LNR MTR4B Overview 

They are remarkably excellent little radios and perfect for /P operating. You only need a tiny LiPo for normal operating periods which keeps the whole station weight down. Like you, my telescopic mast is the biggest part of my station but my 6m carbon fibre option is super small and light too. I wish throwing a line into a tree was more reliable!

I use my MTR5b with 12.6v, Steve Weber has spoken about how resilient the finals are on the MTR series. 13v+ is probably asking too much. Check out ad5x's article about reducing voltage, this circuit could address the issue easily. www.ad5x.com/images/Articles/AutoLiPoVoltageReducer.pdf 73 de w8tam

I've not looked at the underlying design to see why the limitation exists. I know I run my MTR3B and MTR5B a little higher than 12V because my 3 cell LiPos are actually more like 12.5V when fully charged despite being officially 11.1V. You could very easily add a single diode in series in the power lead and drop about 0.7V so this would overcome the issue. I basically bought the 3 cell (3S) LiPos just for my MTRs but now use them for other QRP radios...I only use the 13.2V LiFePo on the KX3.

Quoting kd1jv on feb 13 2017, on the at_sprint yahoo group: It’s still a good idea NOT to transmit into a poorly matched load when running the rig at a full gallon and use a resistive SWR bridge. However, seeing that there are now a boat load of rigs with BS170 finals in them out there, if anyone has burnt one out I’m not aware of it. Either everyone of those users has been super careful (which seems unlikely) or there is no need to worry any more (which is more likely). So, the warnings were no longer felt to be necessary. The first few versions the ATS rigs used 2N7000 finals and those did have a problem and after the switch over to BS170’s the high SWR warnings were carried over to be on the safe side. Like the government likes to say “out of an abundance of caution” these warnings are issued, even though there is absolutely no creditable evidence of a threat. Steve KD1JV

There was/is a software bug in earlier versions that means the RIT doesn't work. This can be fixed through a software update but I also found a clunky work around. Turn on the RIT...adjusting it up or down in frequency has no effect but if you hit Fn (displays R=T) and then tap it again to return to normal RIT you can now shift your RX frequency by 50Hz. If you need to move further you have to keep double tapping Fn and then you can shift an extra 50Hz each time. Clunky but it works. Hope that helps.

Yes, the menu and display are essentially identical...not sure if there are any fundamental design differences other than the bands covered. I felt the audio was louder on the MTR4B but there is likely variance from radio to radio. The 4B obviously has the larger case (you could potentially fit internal batteries or an ATU) and the flip down legs but in essence the MTRs are all similar (if excellent) beasts!

Sí Ramón, tienes que conseguir uno! El MTR3B es pequeño pero increíble ...

russkydeutsch When you see my station at ~11:25 I’m powering the radio from a small LiPo...I have Powerpole connectors attached to all my batteries so I can use them with different power leads. Attached to the jst-xh balanced cable on the battery is a cheap battery monitor which tells me the overall voltage of the battery but also monitors the individual cells and alarms if they get too low. Finally I fit an in-line fuse in all of my power cables. That’s it. Enjoy :o)

Jimmy, see the video from about 3:15 for details on power draw but the peak was 600mA with a 12V supply on 80m giving 4W of output power. In receive the radio draws just 19mA at 12V. I didn't measure the space in the bottom of the radio while I had it on loan but it was significant and I think there would easily be room to fit batteries. In fact I think there's room for batteries and something else!

Radio Prepper I should have measured the gap...in my mind you could fit battery and an ATU! You'd want to find a way to charge it in situ to avoid constantly opening the case up.

Thanks, good to know... I have the 3b (also built an MTR2, 3b and 5b!), wondering if I need the 4b ;-)

I can guarantee there is an MTR4B shaped hole in a go-bag somewhere near you :o) With MTRs you know you're not going to be disappointed.

