QSK

I have heard that the new rigs are not the best for sending high speed CW with full QSK. What rigs are best for sending high speed CW with full QSK? I understand the older TenTec rigs are better in this regard than the newer rigs with microprocessors. What makes the older rigs better? Were any of the older vacuum tube rigs capable of full QSK at high speeds? What kind of circuitry is needed for full QSK with solid state and vacuum tube technology. I was thinking of raiding my junkbox to see if I could put together a better rig for QRQ CW with full QSK than those currently on the market.

Joe KH6/W3GW

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Permalink Reply by Steve N4LQ on February 9, 2009 at 7:50pm

Joe:
You have a lot of questions here and they are hard to answer.
There are 2 factors to consider with QSK.
1. Turn around time. (After key-down, how fast can the receiver recover?)
2. QSK side effects. (Annoying and distracting noises between sent characters such as clicks, pops etc.)
Here's how I test a rig for QSK; Tune in a constant carrier signal or generate your own with another rig. Turn off your sidetone. Key your transmitter using dits from your keyer and listen. Do you hear the carrier between dits? Increase speed gradually until you totally loose the carrier. Usually about 30-35 wpm is the limit with most rigs. You will probably just hear a clicking sound. The fastes rig I've ever tested for QSK was the original version of the little IC-706. With an external keyer, I could key it at 100 WPM and still hear the carrier. However the 706 had one glaring side effect, it would truncate or chop the dits and at 100 WPM, not much was actually being transmitted! This calls for some weight compensation which lowers your breakin speed. Also, the 706 has a very loud relay. I hate loud relays!

I became a ham in 1964 and started handling traffic for the NTS a year later. When handling traffic, QSK is mandatory. We seldom passed messages at over 25 WPM so turnaround time wasn't too critical back in those days. Back then, transcievers were designed mostly for SSB and did not have QSK. In fact, they were plain horrible for CW. I'm talking about the Drake TR3, Collins KWM2 etc. CW operators who passed traffic always used separate RX and TX units. There were several schemes to achieve QSK. One was to use your good antenna for transmitting and a hank of wire for receiving. Another was to use a "TR Switch". Both ways worked but these had side effects such as receiver blocking (overload from the tx's strong signal), TVI from TR switches, "suck out" (with a TR switch, the tank circuit of the transmitter would weaken the receiver's signal and of course all kinds of clicks, pops and thumps in the speaker. We would usually turn off the receiver's AGC to improve receiver recovery and put up with all the other side effects. I had a Drake 2B receiver that handled overload quiet well.

I guess the QRQ craze started in the early 70s when cw keyboards were "invented". QSK at 50+ WPM is very difficult. Usually the conversations are vox style...that is, talk, pause, receive, talk etc. Trying to actually break someone with one dit at 60 WPM is asking a lot. Think about it. What's the odds that the breaker is going to hit his dit key at the exact time you are listening between dits? ususally it takes a string of dits or dahs to actually be heard. You don't hear much of this. After all, if you were trying to break someone who is going 60 wpm you will miss a lot of text! Most of us are happy with QSK that works well at 30 - 35 WPM and has no artifacts like clicks and pops. Some of the best QSK rigs aren't necessarily the best of receivers. The old TenTec Triton IV had great QSK but it's selectivity came from the audio filtering, not narrow crystal filters. AGC was derived from the audio circuit and strong signals would cause a loud POP and about split your eardrums! Same goes for the Omni and Corsair series. Horrible AGC but fairly fast QSK. The Corsair had lots of IF hiss (white noise). The Omni VI has a microprocessor and QSK was not impressive although fairly smooth.

So in designing this ultra fast QSK rig....Think about what has to be done and what the effects will be.
When you hit the key, you want RF to be transmitted immediately.
But you don't want that RF to hit your receiver and blast the front end to kingdom come.
So first you need to disconnect the receiver's front end and mute the audio.
Oops....now you're introduced a delay.

I've rambled enough. Maybe something here to ponder?

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Permalink Reply by Joe on March 3, 2009 at 2:48pm

Thanks Steve. I guess I was naive to think that real QSK would be possible at QRQ speeds. I enjoyed your response so much that I translated it into CW using the program ebook2cw! I use the translation during my daily practice sessions.

I enjoyed your recollections of traffic handling years ago. I used to check into SCN ( Southern California Net) with my DX-35 and SX-101 back in the 60's before I left for the service. I do recall using separate transmitting and receiving antennas while riding the RF gain control to keep from blasting my eardrums! Traffic handling is not as popular nowadays. Out here in the lslands, none of the old section nets have survived.

Joe KH6/W3GW

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Permalink Reply by Chuck aa0hw on March 9, 2009 at 5:49am

HI Joe
Great topic and one of the favorites us QRQ guys love to discuss. Steve brings up some excellent points to consider.
I agree with his top "2 factors" and especially the "NOISE" part ! wow....if you have a noisy audio mute that pops and clicks every time it is activated....your ears are in for a world of hurt ! I have not had a rig that could do the mute right without popping or clicking when it activates and the faster you go with it ...the higher the noise level etc..

