[Elecraft] K3 Beta Firmware Rev. 3.57: Synchronous AM Detection (AM-S); misc. improvements

[Wayne Burdick]

K3 beta-test firmware revision 3.57 (with DSP rev. 2.45) is now  
available.

This revision includes Synchronous AM detection, which has a clear  
advantage over the regular AM detector during selective fading. In  
this mode, the K3 can optionally track AM stations that may be  
slightly mistuned, as you might find in an AM round-table on 75 m.  
It's also convenient for automatically zeroing in on AM broadcast  
stations.

There are other considerations when using Synch AM, so you should read  
the release notes (below) before trying it. We'll be further refining  
our AM-S implementation in a later release, based on your feedback.

Please send any questions to k3support at elecraft.com. For instructions  
on how to load beta firmware, see:

      http://www.elecraft.com/K3/k3_software.htm

73,
Wayne
N6KR

* * *

MCU 3.57 / DSP 2.45, 11-7-2009

Misc. Improvements:

* TUNE SWITCH:  “Double beep” with NR on eliminated.

* DATA A: Loss of power when using TUNE corrected.

New Feature: Synchronous AM Receive

* SYNCHRONOUS AM: Outperforms regular AM during selective fading.
Provides optional automatic VFO tracking of AM signals up to +/- 2.5  
kHz.

Select AM mode, then hold ALT to select AM-S. The -S icon flashes
slowly if the signal is noisy. Select AM-S LSB or USB using SHIFT;
one of the two sidebands may reduce QRM. Sync AM also works with
diversity receive. (Note: Some AM broadcast stations encode their
carrier, resulting in a low-pitched noise when Sync AM is turned on.)

With Sync AM you can tune manually, or use automatic VFO tracking:

-- If tuning manually, you need to tune to within +/- 10 Hz of the  
actual 
    carrier frequency, at which point the K3 will phase-lock to the  
carrier.

-- To enable VFO tracking, tap CWT, which turns on the T icon. Or, 
    tap SPOT to engage VFO tracking just long enough to lock. When
    tracking is on, the VFO may “hunt” slowly across a span of several  
Hz.

IMPORTANT:  For AM QSOs, use SPLIT mode when VFO tracking is
turned on. VFO B (TX) will remain fixed while VFO A tracks RX signals.

Limitations: At present, VFO B cannot auto-tune in AM-S. Also, both
VFOs will always be in the same mode (AM-S LSB or USB).

Remote Control Command Changes:

* UP0/DN0/UP$0/DN$0 moves VFOs 1 Hz. Similarly, UP8 and UP9
move the VFOs by 100 and 200 Hz, respectively.