This document applies to the 6M7JHV only, not the 6M7JHV-HD or 6M7.

Two different shorting bar settings have been documented.  One has a deeper null around 50.330 MHz but sacrifices the VSWR below 50.100 MHz.  The second setting is a bit more flat with a 1.4:1 VSWR at 50.100 MHz  You can adjust the shorting bar position outside of the published settings to tweak the VSWR curve to fit your operating preference and to compensate for site specific interactions

Shorting bar position.  Measured outside of DE block to inside of shorting bar.

11.375"  - Optimized for FT8, 1.5:1 @ 50.100 MHz.

10.4375" - Broadband.  1.6:1 @ 50.000 MHz, 1.7:1 @ 50.500 MHz.

Disconnect one end of each loop.

Zero your multi-meter or note the error when the leads or shorted.

Measure from the center pin of the connector to the studs.You should have no more than 0.1 ohms to two studs on one side.

Measure from the shield of the connector to the studs.You should have no more than 0.1 ohms to two the other two studs.

Measure across the center pin to shield.This should be open.

Reconnect the loops.You should now have a short across the connector.

If you do not see these readings, there is a problem in the balun body.  If all of these tests pass, but you are still experiencing a high VSWR directly at the feed, you probably have water damage to one of the balun or phasing cables.

You can contact us directly at 559-432-8873 for additional support.

The M2 Antenna Systems, Inc. FGFD-2-LC-CC-1, Dual-Band feed is designed for either Prime-Focus or Compact Cassegrain configured reflectors. The Dual-Circular L-Band section can support power levels in excess of 100 Watts for transmit applications. Band coverage in L-Band is from 1.0-1.9 GHz (Customer Specific), using precision “N” connectors. The Dual-Circular C-Band section can support power levels in excess of 2 kW for transmit applications and covers the 3.4—4.8 GHz (Customer Specific) frequency range. The interface for C-Band is via the industry standard WR-229 waveguide flanges. Using proprietary Frequency-Selective Surface (FFS) designs, M2 Antenna Systems, Inc, can fit multiple feeds on beam, increasing the capabilities of new or legacy reflectors. If your project is pressed for time, The M2 Engineering staff is ready to assist in sourcing, selection and design of the RF front end electronics, LNA’s, LNB’s, BUC’s, Amplifiers, RF Cabling and referencing. Give us a call with your requirements today...we can help. 

Assistant Laboratory Manager

wb1gcm@arrl.org

The time had come to replace my three-element Yagi antenna for 6 meters. It was a homebrew affair, built during the remarkable solar peak of the late 1950s. The Alliance U-100 rotator that turned it was nearly asold and erratic. My wife, Kathy, KA1RWY, had bought the Yagi back in the 1980s for $20. The used rotator had been another $20, and the feed line was another $20. This $60 antenna system was only supposed to be a temporary arrangement, but as often happens, it ended up lasting for 28 years.

A new antenna was in order if we wanted to continue to enjoy 6 meters, which has many different propagation opportunities. After researching some new, good-quality directional antennas and rotators, I considered installing a loop antenna. The loop, mounted horizontally, does not require a rotator and provides an omnidirectional pattern. A loop is also lightweight and has a smaller wind profile than a Yagi and rotator, and is therefore easier to support. 

According to some antenna experts, using two loops, stacked, might give e close to the same gain as what my old Yagi offered — about 6 dBd (6 dB better than a dipole) — but on all points of the compass. Working stations 

without turning a beam during the VHF contests and roundtable nets that I enjoy sounded like it would work out pretty good, so I figured it was worth a try, and we ordered two 6-meter HO Loops and a stacking harness from M2 Antenna Systems.

The HO Loop is sturdy enough to go mobile, too. M2 offers a large magnetic mount for the enthusiast who never wants to miss a band opening. I didn’t try the mag mount, as I was mainly interested in a new antenna for my home station.

