User comments on the QSK 2500:

Hi Bill.   Just a note to let you know that I'm now using the unit with my K2/100 driving the SB-200 amp and it's working superbly. The QSK on the K2 is very smooth and the QSK 2500 works just great with pops or clicks. Great product, Bill and I wish you lots of luck with its promotion.
Paul, N2PD

I bought an ALS 1306 sold state amp and wanted to add QSK. I first tried an Ameritron QSK-5 and it did not work out well at all. It changed the SWR too much.

Then I saw a review of the DX Connection 2500. I called Bill on the phone and we talked about this unit. Bill is a very nice guy and is very helpful. It was immediately obvious that this was the device I needed. I received it and it now provides excellent, quiet, QSK, with my amp and Flex 6500. It even works well on 6 meters. It changes the SWR very little which is critical for using a solid state amp.
Carl, N4PY
Bill,  The new chip works great on cw and ssb.  Sure works better than the other QSK on the market, it’s very very quiet.   
Rodney , W3KRQ 

"After replacing my ancient Alpha 86 with the ALS-1306, I found I really missed the QSK ability of the Alpha. After reading N4PY's comments on using the DX Connection QSK 2500 with the 1306, I decided to give it a try. Turns out that it works perfectly. The QSK 2500 is about half the size of the Ameritron QSK5, but is a bit more cumbersome to install as cables attach to both the front and rear of the unit. "

73, Floyd - K8AC


Hi Bill,     It arrived today and I had it hooked up in 5-minutes.    Just finished a qso with it and it appears to be working perfectly.    Great product!

73, Ken - N4KS

Bill,    I do QSK now with my 751A.  I enjoy QSK when working NPOTA and DX.   This is an unofficial total, but being able to work CW puts my NPOTA total 40% ahead of the other chasers with the same time and equipment.  QSK gives me an edge over the operators that don’t regularly work CW, trying to get a  park in a pile-up.  Once I add the amplifier; I will have another tool in the arsenal.
    73,  Lou , NO2C

" Bill,  The unit works great.   I use 90 degree coax connectors which make the mechanical hook-up CLEAN.  The unit sits flat on the table since I have the connections "balanced".  The outside coaxes go down and the inside coaxes go up (90 degree connectors).  I saw where one person in their review mentioned that the unit did not want to "sit flat" on the table so that was easily solved... Gotta love those 90 degree connectors, they make everything so clean! 
 I tested the unit on ultra weak signals.  I would find the very weakest signal and then tune off his frequency to make the signal even weaker.  Then I would activate the unit so the amp was "keyed" in the delay mode, but of course I was still receiving.  I could see absolutely NO loss of weak signal reception, excellent design!
  Thanks and 73 - Don W7TNK  (previously WW7CW)"

From Ten Tec Eagle Users Group:                                                                                (Sun Oct 23, 2016 1:59 am (PDT))
…..Of course as Carl said, the QSK-2500 solves all problems and works with every radio/transceiver combination. It costs a lot but it does a lot and IMO is worth the price.
         73 - Rick, DJ0IP
      (Nr. Frankfurt, Germany)

Bill,     I  Just wanted to drop you a note; I've been using my QSK2500 for almost a month now; and I have to say it's great.  I use it nearly every day with my SB220; in the past, I'd rarely even bother turning the amp on; but now it's always on and ready to go. 
 Just wanted to let you know that I think you did a great job with it,  take care and have a pleasant holidays,  
      Joe  KC0VKN
eham reviews
Mike WB9DLC & Bill K3HZP with QSK 2500 at Ft Wayne Hamfest
"QSK 2500 FAQs"

