Planning to Purchase an MTR5B, Questions to Users

Discussion in 'QRP Corner' started by KD8EDC, Dec 1, 2017.

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  1. KD8EDC

    KD8EDC Ham Member QRZ Page


    I need a compact QRP radio to take with me in my travels about the country, and am planning to purchase the MTR5B. I'm planning to purchase the EFT-MTR antenna to go with this radio, and to complete the outfit I'll be grabbing a Palm Pico.

    I'm thinking about power. I'd like to play with the unit indoors to learn my way around it, and I'd like to have a power supply I can plug into the DC port. Is there an AC power adapter that you can recommend? In the field, I'd like to use a very compact LiPO4 battery....what battery packs have you used with success and can recommend?

    Finally, what's your opinion of the radio as you've used it? I'm not looking for a "which radio is best" answer, just anecdotal experience!


    Mark KD8EDC
  2. KC8VWM

    KC8VWM Ham Member QRZ Page

    MTR5B is a nice novelty item, but it doesn't have the same functionality as an FT-817.

    I have travelled all over the place and setup on beaches, motel rooms, mountain tops, camping, backpacking and sometimes just in my own backyard.

    While these other rigs might seem interesting to operate, they just simply don't have everything the FT-817 has to offer. Everything else is always a compromise in one way or another.

    Also forget about the LiPo battery. Get the LiFePo4 battery instead. These are superior in many ways I could get into an entirely separate discussion about but more importantly, they don't catch fire like LiPo batteries often do.

    If you're interested, I can tell you where you can get a 5Ah LiFePo4 battery pack with built-in BMS for $50. They can be charged with any kind of wallwart that puts out 14-18 volts. The BMS built inside the battery pack regulates the charge, so no special external charger is required.
    Last edited: Dec 3, 2017
    K5ITM likes this.
  3. N6MST

    N6MST Ham Member QRZ Page

    Watch your voltage with the MTR, you REALLY don't want to supply more than 12 volts. Many 12v batteries actually provide voltages higher than 12 when fully charged. If that's the case with LiFePO4 batteries (I don't know, never used one myself) you stand a good chance of frying your radio unless you use some sort of regulator to step down the voltage.

    That said, I LOVED my MTR3B. I sold it to buy a KX2 and now I am seriously looking at buying another MTR!
  4. KD8EDC

    KD8EDC Ham Member QRZ Page

    Thanks for the responses!

    With respect to the 817, I'm really only looking for a very small CW only rig. If I want more bells and whistles, I can always take my KX3 along. That said, I am interested in a good LiFePO4 battery....did I say LiPo? Must have been sleepy. I know better! Per a subsequent post, to power the MTR5B I'd need to be sure the output is no more than 12 Volts. Is that the case with the battery you're referring to? If so, I'd be very interested in where they are available.

    Thanks for the help!

    Mark KD8EDC
    KC8VWM likes this.
  5. KC8VWM

    KC8VWM Ham Member QRZ Page

    Practically any battery you purchase that is labelled as "12 volts" is going to be delivering more than 12 volts.

    What some people do is they install a silicone rectifier diode on the positive lead to drop the voltage back. Each diode you install represents a .5 volt drop. Another approach is to install a small buck converter. These are quite inexpensive on eBay and you can just simply "dial in" the output voltage you desire.

    Buck converter:

    12.8v LiFePO4 Battery with built-in BMS:

    Hope that helps.

    Charles - KC8VWM
    Last edited: Dec 3, 2017
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  6. KD8EDC

    KD8EDC Ham Member QRZ Page

    This information is exactly what I needed. It appears that the most convenient and flexible way to go would be to combine a LiFePO4 battery pack with a buck converter. That would allow me to use the same battery pack for both my KX3 and a MTR rig; using a meter to dial in the voltage for each application would assure proper voltage and prevent damage to the MTR from exceeding 12V. Actually, it's more likely I'll grab 2 or each and set each for its respective voltage output. Less likely to forget and fry something that way....... ;)

    Thanks again.

    Mark KD8EDC
    KC8VWM likes this.
  7. N6MST

    N6MST Ham Member QRZ Page

    The KX3 user manual advises 12-14 volts for the radio, so no need to use a buck converter if the battery doesn't supply more than 14 volts. For the MTR, check on eBay or Amazon, there are inexpensive buck converters out there that have built in displays that will tell you that voltage the converter is putting out, no need for a separate meter, plus that's a nice thing to have out in the field!

    Buck converter with voltage display:
  8. KC8VWM

    KC8VWM Ham Member QRZ Page

    What bothers me about the MTR is they know most portable 12v batteries on the market people are using for QRP operation typically supply between 12.8 - 14 volts.

    Also if you happen to be charging the battery while you are using it, (solar panel charging scenario etc.) the battery voltage to the radio could easily reach, or exceed 14.4 volts. So why isn't there internal circuity already built into the MTR to handle these higher voltage variations?

    Seems odd to make a radio that can't exceed 12v, when practically all 12v batteries we are using for QRP already do.

    ...I don't get that.
    KD8EDC and W4CDO like this.
  9. N6MST

    N6MST Ham Member QRZ Page

    Idk, cost? Weight? Unnecessary complication? The MTR series of radios excel at being EXTREMELY lightweight while still being very functional, especially for the cost. I believe the supply voltage is listed at 7-12 volts? A 40 gram alkaline 9V battery works great on a high summit with a lightweight dipole, a Pico Paddle, and some earbuds. I think the fan base for Steve's radios is a small subset of the ham community, but that subset is one that tends to diligently weigh things. From California I had a QSO with a guy in New Hampshire on my MTR3B. Anecdotal, I know, but I am still proud of that contact. I think my station weighed less than a pound or somewhere in there.
    KD2RON, N8TGQ and KC8VWM like this.
  10. M0LEP

    M0LEP Ham Member QRZ Page

    Spot on!

    Take a look at the "PP3 Challenge", "How many QSOs from a PP3" and "1 kilo HF Challenge" threads on the SOTA reflector if you want more evidence.

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