The 50 MHz Station

Six meters is considered a "bread and butter" band. A good station on this band is a requirement for any contests station wishing to do well and be competitive. In 2007, I finally got around to updating the aging six meter antenna system. Our approach here is to tailor the station to be as versatile as possible. We have had a substantial antenna array here since the mid 80's, and made variable to accomodate changing band conditions. It really was always a work in progress, and a test bed for evaluating different arrival angles during Es or F2 openings. It was never finalized into a real workable array. Only the top two yagis could rotate, and even the second side mounted yagi could only turn from 180 degrees thru the West and up to about 10 or 15 degrees East of North. Much was learned from using this setup over the years, however. Having a choice of antenna operating angles was a boon to digging out missing grids. Of course, the trick is to have someone operating who can sense what the band is doing at all times, and can take advantage of the options available. That is a big order. When the band is full of strong signals, it is easy to miss the weak stuff buried down near the noise floor.It is the weak stuff that will tip you off with what is really happening.

 

Photo of the 50 MHz operating position. TIC Ring control boxes stacked up to the left!

The maze of cables and relays on the wall above the operating bench is the array switching matrix. Four phase matched 7/8" Heliax cable runs come into the shack through the floor, from the tower for each of four 7 element yagis. They are all switched indoors in varying combinations. The exciter is a Ten Tec OMNI V with a DEMI transverter. The levels are set for minimum gain in the transverter. It has about 7 dB of gain but still maintains a noise figure well under 1 dB. Signals on six tend to be very loud, especially on Es openings. The high dynamic range of the OMNI V is very handy on this band. The receiver has been optimized with three tandem 2.4 KHz.SSB filters for exceptional skirt selectivity. A fair amount of testing has been done with various receivers. There are many rigs that tend to fold up and die with strong signals. Older Japanese radios such as the Kenwood TS-830S will work well up to about 90 dB of dynamic range, but then, when they start to overload, they fail badly as the band fills up with spurious signals and a rapidly rising noise floor. The OMNI V has much more useable dynamic range, (about 25 dB better!) and when it starts to fail, it fails gracefully. Many problems can be traced to the noise characteristics of the receiver LO. Noisy oscillators can cause the band to become unuseable in a hurry. If you are a dedicated six meter operator, it would be time well spent to look at the dynamic range ratings of the many commercial HF and six meter radios on the market. ARRL product reviews and websites such as W8JI, Sherwood Engineering, and Elecraft publish dynamic range figures for many radios. The results may surprise you. I trust the results listed.

Lately we have been using the Elecraft K3 on six meters. the OMNI V was used in the past as well on 50 thru 432 MHz as the IF radio. While being an older radio, The OMNI V still has very good dynamic range coupled with a relatively low used equipment price. (OK, I am a cheap BUM!) That combined with the latest DEMI transverters produces a very nice performing receiver on each of the lower four VHF bands. The K3, in addition to having a bullet proof front end, has plenty of bells and whistles for 6M DXing. A second receiver, dual diversity, built in SSB & CW keyers, better CAT control, and a small footprint. There are other radios that work well in high dynamic range situations as well. We have tried and like the K2 and Ten Tec Orion series. Most others are beyond my price range. The trend lately, in HF radios, is to price them similar to that of a compact car. I would rather spend my hard earned $$ on antennas instead!!

Also visible in the "shack" picture, is a contest logging computer on the right, with a WSJT computer above it on the shelf, along with the Ten Tec power supply. The rotor control boxes are located to the left of the OMNI V, and to their left is a small switch box that controls the antenna choices or options. This small box is quite important in optoimizing the array parameters to match the band conditions. The contest laptop computer is outfitted with WAV files for voice keying, along with CW messages for CW keying. Manual CW keying is possible with a standalone electronic keyer and paddle combination as well as the computer keyboard keying mode. Some of the four 7/8" Heliax feedlines are visible at the base of the relay board on the far wall. A link to the 1989 Pack rat presentation on the old switchable 50 MHz antenna stack is here. A new revision of the old paper is also available. This was presented at the SEVHF Conference in April of 2008, and contains much updated information. See 50MHZNEWS.PDF This updated paper includes data on contest results to show the effect of variable beam steering techniques.

