K3 Enhancements and Application Notes
Updated July 14, 2008
The following performance enhancements have been incorporated into new production K3s in response to customer requests or as part of ongoing engineering improvements. Any change that was made after a particular K3 was shipped can be added later, if desired. All changes are optional, and some apply only to specific operating conditions or configurations.
To determine which changes are applicable to your K3, check the Production phase-in date in the table below. If you were close to the cutoff, refer to How do I determine if I already have this?
The reason for each change is provided in the description column. Additional details can be obtained by clicking the document name under Enhancement / Modification.
These enhancement parts kits are available for no charge. (Customer pays shipping.) To order, see our parts order page.
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Enhancement / Modification Click for Document |
Description | Production phase-in shipping date |
How do I determine if I already have this ? |
| K3 Negative ALC Mod | This customer mod adds the capability for
negative ALC amplifier feedback to the K3.
Note: Most rig / external amplifier combinations do not benefit from hooking up ALC and in fact generate more distortion than without it, due to overshoot from the widely differing ALC voltage, loop gain and ALC reaction times generated by different amplifiers. Many amplifier manufacturers (Alpha, Acom etc.) recommend not using ALC. If you do decide to use ALC, set the K3's power on each band to the level just below where it activates amplifier ALC. (The K3 has a menu option to the remember power level on each band, or globally.) Running the rig at a power much higher than this and relying on ALC from the amplifier to control amplifier drive is a formula for severe distortion and splatter/key clicks. In general ALC should only be used as a fail safe mechanism for those amplifiers that can not tolerate being over driven, need SWR shutdown of the driver etc. |
Customer Mod |
See doc for mod details |
K3
Front Panel (Rev B) Modification (pdf) 
(Important Change.) (If you are unable to make this modification, Elecraft will perform it at no charge.) |
Incorrect VOX operation (VOX 'hangs') and/or low or corrupted TX audio, when using a front panel mic which requires BIAS to be supplied to the mic through the audio pin. (Elecraft MH2, MD2, Proset-K2 with electret elements etc.)
Modification involves addition of 1 wire to the rear of the K3 Front Panel board. Rear panel mic connections do not exhibit this problem. Dynamic microphones do not exhibit this problem. |
Approximately April 23-24, 2008 Serial numbers 660 through 782. (As early as S/N 654 may demonstrate this problem, but we think the problem starts with S/N 660.) |
See phase in date and s/n range. Also check for the symptoms described under the Description section. |
| Receive Antenna TX Isolation Improvement (RXA Mod Kit for the KXV3) | Some operators have very strong pickup of their transmit antenna signal on their dedicated receive antennas. (Beverages, loops etc.) If the the receive antenna is not externally isolated during transmit, this energy could feed back into the K3 via the KXV3 RX antenna in port. Existing transmit isolation in the KXV3 is sufficient for most installations, but in some cases additional isolation is needed. The RXA Mod Kit for the KXV3 significantly improves isolation. (This change has been made to revision B KXV3 main boards.) |
RXA Boards added: Approximately Feb 20, 2008 Rev B KXV3 Main Bd: March 14, 2008
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If the RXA board is already installed, or if the KXV3 Main board is Rev. B, you already have this change. See details in the installation instructions. |
| K3 CW Keying Rise Time Reduction | Some owners prefer a faster CW keying waveform rise time. The rise time can be reduced from about 8 milliseconds to 5 milliseconds without affecting the fall time by replacing capacitor C222 on the K3 main RF board with a 0.1 uF capacitor. This change will also allow a future firmware revision to further reduce rise time via a menu entry. |
Approximately Jan 20, 2008 Approx. s/n 211 |
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| Hardware AGC threshold change (HAGC Mod Kit)
Through hole HAGCMDKT instructions Both through hole and SMD parts are included. Users can install either set of parts. |
Some users prefer tuning the band with a wide filter bandwidth selected (for example, using a 2.7 or 2.8 kHz SSB filter in CW mode rather than a 500 Hz or narrower filter). Strong off-frequency signals (above about S9+5) that are inside the crystal filter passband can then activate the hardware AGC circuit, reducing the level of desired signals.
This modification raises the hardware AGC threshold from about S9+5 to about S9+25 to +30. The new threshold still protects the DSP's analog-to-digital converter, while providing better receive performance when wider crystal filters are used. This is not as significant an issue when using narrow CW filters (500 Hz and below). |
Approximately Jan 20, 2008 Approximately s/n 211 |
K3 RF Rev A boards with a leaded resistor
added between C196 and C197 have this change.
All Rev B RF boards have this change. See through hole instructions and SMD instructions for details. |
| Tuning the K3's 60M bandpass filters for some Eu 60M bands |
The K3 is supplied with its 60-meter band pass filter adjusted for the USA frequencies. This filter can be readjusted for optimum performance on the 60 meter channels for use in some European countries. |
n/a |
n/a |