A review of the LnR Precision Mountain Topper MTR-4B ultra-portable QRP transceiver

The following article originally appeared in the November  2022 issue of The Spectrum Monitor magazine:

A Review of the LnR Precision Mountain Topper MTR-4B V2

by Thomas (K4SWL)

I confess, there is something that I’ve come to believe is almost a rite of passage in the SOTA (Summits On The Air) community. And, no, I’m not talking about activating an All Time New One (ATNO) summit, or completing a particularly challenging activation on a snow-capped peak.

I’m talking about owning one of the iterations of the amazing “Mountain Topper” pocket-sized QRP CW transceivers designed by Steve Weber (KD1JV).

This little radio first caught my attention at a Four Days In May (FDIM) QRP conference over a decade ago: a ham friend in the SOTA community proudly showed me a very early version of the Mountain Topper that he built from a kit. The first thing that struck me was how impossibly small and extraordinarily lightweight it was. But when he showed me the 9-volt battery he used to power it––a power supply not only small, but convenient––I was mesmerized.

Over the years, the Mountain Topper has evolved.  There have been many models, ranging from two bands to five. To my knowledge, they’re no longer offered in kit form, but LnR Precision manufactures and tests these in North Carolina, and they’re better than ever in terms of features and performance.

At present, the MTR-4B V2––the second version of the four-band Mountain Topper––is the only model in production, and if you’re hoping to acquire one, due to supply chain issues (at time of publishing) there’s a rather long wait time. They retail new for $350 US, and frankly, the used ones I’ve seen posted in ham radio classifieds ads have been equal to, or even over, the listed price for a new rig.  Obviously, demand for these radios is much higher than supply.

So, how could it be that this minuscule QRP radio performs well enough to produce some serious DX from a remote summit…so well, in fact, that people are willing to wait in line for one?

Magic or method?

As any CW operator will tell you, the magic is in the mode. CW is such an efficacious mode that it cuts through the ether like a knife, even when conditions are less than favorable.

Obviously, pint-size radios like the Mountain Topper are QRP––low power––so designing them around such a simple mode is a very smart choice. CW transceivers are much less complex than a similar SSB transceiver, thus have less components, less mass, and are in general more affordable (when compared to those with similar receiver performance).

My comprehensive MTR-4B field kit (the MTR-4B is in the mesh pocket).

In addition, the Mountain Topper is designed with the field activator in mind:  specifically, SOTA activators, but of course, POTA (Parks On The Air), WWFF (World Wide Flora and Fauna), IOTA (Islands On The Air), or any other popular “-OTA” field activity. As a field activator in one of these programs, you are the DX. This means chasers and hunters are actively seeking your signal, and thus you are not competing with blowtorch stations to punch through a pileup.

I can also assure you that standing on a tall summit also gives you a brilliant starting point for your QRP signal. Some of the best DX I’ve ever worked has been from a summit.

So, for the average CW SOTA activator, QRP is preferred because QRO simply isn’t necessary––indeed,  in my opinion it’s a bit of an overkill. At least that’s been my experience now with my few hundred SOTA, POTA, NPOTA, SOTA, and even one Lighthouse On The Air activations.

So this brings us back to the wee Mountain Topper series and the model being reviewed here in the pages of TSM: The Mountain Topper MTR-4B.

First, let’s get some “cons” out of the way…

If you’re not familiar with the Mountain Topper series, let’s first get a bit of lack-of-feature shock out of the way, since this radio is quite bare-bones as compared with most modern transceivers.

Note the following list of “cons” or limitations of the MTR-4B:

  • No built-in volume control or AF gain
  • No RF Gain control
  • No rotary encoder
  • No signal meter
  • No variable AGC control
  • No factory built-in battery option
  • No factory built-in ATU option
  • Limited to four ham bands; not general coverage
  • No DSP
  • No notch/passband filtering
  • Only one filter width and no other internal options
  • No built-in speaker
  • No CAT control
  • No option to work digital modes

I’ll be honest:  these shortcomings may very well be off-putting for the average ham. Can you imagine purchasing a new radio for the shack that lacked a volume control, for example?

And yet…why is there a waiting list for a radio this basic? Let’s look just a little closer.

Purpose-built for SOTA…or espionage

One look at the Mountain Topper and you can see that it was designed for a specific subsection of amateur radio enthusiasts.

I’ve often thought another target market might be those who wish to perform a little espionage. With the exception of the candy-apple-red paint job, which I’m guessing most spies wouldn’t prefer, it actually looks like some spy transceivers I’ve seen, even down to the symbols indicating paddles, antenna, and battery. And the radio is so small, it could fit in the hidden compartment of the briefcase your country issued you prior to sending you across enemy lines.