1)  Can I use the QSK 2500 without using the Key/Paddle input?  I have adequate delay in my transceiver.
Reply:     If there is adequate delay in your transceiver for the Amp T/R relay, then it is not necessary to go through the 1/4” Key/Paddle IN jack.  The QSK 2500 and the amp will be keyed by the signal from the transceiver going into the Amp IN phono jack.   Assume that the Amp T/R relay requires 12ms delay and that the transceiver provides 15ms delay,   Then it is not necessary to use the 'Paddle/Key IN' jack.  Just plug the paddle or key into your transceiver and use it as you would normally.  Make sure that the amp key signal from the transceiver is connected to the Amp IN phono jack on the front of the QSK 2500.  The QSK 2500 requires 8ms or more delay in the transceiver when NOT using the 10ms delay channel.  Most amp T/R relays require much more than 8ms so this is normally not a concern.
2)  How do you estimate the ready time of the amplifier T/R relays from their specifications?
Reply:    Relays are generally specified by both operate time and bounce time.   The amp T/R relay is not ready for RF until the end of bounce time.  This time is estimated by adding operate and bounce times.  For example, 8ms operate time and 4ms bounce time means the relay is not ready for RF for 12ms.
3)  If I use the QSK 2500 delayed Key Out signal and have it set at the factory default value of 10ms delay, does it maintain the full length of each dit and dah?
Reply:     Yes.  Whatever goes into the Paddle/Key Input appears on the Paddle/Key Output 10ms later.  The amplifier & QSK 2500 stay keyed on as long as there is RF on the input connector of the amplifier.  No RF signal from the transceiver is lost.
4)  I just hooked up the QSK 2500 and it stays keyed on.  What is happening?
Reply:     The most likely cause of this condition is that the 1/4 in Paddle/Key input plug is a mono plug, not a stereo plug.   Since the QSK 2500 can accept either a paddle or key input, it always maintains 2 active channels for the paddle.   When using a key, computer, or keyer, a stereo plug is still required.   The sleeve connection must be open to avoid keying (i.e. shorting to ground) the unused channel.        
Update:   The current QSK 2500 accepts a mono plug.   The QSK unit checks for the ring being grounded at power on.   If the ring is grounded, the ring channel is disabled until power off.

5)  Why is my amplifier continually keyed while I am sending with QSK?

Reply:   The amplifier T/R relay is not fast or rugged enough to be closed and opened for each dit and dah of a transmission.  To overcome this shortcoming, the QSK 2500 keys the amplifier T/R relay at the beginning of each transmission and keeps it keyed for 3 seconds (adjustable from 2 to 10 sec) following the last dit or dah of the transmission.  Also, the continual keying eliminates the loud T/R relay hammering noise during the transmission.
5)  Why use the QSK 2500 for SSB VOX?

Reply:   SSB VOX operation is very similar to QSK operation.   Normally, VOX operation involves many short transmissions closely spaced in time.  VOX operation of an amplifier can cause annoying T/R relay noise and may reduce T/R relay life.  The QSK 2500 greatly reduces the number of amplifier T/R relay operations.  It holds the amplifier keyed until there is a 31 second or longer gap in transmissions.  SSB VOX receive operation is unaffected.  The internal QSK switching connects the receiver to the antenna during receive time independent of the amplifier's keyed or unkeyed state.

6)  Why does my K1EL WinKeyer not key the QSK 2500 ?

Reply:   The problem is that the keying chip in the WinKeyer does not key the output to ground.  This keying chip only reduces the voltage to about +1 volt above ground.  The voltage must be reduced below +0.6 volt to key the QSK 2500 (and several transceivers).   Replacing the socketed original Toshiba TLP627-2 chip with a Panasonic AQW210EH chip solves the problem.  (Thanks to Floyd K8AC for this information.) 
Update:  I have been told that the new WinKeyers have a keying IC that reduces the amp key voltage below +0.6 volt,  eliminating the problem.
K9ZTV's Modification of Yaesu CT-58 Transceiver/Amp interface cable for QSK 2500
 W. Rodgers K3HZP
 5727 Buckfield Court
 Fort Wayne, IN 46814
Telephone:   (260) 432-8223
YouTube video:   Adding QSK to unmodified HF Amplifier

Good references for QSK information:

(1)  Good technical discussion of amplifier QSK considerations at W8JI website.
(2)  Timing measurements performed on ICOM and Elecraft K2 radios at W0QE website.
(3)  Timing measurements performed on the Ten Tec OMNI VII at W7KF website.