enough to risk looking silly or covering old ground.
>
> I gather that the slot position dependencies are the result of data 
> pulses bouncing backwards and forwards along the atlas bus. Is this 
> right? In other words the bus lines are transmission lines and the 
> reflections are the same as we'd see in an unterminated RF 
> transmission line (standing waves and all). Yes?
>
> Can we apply the same solution to Atlas as we'd apply to our 
> transmission lines and apply a correct load or termination? This could 
> be tested by putting a waveform generator on just one of the lines and 
> trying a termination at the end or ends. An oscilloscope would reveal 
> the difference. If it's effective then a card could be built with 
> nothing but terminating resistors for placement in the end slot (or 
> maybe both end slots?). Is the impedance of the bus is already known? 
> At at any rate the best termination value could be found by trial and 
> error pretty quickly, if indeed this is effective at all.
>
> Just a thought.
>
> Murray - VK6HL


 1233845148.0