Illustrated Example
USE IT AT YOUR OWN RISK!
IF YOU DAMAGE YOUR K2, IT IS NOT MY FAULT!
Please carefully note that in this project I am simply splitting the K2/100 radio in half and the KPA100 section is incapable of working without the K2. It will not work with other radios due to its need for real time communication with the K2's main microcontroller.
The 270-ohm resistor mod from the 2002 June 12 update is not required if you have the Elecraft KPA100MODKT installed. If your KPA100 was purchased after 2004 April 02, or contains firmware version 1.09 or later, it probably includes this mod.
There was a question on the Elecraft reflector about hooking up a KAT100-1 to a K2 which has no KIO2 or KPA100. The plan is to eventually add an internal KPA100, and the individual wanted to avoid spending $89 for a KIO2 which will become redundant once his KPA100 is purchased. A design is presented here which, while untested, ought to work.
If you build this and it works, please let me know!
My KAT100-2 wasn't acting like everyone else's in the Field Test, so some investigation was in order. I had used an ELPAC desktop switching supply for my K2 for nearly two years and didn't suspect it might be the culprit. But it was!
The KAT100-2 150 watt Antenna Tuner easily integrates with the KPA100 to provide an even better K-Twins station. You have the advantage of a fully-featured K2 that is completely removable from your home station. And the home station includes a 100 watt output capability and a very flexible Antenna Tuner!
Field tests indicate a 270-ohm 2- or 3-watt resistor should be installed on the KPA100 RF input to ensure stability if the KPA100 is not installed in the K2's enclosure. I performed this mod and added it to the step-by-step instructions below.
Please also see KI6WX's website for details on this as well as an alternative approach to remoting the KPA100 in the EC2.
The KPA100, at a minimum, requires RF input, DC power and control information.
In its normal configuration, the KPA100 receives +13.8 VDC from an Anderson PowerPole connector on the rear panel. It provides +13.8VDC to the host K2 via a 2-pin, 0.156" spacing, polarized connector, J4. This connector normally plugs into the K2 RF board at P3, labeled AUX 12V on the K2 RF board.
The KPA100 need not provide power to the K2, but the K2 will need power from either another power source via the K2 12VDC rear panel connector or from its internal battery if the KBT2 option is installed.
The KPA100 RF connection is by another 0.156" spacing polarized 2-pin connector, J1, which mates with P6 AUX RF on the K2 RF Board.
The KPA100 speaker normally gets its audio from the K2 RF board at P5, a 0.1" spacing 2-pin polarized connector on the K2 RF board, labeled SPKR. The lead from the KPA100 is called J5.
Finally, and perhaps most importantly, the KPA100 receives power for its microcontroller, as well as all control information, via a 10-pin dual row header, P1. This is normally mated to a short 10-pin ribbon cable which then mates to P4 on the K2 Controller Board.
The first example will show how to wire things up assuming that your K2 includes the KIO2 Remote Control Option. It may or may not include the KAT2 Antenna Tuner or KBT2 internal battery.
Note: These are the same connections shown in the KAT100 Manual, Figure 17, page 25.
I planned to someday make a printed circuit board with all the interfaces as well as additional accessories for my K-Twin station. In the meantime, I decided to pass all the cables through one small hole in the rear panel of my EC2 Enclosure. I centered the hole on the location where a DE-9 PC mounted connector might eventually go. In my case, the hole is 0.25" (6.3mm) in diameter, and is located 0.75" (19 mm) from the edge of the bottom plate and 0.66" (17 mm) from the underside of the bottom plate as measured from the outside (or 0.6"/15 mm from the inside surface of the bottom plate). All the wiring except the control cable passes through this hole.
Remember, you must pass the cables through the hole before you terminate both ends! In my case, I terminated the K2 end of the cables first. That's probably backwards...
The top cable in Figure 1 is the RF cable. It is essential! In my installation, I used a 15" (38 cm) length of Teflon-insulated coax, Harbour Industries 2747B. I chose it, not only because I happened to have some laying around, but for its small diameter of 0.1" (2.5 mm) and the fact that it already had a BNC connector on one end! RG-174/U would be another good choice. The keys are that the cable has a small diameter, is flexible and you have or can easily get a BNC connector for that diameter of cable.
I ran the cable inside the case for a distance of 1.5" (40 mm) after the connector was attached. It should be at least 12" (30 cm) long outside the case, and 16" (40 cm) is better. My cable is 12" (30 cm) and just barely reaches the ANT1 connector on my K2, but still allows me to place the K2 on either side of the KPA100/EC2.
