[Elecraft] Price Comparison and Comment

[w2bvh at comcast.net]

Bill,

I've had my eye on the Orion since it came out. I almost got to the point of clearing getting one with my xyl, but about that time the QST review came out and it wasn't all that kind to the Orion. So I've held on to my K2. I've been happy with it, but it's human nature to always look for a bit more.

The reason I'm writing you is I'd like to know if you think the (2) QST reviews were unfair and what you think of the Orion... (Your reply, below, is quite complimentary; but are you coping with other deficiencies to get the raw performace the Orion is giving you?)

Tnx in advance & 73,
Lenny W2BVH
 -------------- Original message ----------------------
From: Bill Tippett <btippett at alum.mit.edu>
> At 07:34 PM 5/4/07, Don Wilhelm wrote:
> 
> >All of what you say is true *EXCEPT* for one item - and that is the AGC.
> 
>          Don you are absolutely correct.  The reason
> I never considered it is that I have never experienced it
> with my Orion.  I seldom operate with strong signals
> spaced much closer than 500 Hz.  The most severe
> case of this may be in the CQ 160 CW Contest where
> it's not uncommon for S9+20 to 30 signals to be spaced
> every 500 Hz.  With typical key click bandwidths, very
> few people will try to get closer than 500 Hz.  Given
> 500 Hz signal spacing and given a 500 Hz BW filter,
> the filter easily knocks them down to a reasonable
> level, since the filter BW is +/- 250 Hz and the signals
> are +/- 500 Hz.
> 
>          Orion uses a two-stage AGC system, one is
> analog and ahead of the DSP.  It has has the main
> function of preventing over-driving the DSP stage.
> 
> "ADC overload can never be allowed to occur because when that 
> happens, signals are irrevocably corrupted. Signals that are larger 
> than the full-scale range of the ADC must force reduction of gain in 
> the analog section of the receiver. So both analog and digital AGCs 
> are used in the Orion. Resort to analog AGC only need be made when 
> signals inside the roofing bandwidth exceed about S-9 plus 30 dB. At 
> that point, sensitivity is reduced but what we are discovering is 
> that phase-noise performance-- as determined by reciprocal-mixing 
> measurements-- already limits what you can hear. So performance is 
> phase-noise limited and not DSP limited. Even so, the Orion gives you 
> the option of kicking in a crystal filter, preventing movement of the 
> analog AGC and the sensitivity reduction described above."
> 
> http://www.doug-smith.net/orion.htm
> 
>          As stated, this analog AGC does not activate
> until signals reach the S9+35 range.  The second AGC is
> digital and internal to the DSP (which works very well).
> 
> "As the resolution and speed of ADC hardware improve, digital radio 
> receivers become less dependent on analog AGC to meet dynamic-range 
> requirements. State-of-the-art 24-bit IF-DSP converters, such as 
> those used in the Ten-Tec Orion, produce about 100 dB of dynamic 
> range. That means a receiver can handle signals from the noise floor 
> to almost 40 dB over S9 without analog AGC. Above that level, analog 
> AGC is still necessary to maintain the linearity of analog circuits 
> and to prevent overload in the ADC hardware."
> 
> http://www.doug-smith.net/dspdynamics.htm
> 
>          I haven't seen much about the K3 AGC but I
> hope it uses a similar same technique as Orion.  I have
> NEVER heard any AGC pumping in Orion, even under
> severe situations like the CQ 160 CW Contest which
> I consider the ultimate test for any receiver.  I guess
> that's why it did not occur to me to mention it.  Maybe
> one of the Elecraft folk will tell us more abour the K3
> AGC.
> 
>                          73,  Bill  W4ZV
> 
> 
> 
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