Bare Bones SO2R

Single-op two-radios (SO2R) must almost seem perverse to non-contesters. At least that's my experience when the subject comes up in conversation. For contesters with the ambition to compete at a high level it has become a necessity. It's a necessity because our competitors are doing SO2R and are significantly boosting their scores.

It isn't easy. Aside from the technical challenge it requires practice to become effective. It can be mentally gruelling. The truly talented are able to run on two bands simultaneously, and their results are impressive. Like any competitive event, be it sports or radio sports, winning is hard work. In other words, if you find contesting easy or comfortable you're leaving points on the table because you could be working harder. There's nothing wrong with taking it easy, provided you don't care about winning.

SO2R rookie

During this past weekend's NAQP CW contest I had my SO2R debut. In one important way it was the ideal contest to do this: all competitors are limited to 100 watts. Therefore I could measure myself against both my expectations and the results of better contesters, after accounting for station size and geographical advantage. I can definitely say that it helped, increasing my score at least 10% if not 20%. It is no surprise that contesters with well-honed SO2R skills ran circles around me.

Operating SO2R along with its advantages and disadvantages is a topic I must push off to the future. I am as yet unqualified to discuss it. In this article I will show how I added to and configured my station to be SO2R capable. This is about as simple an SO2R as you'll find anywhere. It is just enough to give it a try with minimal effort and expense. I'll go further when I'm ready to do so.

Operating position

The display is front and centre, right where I believe it ought to be. I remain entirely skeptical of contesters who put the rig in front and the display on top. As the station and operator improve the rate also improves, including near continuous running, requiring less attention to the rig. It's just type, type, and more typing.

You will fatigue far faster when you have to constantly lift your neck and eyes to that degree as your attention flits between display and keyboard. Most modern contest software enable keyboard control of common rig features. One of the most used is RIT as stations call off frequency and your filter is narrow to manage congested band conditions. Controlling that by keyboard is a tremendous stress reducer.

You will likely notice a few problems with placement of some items. Of this I am aware and they will be dealt with. Perfection is nice but not mandatory, so I went with what I had for this first outing. The FT950 is not a good contesting rig because the receiver performs poorly and the DSP filtering is several generation old. But it was there and just gathering dust as a backup rig. I'll get something better later.

Antenna switching

Station automation is lacking and remains on my lengthy task list. For the present a manual switch controls the remote 2 × 8 antenna switch. Left and right radios have their respective switches on the top row of the enclosure. Antenna positions are identical on both sides. Hardware interlock in the antenna switch prevents the disaster of one antenna being selected on both sides.

The rotary switch has 6 positions: 4 allocated to antennas and the extreme right and left positions select no antenna. Outside of contests the second radio is normally at the latter setting. The switch next to the knob selects between antennas 1-4 and 5-8. By careful placement of antenna ports a desired antenna for a given band is almost always one step or switch click away.

On the bottom row there are blanks. The rotary one on the left is reserved for selecting the direction of the 80 meter vertical yagi. The one on the right will eventually be used to select receive antenna direction. Both radios will share the receive antenna. That's okay since it will most often only be needed for 160 meters.

RF interactions and filters

Most of my antennas are not adjacent, and that helps manage fundamental and harmonic interference with the other radio's receiver. This is important since I do not use band pass filters. Many contesters will be shocked by this yet it was common many years ago. I fondly remember running two kilowatt stations side by side during multi-op contests and having to coordinate with the other operator to avoid having the lower band station's harmonic clobber the other operator.

Yes, sensitive receiver front ends can be damaged. Although it has happened to me the fix was to replace the small incandescent lamp used as a fuse in the antenna line when it took the brunt of the abuse. A spare transceiver was always on hand for swapping in when this happened, and so avoid more than a few minutes of down time.

With 100 watts the risk of receiver failure is quite low. The greatest risk is when yagis on the same mast are in use by each station. The fundamental and harmonics can be very strong. The higher end rigs used by contesters usually have low-Q front-end filters ahead of the pre-amp that apply enough attenuation of the fundamental signal from a transmitter on another band to avoid a catastrophe or fundamental overload. The FT950 on the right is more susceptible than I like.

Band pass filters help in two ways: attenuate harmonics from the transmitting rig and attenuate the fundamental energy on the receiving rig. If you use an amplifier it will happily regenerate harmonics that the filter removed since no amplifier is perfectly linear, and this is even more so with RF power amplifiers, especially solid state amplifiers. Amplifier harmonic reduction requires tuned stubs or high power (and expensive) band pass filters.

Before the contest I ran through every combination of antennas and bands on both rigs to test for harmonic energy. All was as I expected. The worst case was transmitting on the 40 meter yagi where the second (20 meters) and third (15 meters) harmonics were very strong on the TH6 3 meters below it, hindering effective use of segments of those bands. The easiest solution was to switch to the TH7 at half the height.

Even with the best filtering there will be band segments wiped out by harmonics. It helps to run at a higher frequency on the lower band so that the harmonics on the higher band are less likely to be encountered. I made this mistake numerous times during the contest.

Audio switch, and using it effectively

One week before the contest I built a manual switch to feed receiver audio to the headphones. The wiring is straight-forward and can be easily figured out by anyone wishing to build a similar unit. There are stereo 3.5 mm jacks on the back for the left and right radios and one in the centre for the headphones. A splitter on the headphone jack can direct headphone stereo audio to a recording device, which is strongly recommended for top competitors in major contests.