I used one of the 2-pin male polarized plugs from the KPA100 kit to mate with the RF cable coming from the KPA100 inside the EC2 enclosure. If you don't have a spare, you can use a Molex 26-60-4020 (Tin plated, DigiKey part number WM4620-ND) or Molex 26-61-4020 (Gold plated, DigiKey part number WM5224-ND). The Elecraft-supplied part is gold plated.
Remember, these are polarized connectors. Refer to your K2 and KPA100 kit documents for details, and be sure you get it right! You can download a copy of the current manuals here.
The second cable is the power cable. This cable is optional. If you don't make it, be sure the cable with J4 at one end coming from you KPA100 is protected against accidental shorts inside your EC2 enclosure! It uses the same connector type as the RF cable, a 2-pin polarized male. Note that the ground pin is opposite to the ground pin on the RF cable!
I ran this cable 4" (10 cm) into the case. This provides natural separation from the RF cable and makes it less likely that I will accidentally swap the RF and power cables... It should be about 10" (25 cm) to 16" (40 cm) long outside the enclosure. With the hole located as shown, 10" (25 cm) is just long enough to allow you to place the KPA100 on either side of the K2.
The third cable shown is the audio cable. This is used to pass speaker audio from the K2 to the KPA100's internal, top-firing speaker. As with the power cable, this one is optional. In fact, it may be more optional than the power cable, since the speakers are exactly the same and this cable adds resistance to a low impedance circuit. But, if you decide to stack your KPA100 on top of your K2, you might want to use this!
This cable uses a different 2-pin connector, Molex 22-23-2021 (Tin plated, DigiKey part number WM4200-ND) or 22-11-2022 (Gold plated, DigiKey part number WM2700-ND). The Elecraft-supplied part is tin plated.
I made this cable project 3" (8 cm) into the EC2 case. Externally, this cable should be 16" (40 cm) to 18" (45 cm) in length. This will allow you to place the K2 on either side of the KPA100/EC2.
Be sure to properly insulate the connections to all of the connectors you have installed after you have soldered them. I used a short length of heat-shrink tubing on each connector as shown in the photograph below.
Note that the 10-conductor ribbon cable has been removed from P1 on the KPA100. I have operated my K-Twins with and without this cable dangling inside the case. I experienced no problems leaving the cable attached, but I decided it was better to not have an unterminated cable hanging next to a 100-watt output RF power amplifier.
If you may have considerable separation between your K2 and the KPA100/EC2 - in the trunk of your car for the KPA100/EC2 with the K2 near the driver's seat, for example - then you should perform this step. If you are sure you or the next person that owns your K2 will never do this, you may consider skipping this step. If your KPA100 includes the KPA100MODKT, or was manufactured after 2004 April 02, you don't need to perform this step.
Obtain a 270-ohm 2- or 3-watt metal oxide resistor. I used a DigiKey part number P270W-3BK-ND. Carefully solder this resistor slightly above R21 on the KPA PC board. One end goes to the junction of R21/R22/R23. The other end goes to ground, conveniently at the shield of the cable labeled "RF IN" on the KPA100. Note that if you can't easily locate such a resistor, you can parallel some 1 watt resistors. A pair of 470-ohm 1W, or three 680-ohm to 1K-ohm 1W, should work fine.
This resistor will help stabilize the amplifier section of the KPA100 in the event a long cable is used between it and the K2 driving it. I measured no difference in output levels or spurs on my spectrum analyzer after I did this mod, and I know I'll never use a long cable to feed it, but I have no idea what a future owner may do...
Now we are ready to assemble the KPA100 into the EC2 enclosure.
The last cable is the DE-9 control cable. I used a spare length of the Elecraft-supplied shielded cable for use with the I/O port option for this short jumper cable. I made mine with a 12" (30 cm) length of cable - you may want to make it 16" (40 cm) to allow more slack or for later re-work.
If you want to be consistent with the color-coding used by Elecraft for these signals within the K2 (for the KAT2 and KIO2 options), wire it as follows:
If you want to use an external device, like a PC running a logging program, you must add the DE-9S connector as shown in the schematic and it must be at the K2 end! This is because the RS232 control information is only present at the K2 end of the cable when you use this method of communicating between the K2 and the KPA100.
And you probably thought you only had to make the cables and you'd be home free!
Unfortunately, you're not. If your K2 incorporates a KIO2, you need to do a modification inside your K2. But, hey! You're an Elecraft owner, so you are up to the task!
