K3 Stereo Diversity Reception and SO2V Contesting
From Zerobeat
Contents |
Stereo Diversity Reception
For purposes of this topical discussion, stereo diversity reception will be defined as two receivers tuned to the same frequency, operating in the same mode of reception, connected to separate antennas, with their audio routed to separate speakers/earphones. Antennas are normally chosen with either differing azimuthal and/or altitudinal gain patterns, separated by several wavelengths, or with different polarization. The signals from the two antennas are not externally combined - all processing/combining is done by the brain fed with two separate audio signals.
The K3 is an excellent platform for stereo diversity reception due to its two identical high performance receivers with appropriate routing of antennas, VFOs and stereo audio. A bonus for stereo diversity is the phase-locking of the two VFOs and ultimately of the K3 receivers' audio. The receiver control interface is not completely finalized yet, particularly for the subreceiver. However, the K3 is already proving to be a success both functionally and ergonomically for stereo diversity use.
Prior to the K3, the only commercial amateur transceivers capable of stereo diversity reception as delivered were the Ten-Tec Orion and Orion II. However, the Orion subreceiver is vastly inferior in performance to the main receiver and the two receivers are not phase-locked. Even with these limitations, the Orion has certainly proven the concept and advantages of stereo diversity reception for amateur use in not only improving signal readability in the presence of noise (QRN), interference (QRM), or fading (QSB), but also in creating a sense of stereo depth to received signals and pileups in routine use. When using directional antennas, stereo diversity can be of great benefit when trying to pick out callers from a desired direction in a pileup. As far as other commercial dual-receive amateur transceivers that come close to meeting the requirements of a stereo diversity platform, the Yaesu FT-1000D can be modified to add stereo diversity capability and the Icom IC-7800 lacks the capability to slave the two VFOs together to tune the two receivers in tandem.
KRX3 Subreceiver Availability
The KRX3 subreceiver began shipping in small quantities in May '08 and in production quantities in July '08.
Antenna Selection
The K3 Owner's Manual includes a section titled Main and Sub Receiver Antenna Routing and the information is also available in a separate Antenna Routing description. The main receiver can be routed to the transmit antenna (ANT1 or ANT2 if KAT3 is installed) or RX ANT (KXV3 is installed). The subreceiver can always be connected to the same antenna used by the main receiver when diversity reception isn't being used. For diversity reception without the KAT3 option, the subreceiver is connected to the aux RF Jack. With the KAT3 option, the user must choose to wire the subreceiver's independent antenna selection to either the aux RF Jack or the non-transmit ANT1/ANT2.
Although the K3 can be connected to two receive antennas (KXV3 and aux), it lacks flexibility in assigning either receive antenna to either receiver. If a user has more than one receive antenna, an external switchbox must be used to provide antenna-to-receiver routing.
VFO Selection
The K3 VFO assignment scheme is as follows: VFO A controls the main receiver and transmitter (normal mode) and VFO B controls the subreceiver and transmitter (split mode). The two VFOs may easily be "linked" to the same frequency and tuning encoder to facilitate diversity reception tuning. A future firmware upgrade should provide for diversity reception in split mode.
Receiver Audio Routing
With the subreceiver off, the main receiver audio is routed to both channels. With the subreceiver on, the main receiver audio is routed to the Left channel and the subreceiver audio is routed to the Right channel. However, there's also a "headphones mono" switch in firmware. With headphones mono, both receivers' audio is routed to both channels and you can vary the weighting by using the AF Gain controls.
K3 Subreceiver Controls
The Subreceiver has a full complement of identical (and independent) controls to the main receiver. However, when operating in stereo diversity reception mode it can become very tiresome to have to constantly adjust two sets of controls on the two receivers you are listening to. Beginning in firmware release 2.31, Elecraft is providing improved ergonomics for stereo diversity operation.
A -> B tap twice to transfer all settings from mainrx/VFOa to subrx/VFOb SUB press to toggle subreceiver On/Off; hold to link VFOa/VFOb; hold 2 sec to set diversity mode BSET for front panel to control/display subrx instead of mainrx KRX3 (config menu) set to AUX RF or KAT3 for subrx antenna
Diversity the Khz decimal point of vfoA flashes to indicate diversity mode in effect
shift, width, freq, RIT, AGC settings of main rx are mirrored by sub rx
vfoB is locked while in diversity mode (diversity split not yet implemented)
At this time, the subreceiver uses the same settings as the main receiver for the following functions: PRE, ATTN, NB, NR
Roofing/DSP Filter Selection
For best phase coherence between main and subreceivers, be sure to have IIR filters OFF in order to use the FIR filters, which have constant delay. To switch between IIR and FIR, tap '7' on the keypad when you're in any filter setup menu entry (e.g., CONFIG:FLx BW). To use the FIR filters, tap '7' until you see"IIR OFF".
For diversity reception, matching roofing filters should be used in the main receiver and subreceiver. With 5-pole filters, the measured offset frequencies of the two filters should be fairly close in value so that the same offset frequency can be used in the config menu for both filters.
SO2V Operation
SO2V (single operator two VFO) is a method of contest operating that mimics some of the capabilities of SO2R (single operator two radio) on a single radio equipped with dual receivers and VFOs. In SO2V, the operator can tune on two different receiver/VFOs in search of the next QSO with contesting software that allows fast toggling between the two receiver/VFOs as well as fast assignment of the transmitter VFO to the desired frequency before transmission and optionally switching mono headphone audio to the focus receiver/VFO. When contesting with assistance, packet spots can be pulled at will from both VFOA and VFOB Bandmaps while monitoring the main and subreceiver audio in stereo headphones and targeting the next contact.
After a brief trial run with the K3 in SO2V under N1MM Logger, it seems that there is some SO2V functionality but no main/subrx audio switching capability from the keyboard that is provided for other SO2V rigs such as the Ten-Tec Orion. In addition, there is a specific warning in the N1MM Logger manual to avoid using SO2V mode with the Elecraft K3. So unfortunately, SO2V support for the K3 still suffers from uncertainty around the K3's CAT command implementation and unfamiliarity of the programmers with the dual receive K3 platform.
External Links
N1EU Web site (Diversity & SO2V Pages with sound clips)
Page Manager: Barry, N1EU
