Many thanks to SWLing Post contributor, Matt Blaze, for the following guest post:
The “Signal Sweeper”, a portable Wellbrook antenna setup
by Matt Blaze
Here’s a very simple construction project that’s really improved my travel shortwave and mediumwave listening experience.
When I go somewhere interesting (whether a day trip on my bike or a longer excursion to an exotic locale), the two things I’m sure to want with me are my camera gear and at least one good receiver. Fortunately, there are plenty of good quality shortwave receivers to choose from these days; the hard part is packing a suitably portable antenna that can do justice to the signals wherever it is I’m going.
I’ve long had a Wellbrook antenna on my roof at home. These wide-band amplified loops famously enjoy a reputation for excellent intermod and noise rejection, as well as an almost magical ability to pull in signals comparable to much larger traditional HF and MF receive antennas. A portable Wellbrook – something I could pack in my luggage that performs as well as the one on my roof, would be just ideal.
Fortunately, Wellbrook sells a “flex” version of their antenna intended for just this application, the model FLX1530LN. It’s essentially just the amplifier of their fixed-mount antennas, equipped with a pair of BNC connectors for you to attach a user-supplied ring of coaxial cable that serves as the antenna loop. This way, you don’t need to travel with the awkwardly large 1 meter diameter ring of aluminum tubing that makes up the normal Wellbrook. You can just bring a compact spool of coaxial cable and configure a loop out of it when you arrive at your destination.
The tricky part is how to actually form a stable loop out of coaxial cable without needing lot of unwieldy supporting hardware. In particularly, I wanted something that could be set up on a camera tripod to be freestanding and easily rotated wherever I happened to find myself wanting to play radio. The key would be finding or making some kind of mostly non-metalic support for the coaxial loop that could be folded down or collapsed to fit in my baggage or backpack for travel.
And then I found it: a humble 3-section telescoping broom handle sold on Amazon for about $15 that’s exactly the right size: the “O-Cedar Easywring Spin Mop Telescopic Replacement Handle“. It collapses to 22 inches (just short enough to fit in my suitcase), and extends to 48 inches (comfortably long enough for a one meter diameter loop).
Normally, a wire loop would need both vertical and horizontal supports in a cross configuration, but by using a reasonably stiff coaxial cable, I figured I could get away with just using the broom handle vertically. I found that LMR400 (the basic kind, not the “Ultraflex” version) holds its shape quite well in a one meter loop supported this way.
At this point, it was just a matter of the details of attaching and mounting everything together into a portable package.
A one meter diameter loop, which is the ideal size for the Wellbrook amp, can be made from 3.14 meters of cable (ask your middle-school math teacher). That’s about 10 feet for Americans like me. High precision is not required here, so I just cut 10 feet of LMR400.
The next step is to attach the middle of the cable to the top of the broom handle. The O-Cedar handle has a loop at the end for hanging it on a hook in your broom closet. It happens to be just the right diameter for LMR400, but not with BNC connectors attached. So you’ll have to thread the cable through before you crimp or solder on the with connectors. (See photo above). I used the Times Microwave crimp-on BNC connectors, which I had some extras of lying around. I also put some shrink wrap on the cable at either side of the broom loop, just to keep it from slipping out and becoming unbalanced, but that was probably unnecessary.
Now I needed a way to to attach the Wellbrook amplifier to the other end of the handle, as well as some way of mounting the whole thing to a camera tripod. My first thought involved a lot of duct tape. But I wanted something more permanent and reusable.
The key is something called an “L-Plate”, which is a piece of hardware intended to allow you to mount a camera to a tripod in either “landscape” or “portrait” mode. It’s basically two tripod dovetail mounts attached at a 90 degree angle. I used one that was in my junk box, but you can buy them new or used on eBay. I also needed a clamp to attach the L-plate to the broom handle. I used the Novoflex MiniClamp 26, which I got from B&H Photo. The clamp attaches to the inside of the L-plate with a captive screw. (See photos)
Next, I attached the amplifier to the other side of the L-plate using an ordinary screw-on hose clamp. Easy enough, and surprisingly sturdy.
And that’s it. To assemble the antenna, just extend the broom handle to about one meter, allowing for a roughly one meter diameter loop that’s as round as you can make it with the amplifier at the bottom. Then clamp the L-plate to the bottom of the handle so that the handle is just above the base of the plate, and attach to the tripod. (See the photos).
