LNR version of the MTR - an overview

This year I plumped for an MTR as an option for SOTA & /P operating. Maybe not as cool as the self build kits but the 3 band MTR is now available as a pre built transceiver from LNR Precision in the US (http://www.lnrprecision.com/). I was struggling to find much in the way of an explanation as to its features and how it worked so I’ve created a little ‘review’ video which you can see here…
Mountain Topper Radio Review (MTR3B) - YouTube

I know there are already quite a few converts here but if you haven’t tried one I highly recommend it :o)

Michael (G0POT)


Excellent review Michael.

Good work Michael.



Enjoyed your review greatly, good audio and sufficient detail to show how it works. Size, weight and capability are all excellent for a SOTA cw op. I especially like the 500 Hz bandwidth, and the programmable keyer. It’s on my wishlist!
Andrew VK1DA

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Great review video Michael. If I knew CW I’d get one, the size is incredible!

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You say 2.5 watts and also 9 to 12 volts.

It’s actually 2.5W at 9v and 5 watts at 12.0 volts. Note that it’s not like most nominal 12v rigs which are happy up to 13 or so volts. The MTR really does not like anything above 12.0 volts.

Colin G8TMV

Good job!

I’m asking a lot of question that you answered.


73 de pedro, CT1DBS/CU3HF

Hi Colin, I’ve heard from someone who built the kit who suggested they got 2.5W at 9V but I didn’t get anything like this from my stock example of the LNR produced version.
I tested at 9V, 11.1V and 12V to cover the different battery types I had and also tested on 20, 30 and 40m at each voltage and created a table of current drawn and power output.
I had as little as 1.5W at 9V up to a peak of about 3W at 12V…as you say, no more than 12V advised.

I’ll add more detail in the comments on the video.

Michael (G0POT)

That sounds to me like they are not optimising the coil spacing on the output filters when they build the rig. On the kit built MTR rigs it is part of the final calibration and setup to tweak the filters to peak the power output.

Colin G8TMV

Haven’t had the opportunity to view the video yet, but Colin is right, kit built MTRs will pump out a lot more than 3W.

It’s possible to get around 6 to 7w out at 12v, but I’d be worrying at that level.

The new MTR-5Bs that I built both showed lots of power - I was seeing around 3w at 9v on all bands. I actually tweaked the coils to get them under 3w at 9v as Steve says to set them at around 2.5w.

Note that a 9v ‘smoke alarm’ battery is not up to the job of running an MTR on TX for power o/p tests, the battery struggles to cope with current demand and the voltage sags a whole load.

73, Colin M1BUU

Yeah, for the 9V tests I used a 20A variable supply to ensure I didn’t getting any volt drop through over current.
I’ve commented back to LNR on the power output I’m seeing to see if mine is off spec or as they have designed it. If it’s off spec I’ll have a play but to be honest I’m used to operating at 2 - 4W typically so it’s no great concern :o)

Michael (G0POT)

Great video Michael!

I built a number of 2 band MTRs and by the last couple of kits, I’d really nailed how to set the inductors to get the correct power output. Each version has been slightly different due to different caps being used - the first run MTRs used through-hole caps, whilst the second run MTRs moved across to SMT caps.

Will be in interesting to hear what LNR answer with. As far as I know, Steve has been very involved with making sure that the rig is up to scratch.

My first run MTR cost about £65 I think! Amazing price for such a great kit :smile:

73, Colin M1BUU

Colin, after your comment I dropped LNR an email about my findings and Ryan did come back to me and recommend tweaking the output by spacing out the windings on the coils. The 40m and 30m toroids were quite packed so there was little spacing to be done but I evened things out a bit and 20m had plenty of room for improvement. I’ve now got the following:
12V - 20m (4.2W), 30m (3.4W), 40m (3.3W)
9V - 20m (2.4W), 30m (1.9W), 40m (1.9W)
The windings are quite loose and the toroids unsupported so I may do some further work on these. It’s possible some tweaks in the number of turns on the 30 & 40m windings may help. I must search out the original build instructions for the kit version.

Michael (G0POT)

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Fine job Michael, that’s the right way.
KD1JV explained the spacing is important to get max power.

Once you have achieved the maximum spacing in your toroids maybe you can drop some liquid glue to fix them and avoid further tweaking or random displacement on them.

Good luck and thanks for your nice video Tutorial.
VY 73 de Ignacio

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With my tribander also found by adjusting the spacings of the windings on the toroids could get a better match and more power.

Secured the windings and the toroids to the PCB with silastic so as to prevent any further movement.

This the practice of Codan with their range of H.F outpost radios.

I would advise against using liquid glue in case at some time repairs have to be made.

Silastic can be cut with a sharp knife.

73’s, Nick

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Your power output is moving in the right direction. I wouldn’t start removing turns on the toroids, you should be able to peak things nicely with the standard number of turns.

The build instructions are held on the Yahoo group but I saved a copy to my Dropbox for anyone who’s interested.

73, Colin M1BUU

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For those interested in buying an MTR in the UK (or Europe) Dennis at Kanga is advertising a small number of these for sale on his website -


I recently had a look at one of these rigs and I was impressed, they really are smaller than you imagine! Output power on the one I tested was ~3 watts across each band with 9v supply, so no worries there.

73, Colin M1BUU

Good price too. If you get it from the US built it will cost around £250. Amazing little transceiver with some very good features. They were out of stock on LNR’s Web site recently also.