Or––presuming you’re not a spy––it’s small enough to fit in the backpack of, say, an Appalachian Trail through-hiker! And in such a backpack, every bit of weight is scrutinized.

It’s purpose-built to accomplish a goal.

An analogy

I recently spoke with a friend––a car enthusiast––about the MTR-4B, and tried to describe its unique appeal with an analogy he might understand.

Formula One cars (Photo by Bill Stephan)

The MTR-4B, with its pared-down functionality, might be likened to…a Formula One car.  Out of context, I explained, even Formula One cars seem freakishly lacking in creature comforts: only consider the open cockpit, exposed wheels, seat for the driver only with no room for any passengers, that they’re geared like no other car on the planet and sporting large front and rear wings––? Let’s face it, if you’re going on a road trip with the family, a Formula One car would not be the best choice.

Then again, if you’re racing in the Monaco Grand Prix? It’s all about Formula One. Can you imagine competing in that race with, say, a family minivan?

MTR-4B strengths

Since the MTR-4B was was designed for hams who enjoy ultra-lightweight, ultra-portable, ultra-effective radio communications––and who plan to be doing most of the CQ-calling in the field themselves––its feature set is designed around this very strategic list:


  • Insanely low current drain (approximately 27 mA)
  • Three CW message memories that are easy to program in the field
  • “Full gallon” QRP 5 watts of power when supplied with 12V DC
  • Super lightweight
  • Super compact
  • Full break-in (QSK)
  • No relay clicking (PIN diode switching)
  • Informative LCD screen that can now display SWR (compared with previous versions that could not)
  • Cabinet designed to protect the front face of the radio
  • Well-chosen receiver settings and filtering for CW
  • A direct-frequency entry function using CW instead of a keypad

It’s a feature set I certainly appreciate. The current drain, CW message memories, and QSK alone sell me.

But at the end of the day…are these positives enough to outweigh the lack of features expected in most other transceivers?

On the air

The only way to answer that question was to put the MTR-4B on the air––both in the shack, and more especially, in the field!

Over the past few months I’ve logged well over 100 individual contacts with the MTR-4B, and have activated several sites with it.

We’ve already clarified that the feature set is limited for a radio in this class. But I’ll follow up by saying that, performance-wise, the MTR-4B exceeds what I would expect from a radio of this size and in this price class. There’s only one filter width, but it is well-chosen for CW operation. The receiver audio bandwidth is 400 Hz, centered at 600 Hz, which, to my ear, equates to a 500 Hz-effective width. So while I’m not sure I’d choose the MTR-4B for a CW contest, it has proven effective in the field at mitigating adjacent signals in crowded conditions.

The receiver noise floor is extremely low. In fact, the receiver noise floor is so low that, more often than not, I’ve feared there was an issue with my antenna when I turned on the radio. There’s hardly any static and no internally-generated hash or noise as is often found in lower-priced portable radios.  The audio fidelity is very pleasant for long sessions on the air; this is not a radio that will lend to listening fatigue.

The CW sidetone by default (at least, in my unit) was a little loud initially. Sidetone level is adjustable via a small hole in the bottom of the chassis:  simply insert a nylon or dielectric screwdriver and turn the pot to change the audio level. (In previous models, to change the sidetone one needed to pull apart the chassis.)

The fixed receiver volume level is comfortable for perhaps half of my earphones and headphones. On some earphones, it’s a little on the high side for me. Most Mountain Topper owners purchase an inexpensive in-line volume control for their MTR-4B that allows you to change the volume control on the earphone cord––it’s important to get an analog control, though, as many in-line volume controls these days are digital and assume you’re using a smartphone or tablet. I keep an old pair of Sennheiser earphones with in-line volume control in my MTR-4B pack.

You can see the Sony digital recorder on the right side of the radio.

Another option:  more often than not I record the audio of my activations for my activation videos, but also as a record of each activation in case there’s a discrepancy in my logs. I use an inexpensive (a $20 thrift store find) Sony digital recorder connected directly to the MTR-4B’s earphone port. I then hook my earphones into the digital recorder and use the recorder’s excellent volume control to make adjustments.

The CW electronic keying in the MTR-4B (and all of the MTR series) is absolutely top-shelf. The MTR-4B uses super quiet PIN diode switching that provides silky-smooth full break-in (QSK) operation. The keying feels natural and fluid.

