Ostracus on To Give Is Better Than To Receive.Somehuman on Labor Day BBQs May Feature NYPD.Observer on Make Better 3D Printed Molds, For Thermoforming Plastics.CityZen on On Vim, Modal Interfaces And The Way We Interact With Computers.Somehuman on Hefty 3D Printed Quadcopter Meets Nasty End.Retro Gadgets: The 1974 Breadboard Project 31 Comments Posted in Radio Hacks Tagged amateur radio, amplifier, ham, LDMOS, push-pull, RF, transmission line transformer Post navigation The video below gives a tour of the amp and shows some tests with impressive results. Even the heatsink compound is special rather than the typical silicone grease, he chose a liquid metal alloy called Gallinstan. paid a lot of attention to thermal engineering, too, with the LDMOS transistors living in cutouts in the custom PCB so they can mate with a hefty heatsink. A pair of the LDMOS devices form the heart of the push-pull amp, as do an array of custom-wound toroids and transformers including a transmission line transformer wound with 17-ohm coax cable. While LDMOS transistors aren’t exactly new – laterally-diffused MOSFETs have been appearing in RF power applications for decades – the particular parts used for the amp, NXP’s MRF300 power transistors, are pretty new to the market. One of the great joys of being a ham is being able to build your own gear, and to incorporate the latest technology long before the Big Three manufacturers start using it. We’re really impressed with the work that put into this power amp. That’s where builds such as this well-engineered 600W broadband RF amplifier come into play. But sometimes quantity has a quality all its own, and getting more power into the ether is what the contact requires. That’s just part of being a good spectrum citizen, and well-earned bragging rights go to those who make transcontinental contacts on the power coming from a coin cell. It’s not the most elegant solution but it works fine.Typically, amateur radio operators use the minimum power needed to accomplish a contact. For extended operating sessions, I throw 4 extra cells in my backpack that I can swap in if needed. I haven’t done any formal testing of this battery arrangement, but it has provided adequate power for an afternoon of portable operating. The D4 works with a variety of battery types (Ni-Cad, NiMH, Li-Ion, etc.) so it is a handy accessory in the shack. Each bay works independently, so balanced charging is not an issue. It automatically detects the type of battery inserted and applies the proper charging method. Battery pack as I normally use itįor charging, I remove the cells from the holder and charge them with a Nitecore D4 charger. In use, I lift one corner of the lid to bring out the connector. When not in use, everything is neatly tucked inside the container. It turned out to be the perfect size to hold everything snugly. To package it, I had a sandwich-sized Rubbermaid container that wasn’t being used. I also added a 2-amp fuse and an Anderson Powerpole connector. This brings the voltage down to about 13.7 volts with fully charged cells. To keep the voltage below 14 volts (the maximum for my HB-1B), I put 3 silicon diodes in series with the output. With 4 fully charged cells, the voltage can exceed 16 volts. To put it together, I bought a 4-cell battery holder for 18650-size cells. There are much cheaper unprotected cells but I’d rather be safe than sorry. These particular cells are the “protected” type each cell contains some circuitry that prevents overcharge and over-discharge. I haven’t actually verified the claimed capacity but most cells tend to be somewhat over-rated. They are 18650 cells with a 6000 maH rating. I already had some Li-Ion cells on hand, so I wanted to make use of them. I wanted something relatively lightweight and inexpensive that would put out at least 13 volts. Here’s a little battery pack I put together for use as an external, portable power source for my YouKits HB-1B.
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