Monday, December 23, 2013

Simple, light weight, stealthy QRP dipole

In a few weeks we will move from our current QTH, with room for antennas, to a flat on the 28th floor, with a small balcony and restrictions on what can be put out there. (We'll be back but not for 8 months).

I have a new interest in stealth QRP antennas and have been experimenting...

Targeting 20m, I've built this very successful dipole. The wire is 10.1m, cut in half, with the ends folded back on themselves for tuning.

The feed line is thin RG-174 co-ax that runs directly in to ten turns on an FT114-43 toroid. A twin screw terminal block is used to attach the dipole wires. The design comes from n5ese but has been further simplified.

Everything is held together with cable ties and it's light enough to be suspended by the dipole wires. At resonance the SWR is very low but for some reason the impedance is a little low too.

The FT114-43 should work on any band from 0.5 to 30MHz by the looks of it. My plan is to use this for 10W which should be fine.

I'm looking for better options for connecting the legs of the dipole but the screw terminal block will do for now. Waterproofing is plastic wrap for now.

This probably won't survive very long.

This arrangement is very light, removes the need to have a connector at the balun, which saves both an potentially crackly connection and the weight of plug and socket. Running RG174 coax is light and less visible than other alternatives.


I've had a series of test contacts with Mal, VK2BMS. This antenna is better than the short Ozi-pole dipole but not as good as a full dipole on the roof - pretty much what you'd expect.

Thursday, December 12, 2013

Getting started with Bluetooth LE iBeacons

Recent devices include Bluetooth 4 which is able to run in a low energy (LE) mode and ping out a beacon running on a small battery for up to a few years. I purchased a few samples from Estimote that look like this:

It's also possible to use a Raspberry Pi with a USB bluetooth 4 dongle (I bought a Targus one for $40) to make a beacon. I followed instructions and it worked out of the box.

With this software you can make a beacon that emulates either Apple's AirLocate samples or beacons from any other vendor including Estimote, Radius, RedBear Labs, TwoCanoes or any others.

To scan for beacons, (without writing a specific app), there are a few iOS apps including the Estimote app and "Locate iB". On MacOS there's an app that can find any beacons in range called iBeaconScanner:

By pretending to be an Estimote beacon you can use their app to scan too:

All good fun. I'm sure we'll see these things everywhere within the next few years.

Sunday, December 08, 2013

An earth stake for the shack

I seem to have problems with RF feedback in the shack when using any kind of end fed antennas. Dipoles do better for me. I'd commented on this a few times and today local amateur, Robert, VK2ZNZ very kindly arranged for a beautiful copper coated steel stake to be hammered in to the ground.

Robert has been mysteriously absent from the Sunday morning 80m callback in recent weeks but it turns out the reason was that he's had a hip replacement so he availed himself of my shack's comfy chair:

Thanks very much for your kindness Robert!