Remote-Ready   Antenna 

SKY-SDR Questions and Answers




1)  Who designed the SKY-SDR?

  • The SKY-SDR was designed by Dobri, LZ2TU, aided by Nick, LZ1JY.  Its software was written by Sergey, RA9YTJ. 


2)  Did the designers copy the LNR Precision LD-11 QRP Transceiver?

  • NO!  The designers listed above designed and built the "bare bones" of the LD-11 in Bulgaria.  LNR added their own red enclosure.

​3)  Is the SKY-SDR identical or nearly identical to the LNR LD-11?

  • NO!  Though they look similar, there are significant differences. The SKY-SDR is the next generation above the LD-11.
    • ​First Generation was the LD-5
    • Second Generation was the LD-11
    • Third Generation is the SKY-SDR

4)  What are the main differences between the SKY-SDR and its predecessor, the LD-11?

  • The core difference is in its software.  Whereas the LD-11 uses single-threaded software in its firmware, the SKY-SDR uses dual-threaded software.  This has cut CPU latency in half. 
    • Lower CPU latency enables the use of more aggressive filters (steeper/deeper) without causing distortion.
  • The SKY SDR has had continuous improvements over the past 18 months, whereas the LD-11 with its single-threaded software has remained unchanged.  The changes include:
    • Re-designed knobs
    • More practical mic cable
    • ​Improved audio gain
    • Improved sidetone volume
    • Improved noise floor (was already excellent, now even better)
    • Improved DSP filters (sharper slopes, deeper nulls)
    • Improved notching of carriers in SSB mode
    • Increased mic gain
    • Improved mechanics to the VFO encoder 
    • Improved panel labeling
    • Informative User Manual


5)  Why is SKY-SDR the same color scheme as the first generation LD-5, rather than the red color of the LD-11?

  • Although the LD-11's red enclosure is beautiful, it was determined that a transceiver designed for rugged field use would not show scratches as much when silver as with a red-color enclosure.
  • Although we actually like the LD-11's red color, some people totally dislike it.  We found silver to be a much more neutral color which everyone can accept.
  • Darker color enclosures do not have such good contrast as dark labels on light background enclosures.  The color scheme of the SKY-SDR makes it easier to read in operating conditions with poor lighting.

6)  Why did the SKY-SDR revert to the square push-buttons of the LD-5, rather than using the round push-buttons of the LD-11?

  • For ergonomic reasons, with limited panel space and close proximity of the buttons, we found the slightly larger square buttons easier to use than the smaller round butttons.


7)  What is the underlying technology used in the SKY-SDR? 

  • The SKY SDR is a direct conversion, software designed technology using a homodyne design.  It uses the same path for transmit and for receive, resulting in the TX path being as clean as its RX path - specifically, having equal dynamic range.
  • It has unique differential ​processing in its front end, which carries on throughout the radio, resulting in lower noise level than its similar competitors.

8)  What advantages does this technology have over traditional analog technologies as used in radios like the FT-817?

  • Fundamentally this is an unfair question; the FT-817 is a 25 year old design, whereas the technology used in the SKY-SDR is only a few years old.
  • The primary advantage is very high performance at a relatively low price.  The performance of the SKY-SDR's receiver is better in all important aspects than any of yesterday's analog transceivers costing less than $2500.
  • In a side-by-side comparison with most analog transceivers costing less than $4000, when listening to the SKY:
    • The first question is "where did the noise go?
      • ​Using specific differential DSP and software, adjusting phase and amplitude and proportionally adjusting stage gain of each stage, maintaining uniform gain, we managed to decrease the noise floor even further, resulting in the highest possible Reciprocal Mixing Dynamic Range (RMDR).
    • The second question is, "where did the QRM go?"
      • ​Using the unique differential software technology, we achieved an excellent balance of all receiver specifications, (e.g., filter passband slope, ultimate attenuation, etc.) resulting in reduced interference and a stronger wanted-signal.
  • ​The SKY-SDR has a built in Pan-Adapter (Bandscope).  This was impossible on a pure analog radio.
  • Expensive "Bells and Whistles" found on analog radios, such as 2nd VFO, multiple IF filters, etc., are easily and cost-effectively implemented in software with this technology.
  • Digital features, unthinkable on an analog radio, such as Noise Reduction, Audio Equalizers (on RX and TX), automatic notching of unwanted carriers, etc., are also easily and cost-effectively implemented in software.


9)  Does the SKY-SDR have reverse voltage protection?

  • Yes, a 20 A diode is across the power jack.


10) Is there any thermal protection?  The case seems to get hot.

  • The radio case is OK up to 60 degrees Centigrade (140 F) then thermal protection decreases the output power.
  • The SKY-SDR is rated 5 Watts.  Users should never exceed 6 Watts of output power.  


11) What are the switching voltage and current limits of the PTT OUT?

  • Up to +40v D.C.
  • Up to 700 mA


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