ELECRAFT K3 HIGH-PERFORMANCE 160 – 6 METER TRANSCEIVER KRX3 HIGH-PERFORMANCE SUBRECEIVER INSTALLATION AND OPERATION Rev. F1, March 14, 2014 Copyright © 2014, Elecraft, Inc.
Contents See Appendix A to install or change crystal filters in a previously assembled KRX3 Introduction............................................................................................................................................... 3 Customer Service and Support ............................................................................................................................ 4 Technical Assistance .....................................................................................
Introduction If your KRX3 is already installed in your K3, turn to Using the Sub Receiver on page 46 for operating instructions. The KRX3 subreceiver features specifications identical to the main K3 receiver including up to five roofing filters and an independent, dedicated DSP system. The subreceiver can tune the same range of frequencies as the main receiver, including frequencies outside of the Amateur bands when it is equipped with the optional KBPF3 general coverage filter board.
Customer Service and Support Technical Assistance You can send e-mail to k3support@elecraft.com and we will respond quickly - typically the same day Monday through Friday. Telephone assistance is available from 9 A.M. to 5 P.M. Pacific time (weekdays only) at 831-763-4211. Please use e-mail rather than calling when possible since this gives us a written record of the details of your problem and allows us to handle a larger number of requests each day.
Preventing Electrostatic Discharge Damage There is no climate or work location where the components of your K3 are safe from Electrostatic Discharge (ESD) unless you take specific steps to prevent such damage. Many of the components in your K3 can be damaged by static discharges of only a few volts: far too little for you to notice. Those low-voltage but destructive discharges easily happen anywhere and in almost any environment. ESD damage may not be apparent at first.
We strongly recommend you take the following anti-static precautions (listed in order of importance) to avoid trouble: Leave ESD-sensitive parts in their anti-static packaging until you install them. The packaging may be a special plastic bag or the component’s leads may be inserted in conductive foam. Parts which are especially ESD-sensitive are identified in the parts list and in the assembly procedures. Wear a conductive wrist strap with a series 1-megohm resistor.
Parts Included The following parts should be included in your kit. Check to ensure you have them all. If any parts are damaged or missing, contact Elecraft for replacements (see page 4). Circuit Boards and Enclosure Note: Some pins on the male connectors may have been removed and some holes in the female connectors may have been plugged. This is intentional to help you align the connectors properly during assembly. ILLUSTRATION DESCRIPTION Auxiliary DSP Printed Circuit Board Assembly QTY.
QTY. ELECRAFT PART NO. 1 E850331 KNB3 SUBOUT Board 1 E850332 KRX3 Enclosure, Top (with tall standoffs) 1 E100334 KRX3 Enclosure, Bottom (with short standoffs) 1 E100334 QTY. ELECRAFT PART NO.
QTY. ELECRAFT PART NO. Standoff, Hex Male/Female, 7/16” (11mm) 3 E700017 Unthreaded Sleeve Spacer, 7/8” (22 mm) 2 E700161 Screw, Zinc, Pan Head 4-40 1/4” (6.8mm) 8 E700005 Screw, Zinc, Pan Head 4-40 1/2” (13 mm) 2 E700196 Screw, Black, Pan Head, 4-40, 1/2” (13 mm) 2 E700030 Screw, Black, Pan Head, 4-40, 3/16” (4.8 mm) 4 E700015 Screw, Zinc, Pan Head, 4-40, 1-1/2” (38 mm) 4 E700157 Note: 1/2” (13mm) long screws (E700022) may be supplied instead.
E850249 I.F. Crystal Filter Bag (or Box) NOTE: If the optional 8-pole 2.8K filter is purchased instead (see next item) this filter is not supplied. ILLUSTRATION DESCRIPTION QTY ELECRAFT PART NO. 1 E850249 KFL3A-2.7K Filter Note: This filter is not supplied if you purchased the optional 8-pole 2.8 kHz filter with your K3 kit. or or Screw, 4-40, either 1/4” (6.4 mm) Zinc, Pan Head or 3/16” (4.8 mm) Black Pan Head screw.
Installation Procedure K3 KIT BUILDERS: If you were directed here to install the KRX3 Subreceiver as part of the initial K3 assembly, remove the top cover as shown below, and then go directly to Checking and Modifying Resistor R91 on page 21 since you have already installed the Auxiliary DSP board. Disconnect power and all cables from your K3. Remove the nine screws to free the top cover as shown in Figure 2. After the cover is open, lift it gently to reach the speaker wire connector.