 

2007 ANTENNA PROJECT, half finished! JUNE 12, .......TWO UP.......TWO TO GO!

JULY 12, 2007 ALMOST DONE! That second antenna from the top needs a "hanging bracket" like it's lower sisters!

The six meter antenna system used to be very hard to photograph. Not any more, we cut down several trees that were blocking the array from view. The trees also impeded our ability to assemble the new array and guying system. Trees have a nasty habit of getting bigger with time!! The top antenna is at 101 ft, while the lowest yagi is at 29 ft. The antennas are four stacked computer designed seven element yagis on a 30 ft 8" boom. These antennas were designed with a very clean E and H plane pattern. The E plane cleanliness helps with QRM and power line noise, while a clean H plane allows for efficient stacking in an array.

If you look at the first picture on this page, you will see a group of coax relays on the wall above the operating position. They allow a choice of receiving options as follows:

Position 1------ Top antenna only at 101 ft.

Position 2------- Both upper antennas, at 101 and 77 ft. in phase

Position 3------- Single yagi at 77 ft

Position 4------- All four yagis 101,77,53, and 29 ft.

Position 5-------All four yagis with electrical beam steering for a 9 degree uptilt.

Position 6-------Bottom two yagis at 53 and 29 ft.

The 2007 50 MHz antenna project changes things in a positive manner, and allows much more versatility with full 360 degree rotation for all four yagis. In the old pre 2007 system, the bottom two antennas were not rotatable, and the second yagi from the top was only partially rotatable from South to West to North. Still, the old array was a good test of the concept and was the subject of a VHF Conference presentation in 1986 and again in 1989. The original setup had a metal box on the tower with all coax relays inside. Every winter took its toll on the relays, and that idea was abandoned after many years of trouble. It was much too prone to relay failure with all the bad weather here in Maine. The latest version (2007) utilizes four phase matched 7/8" hardline runs: one to each yagi, with all the relay switching done indoors. Failure rate has dropped drastically. Indoor relays are a good thing!! We are currently evaluating antenna patterns at the new heights, and may come up with a new combination of choices.

The four coaxial feedlines were all calculated with a minimum dimension to reach each antenna position. To minimize excess cable laying around, exact multiples of full wavelengths were cut out of the shorter runs, while still maintaining the minimum length needed to reach the yagi in question. All of this trimming was done with the aid of a network analyzer. You could achieve the same results with careful measurement. Andrew heliax is very tightly controlled with stable velocity factors. The problem comes in measuring the overall length of a 140 ft cable. It is hard to do when the cable does not lie entirely flat! The network analyzer route proved to be a quick and easy method for achieving proper phase relationship between all four feedlines. In my case. I chose a minimum length for yagi #3, and added or subtracted wavelengths to the other runs so as to get them all to reach. With local signals, I am seeing about a 6 dB increase in all four yagis vs. the single top yagi, so I am assuming that I did not mess anything up!

In operation, it is very interesting to switch antennas during reception of DX signals. At times, the single yagi at 101 ft is almost as good as the four stack. It makes you wonder why you did all that work, but, then, a few seconds later, you check again, and see the top yagi down by about 15 dB. Having a vertical stack of six meter yagis really reduces the QSB that is so prevalent during Es or F2 openings. The effect is striking. On other occasions, beam uptilt can help quite abit. The choices we have here are 3 degrees and 9 degrees for all four yagis. The 9 degree uptilt eliminates power line noise. At times, the signals are as loud with the uptilt. (Or louder!) At other times, the uptilt is awful. It all depends on the particular opening. Generally, a fantastic opening includes higher angle arrival angles. Those weak squeaky openings involve lower angles. One of our ideas is to put a single yagi at about 20 ft all by itself, to get some very high angle reception. The results so far seem to indicate that the lower two yagis have a pattern not so different from the top two yagis. The arrival angle peaks are within 3 degrees for both. By having all of the relays and phasing/ delay lines mounted on the shack wall inside, any changes to the system are a simple matter. We may insert a delay line in the bottom pair to increase the arrival angle abit.