Arrival in the Lab

When the loops and power divider arrived, Pete Turbide, W1PT, found everything present (see Figure 3). Each loop is made out of two lengths of 3⁄8-inch OD aluminum tubing and is approximately 30 by 29.5 inches, weighs only 2 pounds, and has a surface area of 0.1 square feet.

On the feed point side, the loop halves come together at a feed block with an SO-239 connector for the feed line. The feed block is part of an impedance-matching assembly with a shorting bar for tuning. (See the accompanying sidebar, “M2 6-

Meter HO Loop: A Description.”) In the center of the opposite side of the loop, the two halves are fastened to a UHMW (ultra-high molecular weight polyethylene) tube, which forms a capacitor. A 3⁄8-inch aluminum tube attaches to the UHMW tube and angles down to a mast clamp to support the loop. Two compression-type clamps are used to attach the loop to a mast or tower leg, and stainless steel hardware keeps corrosion at bay.

The power divider assembly is made of two lengths of unspecified RG-8 size coax, 43" and 143" inches long, with PL-259 connectors, plus a T-connector where the feed line to the station attaches. 

Assembly Using the well-illustrated, step-by-step instructions (available for download from the M2 website), Pete had no difficulty assembling the loops and getting each one to match a 50 Ω transmitter output and transmission line. Most of my operating is from 50.090 to 50.400 MHz, so Pete adjusted the position of the feed block for a minimum SWR (1.1:1) at 50.2 MHz. If two loops are used, the feed assembly block must be reversed on the second loop to make that loop 180° out of phase with the other one. With the antennas built and tested, it was time to put them up at my house with help from Pete and Mike Gruber, W1MG. The ARRL September VHF Contest was coming up — a perfect opportunity to see how well the new system would work.

                                       

Figure 3 — The parts for one M2 6-meter HO Loop prior to assembly.                     Figure 4 — Mike Gruber, W1MG, and Pete Turbide, W1PT,

          put the finishing touches on the M2 6-meter HO Loop antennas.

I had to purchase a new 30-foot mast, with the intention of using the recommended loop spacing of 12 feet (top antenna at 30 feet, bottom one at 18 feet). All of my existing masts were “TV grade” 1-inch-diameter masts, but HO Loop mast clamps require a 11⁄4- to 2-inch diameter mast or tower leg. While good-quality 10-foot, 11⁄4-inch-diameter mast sections are reasonably priced, shipping charges to get three of them to my house would add $100 to the cost. In an attempt to be frugal, I purchased three 10-foot sections of 11⁄4-inch, galvanized metal electrical conduit and two couplers for $45 at a local home improvement store. Unfortunately, the mast bent a bit at each coupling point, and we were very lucky a coupler didn’t break when raising the antenna and mast. Guying the mast stabilized it, but we decided it was a bad idea. For a proper installation, I ordered three 10-foot sections of Rohn 11⁄4-inch mast from DX Engineering. Each section has a swaged end to fit into the next section for strength and is made of 16-gauge  galvanized steel. This created a solid, 30-foot mast, suitable for supporting two loops, a power divider, and coax cables at a cost of $168, shipping included. Figure 4 shows Mike and Pete finishing the assembly with the new mast.

On the Air

The installed HO Loops measured close to 1:1 SWR from 50 to 50.2 MHz (CW, beacons, and SSB) and 1.4:1 on 50.4 MHz (AM). That first evening, 6 meters was open to the south eastern US, with good signals for about 15 minutes. The

n the band closed abruptly (as often happens during sporadic-E openings). Over the next 2 weeks, I made several SSB contacts with stations around the northeast. 

On 50.4 MHz AM, I met up with an old friend — Mike, WA1MTZ — some 34 miles to the northwest, and he had time to carefully listen to my signal, generated by my 1959-era Gonset G-50 running at 20 W. I left the support mast loose enough so I could rotate it, and during our contact, I tried various orientations. We noticed that signal strength varied by 1 to 2 S-units as I rotated the antenna. Signals were strongest with the loops oriented so that the feed point and the insulator of the antenna were in line toward his direction. There could be a couple of reasons why this is so. As noted in the sidebar, “M2 6-Meter HO Loop: A Description,” the exact front-to-side ratio depends on the height above ground, and my lower loop is only 18 feet above ground. It’s also possible that proximity to the roof of our house and the metal chimney affects the radiation pattern. 