If your K3 has the K144XV 2-meter option installed, remove the three 6-32 black flat head screws holding it to the left side panel (see Figure 4). Unplug the cables going to the K144XV module. The red power wire plugs into the K3’s main RF board. Unplug it and set it aside with the module. Figure 4. Removing the K144XV Module.
Remove the screw shown in Figure 6. It is located directly behind the front panel microphone connector. There may be a lock washer under the screw. If so, save it with the screw. Removing the screw ensures the pc boards on the front panel assembly will have adequate clearance when the front panel assembly is removed in a later step. Remove only the screw shown. Leave the other screw in place as shown in the figure. Figure 6. Removing the 2D Screw.
CAUTION Before continuing on with the next step, be sure you have removed the three top Front Panel Assembly screws shown in Figure 7. You may bend and damage the front panel or shield assemblies if the screws are not removed! Use a screwdriver in the pry tool openings to press back against the circuit board while pushing the lip on the front panel assembly toward the front as shown in Figure 9.
With the three screws removed, the main DSP board is held on to the front panel board by two multi-pin connectors. Slip your finger tips between the boards and pull the main DSP board away from the front panel board to unplug it. A large, thick spacer washer should be lying on the front panel near the hole for the phones jack (see Figure 12). This spacer fits between the phones jack and the back of the front panel board to provide a solid mechanical ground connection when the boards are in place.
Mount the three standoffs on the component side of the main DSP board as shown in Figure 14. Be sure that: The standoffs are on the component side of the board as shown. No lock washer is used between the standoff and the board. One lock washer is used between the nut and the board. Figure 14. Installing Standoffs on the main DSP Board. Check to see if the nylon standoff shown below near J51 is mounted on the main DSP board.
Locate resistor R3 on the front panel board (the board still mounted on the front panel assembly). If R3 is positioned above the board on its leads as shown in Figure 16, push it over to one side of the outline as shown. Be sure you don’t push it so far its leads might touch the solder pads for other components on the board. Figure 16. Positioning R3 on the Front Panel Board.
Plug the aux DSP board into the main DSP board by mating P52 and P53 on the aux DSP board (at the narrow end) with J52 and J53 on the main DSP board. When seated, the connectors should be fully engaged with the aux DSP board resting against the standoffs with the holes in the board aligned for the screws (See Figure 18). Note that a two-row 10-pin connector at the top of the aux DSP board does not mate with anything on the main DSP board. That is normal. Attach the boards with three 4-40 1/4” (6.
If R3 was positioned above the board on its leads, look between the DSP boards and the front panel board to verify that the leads are not touching any terminals on either the aux DSP or front panel boards (see Figure 19). If necessary, unplug the DSP board assembly and adjust the position of R3 to ensure the leads are clear of other solder pads before proceeding. Figure 19. Checking Position of R3. Replace the three 4-40 1/4” (6.
Hold the front panel in place against the chassis assembly and turn the unit over to look at the two multipin connectors on the top of the RF board. See if they are engaging the corresponding connectors on the front panel assembly (see Figure 21). Adjust the position of the RF board or the front panel assembly to ensure they are mating properly. Figure 21. Mounting Front Panel Assembly - Mating P50 and P51. With the pins of all four connectors started, press the front panel onto the RF board connectors.
Checking and Modifying Resistor R91 and DAC Input Circuits The value of resistor R91 must be 22 ohms. Perform the following procedure to check the value of the resistor and, if needed, reduce its value by adding a 27 ohm resistor in parallel with it. Two traces must be cut to ensure the Digital to Analog Converters (DACs) receive the proper signal levels. Turn the K3 upside down. Place it on a clean, soft surface to avoid scratching the case.
Installing the KRX3 Module Supports Install two standoffs on the K3 RF board (the large board filling the bottom of the K3) as shown in Figure 24. One standoff is mounted next to battery BT1 and the other is mounted next to FL1. Be sure to use two lock washers between the standoffs and the board as shown. They are required to obtain the proper height. Figure 24. Mounting Standoffs on the K3 RF Board. Replace the forward bottom cover using seven 3/16” (4.