At first glance, you might assume a radio lacking an encoder or keypad for direct frequency entry might be awkward…You would be partially correct there. I’m sure one of the compromises of the MTR-4B to keep it both as lightweight and compact as possible was to eliminate an encoder, which would protrude from the chassis. Tuning requires pushing and holding the Up/Down arrows to move around in each of the four bands. At first, I found this particularly annoying in the shack while hunting SOTA and POTA stations. Inevitably, I’d work a little DX at the bottom portion of the 20 meter band (say, 14.005 MHz), then have to move up to 14.062 MHz to work someone on a summit. Tuning seemed to take ages…that is, until I discovered two ways of dramatically speeding up the process:

  1. Press and hold the Up or Down arrow and then press and hold the Fn (function) button simultaneously to significantly speed up the movement across the band. This is the fast tune mode.
  2. The MTR-4B also offers a DFE (Direct Frequency Entry) mode; one can activate it, then send the radio the last three digits of the desired frequency in CW, and it will immediately jump to that frequency. After using this method a few times, you’ll quickly become a pro.

CW message memories are also very easy to record in the field. Unlike many field radios, the MTR-4B allows you to enter each character and space one at a time during the recording process. This makes it a cinch to record the messages perfectly on the first go. There are a total of three message memories, and here are the messages I load in each memory allocation:

  1. CQ POTA DE K4SWL (my call)
  3. RR TU 72 DE K4SWL

With those three messages, my activation workflow is very straightforward, whether in a park or on a mountain. Playing each recording is simple: I just press the Fn button once, then press either the 1, 2, or 3 button, and the radio will transmit the message. There’s also a Beacon mode you can activate that will play the message (say your CW) on repeat until you stop it.

It’s worth noting that the MTR-4B has three message memory positions, whereas most similar portable radios either only have one or possibly two.

Of course, the magic of the MTR series is how insanely efficient these rigs are on battery power. The MTR-4B draws a mere 27 mA in receive––one of the most efficient QRP radios on the market. It’s so efficient you can perform entire activations on a common 9V alkaline battery. With a small 3Ah battery, you can operate for days.

Three band switches?

A common question about the Mountain Topper:  “Why does the MTR-4B have three individual band switches?

Mountain topper MTR-4B (top) and MTR-3B (bottom)–both have three band switches.

It’s a great question, and the answer can be found in the product manual. The following explanation comes from the MTR-3B manual, but also applies to the MTR-4B (save the 4B has four band positions instead of three):

The band is selected by three three-position slide switches. For proper operation, all three switches must be in the same column[…]. It’s easy to get into the habit of flipping each switch in sequence from the top down.

The top switch tells the processor which band to operate on and connects the Receiver input filter to the first mixer. The middle switch connects the transmitter low pass filter output to the antenna and connects the antenna to the receiver input filter. The bottom switch connects the output of the transmitter PA to the low pass filter.

And the manual is correct:  it’s quite easy to get in the habit of sliding all three switches with band changes. It becomes second nature in short order.

It’s also easy to tell that all of the switches are in the correct position because without all three switches selected appropriately, the receiver sounds deaf and audio-muted. With them in position, the receiver sounds “alive.”  (That said, the noise floor is so low on the MTR-4B, it’s quite possible you might think they’re not engaged properly if there aren’t many signals on the band!) Obviously, it’s easy to visually inspect the switches and confirm they’re in the correct position.


If you can’t tell already, I’m quite impressed with the MTR-4B. If you also like super-lightweight, compact QRP radios that are designed with field use in mind, just go ahead and order an MTR-4B. Especially if you like to hike with a radio, you’ll be so pleased to have a rig that is designed with this very activity in mind.

Do I have any criticisms? Only minor ones.

If there was any way to include an AF Gain or volume control on the MTR-4B, it would be a most welcome addition.  The MTR-4B was the first in the Mountain Topper series that allows the user to check the SWR and power output, which most users, including me, appreciate even more.

Click here for a demo of putting the MTR-4B into straight key mode to display the SWR and Power Output.

Also, I am not alone in wishing that the MTR-4B’s four bands included 17 or 15 meters instead of 80 meters. It’s so rare for a SOTA operator to use 80 meters because the antennas are so large. In the world of SOTA, it’s been my experience that those bands above 40 meters tend to be the most productive.

But again? These are minor quibbles. The MTR-4B and the whole Mountain Topper series is a transceiver designed to focus on all of the features a field activator will need without any extraneous additions that might add to size, weight, or power consumption.

In the end, the MTR-4B hits it out of the ballpark, and this is no doubt because it is merely the latest iteration of a transceiver that has dominated this ultra-portable market.

As I finish off this review, I’m looking at the MTR-4B V2 sitting on my desk. I can tell it wants to go outside, so I think I’ll just pack it up again and head to one of my local summits. I just need to pack my lunch, check the weather, grab a map, snap the harness on my faithful field companion, my dog Hazel––and drop the MTR-4B field kit in my SOTA backpack.

Let’s go play radio!

Click here to check out the MTR-4B at LnR Precision.