I always enjoy the ARRL VHF contests. Besides giving me an opportunity to speak to friends, the contests are excellent occasions to test equipment and antenna systems and try to beat my own last contest score. This time around, I ran 150 W into the HO Loops, which put me in the low power category for the event. Note that a pair of HO Loops is rated to handle 1.5 kW PEP (800 W for a single loop). 

Unfortunately, there was no ionospheric or tropospheric enhancement during the event. With terrestrial propagation only, I was able to hear quite well and contacted 60 stations in 13 grid squares. Based on previous experiences, I’d say the results with the loops were comparable to my old three-element Yagi in terms of distance and signal strength.

Advantages and Disadvantages 

A single loop or stacked loop system is a good option for use on 6 meters. The advantage is being able to hear equally well in all directions. The HO Loops antenna system makes a good listening antenna for the serious 6-meter operator who doesn’t want to miss a band opening because the beam is pointed in the wrong direction. Overall, the biggest advantage of using the M2 HO Loop system is that no rotator is required. Usually, my rotator gets a workout during a contest, and sometimes the station I’m after is gone by the time the antenna is pointed in the right direction. With the growing popularity of FT8 and other weak-signal digital modes, long-distance communication on 6 meters is possible more often than ever before. An omnidirectional antenna, such as the HO Loop, would be ideal for this mode, especially when you have no idea where signals might be coming from.

A disadvantage of omnidirectional loop systems is man made noise, which cannot be minimized by rotating the antenna away from the noise source. I am fortunate to have a reasonably low noise floor on 6 meters. 

The two HO Loops and power divider reviewed here cost $505, not including the mast. That’s about the price of a good rotator and one of M2’s three element Yagis for 6 meters. The most expensive component of the stacked HO Loop antenna system is the power divider, at $189. If you’re handy, you might be able to build your own power divider.

Overall, I give M2 good marks on quality. It looks as though the loops will last at least 28 years, too. Manufacturer: 

M2 Antenna Systems, 4402 N. Selland Ave., Fresno, CA 93722; www.m2inc.com. Price:6-Meter HO Loop, $158 each; Two-Port Power Divider Kit, $189.

**Published with permission of the ARRL**

1.If you are testing an antenna for the first time after assembling it from scratch or have refurbished a used antenna, it never hurts to use your Ohm meter and test for good continuity across each joint.

2.Set your Ohm meter on the lowest resistance range like 0 to 200 Ohms. Short the leads together and note the reading. It may not be 0.00 but it should be below one Ohm. Note this reading and be sure it is repeatable over 4 or 5 tries at shorting the leads together. Some meters drift slightly during your measurement time, so check your “shorted leads” reading every so often. If your readings are inconsistent or vary wildly you may have a poor connection at the meter itself or you may be picking up nearby AM broadcast RF. Correct the lead connection problem before continuing. To eliminate RF pickup, try some ferrite beads or snap on ferrite slugs on your leads as close as possible to the meter itself. For a quick test to see if RF is an issue, short the leads and fold them up in some aluminum foil. If the wild fluctuations stop, it means you should deal with the RF before you can continue

3.Now you can proceed checking the “continuity” across each joint. If the reading is over 0.10 Ohm more than your shorted lead reference reading, be suspicious. Make sure your lead tips are touching clean metal. It may sound silly, but most antenna problems can be found with JUST your Ohm meter. Be sure to take the visible reading instead of listening for the meter beep. Some meters beep even with several Ohms of resistance. Any resistive joint in an antenna can spell disaster or very poor or lousy performance.