The SPDT switches on top correspond to the headphone earpieces: left for left ear and right for right ear. Both switches to the left puts audio from the left radio into both earpieces, and vice versa. When listening to both radios at once the typical switch positions are left rig on the left earpiece and right rig on the right earpiece (as shown above). To concentrate on one radio the audio can be temporarily switched to both earpieces.

I put the switches on top because this is the best ergonomic fit for me. They're a short reach for my fingers that are constantly hovering over the keyboard.

A lot of switching goes on during the contest! The best SO2R control boxes will, under software control, switch the audio for the rig in receive to both earpieces when the other is transmitting, with an option to blend the audio in various ways to accentuate, say, the run radio's audio or to monitor the transmission side tone (CW) at a reduced level.

The way I blend audio is with the AF Gain controls on the rigs. I set the rig side tone level as low as I can while still being able to copy it. The side tone let's me know the progress of memory transmission or for feedback when using the paddles. Experienced operators disable the side tone during memory playback. There is no provision for a microphone. Transmit audio switching is more complicated and my favourite contest mode is CW. The WinKeyer USB takes care of rig switching under control of N1MM Logger+. The software ensures that just one rig transmits at a time in compliance with the rules of virtually all contests for single op entrants.

Ordinarily both audio channels from HF transceivers are identical. For radios with two receivers the stereo wiring brings the benefit of dual receive with no added effort. Split operation is rare during contests but can happen, so you'll be prepared. More common is to use the second receiver to search for stations on the same band and antenna, either while running or to double your S & P potential. This can be useful when sunspots are absent, such as now, when only one band is consistently producing contacts, or for single band contests. I may try this in the upcoming CQ 160 contest.

Don't be surprised if you hear power line hum when the audio switch is connected to both radios. Make sure the interconnect cables are high quality and that there is a low RF impedance bond between radio chassis and other equipment powered by the mains. I had a low level of hum only in the FTdx5000 audio which I traced to the headphone jack and in particular the 3.5 mm to ¼" adapter. Replacing it with a high quality unit resolved the problem. You can learn much more about trouble-free audio interfacing from K9YC, starting at page 40 of the linked document.

In summary, the audio switch is simple and it works. For an investment of a few dollars and a couple of hours it gives me a good entry point to try out SO2R. When or if I go all-in for SO2R a more substantial investment on a control box will be warranted.

Software

N1MM Logger+ software is smarter than I am. The SO2R features have been designed by contesters who have learned from their own long experience and feedback from the world's top competitors. The choices they have made are good ones. The challenge for an SO2R novice is to understand and use them effectively. I have much to learn.

The software chooses where next to transmit (left or right radio) and position the text cursor from context. It is not what you might expect or guess. It all makes sense once you get used to it. I wasn't used to it so I made many mistakes. As the contest progressed my error rate declined. You can learn a lot in just a few hours. There is nothing like a real contest to spur learning, far better than offline practice (which I also did).

The SO2R feature is well documented so I will simply point you there. Other popular contest software packages support SO2R as well, including interfacing with external control devices. I am obviously making use of the minimum set of features to get started with SO2R. This will change as I progress to phone SO2R, a superior audio switching system and more aggressive operating, including simultaneous running on two bands.

One feature I plan to make use of soonest is two keyboards, one for each rig. When done properly there is less fatigue and fewer typing/transmitting errors.

Distractions

At first it can be difficult to concentrate on copying the signal heard in one ear and not be distracted by what's being heard in the other ear. A momentary lapse means requesting a repeat, resulting in lost time for you and the other station.

Other types of distractions I experienced include:

• Sudden appearance of a noise burst or a loud signal in the other receiver.
• A CW tone close to or equal to that of a signal in the other receiver can be disorienting.
• Locking your attention on a weak caller takes longer when you're listening to both receivers.
• Poor timing of transmissions can have you paying attention to the wrong side. For example, answering a CQ on one rig a second or two after your CQ on the other radio ends. You're focussed on making your call and fail to copy the station calling you.

Put in the time and you'll get better at dealing with these and other distractions. The danger is that you become so anxious about mistakes that you abandon SO2R entirely. Don't do that; don't be afraid to make mistakes. It's better to stick with it and climb to the top of the learning curve. I know that I have more climbing to do, and I will surely make many more mistakes.

Whew!

It sure was nice when the contest ended and I could get a proper rest from SO2R. Several times during the contest I retreated to a single radio to reduce the stress level. It is not necessary to use both rigs all the time, especially in a long contest. As proficiency improves the stress will become managable. That's when you can challenge yourself to accomplish even more with SO2R.

I am considering a follow up article on the the nuances of SO2R and how some (not me!) push themselves to the maximum effort, and score. NAQP is a contest where SO2R makes a difference unlike most other contests. For once it was nice not to have the lowest score among my more exalted team members, which includes two WRTC competitors. I salute them.

Now it's on to practice, practice, practice. I intend to do SO2R again, though hopefully in a contest not quite so intense. My bare bones SO2R setup will transition to one more sophisticated as my schedule permits. Most of what is built for SO2R is needed for multi-op contests --filters, switching, automation and software -- and that I intend to do by the end of 2019. For now I am happy that I can achieve some of the potential score boost due to SO2R.

I hope I have inspired others to try SO2R. The thing is you don't have to do SO2R 100% of the time. Like beginning runners, you can alternate walking and running until your body is tough enough to go the distance. Pick your places and you can increase your contest score from a modest effort. With the availability of off-the-shelf software and hardware to take care of SO2R mechanics it's never been easier. Others are doing it so why not you.