The LNR Precision MTR transceivers are designed to be efficient portable CW rigs. Whether climbing a mountain and operating SOTA or just out for an afternoon in the park, the MTR’s small size, light weight and meager battery requirements makes it a great choice for these activities.
Update (9/2/21) - Next production run of MTR4b_V2's are underway. Dependent on supply chain coming through for us, but hope to start taking orders in October/November.
An automatic email will be generated once your unit is ready and will be sent to you with FULL tracking detail from USPS Priority Mail. Also, we will only be shipping out to US Domestic customers initially until we have full assurance that COVID-19 shipping/customs issues are resolved. We simply want to make this great radio available to as many customers as possible and not have units sitting in shipping warehouses, customs offices, or returned. Rest assured, we will certainly be making it available for worldwide purchase soon. Also, LNR does not sell external batteries or power supplies and please contact your preferred supplier for battery options.
Power supply options:
The MTR-4B V2 is designed to put out about 5 watts with a 12.0 V supply. This makes it a good match to a 3S Li-ion pack which produces a bit over 12V when fully charged.
A 2S pack can also be used, with reduced power output. But also with reduced transmit current draw, which will extend battery life. Operation is possible down to the minimum discharge voltage for the cells, about 6V, and still produce over 1 Watt of output power.
A 4S pack produces a bit too much voltage to safely power the rig, but a low dropout regulator can be added to bring the voltage down to one more suitable for the rig.
A 9V smoke alarm battery (once used in transistor radios) can power the MTR-4B for several hours. A tad expensive to do regularly though. But it is fun to see how many contacts you can make using one during a contest sprint. A 9 or 12V battery pack made of AA cells is more long lasting.
A 13.8V bench supply can be used, but this will bring the output power up to 6 to 7 watts. This is fine so long as the SWR is low. At 7 watts, the transmit current is near the maximum the PA FETs can handle and near the point at which the resettable internal fuse will trip (1 A). A high SWR will increase the current in the PA and either trip the fuse or damage the PA.
A simple way of making a 13.8V supply safe to use is to add two silicon rectifier diodes in series with the positive power lead, such as 1N4001 diodes. This will drop the supply voltage to the MTR by about 1.5 volts.
In-line Volume Control accessory: LNR does not sell this, but a popular add-on option is the Koss 155954 VC20 Volume control. It can be purchased from Amazon for $9.99 by clicking HERE.