4.Next, if all the joints are solid, you can try a simple RF listening test. Even if you have the antenna just a few feet above ground on wooden or plastic saw horses, it should sound quite lively with increased noise and signals when the feedline is attached to a receiver or transceiver. You can’t run F/B measurements, but you can listen a bit and if possible compare it to other antennas you may have. You can attempt to check the VSWR with a bridge, wattmeter or analyzer but don’t expect perfection. If possible, sweep across the frequency range plus some on either side of where the antenna is supposed to work. You should see that some peaks and nulls or more pronounced with better VSWR readings “in band” than way outside the band. Of course, it is important to know you have a GOOD piece of 50 Ohm coax for this test setup.

5.If you like what you have seen so far, it may be time to raise your HF antenna to 10 to 15 feet (4 to 7 ft. for VHF or UHF) over ground and repeat the VSWR check. Perhaps the antenna can be side mounted on your fixed tower or on top of your lowered crank up. At 20 to 25 feet over ground, on 20M and higher, you should start to see the VSWR curve take the correct shape. You should see much higher VSWR outside the band than in. Again, a receive test is always helpful and even cranked down at 21 to 25 feet, a F/B check can tell you if the antenna is looking promising.

6.If rotation is possible, you can also watch the VSWR change a bit as the antenna is pointed at or away from large nearby objects. If the VSWR is very good or acceptable at some in band frequency, this is a good sign even though the match may not be exactly where you want it. In a three element beam for instance, the reflector influences the lower end of the band and the director can pull the match to the high end. It may be helpful to think of the two parasitic elements in a tug of war with the driven element being the middle line in the battle. If you could somehow short out the director for a moment you would probably see the VSWR curve slide down a bit. Same thing if the reflector is momentarily shorted out, the VSWR curve should slide up a bit. If one or the other parasitic elements are not working properly or on the wrong frequency, this may cause the VSWR to be off a bit in frequency. This is not always the case, because the driven element could be off one way or the other and have a similar effect. It helps to know what affects what to analyze where to look for a potential problem.

7.The height over ground can also have some affect on the VSWR and where if is in the band. Generally, as you increase the height over ground, the antenna’s match and performance will move slightly higher in frequency. In most cases the match or VSWR was probably optimized by the manufacturer at a good working height of at least ½ wavelength of more. So, if your tests and measurements have been good up to this point, the next step may be to raise the antenna to it’s final working height and hopefully take some final measurements. This is much easier if the antenna is mounted on a crank up tower. If you are not happy and confident of your readings at 20-25 feet, don’t put the antenna all the way to the top of your fixed tower until you have made some more tests and measurements. Perhaps just raising it another 10 feet will give you numbers that look good. If nothing is jiving, it is probably best to get the antenna back on the ground and go over your measurements and assembly manual another time. It can be very helpful to have another person look over your shoulder to double check your efforts.

It is important to note that antenna gain is different than amplifier gain. Antennas do not have a power source that allows the antenna to create additional energy to boost the signal. An antenna is similar to a reflective lens in principle - it takes the energy available from the source and focuses it over a wider or narrower area.

Antenna gain is then a measure of the amount of focus that an antenna can apply to the incoming signal relative to one of two reference dispersion patterns. Digi specifies all antenna gains in dBi.

dBi is the amount of focus applied by an antenna with respect to an "Isotropic Radiator" (a dispersion pattern that radiates the energy equally in all directions onto an imaginary sphere surrounding a point source). Thus an antenna with 2.1 dBi of gain focuses the energy so that some areas on an imaginary sphere surrounding the antenna will have 2.1 dB more signal strength than the strength of the strongest spot on the sphere around an Isotropic Radiator.

dBd refers to the antenna gain with respect to a reference dipole antenna. A reference dipole antenna is defined to have 2.15 dBi of gain. So converting between dBi and dBd is as simple as adding or subtracting 2.15 according to these formulas:

• dBi = dBd + 2.15
• dBd = dBi - 2.15

Specifying antenna gain in dBd means that the antenna in question has the ability to focus the energy x dB more than a dipole.

Beam Width

Because higher gain antennas achieve the extra power by focusing in on a smaller area it is important to remember that the greater the gain, the smaller the area covered as measured in degrees of beam width (think of an adjustable beam flashlight). In many cases a high gain antenna is a detriment to the system performance because the system needs to have reception over a large area.

