From Low-Band DXing to Contesting

Amateur Radio is all about satisfaction and self-fulfillment.

My Elmer was ON4GV, who was also my uncle. At his home I saw my very first Amateur Radio station. I was not quite 10 years old. That was around 1950.

Fifty years ago Amateur Radio in my eyes was adventureland and wonderland, all in one. To a young boy, telecommunication was Amateur Radio. You must realize that in the early years after WW II, out in the countryside where I lived with my parents, we still had hand-cranked telephones with manually operated telephone exchanges. These exchanges closed down at 10 pm—we had no chance to telephone anyone during the night. If you wanted to communicate with someone across the ocean you wrote a letter. If you wanted to travel across the water, you took a boat.

But for all I knew, if you wanted to talk to someone anywhere in the world, you needed to be a radio amateur. Being a ham made you an explorer, a discoverer. You could expose yourself to worlds others had hardly ever heard about. It was this magic, this thrill of radio that lured me into this hobby.

I will never forget the oh-so-typical smell of Bakelite, wax and tar-filled capacitors and transformers that was very typical for the early-day radios. And the white filament glow of early tubes. Some of the early-day triodes were so “brilliant” that you could literally read a book by them at night. My very first hands-on experiences with electronics (not that it was called that, in those days; we called it simply “radio”) were in building small audio amplifiers, using directly heated triodes, such as the E, A416. My father’s wooden cigar boxes served as chassis for building three-stage audio amplifiers using heavy 3:1 interstage transformers. This was all about discov­ ering an amazing and intriguing world, the world of radio.

It was technology (a modern word for these early-day sensations) that hooked me to Amateur Radio. For a while my discovery trips were somewhat curtailed and it was not until I was 20 years of age, in high school, that I finally got my license. The challenge then was to prepare for the license, and get it on the first try. The sense of fulfillment, once you got it, was enormous, as was the first antenna you built, the first QSO you made. I was doing something not every one else could do! Now I was part of them…

In the early 1960s I stumbled across some guys working DX on 80 meters. I remember a few calls: GI6TK, GI3CDF, GW3AX and G3FPQ. Only David, G3FPQ, is still there and still a very active low-band DXer. This really seemed like something else—working across the  pond  and  into  New Zealand on frequencies where the others would work stations in a 500-km range. What a challenge! This really put you in a separate class among hams.

Working the elusive DX on the low bands was my next challenge, and it became my passion. This time I found out that, in order to be part of those low-band DXers, you needed to have a good signal. That meant you needed to have the know-how to do it. Amateur Radio was no longer a commu­ nicating hobby for me, but became an experimenter’s hobby: building new, better and bigger antennas, experimenting with and learning about propagation, becoming a better technician and becoming a better operator.

DXing on the low bands is all about overcoming difficult hurdles: everybody can work DX on 10, 15 and 20 meters. There is not much sense of satisfaction involved. In 1987 my last iron curtain was lifted. We finally got 160 meters in Belgium. The last frontier. A vast terrain for chasing difficult game. And yes, Top Band certainly is where the DXer can get the ultimate sense of satisfaction. Technical knowledge and technical achievements are undoubtedly great assets in achiev­ ing success in low-band DXing. But, even with a modest station, provided dedication, patience and operating experi­ ence, you can be a successful DXer.

If so, what can provide you with the ultimate sense of achievement, of  technical excellence, in  Amateur Radio?

Throughout history, competition has been one of the impor­tant leverages for progress in many fields. So is contesting to Amateur Radio. To be a very successful low-band DXer you need to be a very good operator, know propagation, be patient, be persevering and have a “decent” antenna system and sta­ tion. You can determine yourself whether or not you are successful. You can set your goals as a function of your possibilities, and if you have worked 300 countries on 80 and 200 countries on 160 from an average urban-lot QTH, then you are, by all standards, a very successful DXer.

To be successful in “big game” contesting, you cannot compromise with yourself. You need to have the best antennas, the best station, the best operators, nothing but the best if you want to score high in world ranking. The best multi­ operator contest stations are all built, improved, maintained and run by engineers. This is no coincidence.

Undoubtedly international contesting is the ultimate chal­ lenge—it provides the truth by excellence. It is truly the Formula 1 competition in Amateur Radio. This is what at­ tracted me to this radio-sport.

Jim Reid, KH7M, was an operator at Stanford Univer­ sity, W6YX, in the years when SSB techniques were worked out there by Art Collins (yes, later from Collins Radio) in the ’50s. He was a witness to how Amateur Radio contributed to important advancements in communication technology, now almost half a century ago.

He made an interesting comparison between the world of contesting and the world of car racing.

“Today, about the entire globe, the most sophisticated, and elaborate HF band stations are owned by contesters such as CT1BOH, WB9Z, IR4T, PI4COM, IY4FGM, GW4BLE, JA3ZOH, PY5EG, W3LPL, K3LR, VE3EJ, and so on (ON4UN was also mentioned—thanks Jim!). Each of these stations has elaborate and multiple rig setups, multiple antenna installa­ tions, many computers with each operating position net­ worked with logging programs, band mapping programs, propagation monitoring radios, and so on.

