By Dave Jensen, W7DGJ

Going portable is a blast, right? I can't count the number of times I've awakened with a smile on my face knowing that after my coffee I'd be loading the car for an upcoming trip to our Arizona back country. But as you know, there's a limit to how much gear you can carry along. While it may be OK if I was to work from a park bench, my amps stay at home. The focus for POTA, and certainly for SOTA, is on keeping it lightweight and easy.

That's why the big guys stay in the shack. Instead, most serious outdoor activations are restricted to either QRP operation or perhaps a compact transceiver like the ICOM IC-705 or Yaesu FT-891. I've never run into anyone running a linear amplifier on an outdoor mission, unless it is a DXpedition or a show-off at Field Day. Truly remote stations absolutely need the signal boost due to their distant locations but getting there can be quite the struggle with those bruisers from the old-line amplifier companies.

Perhaps the new LITE from KM3KM Electronics will also be of interest to outdoor enthusiasts or POTA participants. (The photo to the left is a shout-out to my YouTube friend Jason, except I can't get the goofy grin.) KM3KM Electronics is a company founded by ham operator Kenny Martinez of Florida who has been profiled in this earlier T&E edition. Martinez thought that there was a need for a lighter, battery operated solid-state linear amplifier with a small footprint -- one enjoying the same features as some of his more expensive products (such as the Mercury IIIS or the full legal-limit amp, Mercury LUX).

I've now had a chance to work with the Mercury LITE, both from my home shack as well as from a park bench. It's clear that this amplifier changes the landscape of portable operations; QRP operators may wince as I say this, but for many, the promise of making a step change in the number of QSOs from their field trips is intriguing.

It appears to me that the LITE is built with the same kind of care and concern for ease-of-use that has made Martinez's other designs so popular.

However, I was initially skeptical about his choice of power for this amp (48v using e-Bike batteries). I've changed my mind on that one after using it in the field. In fact, someone should have thought of this earlier. Batteries like these are very commonly available and built to be long-lasting . . . here they provide a solid 8 hours of use (or more) in continuous SSB, with a lifetime that is generally over a thousand cycles. The LITE specs out at 600W output in all modes through the use of two MRF300 LDMOS, and after my testing, I can state that KM3KM's specs are quite conservative (in most cases, max output was 10% over the KM3KM specs).

In my testing, I've combined this new amp with a terrific antenna -- a "classic" at my shack. The HexTenna by Alpha Antenna was introduced in 2019. It's still the cream of the crop in the collapsible metal whips category. I've tried the Aliexpress whips and they pale in comparison. At QRZ we use it for many tests of reviewed equipment, primarily because of its quick and easy deployment and all-around resonance.

Power handling on the HexTenna is a good match for the LITE amp . . .  I use it all the time at a Kilowatt-plus, so I knew that 500 or 600W would be comfortable. The HexTenna operates from 2m to 40m and is infinitely adjustable -- for 40m, a clip-on wire extension is required. With the Mercury LITE's built-in antenna tuner, I simply needed to rough it in and the amp took care of the rest. In that way, 10 minutes into my setup I had the antenna up and ready.

The KM3KM Mercury LITE Specs and Design Details

While the Mercury LITE is substantially smaller than most other amplifiers, it still adds 14 lbs to your kit. It's dimensions are 7"W x 4.5"H and 11" D, which is really tiny for an amp in its class. Compare that to the next smallest, the ACOM 500 (reviewed in these pages) which is several pounds heavier (11.5"W x 6.2"H x 19.7" D) and significantly more expensive. ACOM chose to make theirs wide, while KM3KM put the footprint into a skinny-but-deep configuration.  That makes it more accommodating to your shack shelves. 

When you add the 48v e-Bike battery, you may need a "go crate" instead of a go-bag. Still, think about this in terms of what we know about powerful amplifiers . . . the amp I had until recently was an Ameritron AL-80B, and I almost broke my back packing its 50 pounds into a box for the new owner. The Mercury LITE, the ACOM 500S, Mercury IIIS, and other solid state linear amps have made this heft a thing of the past. While the LITE and it's battery will mean it is out of the running for most SOTA expeditions, I forecast that this amp will make a big impact on other kinds of portable ham stations.