Installing the Auxiliary KSYN3 Synthesizer The KSYN3 is supplied with a stiff metal plate covering the front of the pc board. This plate keeps the board from vibrating, especially if the K3 is operated with its internal speaker at high volumes. Do not attempt to remove the plate. It is attached to the board with adhesive. Remove the KSYN3 board from its ESD protective packaging and confirm that the screw, washer and nut are mounted on the bottom corner of the KSYN3 board as shown in Figure 25.
Locate the four coaxial TMP cables supplied and sort them by length. There are two 5” (13 cm) one 10” (25 cm) and one 12” (30 cm) cables. These are approximate measurements measured from the tip of one connector to the other. Check the cables as shown in Figure 27 to ensure there are no excess strands of the center conductor extending beyond the tip of the connector. . Figure 27. TMP Cable Connectors. CAUTION When inserting or removing the TMP connectors, always use the grip as shown in Figure 27.
Install the Auxiliary KSYN3 board on the back of the front panel shield between the KREF3 board and the side panel. Use the hardware exactly as shown in Figure 28. This is most easily done as follows: You may find that it helps to elevate the front of the K3 so that the lock washer on the screw (left side of Figure 28) tends to slide toward the Aux KSYN3 board. Place an inside tooth lock washer over each 1/2” (13 mm) pan head screw, then place the screw in the hole in the KSYN3 board.
Auxiliary KRX3 Antenna Input (Optional) Normally, the KRX3 subreceiver will share whatever antenna is in use by the K3 main receiver. If you plan to use the KRX3 subreceiver to listen on one band while the main K3 receiver is on another band sharing the same antenna, there are limitations on the combinations of bands you can choose because of the effect of the bandpass filters used by the main K3 receiver. See Sub Receiver Antenna Selection on page 46 for details.
Route the cable across the back of the K3. When the KRX3 module is installed, it will connect to the KRX3 at a point directly in front of the KIO3 board in the left rear side of the K3. If you have the KPA3 100 watt option installed, route the cable between the fans and heat shield and out through the hole in the KPA3 shield as shown in Figure 29. The loose end will be connected later. Figure 29. Optional KRX3 Antenna TMP Cable to KAT3.
Remove the screw holding the KANT3 (or, if installed, the optional KAT3) board to the standoff and the screw holding the 2D fastener to the rear panel near the SO239 antenna connector shown in Figure 31. Do not lose the lock washer inside the K3. It is easier to keep the hardware from falling inside if you set the K3 on its side feet and remove the screw and lock washer holding the KANT3 or KAT3 board first, then set it on its bottom feet and remove the flat head screw from the 2D fastener. Figure 31.
Check the BNC-TMP cable assembly to see if the nut and lock washer are already threaded onto the BNC connector. If so, remove them completely, working carefully to slide them over the ground braid and lug. (Lay the lug attached to the ground braid along the cable to slide the parts over it.) The dense, highly scratch-resistant powder coating on the rear panel may interfere with the fit of the BNC connector through the hole.
Mount the solder lug attached to the braid as shown in Figure 34, using a 4-40 3/8” (9.5 MM) black pan head screw, #4 inside tooth lock washer and 4-40 nut. If you do not have a KAT3 installed, there will be no connector in the ANT2 hole. In that case, the solder lug is directly against the unpainted inside surface of the rear panel. Figure 34. Installing AUX RF Connector, Part 2 Thread the coaxial cable between the edge of the KANT3 or KAT3 board and the rear panel as shown.
Replace the 4-40, 3/16” (4.8 mm) black flat head screw that secures the back panel to the 2D fastener as shown in Figure 31. Replace the two 4-40 3/8” (9.6 mm) black flat head screws, lock washers and nuts to secure the heat sinks of U13 and U12 to the side panel as shown in Figure 30. Assembling the KRX3 Subreceiver Module Install four standoffs on the bottom half of the KRX3 shield assembly as shown in Figure 36. The bottom of the shield has the shorter permanently mounted standoffs.
Install four standoffs on the KRX3 main circuit board as shown in Figure 37. Be careful to use the correct length standoff and the exact combination of washers shown in each location, and carefully follow the instructions for installing the standoff at E5 to avoid damaging the board. Figure 37. Installing Standoffs on the KRX3 Main PC Board. Check to ensure that you installed all four standoffs exactly as shown in Figure 37 above. Locate the crystal I.F. filters.