These Amateur Radio stations are all Contest/DX sta­ tions. They each have the most sophisticated and up to date technology possible. Each has invested into it what would be comparably invested into a stable of Ferrari racing automo­ biles; and I have seen both, especially in Southern California!!

These guys have pushed and pushed at manufacturers, at antenna designers, at software writers, and continue to do so. The station owners themselves are all first class operators and technicians. They spend virtually all of their time “tinkering” and pushing the state of the HF art, in every way feasible. Every station I listed represents thousands of man-hours of work, every year to maintain and remain in the top ranks of competition in the sport of DX contesting, which of course has no more purpose than the sport of auto racing: fun to have and maintain and win with the BEST.

The owners of these stations have pushed the state of the art of Amateur Radio every bit as directly as the owners of Indianapolis racing machines have pushed the state of the art of tires, lubricants, engines, brakes, frame design, and so on.” In the highly competitive sport of international contest­ing, it does not suffice to have the best car or engine; you also need the best drivers, the best mechanics, and the best engi­ neers. Contesting is indeed very much like car racing.

In DXing you can get the fulfillment of working all countries on 40 or 80 or even 160 meters. Once it’s done, the game is over. Not that the game of working all countries on Top Band will ever be over, I guess. But in contesting, there is a new competition calendar every year. Every year you can measure the station’s performance, you can measure your improvements, plan your progress and enjoy the fulfillment of your victories, over and over.

That is why international contesting is the ultimate play­ ground of  ever  advancing, competitive and  self-fulfilling Amateur Radio.

Now and then I read on the Internet how a proud antenna builder tells us all about the wonderful performance of his new antenna. He is trying to convince the world by telling us all about the rare DX he worked with his new antenna. What does that prove? Very little, really. Working DX is in no way a proof of technical performance of an antenna. Not in the strictly technical sense, in any case.

Working rare DX can be the proof of outstanding oper­ ating, dedication and perseverance, when it’s done from a modest QTH with small antennas.

If you want to prove the technical capabilities of the station, there are really only two ways. Number one consists of elaborate full-scale field testing and measuring in a precisely controlled environment. This is beyond the reach of almost every ham.

The second possibility consists of testing your weapons, not in a shooting range or in a lab, but on the battlefields. These battlefields are the major international contests. Con­tests are possibly as close as we can get to a controlled environment, simply because it is extremely unconditioned. In major international contests you are competing against all the best-engineered and equipped stations, under a variety of continuously changing conditions, which really makes it a fair and equal battle and test.

This is why, after having been an “occasional” contester for almost 40 years, I decided to get into some serious contest­ ing, thereby putting emphasis on the low frequency capabili­ ties of my station.

In order to convert my station into a successful contest­ ing station the first decision was—“we want to win—but in which category?” In other words, what is the appropriate battleground for the weapons we have?

The biggest and probably best-known stations are the multi-multi stations. The most successful of them have two stations per band; that means 12 fully equipped stations. These stations are on each of the six bands, 24 hours per day, and they must catch every single opening. They need to have access to a wide variety of antennas with different wave angles. Therefore, they are generally equipped with various stacked Yagis for the HF bands, even including 40 meters. The second station, whose task it is to look for multipliers, generally has access to a simpler antenna setup. It is located as far away as possible from the running station’s antennas, to minimize interference, although eliminating same-band inter­ ference is quite impossible.

Interstation interference is the most challenging techni­ cal challenge in multi-transmitter station design. With multi­ multi contest stations, though, each of the band stations can be completely (galvanically) separated from each other, which certainly helps prevent leakage paths for unwanted coupling between stations. In this respect a multi-multi is simpler to design and make than a so-called small multi-single, where all of the antennas have to be accessible by both stations. This makes eliminating leakage paths much more difficult.

There are a number of multi-single stations, which as far as station design is concerned really fall in the category of multi-multi stations. I call them big multi-single stations. They have six well-separated stations, one of which “runs” while the five other stations are manned and are checking each of the five other bands simultaneously. In this configuration as well, it is possible to achieve better isolation between bands because there are six completely separate stations. These big multi-single stations normally also have antennas for each band on separate towers. To build a really top-notch multi­ multi station you probably require at least 2.5 to 5 acres (1 to 2 hectares or 10,000 to 20,000 meters2) of land—and that does not include what you need for Beverage antennas.

For a big multi-multi setup, in addition to the financial limitations, there is simply not enough space for putting up additional towers in my backyard. This is why we decided on going for the category of multi-single, or—as I call it—small multi-single.

Small multi-single stations can be built much smaller than multi-multi stations. A small multi-single is a station with only two operating positions, one for the “run” station, and one for the “multiplier” station. The operator of the multiplier station has to scan all bands for multipliers. In general both the run as well as the multiplier station will have access to all antennas, which means that a fairly complex antenna switching system is part of the setup. Such switching systems increase the potential for unwanted coupling between the two stations. This is what makes designing a small multi­ single station technically more difficult than a large multi­ single or a multi-multi station. It goes without saying that a station designed for small multi-single is also well suited for single-operator two-radio (SO2R) contesting. In recent years SO2R has become quite popular. In concept and in layout it is very similar to a small multi-single station, where, however, the two operator seats are replaced by a single one.