In my day-to-day use, I have it on my desktop with its battery for a station centered around my Discovery Labs TX-500 and ICOM IC-7100, both of which have available amp keying cables. After every few days of use, I plug it into its trickle charger and refresh it so that it's back to its 8-hour operational status (continuous rag chewing on SSB). I haven't yet been troubled by the fact that this amp doesn't include a desktop 48v power supply, as it is intended to be primarily a portable amp. Contesters using the LITE may want to acquire a second battery to make quick swaps when necessary, while others may purchase a DC power supply. I investigated these on Aliexpress and eBay and they run from $100-200 or thereabouts.

The battery that I bought from Amazon taught me a lesson . . . there is more than one version of the "e-Bike yellow plug." Just as we have BNC and PL-259's and so on in our hobby, for the e-Bike hobbyist they have XT60's and XT90's. Just make sure you are getting a battery or power supply terminated with an XT60, or be prepared to do some soldering or buy an adaptor. For me, I am vision impaired and terrible with a soldering iron. These kinds of batteries are available as well on eBay and on AliExpress.

Use Experience

Everything felt different outdoors with the LITE.  600 watts can make a heck of a difference when you are sitting in a park. For me, while I didn't activate a POTA location, I sat on a local park bench and blew myself away with the ease of reaching distant stations. After all, 600w is a big step . . . while it's not a Kilowatt, it's close enough to have much of the same punch. I felt like I was knocking it out of the park, consistently reaching 600w out on 10, 12, 15 and 20 meters that day.

My only real negative was that, to these aging eyes, the screen didn't get bright enough for me to be comfortable seeing everything properly in the daytime. By early evening I had no issues. That Arizona sunlight made it difficult to read during much of the day. 

Other Comments, Pros and Cons:

- The Internal Tuner works like a champ. I wouldn't be surprised if Kenny used the same algorithm from his very successful ATS freestanding tuner. The HexTenna will resonate on just about any band, so I switched over to my Buckmaster OCF Dipole (much fussier) to test the tuner. This antenna states specifically that it can not be used on 15m. I was able to get an SWR of over 5-to-1 down to 1.3-to-1 in a few seconds, and I enjoyed a number of QSOs at full power on 15m with an antenna that isn't intended for that band.

- The amp has a setting that allows a low powered QRP radio to drive it to its full output. If you have 5 or 6 watts, no problem . . . you'll be operating with 600w output. But that setting needs to be carefully observed. It's very nice to have the ability to use a standard transceiver with the linear and get full output but for that there's a different setting. While the amp has all the protections you'd expect, there's still a serious warning dialog for you when you turn the low power exciter feature on. In that position, 10w is tops. It didn't take long to get used to this, but it's something you need to be careful with if you use the amp with multiple radios. KM3KM has it set so that upon start up the amp is always in the higher power input position (which makes sense from a protection standpoint).

- There's no 160m on the amp. I'm not a fan, so it makes no impact on my shack. And, I don't think there's a lot of action with portable stations on 160. That would be one hell of a whip antenna.

- The offered warranty is, in my opinion, the best in the business.  Shipping from Florida is safe due to the terrific "box within a box" packaging system that KM3KM uses. Retail price is just under $2000.

Conclusion

I can't imagine going out into the field at this point without the Mercury LITE. They are going to have to pry this thing out of my hands. While I reviewed a final design model, production has now begun and availability will be in May . . . as with other KM3KM products, there's going to be serious demand and you might want to check back with their web page regularly.

73 for now! Won't you please add a comment or question to our forum below? That's how we measure audience interest in the topics here.

Dave W7DGJ

[PS - Added later . . . I got completely nailed by two Facebook forum groups after I published a short statement about this amp. No one believed me. I didn't use links or even mention the product name, as I wanted to follow the rules. That's how different and unique this amp is. Two aspects of the amp, the exciter input selector that allows you do use either a QRP rig or a standard transceiver, and also the 48v power with eBike batteries . . . those two features are very unique (as well as the size). I like unique stuff here and will continue to report on new FCC Certifications as I watch that closely.  Please add your comments to the forum. --D. Jensen]

Have a comment or question? See what others are saying now in our Forum discussion!