How to tune: Pairing the Emtech ZM-2 manual ATU with the Mountain Topper MTR-4B on the Blue Ridge Parkway

You’ve no doubt heard me brag about the Emtech ZM-2 ATU in previous field reports. I think it’s an accessory every field operator should have.

The ZM-2 is a very capable manual transmatch/ATU and is also one of the more affordable tuners on the market. It’s available as both a kit and a fully-assembled unit. Both well under $100.

I do believe the “manual” part of the ZM-2 scares off some and it really shouldn’t. We are used to simply pressing a button these days and allowing our automatic ATUs to do all of the matching work for us.

Manual ATUs do require some amount of skill, but truth is, the learning curve is very modest and intuitive.

Manual ATUs require no power source in order to operate–you adjust the L and C values by hand–thus there’s never a worry about the ATU’s battery being depleted. They also are easy to manipulate outside the ham bands because they require no RF in order to read the SWR–you simply make adjustments to the L and C until you hear the noise peak.   This is why many shortwave broadcast listeners love the ZM-2 so much. It’ll match most any antenna you hook up to it!

I also argue that everyone should have a portable ATU even if you operate resonant antennas. Think of an ATU as a First Aid Kit for your antenna: if the deployment is less than ideal, or if you damage it in the field, an ATU can help you find an impedance match your radio can live with. ATUs have saved several of my activations.

Mountain Topper MTR-4B V2

I’ve also mentioned that I’ve had an MTR-4B on loan from a very kind and generous reader for most of the year. He was in no particular hurry for me to send it back to him, but I wrote him in early November and said, “I’m doing one more activation with this little rig, then I’m shipping it to its rightful owner!”

He had a request, and it was a good one:

I think it would be a good little twist to the usual YouTube if you paired a random wire with the ZM-2 and the MTR-4B…showing how to tune the ZM-2 with a Mountain Topper…

I really liked this idea, so I made plans to to hit the Blue Ridge Parkway nearby and give it a go.

The first time I tried this in the field, I paired the MTR-4B with one of my Sony amplified speakers because the MTR-4B 1.) has no internal speaker and 2.) has no volume control. During the video, however, I realized that there simply wasn’t enough audio amplification so that the viewer would be able to hear a noise peak as I manually tuned the ATU. I decided to scratch that video and just do the activation on my own. I really wanted to show how the tuning process worked in the video.

I went back to the field the next week–on November 10, 2022–with my Sony in-line digital recorder knowing it would be much easier to hear how the L/C changes affected the band noise.

Blue Ridge Parkway (K-3378 NC)

Hazel decided to accompany me on this activation.

Actually, she’d join me on each of my activations if I could allow that!

She’s particularly fond of the BRP site I chose–the Folk Art Center–because of the abundance of squirrels running around. Poor thing, though: a leash prevents her from chasing them. It’s more like squirrel TV for her. 🙂

Other than squirrels, we pretty much had the whole place to ourselves (mainly because it was a very rainy day).

First thing I did was deploy my Tufteln 9:1 random wire antenna. I use a 31 foot radiator and 17 foot counterpoise with mine. I find that combo can typically take me from 60-6 meters with most ATUs.

Next, I set up the MTR-4B in a way that would protect it from getting wet if the heavens were to properly open. I used my GoRuck Bullet Ruck as a dry place to nest the MTR-4B.

Note that I used my 9V 3Ah LiFePO4 battery since I knew I might be transmitting with a high SWR for brief periods of time while demonstrating the ZM-22. With the MTR-4B, if using a 13.2+ volt battery–which is fine with the MTR-4B (not 3B) the match needs to be a good one.

In the activation video (see below) I demonstrate how to put the MTR-4B V2 into “straight key mode” so that the LCD display will show not only the SWR but power output as well. The MTR-4B must be in straight key mode to show the SWR.

Next, we tune the ZM-2–again, it’s all in the video, but you can also read a quick tutorial on tuning the ZM-2 in this post.

Time to hop on the air!


On The Air

I first hopped on 20 meters, started calling CQ POTA, and within nine minutes, I worked the 10 stations necessary for a valid POTA activation. Woo hoo!