1. A round plate model will fit inside Rohn 25G, but the mast clamp bolts need to be cut down or the diagonal braces bowed out slightly to clear the bolts when rotating. This is for mounting inside a “straight” section. Installation is challenging, but it will fit and rotate. (M2 report)

2. Hygain HG-52SS: A round plate model fits. (TNX W2YR). It looks like an oval plate model might fit also. (M2)

If you know of any towers that have no issues and not listed below, or even ones that will not work, please let us know by either calling us at (559) 432-8873 or send us an email to sales@m2inc.com.

The following is documented in the OR2800PX Manual; Standard Ham M etc. 3” x 3” bolt pattern +2 extra holes (OR2800PX Hole Pattern). Fits inside towers like Rohn 25G & up, Triex LM-354 & up U.S.Towers TX438 & up.

COMMON ANSWERS TO COMMON QUESTIONS

QUESTION: When measuring tube or shorting bar position, “where do I measure from, inside to inside or outside to outside?

ANSWER: Refer to your individual element dimension sheet. It is much easier to determine witch side of the tube or shorting bar to reference. Note: M2 has used to two inner shorting bars as points to hook your tape measure onto for ease of measuring, so generally hook your tape measure on to a inner shorting bar and measure to the inner edge of the outer shorting bar or to the end of a tube. 

QUESTION: Is the gap between the capacitor caps critical?

ANSWER: No, the gap can be 1/8”-1/2”. The reason for the gap is to prevent water from sitting in a location where water could over time “wick” into the capacitor tubes. Water in the capacitor tube can change the capacitance witch can change the tuning of the antenna.

**IMAGE FOR REFERENCE**

QUESTION: If I end up with some unacceptable VSWR on one or more bands can I adjust it out with the “T” match?

ANSWER: No, In fact this is not a true “T” match. We found in the early stage of the original design that only a small amount of VSWR improvement occurred when we adjust the “T” match. Just set it to the dimension sheet and forget it. Other factors are causing your VSWR problems. Recheck your dimensions.

QUESTION: I have a good, but not perfect VSWR, Will it help to replace the balun?

ANSWER: Probably not. If your balun is broken inside your match will be poor ( up to 4:1) on all bands. Save your money, recheck your dimensions.

QUESTION: How can I be sure I have the capacitor caps on the tube all the way?

ANSWER: The capacitor caps over lap the tubes by 3/8” (.375) so when both caps are fully engaged with the tube the dimension from the inside of each cap should be 3/4”(.750) less than the capacitor tube being measured.

QUESTION: I am doing a upgrade to my KLM Tribander. Do I need to replace the capacitor tubes?

ANSWER: If you are purchasing the UPGRADE KIT, KT34XA to KT36XA the capacitor tubes are provided with the kit.  However if you are purchasing the UPGRADE KIT, KT34(A) TO KT34M2 they are not included.  You will want to check your existing tubes to see if they can be cleaned up.  However if they are damaged or not able to be refurbished you will need to contact us us for the cost of replacing them.

QUESTION: If I am having a problem on a specific band of my tribander what part of the antenna element do I look at?

ANSWER: You will want to follow the path on each half element. Please see the image below for reference.

     Having built linear loaded 80m Yagi’s since 1980, I know the concept works. I physically modeled the first dual driven, linear loaded 4 element Yagi at a frequency of 144 MHz. Scaling the element sizes was difficult but I was able to optimize spacing and linear loading location. Once the model worked at 144 MHz, I then measured the resonance of each element individually and scaled the results by 38:1 and I had a full size starting point. It turned out to need very little tweaking.

     The first 80M4ll was built for Arnold Tamchin, (W2HCW). Arnold wanted 20dB front and back and that is what he got. He wanted good bandwidth and the dual driven element and I gave him just that. Elements ended up at about 94 ft long and the boom was 76 Ft. Big? Yes, did it play? Yes, enough to make Arnold gush! I put up the same thing on the West Coast and started working for Europeans reliably in the dx window at 3.790-3.800 SSB.