Enter the FREQ OFFSET shown on each filter. The optional 8-pole filters have no offset marked on them. Enter a zero in the FREQ OFFSET column for those filters. On the 5-pole filters the frequency offset may be negative, indicated by a minus sign (single dash) ahead of the number. Table 1. Installing Crystal Filters. FL1 is to the right and FL5 is to the left. In the next step you will install the filters rightto-left on the KRX3 RF board as well.
Mount the Mixer and KNB3 boards on the main KRX3 board as shown in Figure 39. Be certain the connector on each board is properly aligned and mated with the connector on the main KRX3 board. The boards should be parallel to the KRX3 board. If they are tilted, check to ensure the correct number of washers were installed under the standoffs and that you used the correct standoffs as shown in Figure 37. Figure 39, Main KRX3 Board Ready for Installation.
If you have the KPBF3 option, install the board now with 4-40 1/4” (6.4 mm) pan head screws and #4 split lock washers as shown in Figure 41. These screws and washers are supplied with your KBPF3 option. Be sure all three connectors on the KPBF3 are properly mated with their counterparts on the KRX3 board. Figure 41. Mounting the KPBF3 Board. Locate the subreceiver RF module top cover. It has a label with places to record the bandwidth (BW), and frequency offset (FRQ) of each filter.
Place a 7/8” (22 mm) unthreaded sleeve over each of the long screws so they rest against the top of the circuit board (see Figure 42), then place the top cover over the assembly and adjust its position so the edge of the top fits inside the bottom and rests against the KRX3 main board on all sides. The long screws will pass through holes in the top cover. Secure the top with knurled nuts tightened only enough to hold the cover in place so it isn’t loose. Figure 42. Installing the Shield Top.
Place the battery cover on BT1 on the K3 RF board as shown in Figure 44. Hint: gently squeeze the narrow ends of the cover to make the sides bow outward to fit over the battery clip more easily. The cover is held in place by friction against the battery holder and will be trapped under the KRX3 enclosure. Figure 44. Installing the Battery Cover Remove jumper W4 from connector J64A on the K3 RF board. J64A is near the KIO3 board as shown in Figure 45.
Plug the SUBIN interface board into J64A on the K3 RF board as shown in Figure 46. J64A is directly in front of the KIO3 board in the rear left corner of the K3. Be certain the connector on the SUBIN board is aligned with J64A so all pins are engaged. Figure 46. Mounting the SUBIN Interface Board. Locate J64B on the K3 RF board. It is between the crystal filters and the front panel shield that holds the KREF3 and KSYN3 boards.
Position the TMP cables so they will be out of the way when you install the KRX3 module. Figure 48 shows a suggested arrangement. The exact cable positions are not important as long as they are below the top of the SUBOUT board and so they will not interfere with installing the KRX3 module. Avoid kinking the cables. Arrange them with smooth bends. You may need to unplug one end of the cable and twist the coax slightly so it will lie in smooth curves where needed. Figure 48. Positioning the TMP Cables.
Hold the assembled KRX3 module directly over the K3 and attach the TMP cables to J82 and J85 on the module as shown in Figure 49. Figure 49. TMP Cable Connection Pictorial Diagram.
If installed, attach the antenna cable connected to either the KAT3 or to the AUX RF BNC jack on the rear panel to J92 at the end of the KRX3 as shown. This connector is angled upwards to provide clearance between the connector and the KIO3 board when the unit is installed. Be certain the TMP connector is fully inserted in J92. When the KRX3 module is installed the clearance between the connector and the nearby KIO3 board is very small.
Secure the KRX3 module to the two standoffs using 1-1/2” (38 mm) 4-40 pan head screws as shown in Figure 51. The screws will pass through the internal standoffs and circuit board inside the enclosure and screw into the standoffs you mounted on the K3 RF board earlier. Place an inside tooth lock washer under each screw head. Figure 51. Installing the KRX3 Enclosure. Position the cable between J84 on the Aux KSYN3 board and J85 on the KRX3 module as shown in Figure 52.
Final Assembly Remove the covering over the self-adhesive side of the foam pad and press the adhesive side against the speaker magnetic shield (see Figure 53). The pad will compress between the loudspeaker and the top of the KRX3enclosure when the cover is installed. Figure 53. Attaching the Speaker Pad. If your k3 is equipped with the K144XV 2-meter option, refer to the K144XV manual to reconnect the cables and remount the module on the left side panel.
