Many thanks to SWLing Post contributor, Bill Hemphill (WD9EQD) who shares the following:
I went to the Warminster Amateur Radio Club (WARC) hamfest [yesterday] in Bucks County, PA. For some time, I have been thinking about making a loop antenna for AM DXing. It was my lucky day. When I walked to the inside tables, on the very first table was this homemade loop antenna gentleman was selling from an estate.
I snatched it up for $40.
Attached are some photos of it. It’s 25” by 25”, with a swivel base. There are 23 turns of wire and I have no idea what size the capacitor is. I did some preliminary tests and it tunes from 280 kHz to 880 kHz. So it’s the covers the high half of the long wave band and the low half of the AM band.
It’s very well made and I fugue I can modify it to cover the entire AM band.
[…]I hooked the SDRplay RSP2 to it and was getting good signals of major stations all the way to 15 mHz.
That’s with it sitting on my dining room table. Of course the capacitor wouldn’t peak the signals.
So it was a great day at the hamfest!
Indeed that was a great find, Bill! Someone spent a decent amount of time building that furniture-grade loop support. Indeed, it’s very reminiscent of 1920s-30s mediumwave loops!
What I love about your loop (and that of Thomas Cholakov) is that one can see how simple these antennas actually are to build. The only complicated bit is the support, but even that’s simple if you use the shield of a heavy coax or flexible copper tubing.
Thanks for sharing and enjoy logging DX with your new-to-you loop!
Brilliant video, Thomas! I love the fact you included a demonstration with your SDRplay RSP1A as well. Via the spectrum display, it’s easy to see the the loop’s bandwidth and also the gain it provides when tuned to a station.
I love your AM loop antenna as well–such a simple design and ideal for demonstrating the mechanics of a passive loop antenna since all of the components are visible. I’m willing to bet you built this antenna for less than $10. Smart design as it’s both portable and effective! Keep up the excellent work, Thomas! We look forward to all of your future videos.
This is just a quick Field Update for my Backpack Shack 2.0 antenna. It is not the most powerful antenna but in the right location it can be useful, especially with using an SDR. It was used during February in two Forest Preserve (County Park) locations outdoors and once from my usual Grocery Store parking lot!
Please excuse some of the computer generated noises (caused by a slow CPU) as well as some audio connector problems on a couple of recordings.
Each Time is in UTC and Frequency in kHz. Where can you hear unique programming like these samples except Shortwave Radio??? Enjoy!
Many thanks to SWLing Post contributor, Chris Freitas, who writes:
“I am thinking of the new RSP1A SDR. Would you know of a good indoor antenna that would work well with it?”
Your antenna question is simple, but the answer is complex!
First off, I think the RSP1A is a great choice as it’ll give you proper exposure to the world of SDR (1 kHz to 2 GHz!) at a modest price.
Unlike a portable radio of course, your SDR must be connected to a PC, laptop, tablet or some sort of mini computer like Raspberry Pi. This limits your ability to easily try different antenna locations within your home compared to, say, a battery-powered portable radio. It might take some dedicated experimentation and patience.
Indoor antennas are so vulnerable to the radio noise within your home.
If you live in an off-grid cabin with no radio interference nearby, even a simple $1 random wire antenna hooked up to RSP1A’s SMA connector would yield results. I occasionally spend my summers in an off-grid cabin and it’s simply amazing what you can do with a modest setup when there are no man-made radio noises around.
Listening to the final broadcast of Radio Netherlands in an off-grid cabin on Prince Edward Island in 2012.
But how many radio enthusiasts live in an off-grid cabin? Answer: very, very few! Most of us only get to experience off-grid life during natural disasters when the electrical grid has been damaged in our neighborhoods.
The reality of indoor antennas
You’ve told me previously that you live in an apartment in an urban setting, hence you probably cope with a lot of RFI.
When an antenna is indoors, it is forced to function within this RFI-dense environment. Your telescoping whip or wire antenna doesn’t discern between radio noise and your target broadcast signal. Thus, noise can overwhelm your receiver, essentially deafening it to all but the strongest shortwave broadcasters.
This is why if you had a means to put a small random wire antenna outside–even if it was simply draped outside a window–it would likely perform better than an indoor antenna. I’m guessing this isn’t an option for you, Chris.
A broadband loop antenna (image courtesy of wellbrook.uk.com)
While you can build an amplified mag loop antenna (like our buddy, TomL) it’s not a simple project. Passive single turn loop antennas, on the other hand, are quite easy to build but are narrow in bandwidth (here’s a very cheap, simple passive loop project). You would likely design a single passive loop to serve you on a specific brodcast band and would have to retune it as you make frequency changes. You could build a passive loop antenna for less than ten dollars if you can find a good variable capacitor. Here’s another tutorial.
Commercially produced amplified wideband magnetic loop antennas are not cheap, but they are effective. If you’re a serious SWL, a good mag loop antenna is worth the investment.
Here are a few of my favorites starting with the most portable:
W6LVP sells two versions of the antenna–since you’re not operating a transmitter, this $250 model would be all you need. indeed, if I were in your shoes, this would likely be the loop I purchase–very cost effective.
Wellbrook antennas are the staple magnetic loop antenna for many DXers.
Wellbrook makes a number of loops, but since you have no plans to mount this outside, I believe their indoor model would suffice.
Other loop options
There’s no shortage of magnetic loop antennas on the market, but most are pricer than the models I mention above and I know you have a tight budget. Here’s are some models we’ve mentioned on the SWLing Post in the past:
I hope this helps, Chris! This post is by no means comprehensive, so I hope others will chime in and comment with their experiences. Good luck fighting urban noise and I hope you enjoy your journey into the world of the SDR!