     Now along comes “Computer Modeling”. Fortran based in the beginning and then in basic. Nec and mininec followed and Brian Beezley. K6STI produced YO (Yagi Optimizer) and AO (Antenna Optimizer), mininec based programs. Roy Lewellen (W7EL), followed with eznec and elnec, nec based programs.

     This started a modeling frenzy. There was one problem however, nec based programs do not model linear loading accurately. But many modelers using nec based modeling built linear loaded antennas and found they did not work?? Substituting coils for the linear loading did the job however.

     I was the proud owner of many versions of YO and AO. Linear Loading in mininec based programs does work so many linear loaded antenna designs followed with good performance results. Some others built linear loaded antennas as well but for many reasons they did not work well so linear loading started to lose its credibility. All sorts of half baked theories filled the airwaves about current cancellation and whatever caused the loss of front to back and again.

     To most antenna designers coils seemed like the logical solution. Mechanical design issues are important with both coil and linear loading designs. Efficiency is a serious issue when doing a coil design. A Few perceptive designers realized quickly that coil Q was extremely important, particularly at 40M and 80M! 160M is another story for another time.

     Here is an interesting side note. When coils are used in a dipole the coil Q is not much of a factor when related to efficiency. Poorly designed coils still work reasonably well. But, when the dipole placed, physically and electrically, close to another similar element, the current in the element goes up dramatically and losses can completely kill the gain! If the modeling program either does not calculate final efficiency or the modeling ignores it, the low Q coil design looks great but it doesn’t work well in the field.

     Linear loading is much less critical to wire and tubing diameter losses but it still does show up once the antenna becomes a parasitic, directional structure.

     So to put this into perspective, extensive modeling with AOP (antenna optimizer, professional) shows that linear loading designs using decent diameter loading component work very well and are very efficient. Coil loading using wire size and fabrication techniques that maintain a Q of at least 300 works very well and are very efficient.

     The results of the multiple years of simultaneous, on the air testing shows no detectable difference in forward gain or front to back performance using linear loading on one antenna and coils with a Q of 500 on the other antenna.

     Modeling of each antenna showed virtually identical results meaning gains within .2 dB and F/B of 24 dB plus/ minus 2 dB. So it comes down to personal choice based on your local weather and esthetics.

     The new concept in the coil fabrication that Matt Staal here at M2 came up with allow us to machine the coil from 1/8 wall aluminum tubing leaving a ½”solid tube section on each end of the coil. This makes for extremely low loss, high reliability coil to element connections, because the machining is accurate, the inductance value is the same from one coil to the next.

     It is one thing to wind a high Q coil on very good, low loss dielectrically only to see that beautiful coil compromised with small area, dissimilar metal connections to the element sections.

     The physical covering and joining of the coil to the element is equally important to longevity and performance. M2 coil ends are CNC turned from 4” diameter aluminum billet and further CNC milling to remove excessive weight. A special 360 degree clamping connection insures maximum strength and reliability of the joints. Internally the coil floats on 4 thin strips of machined polyethylene, internally threaded, cover. This fabrication technique is a bit pricey but produces an almost indestructible inductor.

the national association for Amateur Radio® www.arrl.org

Reviewed by Jeff Klein, K1TEO

wa2teo@aol.com

About 5 years ago, M2 Antenna Systems introduced a high power solid state amplifier for 6 meters (model 6M-1000) capable of a full kilowatt of output. It was lightweight and small, making it usable both at home and for portable operations. Later they came out with a higher power 2 meter solid state amplifier called the 2M-1K2. I had a chance to review that amplifier and came away with a favorable opinion.4 Now there is a 6 meter version that is similar to the 2 meter version in look and capabilities the 6M-1K2. It is capable of delivering up to 1250 W of output, uses a 50 V dc supply that can be purchased integrated with the amplifier or added on separately, and like its predecessor is relatively lightweight and small.