While it is imperative for a multi-multi station to catch every single band opening, and therefore needs antennas to match all possible elevation angles, this is not necessary for a multi-single station. The run station will run on the bands at the times the takeoff angle of his antenna matches propagation best. In other words, the height of the antennas should be such as to accommodate the average elevation angle, the angle that produces most QSOs for the longest period of time. This means antenna heights between 18  and  30 meters for  10 though 40 meters. The multiplier station may have to call a multiplier with an antenna that is not at the ideal height. He may not get through on the first call, but this is not as important for the multiplier station.

But there is not only multi-operator or SO2R all-band HF contesting. Any station that is successful in DXing could be a candidate for single-operator contesting. And if the station is not equipped for all bands, a single-band effort can be contem­ plated. Also, if you are not 20 years old any more, single-band contesting is attractive. If you operate the low bands, you have all day to rest. You can still prove the technical excellence of your station on the band of your choice!

The ON4UN/ OTxT/ ORxT contest station was designed as a multi-single and a single-operator two-radio transmitter station. Fig 15-3 shows the QTH and some of the antennas. One tower supports the 40-meter Yagi (at 30 meters height) and the 20-meter Yagi (at 25 meters height). As they are both on the same tower, they cannot be rotated independently. A similar combination exists on tower number 2, where a 6-element 15-meter Yagi (at 24 meters) tops a 6-element 10-meter Yagi (at 19 meters). The third tower is quarter-wave 160-meter antenna, which also serves as a support tower for the 80-meter Four-Square.

About 100 meters behind the house is a fourth tower (18 m) with a Force-12 C31XR triband Yagi (formerly a KT34XA).

This is what we call the multiplier antenna. There are two more multiplier antennas, a 40-meter four-square and an 80-meter low inverted V. See Fig 15-4. These multiplier antennas are used whenever the main antenna is not available for the multi­ plier station; eg, when the run station runs on 20 meters with the big Yagi, the 40-meter Yagi is not available, and the 40-meter four-square must be used to work multipliers on that band.

For a normal everyday DXing station there is practically no rule on how things have to work in the shack. For a contest station equipped for a team effort it is different. Things have to be simple and ergonomic. A hired-gun contest operator is usually someone who doesn’t read manuals. He or she wants to sit down and start operating right away. This means that the whole system must be simple and idiot-proof! I remember the days that we had no safety designs and that operators would start transmitting on the wrong antenna or with the amplifier set on the wrong band, resulting in inevitable damage and lots of frustration. Fortunately those days are over now. It is not possible to describe what the ideal contest station should look like. There are too many variables involved. But a really well designed contest station is very different from a run of the mill DXer station.

Building blocks are available from different sources. Array Solutions, WXØB, carries them all, but many suppliers have the individual parts. Check National Contest Journal (ARRL publication), where they all advertise.

5.1. Antenna Switching at ON4UN

Since two different antennas are available on the higher bands (40 through 10 meters), I have made provision, for either station to use either one of these antennas (the “run” or the “multiplier” antenna) or split the power 50/50 into those two antennas. When the band is open in two directions, you can thus work in two directions simultaneously. Of course, you must realize that you have more QRM/noise and only half the trans­ mit power in each direction. If you are using one antenna, you can quickly switch directions to work a multiplier. It is impera­ tive that the SWR curves of both antennas are flat and similar, so that you do not have to retune the amp while switching.

The unit contains four L-networks (10 through 40 meters) that convert 25 Ω back to 50 Ω. Simple ac-type relays are used for  the  switching, which results in  quite a  bit  of  wiring inductance  (about 8 inches of wire). To compensate for the effects of these long wires, I put capacitors at both ends of each relay wire, creating Pi networks. With about 30 pF on both ends, the SWR is less than 1.05:1 even on 10 meters.

The antennas are selected fully automatically, using the band output data from the transceivers, in my case Ten-Tec Orions. I built a control device using the band data output from the two transceivers to generate the logic signals for selecting the antennas. Fig 15-6 shows the control unit. The switching logic must prevent the two stations from selecting a stack of the secondary antenna on 10/15/20 while the triband antenna is already in use by the other station. The logic has been developed such that when one station uses the tribander, the other one cannot get it, and will remain on the main antenna. It’s first-come, first-served Relay logic is used throughout so the system is totally immune to RF and very reliable. A total of 11 small relays are used for logic switching. A small switchbox mounting two three-position switches and some LEDs is placed between the two transceivers for the operator to use. 

The  left switch is for Radio A, the right one for Radio B (see Fig 15-7). The three positions are:

1. Primary antenna

2. Secondary (multiplier) antenna

3. Both antennas in a 50/50 split.

There are seven LEDs to indicate the status of the switch. When the green LED is on, you are on the main antenna; the orange one stands for the multiplier antenna; and the red one is for both together. Blinking red means that you are trying to select the multiplier antenna, which is not available.

Fig 15-8 shows the block diagram of the system. On 80 and 160 meters, where only one transmit antenna is available, these antennas are fed directly from the six-pack switch. And if for any reason the band data from the switch and the data from the transceiver do not match, the transmitter in the transceiver is inhibited (in the Orion via the TX-EN line).

