Active Loop Antenna, buy a commercial one or roll your own? Part 1.

 If you are in need of a Active Loop Antenna to use with your RX with there are a number of options.

You can buy any number of well known brands for over a 100 GBP or one of the cheaper Chinese designs like the MLA-30+, or you can build your own.

After trying a fair few designs I settled on one, it first appeared around 1984 in a design by G8CXQ.

Below is the circuit as I use it. Q1/Q2 are plastic 2N2222/PN2222 or equivalent. 

T1 is a FT50-43 ferrite ring with 15 bifilar turns of enamelled wire or similar.

A 700C Bicycle wheel with a slot cut across the rim makes a perfect loop. 

I find the best way to construct the circuit is to build it ugly bug style on copper clad board.

Layout the circuit as it is drawn is the easiest way, see image below.

Layout the components out as they appear on the circuit.

Next Image shows it boxed and ready to connect to a loop.

Circuit boxed with banana sockets for connecting to the loop and a 'F' type chassis socket for the coax connection.

Active Loop Antenna power supply

Now on LF/MF/HF these antennas are directional end to end with the null across the flat sides.

But here is the interesting thing, this antenna also works on VHF, especially on Band II FM, but here it is directional across the face of the loop.

So if the loop is pointing East-West for LF/MF/HF, on VHF its best reception is North-South.

I have two of these loops in the loft positioned at right angles to each other. Watch the video to see what happens as I switch between them, first LF/MF/HF and then VHF.

  Another video showing the directional properties on VHF, switching between the two loops on 93.5 MHz lets me receive either the BBC or Radio France International.

'Bicycle Loop' a 18 inch cycle rim is used as the loop.

SDR devices, Fake, Clone or Genuine? Part 1

  Fake, Clone or Genuine? That seems to be the question people ask when looking at SDR devices on online market places.

So the question is what does each of these terms terms mean?

Fake: an item passing itself off as another by using its name etc when in fact it is a completely different device.

Clone: an item that is exactly the same as another in all respects. 

Genuine: An item produced and developed by the originator.

How does this apply in the SDR world?

Well lets take a popular device The SDRPlay RSP1.

The above image shows a Genuine RSP1.

This next image shows a device that uses the same Mirics chipset as the RSP1 

Now nowhere on this device is any mention of SDRPlay or RSP1, so what is it, is it a Fake?

Well no it isn't a Fake because it isn't pretending to be something it isn't. 

Is it a Clone? Well no because quite evidently the device isn't identical to the RSP1.

So is it Genuine? Yes it is a genuine five port SDR device. No it isn't a RSP1, but it doesn't imply it is either.  In fact these new devices are superior to the RSP1, containing many improvements over the original.

A lot of people say these devices steal the intellectual property of SDRPlay because many people use SDRPlay's software to run them, but you don't have to. There are free open source alternatives available.