You know it :-)

Yes, this can be a problem. For headphones I either use ‘over the ear’ style that I can nudge off my ears a bit when sending or, when using ear-bud style headphones, I have a short extension lead with built in volume control like this: smile.amazon.co.uk/Extension-PChero-Headphone-Control-Computer/dp/B08T1YW1JK/ref=mp_s_a_1_3?crid=1V3FFVHHJ61HR&keywords=headphone+extension+with+volume+control&qid=1660979588&sprefix=headphone+extension+witj%2Caps%2C72&sr=8-3

Tim, I only have the MTR3B and MTR5B (I had the MTR4B on loan!), however, I can confirm the following coverage of each band of the two radios I have and I'm guessing the MTR4B is similar: MTR3B 40m : 7000 - 7150kHz 30m : 10100 - 10150kHz 20m : 14000 - 14150kHz MTR5B 40m : 7000 - 7150kHz 30m : 10100 - 10150kHz 20m : 14000 - 14150kHz 17m : 18068 - 18110kHz 15m : 21000 - 21150kHz

Michael Sansom thank you sir. That is the info I needed. 73 de KF7VUT

Great stuff...keep at it with the CW because it opens up a whole world of fun radio. Although there is a 'gentlemen's agreement' that one should respond to a call at the same speed as the caller not all Ham's abide by this. Some Ham's are simply not great at assessing speed and others will respond at the speed that they prefer and expect you to shout 'QRS' if you need them to slow down. I was calling at about 18wpm and can cope up to 22wpm but sometimes operating outdoors with wind/motorbikes/aircraft noise copying can be difficult so people who drop the speed or leave nice big gaps between words are a real help. I dropped my speed to 14wpm to work a Swiss SOTA station and he copied everything first time whereas the other stations calling in at 16wpm+ had to repeat lots...for me it's just a courtesy to match the other stations speed. If people won't slow I just respond "SRI QRM 73" and QSO with someone else!

For SOTA activations I use a super small LiPo 3S, 460mAh battery. It gives me plenty of power for a few hours of constant operation. Note my comments in the video about supply voltage as the 3S LiPos do start off at 1~12.5V when fully charged. Here's a link to the actual battery I'm using: hobbyking.com/en_us/turnigy-nano-tech-460mah-3s-25-40c-lipo-pack.html The speaker is just a little portable unit (no brand name). I confess it can be a little quiet on a windy hillside and I prefer to use headphones but for filming a little speaker makes recording the audio easier! If anyone has a good suggestion for a small/flat portable speaker with a decent amount of amplification I would love to hear the details :o)

Michael Sansom. Michael, Thanks for a good review. I have severe hearing loss, so have to have considerable help with any MTR series radio. That means a tiny rechargeable headphone amp if I use 'phones, and for open audio use I have a speaker which is about the same size as the MTR5B, made by Altius, model number ADP-108BT (got it from ALDI I think!) its a re-chargeable stereo unit (two separate speakers) but I run with just the one which takes the input cable - lighter and less current drain on the unit. Send me an email if you want a picture of it (probably available under different brand-names if you know the shape to look for). Les g0nmd

DK1TOM It’s a Begali Traveller...a really nice key :o)

Thanks for the quick response, Michael!

The3DMoviemaker There is no built in signal meter on the MTRs (at this time). Readability and Tone are subjective anyway but for Signal strength I guess based on the ‘size’ of the signal in terms of volume and clarity.

Terrific video! Thank you!

lonestarprepper01 Yes, if you plug in a mono 3.5mm plug it defaults to a straight key but you can also toggle between straight key and paddle by using the Function button to enter the speed adjustment and then select RIT. I have to do that because I fit stereo plugs to all my keys...even the straight keys...it’s just what I have to hand.

This transceiver is now at version 2.3 and can be bought (when in stock) direct from LNR Precision: www.lnrprecision.com/store/Mtr4b-V2-3-Mountain-Topper-p271367005

There is an online manual here: www.lnrprecision.com/wp-content/uploads/2020/12/Mtr4BV2manual_12_16_20.pdf and I power my Mountain Toppers using 3s LiPo batteries…something as small as 1Ah is sufficient for many hours of operating.

Don’t look at me...look at that wonderful little transceiver :o)