5.2. Antenna Directions

On the receiving side the visual direction indication of the Beverage antenna selector proved to be very helpful. At the lower left in Fig 15-9 you can see my Beverage selector box, which uses a 12-position rotary switch with LEDs for each azimuth direction.

Point-and-forget rotators: In the heat of the battle you don’t want to sit and press that turn-left or turn-right button— just select your direction and press one button. On commercial rotator controls these buttons are too small, however.

5.3. Radio-Computer Interface.

Computers and contesting software is covered in detail in Section 7 of this chapter. Top-notch contesting without top­ notch contesting software is a no longer possible. All contest­ ers control a great number of functions of their radio through the computer, starting with sending CW, changing frequen­ cies, bands or modes, etc. You name it. Connection between the computer and the radio is nowadays still done largely by serial ports, although we likely will see them disappear from modern computer in the near future. We will then require converters for changing USB signals to serial-port signals, as long as our radio manufacturers don’t go USB. While most radios seem to be giving band data as BCD codes, this requires a decoder in the communicating device. Ten-Tec, with its Orion has chosen simply to provide one line per band, which simplifies switching, since it doesn’t require any additional conversion!

5.4. Easy-to-Tune Power Amplifiers

In a typical multi-single or single-op two-transmitter contest setup one transmitter is tuned to the main band, where a pileup is worked. This is usually called the “run station.” With the second transceiver the other bands are scanned, and multipliers are picked up between QSOs on the running band. In order to be able to concentrate fully on the operating aspects, band-switching should be  automated as  much as possible.

Tuning the second linear between bands often has been a problem, because:

•  Contest operators often don’t know how to properly tune a linear,

•  It takes them too long.

The minimum to have is labels stuck to the linear front­ panel with all settings for all antennas and modes. Even that sometimes seems to be too difficult for the operators trying to concentrate on moving this very rare and weak KH8 station from one band to another. An amplifier that automatically switches bands, and automatically tunes to preset values of band-switch, load C and tune C, or better yet, performs a fully automatic tune-up, is the answer to that problem.

Since 1998 the ON4UN station has been equipped with an ACOM 2000A linear. The use of this fully auto-tune linear proved to be very helpful for working multipliers by quickly changing bands and antennas.

The ACOM 2000A (see Fig 15-10) is an auto-tune nomi­ nal 1500-W output amplifier (maximum 2000 W) using two Russian-made 4CX800A (or GU74B) tetrodes (replacement cost in Europe typically $50 to $60). This was the first real auto-tune amateur HF-amplifier I had ever seen. By pressing a button on the remote control panel it automatically tunes itself completely within a half second. The auto-tune function is not limited to recalling preset values—it actually tunes for a match for a load within the 2:1 SWR circle (on some bands

up to 3:1)

The amplifier has an absolutely blank front panel, except for an ac on-off switch. This makes it possible to hide the amplifier in any convenient place. All control and monitoring functions are grouped on a remote small control box, which can easily be positioned next to the computer keyboard during operation. The ACOM amplifier can be connected via an RS-232 connector to a PC for either remote control or testing. Its processor keeps track of all the important data (currents, voltages, temperatures).

In case of a fault, you can send the information stored in the INFO BOX for the most-recent 12 faults to the dealer or the factory by means of Baudot code on the telephone— simply put the microphone close to the tiny loudspeaker on the RCU rear, or by means of a personal computer and its inherent communications channels (Internet, modem, etc). Needless to say, the use of this amplifier has greatly increased flexibility and efficiency at the OTxT contest station. Over the past six years, Acom has built a superb quality and service record, and continues to be an excellent choice for serious contesting.

Since Acom introduced fully automatic tuning, Alpha/ Power followed. Its well-known Alpha 87A amplifier was previously equipped with a memory-tune system but now it has been improved to included an auto-tune system similar to the one used by Acom. This amplifier has very similar, but not identical, characteristics (also 1500-W nominal output), and is certainly a valid candidate for a top-notch contesting station linear as well. The Alpha 87A uses two 3CX800A7 triodes, which have the disadvantage of being much more expensive than the tetrodes used in the Acom. The Alpha 87A also has an RS-232 interface port, which allows the linear to be controlled remotely. In addition, key parameter measurement values can be monitored remotely. Not only the 87A, but also other models, including the Alpha 89, and the Alpha 91B are very popular with contesters as well as DXers and DXpeditioners.

In many cases, these amplifiers made it possible for us to hear the DXpedition’s signals on 160 meters.

It is clear that the technical requirements for a top­ performing contest station are far superior to what’s needed for casual, or even serious, DXing. Think of harmonic sup­ pression. Stations built for multi-transmitter operation must transmit the cleanest signals, and their harmonics must be suppressed far in excess of the standard. Another issue is to keep the contest station “up and running” all year long. It takes good mechanical engineering to keep the antennas up.

6.1. The  Operating Table

Even  though  we  were  housed  in  a  small  shack  of 3 × 3.5 meters for years, we nevertheless managed two multi­ single first places in Europe. But we were almost sitting on each other’s laps! So, one wall was taken out, which made it possible to install a single 7 × 1-meter wide operating table.