Overview

The M2 6M-1K2 is a compact amplifier, measuring just 6 × 7.125 × 13.4 inches (height, width, depth) when set up without the optional internal power supply. When configured this way, it weighs 13 pounds. When the optional 2400 W switching power supply is integrated, the package grows to 9 inches tall and weighs 20.5 pounds. This makes it easy to use for DXpeditions or portable operation. We opted for the amplifier/power supply package for this review. In my station, it takes up about the same room as a desktop transceiver.

The amplifier uses a single Freescale LDMOSFET, an MRFE6VP61K25H, to generate power. The device can be driven to full output with about 5 W. Because most of us have transceivers that run significantly more power, M2 has set the amplifier to be driven with 50 – 100 W of input by using a built-in attenuator to achieve the correct drive level. 

To run the optional internal power supply, a 240 V connection with a 15 A maximum is required. If you want to use a different supply, it will need to provide 48 – 50 V dc at about 40 A. 

Front Panel

The front of the amplifier has three switches and five lights that allow the operator to monitor and manage the status. The POWER switch controls the integrated power supply and turns on the 50 V dc. The amplifier can also be placed in or out of line using the READY switch. 

The final switch on the front panel is to place the mode in or out of “JT mode.” JT is shorthand for WSJT, the software commonly used for weak signal digital communications. In JT mode, the amplifier runs closer to Class C, operating cooler and more efficiently for high duty cycle modes such as WSJT and FM that don’t require linear amplification. In JT mode, the rated output drops slightly as the drain current drops from the about 36 A to about 30 A.

The amplifier is protected from both high SWR and overheating. If the SWR is greater than 2.5:1 at the output, the amplifier will shut down and the VSWR/TEMP LED on the front panel will illuminate. If this condition occurs, you can recycle the amplifier quickly by toggling the READY switch to reset the amplifier.

If the amplifier overheats, the same VSWR/TEMP LED will come on to indicate the fault. The instructions say that this condition is “very rare” and if it does occur you should let the amplifier cool for 30 minutes before trying to operate. My operating included several high-intensity periods where the amplifier was used at maximum power with continuous SSB or CW transmissions for up to 2 hours. I was curious to see how hot the amplifier got. The amplifier has two fans on the lower front panel to cool the internal power supply and two on top above the heat sink on the RF section. Though a little noisy (more on this later), they worked effectively to keep the amplifier cool. Even after lengthy usage the heat sink, accessible from the back of the unit, was no more than warm. My experience seems to confirm that under normal operating an overheating situation should be unusual.

Rear Panel Connections

The rear of the unit has two chassis mounted N female connectors for the RF input and the RF output. As I noted in my earlier review of the M2 2 meter amplifier, neither connector is marked, though they are clearly shown in the instructions.

Keying the 6M-1K2 requires a path to ground through a phono jack on the rear of the unit. Keying the amplifier throws the built-in input and output relays. This is done with a built in 15 – 20 millisecond delay (per the instructions; ARRL Lab testing showed the delay to be 12 ms) to be sure the relays are closed before bias voltage is applied to the gates of the LDMOS device. This is a nice feature to help protect external preamps. In my case, I used my receive preamplifier without a sequencer and this delay did work to protect my preamplifier. I’ve damaged it in the past when I’ve used it without a sequencer with other amplifiers.

The other major connection on the back panel is for an external ac power cord when the amplifier includes the built-in power supply. Otherwise there are #10 AWG power leads to hook up an external 50 V supply.

There is also a terminal strip with a number of connections. Two of the screw terminals, connected at the factory, supply 28 V dc to the top cover fan. There is also a connection point for an external relay key return if the operator is keying external components. Another connection point supplies +13.6 V dc at 500 mA, convenient for hooking up external relays and preamps. In my case I didn’t have a need to use any of these connections but they are nice features to have available.

A fuse is also accessible from the rear panel. It protects the internal regulator and components.

