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 Steve has since rescinded the warning as MTRs have proved to be very reliable in the field.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.
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…
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.
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.
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.