By Jock Elliott, KB2GOM

It was a remark from Sebastian Schlüter in response to this post – https://swling.com/blog/2025/10/some-really-inexpensive-ways-to-perhaps-improve-your-shortwave-listening — that sparked today’s post.

He said:

If your RFI is really high, your best weapon is a magnetic loop antenna aka small receive loop. At home, my RFI is so high that I don’t benefit from a larger/longer antenna. For example: Using the telescopic antenna (75 cm) vs using 3m of wire. Reason is that the signal-to-noise ratio is roughly the same in both cases and that all of those very weak signals are below the noise floor anyway, and the ones that make it through the noise are already strong enough to be received with the telescopic only. Conclusion: In a high RFI environment, it’s not about maximising the signal strength but maximising the SNR. You need to find an antenna type that will pick up less of that RFI. A cheap and simple antenna for this is the small receive loop. For a start, you can use a cheap wire terminal with 3.5mm mono jack. Using a 1:1 balun further improves the result.

What really struck my eye was this:

A cheap and simple antenna for this is the small receive loop. For a start, you can use a cheap wire terminal with 3.5mm mono jack.

My CCrane Skywave SSB 2 came with a wire terminal with a 3.5 mono jack, I realized. I hooked it up to my 45-foot horizontal room loop (a single strand of insulated wire run around the top of window frames and bookcases in my radio shack), and then ran the following experiment.

Using the scan function on the Skywave SSB 2, I scanned the shortwave bands using the whip antenna, and then I did it with the loop plugged into the external antenna socket.

The results:

CCrane Skywave SSB 2

Whip antenna: 4 stations detected.                             Loop antenna: 13 stations detected.

Then I tried the same experiment with a Tecsun PL-880.

The results:

Tecsun PL-880

Whip antenna: 8 stations detected                              Loop antenna: 15 stations detected.

Clearly, Sebastian’s suggestion of plugging in a simple wire loop makes a huge difference. And, I should note, I didn’t play fair. I did the test while 3 scanners, an LED light, and two UHF/VHF ham transceivers were operating in the vicinity and probably generating RFI.

So now the question: I ran the experiment with a 45-foot simple loop. What do you suppose would be the minimum wire length for an effective simple wire loop? I look forward to your input.