I worked three more stations on 20 meters, then moved to the 40 meter band (QSY) which required re-tuning the ZM-2.

40 meters was very healthy! I worked an additional 22 stations in exactly 22 minutes!

What fun!

Here are my paper logs:

And, of course, since I used my pricier Rite in the Rain notepad, the rain held off during the entire activation! Never fails!


Here’s what this activation looks like when plotted out on a QSO Map. Really impressed looking at this knowing I was only running 4-ish watts!

Activation Video

Here’s my real-time, real-life video of the entire activation.  As with all of my videos, I don’t edit out any parts of the on-air activation time. In addition, I have monetization turned off on YouTube, although that doesn’t stop them from inserting ads before and after my videos.

Note that Patreon supporters can watch and even download this video 100% ad-free through Vimeo on my Patreon page:

Click here to view on YouTube.

Going to miss the the MTR-4B V2…

I was so happy to pack up the MTR-4B the following day so that its rightful owner could actually enjoy this wee red machine!

That said, I’m going to miss it.

I’m super tempted to buy an MTR-4B and I may some day. In fact, the kind reader who sent this to me also donated half the amount of a new MTR-4B so that I could grab one (or any other radio) should I choose. (Yes, I told you he was generous!)


I have an MTR-3B and I absolutely love it (I named it “Tuppence” in case you’re wondering!).

Because I have the MTR-3B, I haven’t felt the urge to buy a 4B mainly because I so rarely use 80M in the field. Then again, I do like the MTR-4B upgrades (SWR and PO meter for sure).

Time will certainly tell!

I will be posting my full MTR-4B review in the coming days–update: click here to read it–a review that was originally published in the November 2022 issue of The Spectrum Monitor magazine.

Thank you

Post activation, Hazel took me on a walk. 🙂

Thank you for joining me on this activation!

I hope you enjoyed the field report and my activation videos as much as I enjoyed creating them.

Of course, I’d also like to send a special thanks to those of you who have been supporting the site and channel through Patreon and the Coffee Fund. While certainly not a requirement as my content will always be free, I really appreciate the support.

As I mentioned before, the Patreon platform connected to Vimeo make it possible for me to share videos that are not only 100% ad-free, but also downloadable for offline viewing. The Vimeo account also serves as a third backup for my video files.

Thank you so very much!

Cheers & 72,

Thomas (K4SWL)

21 thoughts on “How to tune: Pairing the Emtech ZM-2 manual ATU with the Mountain Topper MTR-4B on the Blue Ridge Parkway”

  1. I occasionally partake of the TCM channel but you are going to have to help me. Tuppence? Soon everyone is going to be naming their radios because of you. I just hope it doesn’t get added as part of the exchange on contests. I have enough trouble deciphering 30wpm without dealing with random names like “Tuppence”.

    1. I know whatcha mean. But realize something, Hazel isn’t yet licensed either, so Thomas isn’t as good an Elmer as he may claim.
      You’d think he’d have her on the air by now. de K9HZL (Her Call)

      Hi Hi de W7UDT

      1. An old YL, I get it now. (Kidding)

        I was in the mining industry for most of my career. Prospectors often named their mining claims after their favorite ‘Sportin’ Lady!’ (True)

        I suppose if one has a certain fondness for something, he’ll name it accordingly.

  2. Re: Rite in the Rain logbooks – I now always use them even in good weather. Those log entries are too precious to risk losing to a coffee spill or (as happened in one of my activations) moisture dripping from a tree.

    For insurance I take a picture of the log before packing up. I transfer logs to HAMRS as soon as I get home. My fat fingers and not-so-good eyesight make it too difficult for me to use a tiny phone touch keypad in the field.

    1. I always take photos of my logs as well. Not just for posts, but as backups. I should consider investing in some more Rite in the Rain pads!

  3. It’s true that tuning up with reduced power is a best practice. That said tuners such as the ZM-2, which incorporate the dimming LED SWR indicator by Dan Tayloe, present a load of ~50 ohms resistive to the transmitter while in “tune” mode.

    This absorptive bridge circuit keeps your finals happy while tuning up!

    But again, the detector requires very little energy to use while tuning, so always QRP.