The new shack layout was conceived with contesting in mind. To provide the best possible RF and safety ground, the underside of the 7 × 1-meter table was entirely covered with a 1-mm thick aluminum sheath. This sheet provides maximum capacity to the equipment standing on the table, and minimum resistance and especially inductance for good RF grounding. Forty ac outlets are mounted on the aluminum sheath, provid­ ing the shortest possible safety ground return for the outlets. Short and wide straps are connected to the sheath and are available on the back side of the table to ground various equipment.

The table is separated from the wall by approx 15 cm, which allows wires to pass and for ventilation as well. The aluminum ground sheath is grounded with a short strap to an excellent RF ground just outside the shack, with a 40-cm heavy-gauge cable going right through the wall.

The table is equipped with three separate mains distribu­ tion circuits, each equipped with a professional-grade mains filter. Circuit one powers all the “run” station equipment.

Circuit two powers all the “multiplier” station equipment and circuit three powers some other equipment plus the main computer.

6.2. A Monitor Scope at Each Station

In the heat of a phone battle, operators sometimes have the tendency to crank up the microphone gain, resulting in poor and distorted audio, unnecessary splatter and so on. I always have a monitor ‘scope connected to the output of each of the stations. I use a second-hand commercial 20-MHz ‘scope, and tap off a little RF using a resistive voltage divider across the output of the linear. This way the operator always has the pattern of the transmitted signal right in view (see Fig 15-2).

6.3. The  Problem of Interband

Interference In a two or more station setup, interband interference is the number one technical problem. But as the saying goes, every problem is an opportunity. In this field lies the opportu­ nity to excel. Here also lies the opportunity for equipment manufacturers to improve their equipment. 

Interference can be minimized by using the following techniques:

• Separate the antennas as much as possible

•  Use vertical and horizontal polarization to take advantage of the additional attenuation of unlike polarization

• Use band-pass filters between the exciter and the amplifier

• Use amplifiers with Pi-L networks, not simple Pi networks

• Avoid common-mode currents on the feed lines

• Galvanically separate the feed lines of the separate bands

•  Use band-reject filters between the amplifier and the an­tenna

•  Push the equipment manufacturers to produce transmitters with much lower in-band noise output.

It  is  obvious that  interference will  be  heard on  the harmonic frequencies. This poses much more of a problem on CW than on phone. The CW band segments are all in the low end of the bands, and the harmonics of 3.503 will be 7.006, 14.012, 21.018 and 28.024 MHz—all right in the CW win­ dow. On phone, if you operate on 3.775 kHz, the harmonics will be on 7.550, 15.100, and so on, all outside the band. There is no real problem with the direct harmonic frequencies when operating phone.

Unfortunately most present-day transmitters do not only transmit just the wanted signal; they also transmit a lot of noise around the transmit frequency. This noise can often make it difficult to copy, even many kHz away from the exact harmonic of the transmit frequency, unless effective filtering is applied. And even then, the final improvement will have to come from the designers and manufacturers of our transceiv­ ers, putting out equipment producing less in-band noise.

My friend George, W2VJN, covers all of these aspects very  thoroughly in  his  excellent publication Managing Interstation Interference, which can be obtained directly from him.

6.3.1. Medium power band-pass filters

There are a few commercial sources for medium-power band-pass filters that are widely used in multi-station contest setups as well as during DXpeditions. I have experience with the ICE, Dunestar and W3NQN units. The ICE units are rated 200 W, and if the SWR is low they will indeed cope with 200 W. The Dunestar filters are rated at 100 W. I have been using all three of them and I did some comprehensive measur­ing on these units.

Table 15-1

1.8 MHz       3.5 MHz       7 MHz          14 MHz        21 MHz        28 MHz

ICE 160 m                         0.4 dB         15 dB       27 dB             40 dB         >45 dB         >45 dB Dunestar 160 m                 1.0 dB          28 dB       >45 dB           >45 dB         >45 dB         >45 dB W3NQN 160 m                  0.2 dB           50 dB        >80 dB             65 dB           50 dB           58 dB ICE 80 m                           25 dB        0.34 dB       17 dB             30 dB         >40 dB         >45 dB Dunestar 80 m                   42 dB          0.64 dB        37 dB           >45 dB         >45 dB         >45 dB W3NQN 80 m                     53 dB          0.4 dB           70 dB             62 dB             55 dB               49 dB 

ICE 40 m                         >45 dB        38 dB        0.8 dB             32 dB         >45 dB           32 dB Dunestar 40 m                  >45 dB         43 dB        0.6 dB         >50 dB         >45 dB           33 dB W3NQN 40 m                     68 dB           45 dB          0.3 dB           >80 dB           52 dB                 48 dB

The ICE and Dunestar units have insertion losses of between 0.3 and 1.0 dB (that is a lot) depending on band. Due to the circuitry used, the Dunestar filters have significantly steeper shape factors. The W3NQN filters undoubtedly have the best characteristics and show 0.2 to 0.4 dB insertion loss, depending on band. If we look at the performance of the 40-meter filters, we see that the ICE filter will attenuate 20 meters about 32 dB, the Dunestar more than 50 dB and the W3NQN between 80 and 90 dB. Fig 15-11 shows the re­ sponse of a 7-MHz W3NQN filter. Table 15-1 lists some of the major characteristics I measured for 160, 80 and 40 meters.