Top six meter yagi at 101 ft

One of the guy wires has been temporarily removed when this photo was taken.

The 2007 50 MHz antenna project finally renovated the six meter antenna system by replacing the old angle steel bolt together tower with a new Rohn 45, and installing ring rotors on the lower three yagis to allow full 360 degree rotation of the whole array. It is all running for September of 2007. This is the first 50 MHz improvement since 1998 when we went to the newer seven element computer designed yagis. The originals were CC 617-6Bs from the early 1980s. They had succumbed to a nasty ice storm in January, 1998. 4 1/2" of ice insured that all the VHF antennas ended up on the ground, or plastered against the sides of the towers. As of August, 2007, there are four yagis up again, and fully rotatable for the first time. The operating position was changed to allow for the extra rotor boxes and provide room for an extra WSJT computer.

This has been the first time that I have tried to use TIC Rings in any application. The usual spot for TIC Rings is at HF Contest sites where numerous antennas are side mounted on big towers. Very few VHF stations utilize them. I had some trouble with the bulk of the 22" diameter ring rotor detuning the elements on the six meter yagi. Due to mounting constraints and guy wires, the 3rd director was close to the ring and caused some detuning as the rotor turned. The problem was solved by building a suspended bracket that hangs below the ring and holds the antenna a few feet away from any metal that may try to detune things. I would recommend this approach when installing 50 MHz antennas on TIC Rings. One of my ring rotors is a 32" model (huge!) The suspended bracket works fine there too, and no de tuning is noticed.

BOTTOM YAGI WITH "HANGING BRACKET" AND 32" TIC RING.

In late June, 2007 with just half of the array completed, I managed to catch a nice European opening late in the afternoon on 50 MHz. For the first time ever, I could swing the second long yagi towards Europe as well as the top one. With the two yagis I knocked off about 115 stations in 15 countries in about an hour and a half. The SSB pileups calling were so intense, that they sounded like white noise! I had never experienced such numbers calling in past years with the single yagi at 90 ft. I received a few SWL QSL cards after the fact. One sport thanked me for being his first ever "across the pond" station heard, then he listed his antenna, a "CB Stick" one meter long situated inside his house. (on his refrigerator no doubt!). I will take that as proof that the antennas were doing something positive. (Memo to French SWL.....Get a real antenna!!) The final touches were put on the antennas the Saturday of the CQ WW VHF Contest. Art, K1BX operated the contest on six meters and put together a pretty good effort with 795 qsos in 179 grids on six meters. This was good enough to place at the top of the pile on six meters nationwide. Conditions were really hot for a few hours Saturday evening, but everything closed down on Sunday of the contest. It was a great test for the newly refurbished array. It performed brilliantly. On Sunday, with very little propagation evident, the array still managed to keep piling up the contacts in fine style. Many received comments were similar: "What are you guys using?" or "The band was only open to Maine all weekend!"

Getting the top nationwide QSO total and grid tally in a contest requires some luck with the propagation Gods. There was some luck involved in the CQ WW VHF Contest. A better test of an array is to compare your results with stations in your geographical area only and gauge how well you do compared to those stations. So far, the newly refurbished array is holding its own. The 2007 September VHF QSO party produced great results compared to other stations in New England, but the Northeast was not blessed with any Es or aurora, while the parts of the Midwest and South experienced some pretty fair Es openings.We placed a distant fourth in grid totals on 50 MHz, but still posted the best Northeast score against some stiff competition. In September of 2008, we managed to do quite well on 50 MHz with 82 grids worked with an apparently dead band. In every September contest since then, this new six meter array has scored at the top or near the top in total grids worked on 50 MHz. From Maine, that is difficult! That is a testimonial to the versatility of the antenna array.

