MTR-5B ufb rig

Gerald,

My pack is much lighter these days, I haven’t replaced the saved weight with anything else, I even bought a lighter rucksack, a Mammut Lithium 32.

I think my gross weight remains the same though, fewer activations means a heavier activator!

1 Like

Hi Jurg,
lucky man, indeed a very nice screen!! Enjoy your new toy.
I wish I had one of these new models…

Colin, If you want a single band model, just carry one of these 2 band models with a single wire length :wink:

VY 73 de Ignacio

1 Like

I will take the liberty to ask in this thread:

What is the max voltage the MTR5b can handle? I saw it is estimated between 6-12volts, but some LiPo can be above 12V - should I avoid them?

By the way, holding it in my hand I cannot believe how small it is even compared to KX1 which I already considered really small! :slight_smile:

Hi

Lots and lots of sites talk about it: No voltage above 12V!

To my MTR-3 I built a simple regulator that Impose not more than 11.9V. Just in case! :slight_smile:

73 de Pedro, CT1DBS/CU3HF

I’ve powered my MTR-3B with a 3S LiPo, which is 12.6v fully charged. It seems to work fine with the slightly higher voltage.

1 Like

Short answer - it’s fine to go slightly over 12v.

The MTR rigs use BS170 FETS in the output stage which are slightly more robust than the 2N7000 used in previous AT Sprint rigs, but the associated warning about poor loading / high voltage was carried over. Steve has since rescinded the warning as MTRs have proved to be very reliable in the field.

Treat MTR rigs with care and there will be no problem. A problem might arise if you were transmitting into a poor load or adjusting a connected ATU whilst powering the rig at the upper end of its voltage range. If adjusting an ATU, use a lower voltage supply first and then swap to your higher voltage once everything is nicely tuned up.

A fully charged 3S LiPo and a nicely matched antenna should happily provide over 5w initially without any worries, and then the power will drop off as the voltage of the battery drops before levelling off to nominal.

Bottom line - don’t worry too much!

73, Colin

1 Like

OK, thanks. I was thinking of power supply up to 13,5V like from a car battery.
I also contacted LTR team, so their response was - yes I can, however, they do not recommend it (well, no wonder - I should expect the seller will not absorb the risk of a potential failure… :wink:

I know it is best to stay with 3s 11.1V LiPo and I am on a safe side. By the way - what is the smallest and reasonable LiPo 3s 11.1V mAh for let’s say 5 hours activations daily (if I do ~3 summits, let’s say)?
I would appreciate any experience shared… Thanks!

I have two batteries: a 500mAh and a 1500mAh. The smaller one is good for at least two activations, and I’ve taken the 1500mAh one out on four activations over a weekend, and still only used around 25% of the capacity, according to my charger. My guess is that 500-1000 mAh will be enough for you.
This is with my MTR-3B, I don’t know if the 5B is more power hungry.

The MTR5B is much less power hungry. The low voltage rail is provided by a switched mode regulator.

My MTR5B was built from the KD1JV kit. Could’ve set the rig up better but I just left it pretty much as it was without tweaking.

I use a PP3 sized 3S and it’s more than ample for me. Can’t just remember what mAh it is but in region of 300 to 400mAh.

73, Colin

1 Like

Thank you all! I just ordered 1300mAh, so it should be plenty… Still less weight than the 2700 I used with my FT817. :slight_smile:

Colin - I am not sure which paint shop you are using, but your gear definitely is well dressed, as national football team… :wink:

Hi Konrad

By chance I came across this video again LNR MTR5B unboxing & build overview - YouTube
It was very well made by Michael, G0POT.

Despite Colin, M1BUU post - their assumptions and precautions seem right to me - one must be careful for the sake of the MTR. :wink:

I suggest that you take a look, especially on the 33 Second.

Vy 73 de Pedro, CT1DBS/CU3HF

I was suggesting that using a fully charged 3S should be fine, they seem to top out at around 12.65 , but quickly fall away to below 12v after short use.

Using a fully charged 12V SLAB would be pushing things a bit - one of my SLABs tops out at about 13.5V.

I have never tested my rigs to destruction, I wouldn’t want to, but I wouldn’t even consider running an MTR from a vehicle battery or supply, I think that’s definitely asking for trouble.

The PA in the MTR was designed to be efficient at 9V, so pumping in more voltage not only increases stress on the PA, but also diminishing returns.

The MTR is a QRP rig, designed for a few Watts output, it seems silly to want it to do more than that. Just like the new Soda Pop single band rig which people are multibanding, I really don’t understand why you would get something designed for a specific purpose, yet want it to do something different!

I run my MTRs from a 3S LiPo because it’s convenient. A 2S LiPo works fine, with around 2 Watts of RF from the MTR, but it’s nicer to have just a little bit more output at times.

73, Colin

1 Like

Thanks, all. I will use 3s 11.1v (indeed it always charged slightly above 12V). 73!

I found out that once charged fully, with its 12.5V it does not discharge too quickly, so it will have to stay above 12V for a while until it gets to <12. Hopefully it will not be an issue.
And to be honest it was listening almost all the time so perhaps sending will drain it quicker.