It is important that the filters be operated at a low SWR. If not, you will likely blow the capacitors. It is important, when driving a linear amplifier through one of these filters, that the linear is switched to the right band. If not, a high input SWR may result. If the exciter is equipped with a built-in tuner, it may try to get the full power into the filter, at a very bad mismatch, which guarantees fried components. There­ fore, you shouldn’t switch the automatic tuner on when oper­ ating with a band-pass filters. Also, it is a good idea to control the selection of the right filter right from the transceiver’s band data output, so you do not dump RF of the wrong band into the filter. There must be many contesters and DXpeditioners who have done that. I am sure replacement capacitors for these units must be a hot selling item!

6.3.2. High power filters

If you run power, it really is a must to run filters beyond the amplifier as well, because the amplifier also generates harmonic power. These filters should not only be designed to suppress harmonics, they should attenuate signals on all bands, also on frequencies below the transmit frequency. It is not uncommon for signals from one of the stations of a multi­ operator station to mix in the linear with other signals (BC or from another amateur band) and create unwanted mixing products. The ultimate filter is indeed a filter that attenuates all other bands, but gives the highest attenuation to the second harmonic.

The most common way of achieving out-of-band attenu­ ation is by using band-reject filters. These can be made with discrete components or by using coaxial cable.

6.3.2.1. Using discrete components

High-power filters using discrete components can be made much smaller than those using coaxial cable, but the components are hard to come by (high-power, high-voltage, high-current capacitors) and the design requires some exper­ tise and the use of a quality network analyzer.

I have designed a series of such filters, which perform very well. Fig 15-12 shows a 10-meter band-reject filter that will take 3-kW continuous-duty power. I built it in a box measuring 25 × 6 × 6 cm. The box is made of double-sided glass-epoxy printed board material, which is ideal for the application. With single-pole series-tuned circuits for each band, an attenuation of 38 to 46 dB was obtained on all five bands, with an insertion loss of approx 0.1 dB. Fig 15-13 shows the response from 1 to 30 MHz for this filter.

The principle for designing such band-reject filters is really quite simple. You design five series-tuned circuits, each one tuned to the frequency you want to suppress and simply connect all these traps in parallel. For the 10-meter filters, all these tuned circuits will exhibit an inductive reactance on 10 meters. You can easily calculate this value: Calculate the impedance of all the coils and all the capacitors (five of each) used in this filter. Since they are connected in series (for each band), you can simply add the values, taking the sign (+ for a coil, – for a capacitor) into account. Then calculate the parallel value of all of these, just as you calculate parallel resistors. Now we can “tune” out this positive reactance by using a parallel capacitor, which resonates the whole thing on 28 MHz. It really is that simple.

For other bands, series-tuned circuits below the design frequency will show as inductors on the design frequency, and as capacitors above the design frequency. By judiciously choosing the LC ratio of the series-tuned traps, you can now design filters where the positive reactance of a group of traps will cancel the negative reactance of another group, which means there will be no need for a parallel capacitor or inductor to tune the filter to a 1:1 SWR on the operating frequency.

Fig 15-14 shows a  high-performance 80-meter filter using a pair of 40-meter traps for improved rejection. The basic configuration is a  low-pass section. The effect of the low-pass section can clearly be seen at the overall shape of the rejection curve. Filters like this can easily be modeled using the ARRL Radio Designer Software, an ideal tool for this purpose. In this case I designed a symmetrical low-pass filter, and arranged the traps on both sides of the inductor to obtain the same capacitance value. A capacitor (900 pF) had to be added on one side to tune the low-pass filter. The value of the inductor can easily be calculated using the LINE STRETCHER module of the NEW LOW BAND SOFTWARE.

If you want to design your own filters, the sky is really the limit. The biggest problem in making such filters is to obtain suitable capacitors. Inductors can be wound on pow­ dered-iron toroidal cores (#2 material). Make sure you calcu­late the estimated power that will be dissipated in the cores. On adjacent bands there may be a substantial amount of heating in the cores, and 2-inch cores may be required in some circum­ stances.

It is beyond the scope of this book to deal with the concept, design and construction of such filters, but they are necessary to make a multi-transmitter station fully competi­ tive.

6.3.2.2. Using coaxial-cable stubs

Let’s work out a situation where we want to operate an 80-meter station and a 40-meter station simultaneously in the CW contest. A single quarter-wave long shorted stub, made of RG-213, cut for 80 meters, will provide about 26 dB attenu­ ation on 7 MHz, 24 dB on 14 MHz, 23 dB on 21 MHz and 22 dB on 80 MHz (see Fig 15-15). The insertion loss on 80 meters will be less than 0.1 dB.

A quarter-wave RG-213 stub cut for 20 meters typically shows an attenuation of 37 dB. The same stub with RG-58 shows about 25 dB of attenuation. A 10-meter stub made of RG-213 can achieve 40 dB of attenuation.