KIO2
If you have the KIO2 installed in your K2, the operating current for it comes from a little PCB you built and installed with the KIO2. This is the AUX2 board. It has a very small, 15-mH inductor, L1.
L1 is rated to power the KIO2 and perhaps an external load of 10 or 15 mA, but not the KIO2 and the control section of the KPA100, which draws about 65 mA in my unit when idling. It could become considerably more, so replace this choke!
Note that, even if you are using the KAT100 in the EC2 case along with the KPA100, you still need to change this choke.
DigiKey carries a possible choke (I have not tried it!):
Or in true Elecraft fashion, you can wind your own on a small toroid! 8 or 9 turns on an FT23-43 core ought to do it. You may use some of the #26 or #28 enameled wire left over from winding toroids for your K2 or its accessories. The wire gauge is not important, as it only has to carry 250 mA and its length is very short.
In my case, I didn't have an FT23-43 core lying around, but I did have an FT37-43. The core mix, 43, is what's important. This defines the permeability of the material as well as its effective frequency range. This stuff has a m of 850, making a few turns go a long way. In the case of the FT37-43, only 4 or 5 turns are required.
So, open your K2, carefully remove the AUX2 PCB, remove L1 and replace it with the new choke. Yes, you will destroy the original L1 in the process. R.I.P.
I purchased my toroid coils as a pre-wound set for my KPA100 to save time. I had proven my mettle in Toroid-Winding 101 by building two K2 transceivers with all the options. But I wasn't going to get away with it. I had to wind one more...
...waiting for the crazy photographer to put the camera down and re-install the lid assembly before something conductive falls into the K2 from the crowded workbench.
Back to the top of the page.
There are a few issues to consider when separating the KPA100 from the K2. Some are technical, some are operational.
KAT2
The KAT2 is placed (and locked!) in CALP mode with ANT1 selected by the main processor in the K2 if the KPA100 is also present. This is because the EL5146 on the KPA100 board overrides the SWR bridge output from the KAT2. Thus, if you want to use an alternate antenna output (for a transverter, say), you must remove power, disconnect the control cable between the K2 and the KPA100, then re-apply power. Turning off the PA in the menu is not enough.
If you disconnect the control cable between the units, be aware that the KPA100 does not provide an RF path from its RF input to the SO239 antenna connector! You must use the ANT2 connector, or disconnect the RF cable to the KPA100 from the K2. If you have the 160m option in your K2, you may also use the RCV ANT connector for reception - its operation is not affected by the KPA100.
If you attempt to operate the KAT2 while the KPA100 control cable is attached, you will see a PA ANT1 message on the K2 display and the KAT2 will be locked into CALP mode.
If you have the KBT2 internal battery option installed in your K2, you must be sure that the voltage applied to the K2 is sufficient to keep the gel-cell battery fully charged. This requires about 14 VDC at the K2. And the internal diode on the KPA100 drops about 0.3V under heavy load, like a K2 transmitting to drive the KPA100.
If your high-current supply isn't able to supply 14.2 VDC - or you feel nervous putting this much voltage on the amplifier - then you should power the K2 with its own low-current (3A) supply. You can easily shorten the lifespan of a gel-cell if you don't use a high-enough trickle-charge maintenance voltage.
Back to the top of the page.
Integrating the KPA100 and KAT100 into the EC2 Case
The Elecraft KAT100-2 makes it very simple to place the KPA100 Amplifier and the KAT100 Tuner in a single case.
You still need to provide the DE-9 interface cable between the K2 and the KPA100/KAT100. You may plug the cable into either DE9.
The RF cable coming from KPA100 J1 (AUX RF) simply plugs into the AUX RF plug on the KAT100 (P6).
The KPA100 supplies power to the KAT100 via KPA100 J4 (AUX 12V) which plugs into the KAT100 AUX 12V (P3).
The 10-pin ribbon cable made as part of the KPA100 assembly goes from KPA100 P1 to KAT100 Aux Control, P4. Be sure to clip or remove pin 4 from KAT100 P4!
I removed the speaker cable from the KPA100 so it wouldn't have an opportunity to dangle and get into any high-potential RF near the KAT100 RF board.
Interconnect is just as easy as the internal wiring. You connect the DE9 control cable, from the K2 to the EC2. You can use either the AUX I/O connector on the KPA100 or the CONTROL connector on the KAT100. If you want computer remote capability, be sure the RS232 part of the cable branches off from the K2, and not from the EC2!