Documentation

The M2 6M-1K2 includes a 19-page printed manual that covers installation, a review of the features, and troubleshooting. It also includes a helpful overview of the theory of operation as well as block diagrams of the amplifier’s components and one showing a typical installation. To assist with troubleshooting there is a full schematic of the RF section and another of the control board. For those not familiar with WSJT, there is an addendum that provides information about the mode, use of the software, and references on how to obtain the software

online.

The instructions are clearly written and should provide the information needed to get the amplifier on the air and help the user understand all of the available features.

Setup

Getting the 6M-1K2 on the air took just a few minutes. Since the test unit came with the built-in power supply, it was merely a matter of plugging in the ac cable that came with the amplifier to provide 240 V. As I already use an external amplifier on 6 meters, the next step was to move the coax from the transceiver to the M2 amplifier and likewise move the amplifier output coax over as well. I key my current amplifier in the same way as the M2 amplifier (ground to transmit) so once the RCA jack was connected I was basically good to go. That was the extent of the setup simple and fast!

If you’re not currently using a high power amplifier on 6 meters, be sure that anything connected to the output has an adequate power rating at this frequency. Coaxial jumpers, feed lines, wattmeters, antennas, and so on all need to be able to handle 1200 W or more.

Using the Amplifier

I drove the amplifier with my Kenwood TS-2000 transceiver which has a digital power indicator. I found that at about 80–85 W input from the transceiver I could achieve the maximum amplifier output as measured in my shack with a Bird wattmeter. I did not notice any significant difference on SSB or CW. The same was true when using WSJT with the amplifier in JT mode. Testing in the ARRL Lab (see Table 6 and Figure 13) showed that 90 – 100 W is needed for full output. It also shows that the amplifier output is only modestly different when running with JT mode switched on. I have used several high-power solid state amplifiers and continue to enjoy the instant on (no warm-up period) aspect. This amplifier is no exception once the POWER and READY switches are thrown the amplifier is ready to use.

Once you turn the amplifier on, you will hear the lower fans come on immediately. They do so with some significant noise and then quickly drop to a lower level. However, during transmit, the fans speed up again to increase cooling, and the fans on the top of the amplifier come on as needed. In JT mode, the fan comes on as soon as the

amplifier is keyed.

Operation

I had a chance to put the 6M-1K2 through its paces in several contests, including the Spring 6 Meter Sprint contest, the ARRL June VHF Contest, and the CQWW VHF Contest in July. I kept the amplifier at or near full power output in each event, and it performed flawlessly. Over-the-air reports were just what users would want inline or out, my signal quality was the same. With its significant cooling capabilities, the amplifier was never more than slightly warm, even after extended periods of WSJT and CW operating. 

If there was one minor concern, it was the amount of fan noise the amplifier generated. When transmitting, the fans tended to race and, though not loud, it was a bit distracting when I operated without headphones. I situated the amplifier on top of my existing 6 meter tube amplifier, close to my operating position and at about head height. That was convenient to allow me to easily use the existing input and output cables as well as the PTT line. That had some impact on the noise generated. If I was using this amplifier on an ongoing basis I would probably locate it farther away because there are no meters to monitor. As long as I have a power output meter in line and viewable, I can confirm the amplifier is working. Of course, it probably shouldn’t be too far away if you want to switch to WSJT mode conveniently when desired. The amplifier switches to JT mode automatically after 5 seconds of continuous duty operation.

Final Thoughts

Overall, I would give the M2 6M-1K2 high marks for its performance. It delivered the power level as expected. Very importantly, it had a clean signal, something critical when operating with nearby stations at this power level. It was about as easy a setup as you would hope to have with a high-power amplifier. On top of that, it would have been very easy to take this setup portable. As with the 2 meter version, I came away with a highly favorable impression of this amplifier and think it would make a valuable addition for any serious 6 meter operator.

Manufacturer: 

M2 Antenna Systems

4402 N Selland Ave

Fresno, CA 93722

tel 559-432-8873 

www.m2inc.com.

Click <HERE> for PDF version of this article

Republished with permission from November 2015 QST ARRL, 

the national association for Amateur Radio® www.arrl.org