Portable DMR hot spot booster antenna design.

DMR hotspot booster antenna dimension calculator

Back to Antenna calculator overview.

On-line antenna designer. Calculate the required dimensions for a light portable and very efficient DMR hotspot antenna construction for any UHF frequency.

Introduction to the DMR antenna concept.

I must admit that I am a classic radio amateur operator, HF, VHF and UHF using radio waves. A dinosaur and extinct breed. I consider DMR in it's current state an incompetent (bad codec, crocodile users, prone to packet loss in a completely unacceptable bad way, and there's more), and unreliable but cheap (potentially) global (sound only) communication medium. However it does not take away that I am totally interested in how it works and love the portability with the plug and play into any (hopefully protected) Internet connection and at the same time want to help to improve it.

Main portable DMR problem.

I use and old OpenSpot. It works okay, but the reach is just terrible! No wonder, as the supplied antenna for this unit is little more than a matching dummy load. In a three story building, with the unit on the top floor, the reception on the ground floor was just terrible. Outside the building I got no further than 300 meters. You may state "What more do you expect from a 100 MW transmitter", well... I would like better reach, else I'm stuck to my hotel room, and I would like to use it while exploring the surroundings outside.

Standard DMR antenna

Old school antenna principles.

What if I could use old principle HF antenna concepts, like full-wave antennas. Would it apply and work for UHF as well?

Got some electrical copper wire and started experimenting. Tried triangles, but got weird matching results, Squares produced about twice the impedance of 50 Ohm I wanted. Thought of trying loops, but left it at thoughts as it made no sense. I then tried rectangles and it was an instant winner with easy spot on matching. The solution was actually so simple and there is even gain to be achieved, just a more than 2.5 db. This was perfect for my requirements.

Next challenge was to make it simple to transport and difficult to damage (as in just throw it in a suitcase with everything else and go). I understand that iron is not agood material to use for antenna elements, but electrical copper wire is just to weak and easily bends and eventually after to much bending will break. Next I tried metal guitar strings, very easy to construct and it maintains its shape, even if packed with other goods in a rucksack or suitcase, but difficult to solder (the nickel outer layer would pull loose from the string in time). It was a great performance improvement, but I was still not happy. After discussing this with friends, a suggestion was made to look into MIG welding wire as building material. This proved to be the winner. Went to the local welding workshop and asked if they welded anything other than iron, and if so, could I please have a two meter session of this wire. Received a stiff piece of wire which was non magnetic and had a brass sheen to it. Built a prototype and never looked back, this antenna is such and improvement, it now goes with me wherever my hotspot goes. It has extended the range of 300 meters to way over 1 kilometer and some locals are even using it as a convenient repeater when setup at my base location.

Enter Frequency (MHz)

Frequency calculations are based on radio waves traveling at the speed of light 299 792 458 meters per second.


A: ? mm
B: ? mm


A: ? "
B: ? "

UHF DMR Hotspot Booster Antenna

DMR Hotspot Booster Antenna

The image shows a prototype DMR Hotspot Booster Antenna built for UHF DMR using this antenna calculator, and still fully operational in the attic.

Full Wave Loop Antenna