Homemade Active Loop for LW, NDBs, MW and HF

I've been experimenting with loop aerials for years as from my very first project I was wowed by their ability to reject local noise and give me back my hobby of short wave listening, which was becoming increasingly difficult as RF noise plagued the ether.

My first loops were ugly and crude but worked extremely well and saved me lots of money. Over the years the designs have improved and looked more like something I was proud to have in the shack.

But being interesting in a huge chunk of radio spectrum, from LW right up to HF, I needed to swap loops around. A lot. And even assuming I could have made a passive tuned loop to cover all of this, I would still have needed to retune each time I changed frequency.

In the end I suppose I compromised and ended up with a wide 2.1 to 18MHz loop for HF (well, most of it) and pretty much neglected LW, MW, and NDB DXing.

So it had long been an ambition of mine to build my own active loop. The Wellbrook loops were too big and too expensive for me, and with the little outside space I have available being plagued by RF, would need to be sat inside the shack, and to be honest I found their design too ugly for this!

The AOR active loops were my favourite, but still they were very costly and I was put off by the very small 30cm diameter. I know from my own experiments that doubling up to, say 60 or 70cm, gave a huge in signal, especially on the 5 and 6 MHz bands, were I do a lot of utility DXing.

So I decided to build my own. And it has been surprisingly straight-forward.

I bought the amplifier ready assembled from Rainville Communications in California. Luke there was incredibly helpful, and after patiently explaining to me what I needed for the project (I was getting confused between an active loop and adding a PRE-AMP to my tuned loops, that would have added more noise and little else) I ordered the LAMP-1A HF Receiving Loop AMP.

Putting it all together was really simple, though you do need to have basic soldering skills just slightly beyond what you might need to build a passive tuned loop, but only ever so slightly. If I can do it, anyone can! I had given months of thought to how I wanted it to look, as this was very important in this build. I wanted a small, somewhat flatter box than my normal bulky looking ones, and a sleeker, lower-profile design. I wanted a little LED to show me when it was on, and ideally to give an indication of the amount of gain I had selected. The variable gain is simply a variable resistor (potentiometer) used to reduce the power (I chose a 1K linear which is about perfect). I used a 75cm Witzig Hula Hoop from onbuy.com and 15mm single hinge clips from Talon to secure the loop to the project box.

So for £50 I ended up with what I think is a very sleek-looking loop which outperforms anything I have ever made before. The AMP is superbly quiet and generates no noise at all, unlike previous supposed "low noise" RF Amps I have bought before from China for £6.

Rainville state it is an HF AMP, but it works extremely well all the way down to 200khz, which was a really nice surprise when I was testing it out. I spent a long time comparing it to a larger passive tuned loop, and in every respect it outperformed it. I was really surprised as I had a pre-conceived notion that any kind of amplifier in a noisy RF environment was a big no-no.

The joy of being able to hope around from NDBs in the 400khz band to HF, back to MW, and all without re-tuning or swapping loops is indescribable. SWLing heaven!

I am attaching some photos of the loop. I have also done Youtube video

Message me via comments on this blog or my Youtube Channel if you want to ask me any questions. I enjoy hearing from you and chatting about this fine radio hobby of ours.

73 Adam