  4. ‘Ya knoooow?,’ I’ve always, kinda, wanted to build one these. It’s like this void in my operations. And I hate not having equipment which one is curious about.

    The ZM-2 tuner has been around since, I don’t know (a long time). Long before I got my license. It’s a proven field tuner… and I don’t have one. It’s like having an embarrassing itch. Ya kinda wanna scratch it, and then ya don’t. Ya know?

    Great video & Post Thomas.

  5. Great video, Thomas. I am always happy to make your log.

    I have bit of a love hate relationship with my ZM-2. I absolutely love the tuner and the flexibility that it adds for activating with a radio without a built in tuner. But… I tend not to use it, because it adds to the level of complexity: tuner, jumper, switches, knobs… I guess I’m a bit of a minimalist, or maybe just lazy.

    So… my radios without tuners tend to find themselves paired with resonant linked EFHW antennas. Of course this makes me leave the operating position to lower, change links, and re-raise the antenna for band changes… I guess it all comes down to trade-offs.

    Best 73.

  6. After first seeing the ZM-2 on one of your blog posts, I looked into it further and ended up buying one. I liked it so much, that I sold My LDG Z-817 and now use the ZM-2 exclusively for my QRP radios.

    If you use an FT-817/818, there is a tuning dongle available from SOTAbeams called the ‘Click2Tune’ that I recommend. Double-tap and hold the PTT on the mic and the radio will switch to PKT, reduce power and transmit. You can then make tuning adjustments on the ZM-2. When you release the PTT, the radio reverts to the original mode/settings.

    It does basically the same thing as the CAT control initiated from the Z-817, but no batteries are required and it gives you real time tuning’ with any automatic ATU that has a SWR retune threshold trigger (like the LDG Z11 pro II). Just double-tap the mic PTT and the tuner will find a match. It’s about $25.

    1. Greg,

      Thank you for finally letting me know what the mic is used for. I’m not even sure where the mic that came with my FT-818 is located.



  7. I always use a random wire, with, since I went fulltime QRP a few years ago, the ZM-2. One point that’s fairly important is to set the ZM-2 _on its side_, not the bottom. (I’ve put rubber feet on both surfaces so the thing won’t walk around on the bench or get scratched up.)

    The reason for having the adjustment surface directly facing you when seated is that the tuning LED is highly directional. If you tune the radiator to “zero light” when the LED is pointed at the sky, then stand up and key down again, you’ll find there’s still a lot of red in there; you just don’t see it from the oblique angle.

    Took me a few operations to realise this.

    So I stuck feet on the side of the ZM-2 and started using it in that position. Problem completely solved. It’s especially useful because I find the tuner needs to be tweaked after large frequency changes — those famous ZM-2 “sharp skirts” — and with the ATU on its side instead of its bottom, it’s as simple as flipping the tune-up switch, keying down and touching up the match, and switching back to transmit. Matter of a second or two.

    I too am amazed how many newer hams are terrified of manual tuners. They’re so completely undramatic. A good one liberates you to do pretty much whatever you want, with no ununs or other complications to mess with.

    Thanks for the post!

  8. Hello Thomas,
    Do you have any recommendations for a storage case for the ZM-2? It seems that I am always stressing out about breaking off something while it is bouncing around in the pack.
    72 DE N5MHM (formerly KI5CDF).

    1. You know? I don’t at present, but I too have been thinking about getting it a dedicated protective case of some sort. I’m guessing, like me, you don’t want anything too bulky–just something to protect it while in the pack.

      Perhaps someone else might chime in if they have a good ZM-2 case.


      1. I have an old Otterbox 2500 from back when they made things other than phone and tablet cases. It’s the perfect size and shape to protect the ZM2. The tuner fits like a glove and there is enough room to put in a short coax jumper. The case isn’t made anymore by Otterbox, but you should still be able to find the dimensions of it and use that to go shopping for a similar hard case.

        1. Otterbox 2500 Internal Dimensions: 5.691″ x 3.063″ x 2.741″

          Looks like Pelican 1050 Micro might be close enough to work. Interior: 6.3 × 3.7 × 2.8“

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