RF comes from the K2 ANT1 connector (if you have a KAT2) or the ANTENNA connector (if you don't have a KAT2) to the AUX RF connector on the KAT100. This is a simple 50-ohm BNC-to-BNC cable. I used a cable of about 24" length because I had one lying around. Really long cables may induce instability in the KPA100, so use one in the 12" (30 cm) to 40" (1 m) range.
You'll need a source of DC for the K2; the KPA can't supply it without some hacks on the KAT100 board or the EC2 case.
You need a 50-ohm coaxial cable from the ANT connector of the KPA100 to the RF IN connector of the KAT100.
Then, connect up your station antenna to ANT1 of the KAT100, attach your station ground to both the K2 and the EC2 (at either GND jack, the KPA100 or the KAT100) and you're ready to operate!
If you have a second antenna or a dummy load, you can attach it to ANT2 on the KAT100. Using ANT1 keeps a relay de-energized; using ANT2 energizes the relay. The KAT100 relays are heavy duty, but they are not latching, so they draw power whenever they are energized.
Here are a couple of photographs showing the rear wiring of the units.
Back to the top of the page.
Beware the ELPAC Switcher (and others of its ilk)!
On the Elecraft reflector about two years ago a lot of folks pointed out the availability of a surplus, desktop switching supply for under $20 that handled the K2 quite well. I bought one and was happy with it - until today :-(
The ELPAC WRI4212 is rated for 100 - 240 VAC input, 12V @ 3.5A output. It is adjustable to a suitable voltage to maintain the charge on the K2 internal battery (KBT2 option). Many people bought these, and you may own one or be thinking about buying one.
The KAT100 is an external accessory for the K2 system. As such, it isn't powered by the same supply as the K2, at least not by an internal connection. I use my KAT100 with a KPA100, as described above, so I had no issues with the ELPAC supply.
But, as a Field Tester for the new product, I needed to run the KAT100 without the KPA100 for alignment and testing purposes. I just couldn't get it to work unless the KPA100 was connected at the same time.
Following some suggestions, I looked into the problem. Here is what I found...
1) With a different power supply, the KAT100 worked just fine with the K2 and no KPA100.
2) With the ELPAC supply, the K2 never determined the KAT100 was connected, so it didn't use it.
Here is a photo of the power supply at the 12V pin of the internal regulator in the KAT100. My bench power supply, with current limiting set to less than 3 amps, is running it. The top trace shows the power (5V/division), the bottom trace (2V/division) is activity on the Elecraft "AuxBus" which the K2 CPU uses to handshake with all attached accessories sometime after powerup. In fact, it occurs about 260 mSec after powerup (100 mSec division).
Here is a photo of the same setup, but with the ELPAC powering the KAT100. Note that the KAT100 draws less than 100 mA and the supply is rated at 3.5A.
Note the terrible power droop for about 450 mSec after initial turn on of the KAT100. The ELPAC supply is powered up and running continuously. All settings on the oscilloscope are identical to the photo above.
Caveat emptor!
Back to the top of the page.
If you want to temporarily remote a KAT100 for eventual use with a KPA100, and have no KIO2, this information may be of help.
Note that it is untested. The risk is entirely yours.
Use the 4-conductor shielded cable that comes with the KAT100. A suitable substitute may be DigiKey W404.
The 10-pin connector which will mate with P4 (Aux I/O Connector on the K2 Control Board) is DigiKey WM2522-ND (shell) and DigiKey WM2556-ND (you'll need 5, and I suggest you use 10, even though 5 will not be connected, for mechanical reasons).
The resistor is standard 1/4 watt 5% carbon film; the capacitors are small ceramic monolithic or disc.
The inductors can be any small 15 uH nominal part, such as DigiKey M7827. These are rated at 150 mA. The KAT100 only uses this for a very low current, so it should be suitable for all three inductors. The KPA100 may draw more current than this, so if you plan on using this cable for anything other than a KAT100, you may want to consider a higher current rating on inductor L1. I suggest at least 250 mA. You may wind such an inductor using the directions given above.
Back to the top of the page.
Some readers of this page have asked about the signals used in the interface between the K2 and the KPA100. Here is the info, based on the K2, KIO2 and KPA100 documentation.
The KIO2 provides buffering of an asynchronous serial port with the microcontroller on the K2 Control Board. It converts the voltages to RS-232 signaling levels and polarities so you can attach an external PC. This is often used by logging programs to either control a radio, or get information (band, frequency, signal strength, etc.).
