KF-382 Coupler Controller

Interface the Harris RF-382 to your ham rig!

The Harris RF-382 (and it's slightly beefier cousin, the RF-351) are wonderful antenna couplers. They can handle 500 watts easily and will couple just about anything to a 50Ω feedline and do it under incredibly harsh conditions - continuously. Hey, they're designed and built for the US Military and they're in use right now in hot spots all around the world.

Including here at W7KF where I push them a bit harder - I routinely run 650 watts CW through these things. Of course, I don't run resonant antennas so the coupler is never subjected to the extremes encountered when end feeding say a half wavelength antenna. I give the coupler a break by always choosing antenna lengths that are not near resonance on any frequency I'm likely to use.

These couplers put typical ham radio remote antenna couplers to shame. Just take a look at the innards of one of these beauties!

RF-382 Innards

If I ran SSB I wouldn't hesitate to run a kilowatt PEP into these couplers. On CW, I hold it down to 650 watts and haven't yet heated one of them up. Truly great antenna couplers.

The problem has always been how to interface these things to a regular ham rig.

Well, it turns out that it's pretty easy. Here's a schematic of an interface that I designed to allow my various rigs (at the moment, a Drake 4-Line and a Ten Tec Omni-VII) to interface with the Harris Coupler. I call this device the KF-382 Coupler Controller.

KF-382 Schematic

KF-382 Schematic (click for full size view)

As you can see, there are no microprocessors! The active components are simple relays. What could be easier?

Here's how it works. You initiate a Tune Cycle (say you've switched from 40 to 20 meters) by pressing the momentary Tune Initiate switch.  This sends a Tune Pulse Request to the RF-382 coupler on Pin E of the 14 Pin connector. The coupler, in turn, sends a Tune Power Request back on Pin F. The Tune Power Request grounds the cathode of the 'Tuning' LED, lighting it up, and pulls in K1 the Pad Enable relay and K2 the Tune relay. K1 enables an external 6 DB RF pad to drop the RF output of the rig to 25 watts or so. K2 does two jobs. First, it opens the key line between the transceiver and the linear amplifier. Next, it keys the transceiver CW or Tune key line. All three of these actions take the amp off-line and key the transmitter and reduce the transmitter's power output so the coupler will have proper tune power to work with.

At this point, the coupler attempts to find a match. There are only two possible outcomes; either the coupler finds a match or it does not.

If the coupler finds a match, it toggles the Tune Power request off. This causes the 'Tuning' LED to extinguish and K1 and K2 to drop out. When K1 drops out it first unkeys the transceiver and then puts the amp back on-line. K2 disables the external 6-DB RF pad. You may now transmit into a glorious 1:1 SWR load with full power. Life is good!

If the coupler does not find a match it will toggle the Tune Power request off and will toggle the Match Fault line (Pin C) low. This causes the 'Match Fault' LED to light and pulls in K3, the Fault Relay. The fault relay opens the circuit for the Tune Relay preventing an endless series of tune cycles and opens the key line to the amp, taking it off-line.

Note that the key is still connected to the transceiver so you can still transmit into the poor load - you just can't apply full power.

Finally, note that there is another possible fault condition - a Thermal Fault (Pin N). A thermal fault will also take the amp off-line while allowing operation to continue.

And, that's about it! There is a switch that allows you to bypass the coupler entirely and another switch allowing you to select High Power or Low Power. This switch merely tells the coupler whether or not you are using an amp and, if so, the coupler will run it's internal fan to dissipate any heat generated internally.  (The older RF-351 coupler has this fan, I don't think the newer RF-382 does..)

The component values are obviously non-critical. The relays must be able to switch whatever voltage and current is on the key line between your transceiver and your amp as well as the transceiver CW key line. K1 is a Hamlin 721C12-10, K2 and K3 are Tyco-Axicom D3002 and K4 is a Zettler 820-2C-12DE. K4 is the only interesting relay in the circuit - it has a make time of 5 milliseconds and a break time of 2 milliseconds. The timing of K4 is altered by the addition of C1 (47 μF) to prevent hot switching the amp since RF from the exciter drops off relatively slowly. The associated 15 Ω resistor is to limit the current through K4's contacts while C1 charges in order to prevent damage to those contacts.

The LEDs need suitable current limiting resistors again, for whatever voltage you are using. Typically, a 1.2K Ω resistor will work for a 12 VDC supply. I found the LEDs to be too bright so I upped the current limiting resistors to 10K Ω. Except for the limiting resistor in the Low/High power indicator. I upped that value to a whopping 57K Ω. That indicator is the only one that is on all the time and it drove me crazy it was so bright. The other LEDs indicate the coupler is tuning or is in a fault or a bypass condition and are rarely lit - I want those indicators to be bright!

The connector on the coupler is an Amphenol MS3102E20-27P so the mating cable connector at the coupler is an Amphenol MS3106F20-27S. The connector on the back of the KF-382 coupler controller is an Amphenol MS3102E20-27S so the mating cable connector in the shack is an Amphenol MS3106F20-27P.

For the front panel toggle switches I used some nice rocker switches I use on lots of projects. The Tune Initiate switch is a momentary pushbutton switch with integral LED indicator.

The 12 VDC supply needs to be able supply up to 4 amps while tuning (3 amps is typical). I found a cheap outboard switcher at Marlin P. Jones and Associates. Their part number is 18599 PS. The matching power jack for the rear panel is from Mouser, part number 163-MJ22-EX a Kobiconn 2.5 mm DC Power Connector.

The case is also from Marlin P. Jones and Associates and is their Part Number 17806BX. The case is just barely large enough to be able to mount the big Amphenol coupler control connector. It comes with a perf board already installed. The case, as received, seemed about twice as deep as it needed to be so I chopped mine in half - but if you don't have a metal cutting bandsaw handy you could just use the case as is. I used an external power supply but if you use the full size case you could probably build a supply into the unit. The perf-board made for quick and easy construction.

The tri-color LED indicators are from Marlin P. Jones and Associates, part number 17137 and I used the same part for all three indicators even if I didn't use all three colors. It was just simpler that way..

Here's what the first one looks like:

KF-382 PerfBoard Circuit Board

I cut notches into the perf-board so the LED indicators could be recessed a little. That made for a nicer looking front panel. I have found that shiny aluminum boxes are difficult for me to photograph but here's what the final controller looks like:

KF-382, Finished

KF-382 Front Panel

Here is a pic of the rear panel. The big 14-pin coupler control cable connector dominates. The connectors for the station interconnect are all standard phono connectors. The On/Off switch is a mini-toggle switch out of the junk box and the DC connector came from Mouser.

KF-382 Rear Panel

So, there ya have it! The KF-382 Coupler Controller.

Caveats? Yeah, there are a few. This interface works best if your transceiver does NOT fold back power in the face of a poor match. The Ten Tec and Drake rigs in use here at W7KF work just fine. Some of the more modern rigs have an external input jack for Tune Power (for example, some ICOM rigs). This input is ideal because it typically provides about 20 watts of RF output and will work in modes other than CW. If your rig has such an input control line you're in luck! If not, you may have to switch to CW mode preferably at low power (20 to 40 watts or so is ideal) in order to complete a tune cycle.

Since I only run CW ife is easy. I can initiate a Tune Cycle without thinking about it - I'm already in CW mode and the controller kicks in a 6 DB pad between the rig and my amp. The pad drops the rig's output power level to the correct value for the coupler. The amp (if powered up) drops off-line, the coupler tunes in about 200 milliseconds, the amp comes back on-line, the 6-DB pad drops out and I'm good to go!

There's nothing quite like a perfect match! Just ask the XYL..