Position the top cover on the K3. Note that the tab on the back center goes under the rear lip of the K3 rear panel. Secure the top cover with the nine 4-40 3/16” (4.8 mm) black flat head screws you removed earlier. REPLACE ALL THE SCREWS! The K3's chassis has excellent rigidity despite its light weight. The screws that hold the top cover in place are an important part of the structural design.
Operation Preparing for Operation If you installed the KRX3 subreceiver yourself, you must complete the following before you can operate the subreceiver: If you have external speakers connected to your K3, disconnect them and use the internal speaker for the following procedure. Enter the CONFIG menu and verify SPKRS is set to 1. (You will not hear any audio from the subreceiver if SPKRS is set to 2 as is frequently done when listening to the main receiver with stereo headphones.
Using the Sub Receiver The KRX3 option adds an independent, highperformance sub receiver to the K3. It allows you to monitor a second frequency, using different bandwidths or modes. Diversity receive is possible if the main and sub receivers use different antennas. The sub receiver’s band cannot be set independently unless CONFIG:VFO IND is set to YES. If it’s set to NO, you’ll see =MAIN when you tap BAND during BSET, and the sub receiver band will always be set the same as main.
You might use MAIN with diversity when comparing main/sub receiver gain, such as when adjusting crystal filter gain compensation (CONFIG:FLx GN). The built-in true-RMS voltmeter is ideal for this purpose. Entering diversity mode will allow you to tune both receivers with VFO A, while VFO B displays the voltage (see Owner’s Manual, VFO B Alternate Displays). receiver signal loss in this case, use the sub receiver’s AUX input.
Appendix A: Installing Crystal Filters in the KRX3 Subreceiver The crystal (roofing) filters in the KRX3 subreceiver are contained in the L-shaped RF module mounted above the main K3 RF board (see Figure A-4). Installing or changing the filters involves removing the RF module and the circuit board inside. The filters plug into the circuit board and are held in place by screws. No soldering is required.
Observe ESD precautions when working inside your K3. Wear an ESD wrist strap or frequently touch an unpainted metal ground while working. Remove the chassis stiffener bar that runs across the top of the K3 (see Figure A-2. Removing the Chassis Stiffener Bar.) . Figure A-2. Removing the Chassis Stiffener Bar. If your K3 has the K144XV 2-meter option installed, remove the three 6-32 black flat head screws holding it to the left side panel (see Figure A-3). Unplug the cables going to the K144XV module.
Remove the KRX3 RF module as follows. The circled numbers refer to Figure A-4 below. Remove the two long screws that attach the KRX3 enclosure to the K3 main board. Grip the knurled nuts and lift the KRX3 enclosure up and out of the K3. The enclosure will unplug , one near the front and the other at the back. Also there will be two coaxial from two interface boards cables attached to the forward edge and usually one cable attached at the back of the enclosure.
Remove the RF board from the lower half of the enclosure as follows (see Figure A-5): Remove the two sleeves from the long screws. If the KBPF3 option is installed, remove the two screws and unplug it from the RF board underneath. Remove the two screws securing the KRX3 RF board to the bottom half of the enclosure. These screws thread into bushings attached to the enclosure with screws.
Important: The information recorded in the next step is required to enable your filters after reassembling your K3. Record the data in the table clearly and completely. If the information is incomplete or incorrect, you will have to disassemble your KRX3 again to retrieve it before you can use your subreceiver. Recommend using a pencil so you can change the data later should you decide to install additional filters. Enter the following data on Table A-1.
CAUTION 1) Do not use screws longer than 1/4” (6.4 mm) to mount the filters. Longer screws may extend into the optional 8-pole filter and destroy it. We strongly recommend you use a 1/4” screw even when installing the 5-pole filters to reduce the possibility of damaging an 8-pole filter should you change them later. 2) Do not over-tighten the screws. Too much torque may pull the threaded bushing out of the bottom of the filter module. Figure A-6. Installing the Crystal Filters.
If you removed the KBPF3 board, replace it. Be sure the three connectors are aligned so all the pins in Figure A-5. Use the engage. The connectors are visible from the sides. Secure the board at locations 4-40, 1/4” (6.4 mm) pan head screws and split lock washers you removed earlier. Do not use inside tooth lock washers.