September 2005, N2EOC strains to hear the weak ones with his Ten Tec Orion. although he looks as if he may also have a huge hangover. I am not sure which is the case. We had quite a learning curve with the Orion. Chuck, N2EOC loved it. The rest of us were reading the manual most of the time. It is quite a sophisticated radio and we managed to keep getting in trouble with it! Note the old "clunker" OMNI V and PS stuffed under the operating bench!

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Another shot looking at 210 degrees azimuth. The 50 MHz 7 element yagis are in the center, with the 144 tower in the background. The auxilliary microwave tower is off to the right, with single loop yagis for 900 thru 3456 in an "H" frame.

 

 

All four 7 element yagis in one picture! The microwave tower is on the far left.

The transmitter is a home brew triode PA running at 1500 watts. Since the station is set up for multi-multi, all of the stations may be transmitting at the same time, so harmonic distortion and spurious radiation must be minimized. I tried several six meter PAs before finalizing the current triode design. It has a five pole harmonic filter inside the PA shielded cabinet. All of the leads entering it are bypassed in an effort to minimize any spur radiation. Station interference is the big issue on a multi operator VHF Contest setup. If you do not solve the interference issue, you will never do very well. We have had no de sensing on other bands from six meters with the present filtering system built into the PA. . Any amplifier that is used in a multi multi environment must be protected against all sorts of operator errors as well. This latest amplifier includes a grid over current cutout circuit, a high voltage sensing circuit that prevents operation if you lose high voltage, an air pressure sensor to detect blower failure, and full sequencing of exciter, transverter, relays, and PA. Without all of the protection circuits, you are asking for trouble with many different operators and operating schedules that run all night! Bleary eyed operators at 2 AM do some weird stuff.

SIX and TWO METER POWER AMPLIFIER RACK

The uppermost panel with the large handles and two rectangular meters, is the six meter triode 1500 watt amplifier, with a companion meter panel just below it. There is a reflected power meter mounted on the left handle of the amp for checking the input tuning circuit of the amplifier. The amplifier started its life as a Henry 3000D on 13.98 MHz, but was rebuilt for 50 MHz in 2004. The amplifier was nicknamed The "Mother of Jesus" Amplifier by K1CA, when he saw it. It is very rugged looking! The 50 MHz transverter and Teletek solid state driver amplifier is just below that. The 50 MHz (MOJ-1) amplifier requires about 65 watts of drive for about 1500 watts output. A 144 MHz W6PO 8877 amplifier sits below the six meter equipment. It also has full protection circuits installed. Any loss of high voltage, excessive grid current, or loss of air will trip that amplifier off as well. There is also a high voltage fuse inside the amplifier. One valuable addition to all the amplifiers is our mouse proofing effort. All of the amps and power supplies are buttoned up with clear plexiglass, so that it is impossible for mice to do their thing on any of the components. There is nothing worse than mouse pee and worse in a bundle of wiring. That stuff corrodes aluminum!!

 

In 2006, we configured each VHF position with automatic voice keying from the laptop keyboard, along with CW generated by the keyboard as well. The voice messages are all stored on the computer as .WAV files. What is nice about audio files is that they can be edited and massaged to increase average power, remove pauses for breathing etc. As a back up, we have stand alone CW keyers at each position and both CW schemes are active in the circuit at all times. The automatic voice operation for CQing is a great improvement over previous years. We had rfi issues with audio from our old voice keyers, and they were not used much as a result. In addition to the voice keying, there are dedicated WSJT laptops for both six and two meters. In the first picture on this page, that depicts the operating position, you can see the WSJT/ FSK441 computer sitting on the shelf to the right, just above the logging computer. In recent years, it seems that FSK441 mode is getting more popular on this band during contests. Many people make random FSK441 QSOs in the late night hours.

In 2011, I spent the Summer ripping gear out of the shack and installing more insulation in the walls, and floor for a heating system. I installed paneling and a photo-voltaic power system with 12, 24 and 115 vac available all from solar power. A small propane heater and a solar hot air heater rounded out the installation and now my 6 and 2 meter ham shack is winterized with heat!