Tom w4bqf has some excellent experience in pursuing the best rigs for QRQ cw. If my memory serves me right...he mentions the icom 781 and the corsair II ...as the only two rigs(in the past) that can QRQ above 100wpm flawlessly...
In a recent email, he told me that he is now very happy with the icom 7700. He tested it around 150wpm and according to his results he says that the icom is perfect in QSK at that speed and might be good up to 200wpm. What excellent news from ICOM ... I think the 7700 is a clone of the 7800 without the extra receiver ?

In the past, I have used 2 rigs and a PIN DIODE switch with an audio mute customized for speed and low noise. You have to have a rig on the reception side that has the ability to turn off the AGC since that will interfere with how fast the QRQ QSK can go. Then you key a voltage sequencer to activate everything in the right order....AUDIO MUTE first of course...
I was able to go above 100 wpm with this system and still be able to hear receiver background audio between words.

my limiting factor was the speed of the rig i was using to receive with, the k2 from elecraft. There was a recovery delay even with the agc off, could not find the right combo in the rigs circuits to keep some op amp from going mahooolah on me ...but i think that could have been solved by someone more familiar with RF design...just never consulted anyone about it...was good enough the way I had it set up...

Tom, w4bgf has some stuff on the web about QSK QRQ cw rigs you might find by searching google with the terms
CW QRQ QSK etc...

also i think i have read on some comments on the net that some qrq guys were happy with the cw qsk of KENWOODS ts 930...

Chuck/aa0hw

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Permalink Reply by Chuck aa0hw on March 22, 2009 at 7:11am

b>There is an excellent discussion on Eham about QSK:
http://www.eham.net/articles/21156

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Permalink Reply by Chuck aa0hw on March 28, 2009 at 10:30am

Here is a nice article about constructing your own QSK BOX from a fellow ham k9ew: http://www.k9ew.us/boat_anchor_qsk.htm

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Permalink Reply by Tom Alderman on August 24, 2009 at 6:45pm

I think I made that comment at one time. I had been using a lot of Ten Tec radios and as the newer ones came out with microprocessors, they just could not perform full QSK very quickly. The radios I've tested in my past 59 years, have mostly been all solid state, with the exception of my old Heath SB-303 rx and Viking II and Thunderbolt amp. Of the radios I had previously tested, the Icom IC-781 and Ten Tec's Corsair II were the fastest with full QSK that I had ever seen on my scope. I recently purchased an Icom IC-7700 and at 120 wpm, I could hear KB9XE's second dit when he was testing my QSK for me, so I'm very impressed with this radio.

I don't like to put a defination on QSK. To me, QSK it just what ever it takes to get the transmitting station to hear you between words. I say 'words' because it's pretty silly to try to be able to hear between dots/dashes when your running much over 60 or 70 wpm. Even in person-to-person conversation, if you want to inject a comment, it sometimes takes you several tries before the other person will pause for you.

Building your own QSK circuit is not a simple task, especially if your running an amp. First you have to find PIN diodes that have a huge reverse voltage breakdown, and they just do not exist. Alpha used HF PIN diodes in their 87A amplifiers, but you will notice that Alpha has reverted to vacuum relays, just like everyone else.

My good friend Lyle/W9FCX does have a really good QSK circuit that he uses with each of his four home-brew amps, so you might QRZ him and see if he would share his schematic with you. For switchig diodes, he uses 1N4007 rectifier diodes.

73,

Tom - W4BQF

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Permalink Reply by Chuck aa0hw on August 25, 2009 at 6:39am

I agree with TOM...

high power HF PIN DIODES are very expensive...especially if they get fried !
Here is one I wish I could get samples of though...

see attached PDF file of the datasheet on this HF KILOwatt PIN DIODE...

Attachments:

kilowatPINdiode.pdf, 275 KB

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Permalink Reply by Chuck aa0hw on August 25, 2009 at 7:00am

I built my QSK BOX using these kiloWATT pin diodes from MICROsemi....(see pic below and PDF for full details in the attachment below)
However, they were samples and would have cost me a few hundred dollars otherwise.
I have had them for over 10 years, but only in a 100 watt transmitting HF setup.
They have worked extremely well over the years, but you have to have a good T/R switch circuit to get the best performance out of them AND an extremely good NO NOISE audio mute..so much switching noise will get through otherwise and destroy the main purpose and goal of using a QRQ QSK setup. The weakest link in my setup was the recovery of the receiver after getting SLAMMED with my own XMIT signal. Even with the AGC OFF, it took a while for the receiver to gain full RCVR audio...but I was using a two rig system, one rig to xmit only, the other to receive only...

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