We can use two identical stubs to almost double the attenuation, but not by merely connecting them in parallel! Connecting a short across a short can in the best case, when the two shorts are equally “good” or “bad,” brings you 6 dB additional attenuation. There is one way, however, to obtain much more attenuation.

Look from the linear amplifier into the feed line. With a well designed and built amplifier, the pi-L filter will provide a good deal of attenuation on 40 meters. But there is some 40-meter power at the linear output. Assume it is 50 dB down from the 80-meter fundamental. At the output of the linear we assume a  low  Z  for  the  second harmonic, an  acceptable assumption at the output terminal of the pi-L filter. If we now put the stub (which is a short on 40) right at the output of the transmitter, we are putting a short across a short, which is not very effective. If we insert a quarter-wave coaxial line be­tween the output of the amplifier and the stub, we have transformed the very low impedance point (on 40 meters) to a high-impedance point. If we now connect the stub at that point, we will have the most effect of the short that the stub represents. All of this holds true only if the output of the amplifier  represents a  low  Z  for  the  second  harmonic (40 meters).

In practice it is a good idea to experiment: install the stub right at the output of the amplifier and check the attenuation on 40. Then insert the quarter-wave line between the linear and the stub. If the attenuation is better (which is likely), leave it there. In theory a quarter-wave gives best results (maximum transfor­mation ratio), but anything from λ/8 to 3/8λ should be OK, as long as you stay away from the region of 3λ/8 to 5λ/8.

Fig 15-16 shows the attenuation of a single 80-meter shorted stub (between 6 and 30 MHz).

But you wanted more than 25 dB. You can install another quarter-wave isolation line between the first and the second stub. I call it an isolation line because it effectively isolates the two stubs. The reasoning is the same as explained above. Two stubs isolated by a quarter-wave coax (on 40 meters) now exhibit 56 dB of attenuation on 7 MHz, and 50 dB on 21 MHz, but only 31 dB on 20 meters and 30 dB on 10 meters. This is

logical, since the isolation line must be an odd number of quarter-waves long on the reject frequency to do its job. This is true on 7 and on 21 MHz only. On 20 and 10 meters we only get the predicted 6-dB improvement. In this case using an isolation line of λ/8 on 40 meters would result in good attenuation on 20 (where the isolation line would be λ/4, on 15 (3λ/8), but not on 10 meters where the isolation line would be λ/2. 

Stubs can also be used as elements in a low-pass configu­ ration, in combination with discrete components. The ex­ ample in Fig 15-17 is a combination of a simple 160-meter low-pass filter with four stubs. The attenuation pattern is amazingly clean, and gives better than 70 dB on all bands.

The impedance of the coaxial cable used for making stubs is irrelevant. The cable loss is important, however. An 80-meter stub made with RG-58 will yield approx. 15 to 17 dB attenuation, while RG-213 gives 25 dB and 7/8-inch Hardline will give 40 dB!

In a contest station setup, you can also install fixed stubs at the feed points of single-band antennas. At my QTH I have a 160-meter quarter-wave transmit antenna that stands right in the middle of the 80-meter Four-Square. You can hardly imagine how to obtain more coupling between these antennas. Without some kind of stub an ACOM amplifier feeding one of these antennas would switch off when someone would trans­ mit on the other antenna because of the large amount of “alien” RF it saw. I put a shorted λ/4 160-meter stub at the base of the 160-meter antenna and an open-circuit version at the feed point of the 80-meter antenna.

Top Ten devices makes a multiband switched stub system that can be driven from the band-data output of most transceivers. (See www.qth.com/topten/ or contact w2vjn@ rosenet.net.)

While I was a very early user of CT (in DOS-days), I was one of the very early users of Writelog when 32-bit Windows was first introduced. More recently I have switched to N1MM’s contesting software. You can’t run the latest all bells-and­ whistles software on a 66-MHz computer, since performance and speed go hand-in-hand. I use one computer for each of the two radios at ON4UN. They are state-of-the-art computers, running the latest operating software (with a 2-GHz clock and Windows XP-Professional).

In addition both are networked by LAN with the main computer. All of this has the advantage of having instanta­ neous backups on the other machines, just in case some­thing goes wrong. If one of them is a laptop, you are even protected against sudden mains drop out. If we do a Multi- Single operation, a third PC uses DXConcentrator program (from ON5OO; see homeusers.brutele.be/on5oo/ Introduction.html). This computer is connected to the Internet via a broadband router, becoming the “master of ceremonies” computer. The Master of Ceremony operator makes sure that we all get the Packet Cluster information available. He interprets that information and decides when and where to run, and when and where to work multipliers. He is really in charge. We have been using this technique quite satisfactorily for years.

7.1 Connecting Computers

For first Multi-Single as OT3T in 1993, we had linked a variety of PCs ranging from 286s to a 386 66-MHz machine with copper-wire serial cables. Despite pounds of ferrite rods and toroids, we certainly did not achieve a totally RF-free situation. Often a computer would hang, without apparent reason. Several times during the  contests logs had to  be merged and  computers started up  again. All  of  this  was certainly far from ideal!

In the second phase we replaced all the copper links with fiber-optic links. This certainly was an expensive improve­ ment, but still not 100% bulletproof. Then we went to an Ethernet solution using software written by David Robbins, K1TTT, and Wayne Wright, W5XD. We found that twisted pair Ethernet cabling worked fine, even in a strong RF envi­ ronment.