I would like to send a special thanks to one of my readers who purchased this radio, brand new, from LnR Precision, had it drop-shipped directly to me, and gave me months to evaluate it. Not only that, but he made it clear that I shouldn’t worry about any of the normal scuffs and scrapes his radio might get in the field during this evaluation period. Thanks so much for your patience and understanding…you’ve got a great little rig here.

A note about MTR-4B availability

At time of posting, LnR Precision is only producing the MTR-4B in small batches due to lack of supply availability for many of this transceivers’ critical components. Because of this, as I mentioned earlier, used Mountain Topper prices are as high as (or higher than) brand new rigs. If you’re interested in purchasing the MTR-4B (current version is V2.3), I’d suggest checking the LnR Precision orders page frequently for updates.

Thank you

I hope you enjoyed this review as much as I enjoyed creating it.

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.

Thank you so very much!

Cheers & 72,

Thomas (K4SWL)

14 thoughts on “A review of the LnR Precision Mountain Topper MTR-4B ultra-portable QRP transceiver”

  1. I really enjoyed this very comprehensive review, what a pleasure to read drinking my morning coffee.

    72/73 de AI5DD

  2. Great review! I’ve got a PFR-3 and could instantly tell the Mountain Topper was a Steve Weber design by the multiple band switches and push buttons. He designs great QRP radios. I hope availability of the Mountain Toppers improves.

  3. I also have a PFR-3 which has a built-in ATU, otherwise a very similar radio. I am not sure I could deal with a bright red radio; I don’t even like the bright yellow of the PFR-3! But, if I could get my hands on one I could maybe become selectively color blind hi hi.

  4. Was lucky and picked one up when a couple were put up on the website. Great mix of simplicity and quality. Just the right mix to be functional for what it was designed for.

  5. Thomas great review, you are doing excellent work in the QRP world and I find myself closely following your recommendations. I am learning Morse Code now; however, I bought the MTR 4B (got lucky to find a lightly used one) and find that its ability to receive signal is fantastic. I am using a 12V Bioenno battery with two diodes to reduce the amperage and thinking of going with he 9v battery as well for a smaller platform in the POTA arena. I am working on learning enough code to send and investigating a suitable ATU for the rig.
    K8MST (Mark)

  6. Nice article. Fully agree with everything you wrote. Been using my 4B-V2 for 2+ years. I’ve never regretted buying the best. It’s great to own an instant classic.

  7. The Mountain Toppers challenge the idea of how minimalist a radio can be and still “work”. But the MT’s are very limited in utility as compared to even an Elecraft KX1. Another “con” for the list is no SSB reception at all (the radio doesn’t even tune up to that part of the band).

    The RX sounds quiet, but that’s partially because it is sort of insensitive. Now, considering that you are only TXing 5 watts, this is not the problem it might seem. If a guy is flirting with the atmospheric noise (eg. high bands) he probably won’t hear you anyway. But Thomas’ observation on the MTR-4B band coverage is spot on. The (tr)uSDX is even worse in this sense, covering two fairly useless (at least in the US) bands for field operation, 80 and 60 meters, making it essentially a 3 band radio. I have a 3 band and a 5 band MT, they are cool but I rarely use them. Overall, the MT’s are somewhat hairshirt for me. For a bit of a penalty in terms of size and weight, you can have a radio that covers 9 bands, multiple modes and has a general coverage RX. But I understand their appeal to others.

  8. Interesting to read that half of your headphones are a comfortable volume and half are too loud. With mine the listening level range seems to be from close to inaudible to weak but marginally serviceable volumes. I sent LNR a message long ago trying to troubleshoot this, but I never got a response.

    I like the design of the radio and of course the form factor, but I have been grabbing my TR-35 mostly because I simply can’t hear well enough using my MTR 4B.

  9. I’m one of the lucky few who got a MTR-3B kit, back when Steve was still prototyping this design and releasing the kitted versions in small batches through his mailing list. In addition to all the fine qualities you outlined here, I can add that the kit was tremendous fun to assemble. I’d never worked with surface-mount parts before, but with a good heat gun and some solder paste, I found them pretty easy to install.

  10. I’ve been haunting the LPR website for a week or so…The Mtr4b V2.3 has been “Sold Out”.

    This morning, US Pacific time, still no joy. Checked again around 1040 hrs and bingo, 10 in stock!

    Snagged one!

    Checked back a few hours later and this batch was all gone.

  11. Thanks for the nice review, Thomas. A great read. I was lucky enough to get an MTR-4B V2.3 this past June. After many SOTA outings and even some operation from home it is my favorite rig. I did have to turn down the sidetone volume using a non-conductive screwdriver, though.

    Like others I wish it had 15m instead of 80m for the fourth band, but I have plans to make use of the 80m capability in the future. The form factor of the rig, receiver, QSK, message memory keying, built-in clock, and SWR/power meter are excellent.

    Vy 73 de KC1MXB

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