Thursday, January 21, 2016

CW Switching with PTT

One of the features of the K1EL WinKeyer that I recently purchased is PTT transceiver keying. I enabled this feature for the first time in the NAQP contest two weekends ago. I did this via the N1MM Logger+ contest software, which only enabled the feature during contest operation. It all worked very well indeed, and enhanced my effectiveness in the contest. This feature is a keeper in my station.

If you are unfamiliar with the use of PTT for CW operation, and you like the advantages discussed below, read on. I'll begin with a review of what PTT (push-to-talk) means in the context of CW -- until fairly recently PTT has primarily been used for phone modes -- and how it compares to other transceiver switching techniques.

As a former boss of mine, a very successful entrepreneur, was often heard to say: "timing is everything." This is very true, whether we are talking of business, personal life or...CW. The advantage of PTT is all about timing, as we'll see.

Receive to transmit, and back again

There are several techniques for switching a transceiver between receive and transmit when using CW. These are:
  • Break-in (QSK)
  • Semi-break in (VOX equivalent)
  • PTT
If you use full QSK you can probably skip the rest of the article since you already use the superior method! This assumes that your rig is capable of QSK and, if you use higher power, that the amplifier can tolerate rapid switching. QSK is a delight to use in DX pile-ups and contest exchanges since you always know what's going on and can instantly react. I love this feature of my Elecraft KX3 since it works so well. But that's QRP, for which solid state QSK is cheap and effective.

It is more typical that transmitters, especially where an amplifier is involved, are incapable of QSK, or it involves the annoying clacking of relays. For long years the switching method of choice has been semi-break in (VOX in older rigs), in which the transmitter turns on when the key is closed and returns to receive following a hang time after code transmission has ended. The hang time is set with a pot in older rigs and a menu item in newer ones.

Although semi-break in works well in typical daily operation there are disadvantages:
  • You cannot hear what is going on while your are transmitting. During the excitement of DX chasing and contest you will often double with other station (both transmitting at the same time).
  • On some rigs, and especially where an outboard amplifier is in use, the first code element may be truncated or missed entirely due to slow turnover between receive and transmit.
  • Hang time may be tied to SSB VOX timing or must be set to a fixed duration, and is not scaled to code speed or responsive to operating conditions.
Setting up

I use a Y adapter on the PTT jack of my FT-950 so that both the WinKeyer and a foot switch can control PTT for CW and SSB, respectively. Until I put in the Y adapter I temporarily used VOX on SSB, which though not my preferred choice on phone the inconvenience was minor since I operate SSB less than CW. The RCA connector and a bit of software configuration is all that is needed to enable PTT. Well, that and disabling break-in with the push of a button on the rig's front panel. The rig's internal keyer must also be disabled when using an external keyer such as the WinKeyer.

Wired back panel of my WinKeyer; for SO2R the second rig has its own set of connectors
When properly configured key closure is detected by the keyer rather than the rig. The keyer closes the PTT line to the rig when the first code element is sent.

Alternatively, some operators use the PTT line for the amplifier and use semi-break in on the rig since the cascade of relays from time of key closure can truncate the first code element. I've heard it happen numerous times during CW contests where high speed is the norm. I don't need to deal with this problem right now since I do not have an amplifier.

You can set a parameter to delay the start of sending by a few milliseconds to ensure proper transmission of the first code element. This isn't necessary on my rig, and should not be on any rig. It is in any case an imperfect solution since the timing offset is unnatural at more than a small number of milliseconds. Set this delay to zero unless you suffer from a sequencing problem with a external amplifier, as described above, yet you still want the full benefit of PTT.

My current WinKeyer settings in N1MM Logger+

Take care that you do not inadvertently use PTT mode when break-in or semi-break in is enabled on the rig. It can result in some puzzling results. My FT-950 has a front panel control for break-in (QSK or semi, depending on menu setting), by which I can easily switch to PTT at the start of a contest.

Paddle operation and setup is a little more complicated with PTT. With memories and software-generated message the keyer knows precisely when the message starts and ends, but not so with a human operator. There are settings to get the timing of PTT switching to suit your needs.

Most important is the hang time. This is the delay from completion of a code element, with neither paddle closed, before switching the PTT back to receive. It is similar to the hang time (or VOX delay) for semi-break in. The WinKeyer uses a variable timer based on keying speed, which is better than a fixed hang time.

Advantages of PTT

I quickly appreciated PTT as I began operating in NAQP.  Good results are most evident when playing memories and software-generated messages. In contests, where everyone is quick on the trigger, you are almost assured of never missing a single dit of the other operator's message due to the hang time delay of semi-break in.

Of course it doesn't help if the other guy starts sending before you've finished, which does happen! Other than that situation you never again have to ask for repeats or wonder if he copied the first letter of your call as A or V: you'll hear those first dits even at 40 wpm.

When you do need to reach for the paddles to send a custom message, or simply to say hello to a friend during the contest, you'll appreciate the speed-responsive hang time discussed above. I recommend using this feature rather than alternatives since it works so well, no matter the speed at which you're sending.

Beyond contests

Several days after NAQP I decided to enable PTT full time. The advantages of PTT also apply to DXpedition pile-ups. Since I've been mixing it up with the horde calling K5P, VP8STI and others this past week it was a sensible step to take.

Now I miss very little of what the DX station is sending. By hearing more of what he's transmitting I more often copy the call sign (or fragment) of the station he's calling. I can therefore better identify the frequency of that station and adjust my transmit frequency accordingly.

I have also reduced the times that I have fruitlessly called when the DX has already responding to another station. This is often done by the sending of a call sign fragment at 35 wpm, which you can easily miss with semi-break in. PTT gets you in and out of the pile-up faster and more successfully. Although I cannot claim that PTT helped put K5P and VP8STI in my log this week I am certainly more effective in the pile-ups.

So even if you're not a contester there are reasons to make the switch to PTT. If your keyer doesn't have this feature this should prod you into upgrading. You may be surprised by how big a difference ~100 milliseconds can make to your operating. Of course you can go full QSK and do even better. But buying a new keyer is more economical than buying a new rig.

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