K9ZTV's MODIFICATION OF THE YAESU CT-58 TRANSCEIVER/AMPLIFIER CABLE FOR THE QSK-2500
After purchasing a new FT-991, I set about interfacing it with a Yaesu VL-1000 Quadra amplifier. To do so requires Yaesu cable package number CT-58. This cable-set is not included with the FT-991 but is available from any Yaesu dealer as a $37.95 accessory for several of Yaesu's HF transceivers including the FT-897D, FT-857D, FT-991, and FT-991/A.
Interfacing the QSK-2500 between the Yaesu FT-991 transceiver and the Yaesu VL-1000 Quadra amplifier is almost plug-and-play, but not quite. A change is needed to just one wire in one of the two cables that comprise the Yaesu CT-58 cable-set.
One of those two cables provides ALC information for transceiver power control and plays no role with the QSK-2500. You can connect it as instructed on page 16 of the FT-991 owner's manual and forget about it.
The second cable in the CT-58 set is the one needing surgery. It conveys band-data, keying, and other information between the FT-991 and the Quadra amplifier. Inside that cable are eight wires. One of those wires is red (in my cable, but verify on yours) and connects the TX GND (pin 2) at the transceiver's TUN/LIN jack to the TX GND (pin 2) in the amplifier's BAND-DATA 1 jack. That red wire needs to be interrupted and routed to the QSK-2500 before it is routed to the amplifier. The following is an overview of the modification:
The red wire inside the bundle of eight wires is snipped at both ends near the connectors. Two new separate wires (I used RG-174) are soldered to the red wire-stubs that go to pin 2 on the multi-pin connectors at each end of the cable. RCA phono plugs are attached at the other ends of the RG-174 runs. Thus, when completed, pin 2 (TX GND) on the transceiver's TUN/LIN jack will be connected via RG-174 to the AMP-IN jack of the QSK-2500, and pin 2 (TX GND) on the amplifier's BAND DATA 1 jack will be connected via RG-174 to the AMP-OUT jack of the QSK-2500.
CAUTION #1: A proper understanding of what pins mate with what receptacles is crucial. Be sure you understand the location of pin 2 in the TUN/LIN jack as pictured on page 16 of the FT-991 manual. Be sure you understand the location of pin 2 in the BAND DATA 1 jack as pictured on page 5 of the Quadra manual. Pin 2 will be labelled "TX GND." Pay particular attention to the note below both diagrams that reads, "as viewed from rear panel." Thus, when you look at the plugs, the pins are reversed from what they are when you look at the jacks. Hold the plugs as though you are about to push them into their respective jacks and note which male pin mates with which female pin. Again, you are looking for pin 2 on both diagrams labeled "TX GND."
CAUTION #2: Forgive the obvious, but you are only interested in the BAND-DATA 1 jack of the Quadra. Don't mistakenly look at the BAND-DATA 2 jack for pin-outs.
The following is the step-by-step surgical procedure on the cable (sterile gloves and antiseptic soaps not required):
1) Pop open the BAND-DATA connector on the CT-58 cable, gently expose the pins, and pry back the black insulation covering the red wire going to pin 2.
2) Snip the red wire at pin 2 (the wire, not the pin!).
3) Expose one inch of the center conductor of a length of RG-174 (or whatever wire you wish) and slide it under the strain-relief boot of the BAND-DATA connector.
4) Solder the center conductor to pin 2 (see picture 1). Be sure the RG-174 shield is not shorting anything.
5) Tuck the red wire down into the bundle and close up the connector.
6) Accessing the red wire on pin 2 of the TUN/LIN connector is not so easy. The connector is molded with no way to open it. Moreover, the metal shroud surrounding the connector is a solid cylinder (not split halves) and is soldered shut at the shroud's bottom (see picture 2).
7) The next best thing is to open the cable about an inch back from the connector, carefully open the braid lengthwise without damaging it, and raise the red wire (see picture 2).
8) Leaving enough red wire coming from pin 2 for soldering, snip the red wire and tuck it back down into the bundle.
9) The conductor inside that red wire is tiny, tiny, tiny. Very carefully scrape the insulation off the red stub still connected to pin 2 until bright shiny copper is revealed. I used an X-acto knife applying a very light and deft touch. Try not to nick the wire.
10) Expose one inch of the center conductor of another separate length of RG-174 (or whatever wire you wish) and solder it to the red wire still connected to pin 2. Apply a small piece of heat-shrink or electrical tape to assure isolation from the RG-174 shield.
11) With an ohm-meter, check for continuity between pin 2 of the TUN/LIN plug and the center conductor of the RG-174 run connected to it.
12) With an ohm-meter, check for continuity between pin 2 of the BAND-DATA plug and the center conductor of the RG-174 run connected to it.
13) With an ohm-meter, check all the other pins of both connectors to make sure there is NO continuity between them and the two RG-174 runs.
14) Repair the "autopsied" cable with heat-shrink tubing, electrical tape, self-sealing silicon tape, or whatever material you normally use.
15) Repeat steps 11-13 above to make sure nothing has changed during taping.
16) Install an RCA phono plug on the end of one of the RG-174 runs.
17) Install an RCA phono plug on the end of the other RG-174 run.
18) Set menu 143 in the FT-991 to LAMP (linear amplifier)
19) Set menu 057 in the FT-991 to FULL
FINAL THOUGHTS . . .
A) RG-174 was chosen because it is small enough to slide under the BAND-DATA connector's strain-relief boot, and because I had lots of it.
B) Be sure you solder each RG-174 run to the red wire still connected to pin 2 of the respective connectors and not to the red wire you buried in the cable!
C) I arbitrarily made the two RG-174 runs the same length as the CT-58 cable, but you may prefer to make them shorter.
D) Put labels on all connectors, and be sure you do so correctly. The RCA phono plug you label "AMP KEY IN" must be the run coming from the TUN/LIN connector. The RCA phono plug you label "AMP KEY OUT" must be the run coming from the BAND-DATA connector. See picture 3.
E) Standard bonehead caution: drop the unscrewed barrels of the RCA phono plugs onto the RG-174 first (with the threads facing the connector) before soldering the center conductor.
F) As stated above, verify for yourself that the pin 2 wire (TX GND) in CT-58 is actually RED. It might be a different color in your cable.
G) By the way, the two RCA phono plugs came with my FT-101E back in 1972. After nearly half a century I was dumbfounded to find them.
H) Total construction time around one hour.
Kent Trimble, K9ZTV
Jefferson City, Missouri