7.2. Connecting to the DX-Cluster

Here too evolution has been staggering. What was ad­ vanced five years ago, looks like museum technology today. Having had access to wideband Internet for several years now, I have quit using VHF or UHF radios to connect to the DX­ cluster system. If you use ON5OO’s excellent DXConcentrator software, you have the whole world of DX-information at your fingertips. We typically connect to 16 clusters around the world, and although some of these are interconnected, you can often gain valuable seconds by having access to a cluster that’s close to the spotter! Being the first-on-the-spot can be impor­ tant. I  give more details about this excellent program in Chapter 2.

7.3. Computer Noise

In all the years we have been using various computers, I have never had a problem with direct radiation from a com­ puter. Of course, if you use an antenna inside the shack very close to the computer, you will pick up all kinds of hash. It is very important that your antennas are at a sufficient distance from the computers, that the feed lines are well-shielded and well-grounded and that the coax connector makes perfect contact with the receptacle.

Computer screens can be very noisy though. If you buy a new display, make sure you can return it if it radiates too much. You may also want to add extra ferrite cores on the cable between the PC and the monitor. Better still, use an LCD monitor, but I’ve heard of cases where the monitor’s switch­ ing power supply needed few more ferrites on the 12-V power cable to silence it. LCD flat-screen monitors are much less fatiguing for the eyes, and this can be important during long contest periods.

Remember why we participate in contests. There are the Formula-1 operators who want to win going full bore. But there is also the technical guy, who wants to see the fruit of his labor, his engine, his station, his antennas win in an interna­ tional competition. This is what it was all about for me.

But at the same time I met a lot of good regular operators and technicians (the always available helpers from the local radio club). This is undoubtedly the important social aspect of contesting.

Since 1993 my station has been tested in 89 international contests (organized by either the ARRL or CQ), which re­ sulted in 54 first places (Europe or worldwide), and 15 second places. This proves that the antennas as well as the station are capable of winning top-notch contests. In the ARRL DX contests the station’s 80-meter capabilities were tested in not less than 20 single-band 80-meter operations (10 on CW; 10 on phone). On phone the results were all first place for Europe or worldwide. On CW there were eight first places and two second places.

The results are further confirmed by the 80-meter coun­ try and zone totals during CQWW CW contests during the same period (’93-’97). During the 1994 and the 1996 CQWW CW contests we scored 5-band DXCC in one weekend, 10 through 80 in 1994, and 15 through 160 in 1996. The 100 plus countries during a single weekend on 160 meters was a first, I believe.

Twelve entries in the CQWW 160-meter CW contests over the past 16 years have resulted in 12 first places (either Europe or worldwide), while 7 participations in the 160-meter phone contest yielded five first place Europe or worldwide. During most of these contests we scored the highest number of country multipliers worldwide.

The results on Top Band and 80 meters not only speak for the performance of the transmit antennas (Four-Square on 80 and single quarter-wave vertical on 160) but also, and even more importantly, of the receiving capabilities of the station.

To stay competitive in international contesting you must improve the station year after year. Our competitors do the same. This is the driving force that leads to technological and conceptual improvements. Really, it is almost the opposite from DXing. The more successful you are in DXing, the more countries you have worked, the less there are left for you to work, the less pressure there is; the more you can relax. The more successful you are in DXing, the easier your call will be recognized in the pileups (that helps, too). No need to add another couple of dBs for those last two or three countries.

With contesting it  is  just  the  opposite. Competition grows and improves steadily, and if you don’t match their efforts, you’ll be at the losing end. Within the limits of where I live there is not much more I can do antenna wise. Over the years competition got fiercer, especially on the low bands. I hope and believe that some of the work I  have put into publishing the techniques and art of Low-Band operations has contributed to the raising of the standards and the increasing of the performance from stations on 160 and 80 meters from all around. That makes me happy.

Another evolution, over the years, is the increase of man­ made noise. Whereas 15 years ago, I considered myself living in a semi-rural area where man-made noise was pretty low, I now consider myself living in a semi-residential area! Not that I have any more close neighbors, but there now are two small­ industry industrial parks within 2 km of my house.

Every year I spend days chasing noise sources and trying to kill them. In the coming years we will have to continue to fight for our RF spectrum. And BPL (PLC) is a real threat and it should be one of our main concerns in the years to come.

I have been quite active in contesting over the past 15 years, and I have proven what I wanted to prove, which makes me happy. I built a competitive contest station, so my success in DXing on the low bands (worldwide highest DXCC score on 80 meters, and highest DXCC score on 160 meters outside the USA), are not coincidences.

I have now turned 63, and I don’t derive the same pleasure from fighting the same contest battles I did years ago. But that is normal, I guess. And by electing me to the CQ Contest Hall of Fame in 1997, my friends and fellow contesters told me I was a good contester, and that certainly made me happy.

As I wrote before, ham radio is about enjoyment, satis­ faction, self fulfillment and maybe a little recognition as well. If we all keep thinking about ham radio in these terms, I am sure we’re on the right track!