The pins used by the KIO2 (or by the KPA100) AUX I/O connector for serial communications are:
However, there are several additional signals present on the KIO2 DE-9 connector that are not related to serial communications. These signals are related to possible future accessories for the K2, and happily they are also the signals we need to split our K2/100 into two boxes as described on this web page.
These expansion signals are:
The cable is wired with Frame Ground (pin 1) at the K2 end going to the shield. The other end of the cable, at the PC, has no connection to the shield.
Transmit Data (pin 2) is wired to pin 2 at the PC end, using the red wire in the shielded cable.
Receive Data (pin 3) is wired to pin 3 at the PC end, using the green wire in the shielded cable.
Signal Ground (pin 5) is wired to pin 5 at the PC end, using the black wire in the shielded cable. At the K2 end, pin 5 goes to ground through an RF decoupling network to help keep RF noise from the PC from being conducted into the radio.
At the PC end, a jumper may be installed between pins 7 and 8 for RTS/CTS loopback. See the KIO2 or KPA100 module documentation for further details.
The serial interface is currently set for 4800 bit/sec, 8 data bits, no parity, 1 or 2 stop bits. The interface command set is based on the Kenwood command set. See the Elecraft website for more details.
Frame Ground (pin 1) is used as the common reference for both power and signals. It is not expected that a cable of any significant length will be attached to these pins.
AuxBus (pin 6) is a logic-level, bi-directional signaling system that is unique to Elecraft. The signaling protocol is proprietary and, at this time, unpublished. It is used to communicate commands from the K2 Control Board microcontroller to auxiliary processors within the K2 radio, and to receive status from them.
Just as almost every Elecraft product seems to include a toroid coil to wind, so most products seem to include a PIC microcontroller. In the basic K2, there is a PIC on the Control Board and RF board. The KSB2, KNB2, KAF2 and KAT2 also have microcontrollers, as does the KPA100.
All of these devices need to be managed, and this is done via the AuxBus. When you change bands from the front panel, for example, the Control Board CPU detects this and sends the appropriate command to the IO CPU on the RF board to select the correct relays, and to the KPA100 for the same purpose. Activating the Noise Blanker means an AuxBus transaction with the KNB2 controller. Setting the clock or reading the time from the KAF2 uses the AuxBus.
It is the AuxBus and its protocols which render the KPA100 useless as a general purpose amplifier for other radios. It is truly an integrated part of the K2, as much as the front panel or RF board.
RF Level (pin 7) is a positive-going voltage which is routed to an A/D input on the Control Board microcontroller. This signal is used in the algorithm to control the output level of the power amplifier, whether it is the QRP 15-watt amplifier on K2 RF board or the QRO 100-watt amplifier in the KPA100 module.
+12V Control (pin 8) is a filtered, low-current source of 12 VDC for powering the control logic of an expansion device. This might include an external antenna tuner, or some other as-yet-unannounced accessory. The KIO2 module is designed to only provide a few mA of current from this pin. See the modification elsewhere on this page to allow greater current to be drawn from this pin for the KPA100.
+8V Receive (pin 9) is a low-current signal used to provide transmit/receive status to an external device. This is one of the signals used by the KPA100 to determine if it should be amplifying (transmit) or bypassed via the PIN diode switch for receive. Note that it is a status signal, not a power source for a receive-only accessory.
Back to the top of the page.
You probably notice that Elecraft and many other companies refer to DB9F and DB9M connectors. But my drawings and text refer to DE-9S and DE-9P connectors. Why?
The original D-subminiature connectors were designed many decades ago. At that time, they were considered almost tiny! The manufacturer created five basic shell sizes: A, B, C, D and (you guessed it!) E.
The A size normally carried 15 pins, the B 25, the C 37 and the D 50. The later E shell carried only 9.
So, the original nomenclature (why does it take a four syllable word to mean "name" which is only four letters?) for a D-sub, shell size B, with 25 male pins, was DB-25P.
While these were the common configurations, numerous variants were developed with coax-connector inserts, larger and smaller pins, etc.
Today, common high-density versions place 15 pins in the E shell, 44 in the B and so forth.
Thus, the common "VGA connector" on the cable from a typical monitor to a PC is a high-density 15 pin connector in an E shell, and may be referred to as a DE-15P. This is quite different than the DA-15P which is often used in game paddles and joysticks for the same PC.
My background in aviation electronics compels me to use this convention in describing these connectors.
Only an engineer would care...
Back to the top of the page.
Back to my home page.
Last updated: 2006 January 09