The Wellbrook is powered over the feedline with a 12VDC bias-T injector. So you need a clean source of 12 volts. I use a cheap Talent Cell battery pack (available on Amazon in various capacities). These actually deliver 11.1 VDC (3x 3.7V), rather than the 12V the Wellbrook calls for, but it works fine in practice. I can also use the same pack to power the radio and digital audio recorder.
In the photos, you can see the finished antenna setup on my roof, with my permanent base Wellbrook on the rotor in the background. The performance of the two antennas is quite comparable.
(Note that there’s an eBay seller that makes a somewhat similar travel loop. The performance is quite good under normal conditions, but it is a bit more subject to MW overload when near a transmitter site. So I prefer the Wellbrook, which is much less susceptible to overload, I’ve found.)
My usual complete travel setup is either a Reuter RDR Pocket C2 radio or a Sangean ATX-909X (recently upgraded to the X2 model). Both these radios work well with the Wellbrook. I use a Sound Devices Mixpre 3 to record airchecks in the field. In the photos, I’m on a rooftop DXpedition listening to Toronto traffic and weather from CFRX on 6070 kHz on a warm later winter afternoon.
The whole setup breaks down for travel pretty easily, and fits easily in my suitcase, backpack, or bike bag (see photos). I usually bring a larger tripod than this if I’m also taking my camera.
The Wellbrook setup has really made bringing a receiver into the field a lot easier and less uncertain. There’s no worry about finding trees or other supports for wires, and packing and unpacking is quick and easy. Have fun!
Paul Walker’s battery-powered Wellbrook antenna in remote Alaska.
Many thanks to SWLing Post contributor, Pete Jernakoff, who writes:
[…]I’m hopeful that one of your readers might be able to suggest a solution to my problem.
I have an older Wellbrook Communications active loop antenna that is powered by a 12 v AC-to-DC, center pin negative, plug-in power supply (Stancor AC Adapter, was supplied with the antenna).
I’d like to power the antenna from a rechargeable battery in order to make the antenna portable and to eliminate any noise that might be emanating from said power supply (which, as an aside, runs very warm when in operation).
My problem is that I cannot find any rechargeable batteries (lithium ion preferred) with a center pin negative output. All of the ones that I can find online have center pin positive outputs (such as the TalentCell 12V/6000mAh rechargeable battery that I’ve purchased to power my other, more recently produced, Wellbrook Communications active loop antenna whose amp needs a center pin *positive* input).
Thanks in advance for consideration of my request. Btw, love your blog! I’ve been an avid reader of it for quite some time now.
Post readers: If you have any suggestions for Pete, please comment with any relevant links to help him make the purchase. I’m guessing Pete isn’t interested in re-soldering a coaxial plug for negative tip polarity at this point.
By the way, I used a photo of Paul Walker’s Wellbrook at the top of this post because I recall that when he lived in Alaska, he powered his Wellbrook loop with a rechargeable pack (and during the winter, I also recall he struggled to keep it warm enough to provide power for any length of time!). Perhaps Paul can comment.
Wellbrook Mag Loop antenna at Mark Fahey’s QTH near Sydney, Australia.
Many thanks to SWLing Post contributor, David Goren, who writes:
I need a new power supply for one of my Wellbrook loop antennas.
Do you know of good source for reliable ones? I forgot where I obtained the last replacement which worked fine until the wire attaching to the plug worked loose.
Here are the specs:
Plug in Class 2 Transformer
Input: 120VAC 60 Hz 9W
Output: 12V DC 300mA
manufacturer: Sandin Ltd.
Searching online delivers a mixed bag of somebody’s old power supply.
Post Readers: Any suggestions for David? I’m sure he’s particularly interested in a good quality power supply–one that’s quiet and would last a few years. Please comment and include links when possible!
Many thanks to SWLing Post contributor, Mike Ladd, who shares the following video by Rick King who compares four mag loop antennas: the MLA-30, Cross Country Wireless, Bonito ML200, and the Wellbrook 1530LN.
Although we’ve previously posted reviews and comments about the MLA30, I’m quite impressed that it gave the venerable Wellbrook a run for its money. I’m not surprised the Bonito ML200 was the winner here–Bonito quality is second to none.
I live here in South Florida and am unable to erect anything outdoors. I do get pretty good reception on my Grundig Satellit 800 and Tecsun PL-880. For these, I use either an indoor slinky antenna I bought on E-Bay; or an active indoor tunable loop antenna. This is one of the models past reviewed by you. It is Australian made, and covers 6-18 MHz. Please comment if you can on antenna usage.
Thank You very much!
First of all, I’m glad you enjoy the SWLing Post, Tim!
Great question: no doubt you understand that the antenna is the most important part of your radio equation!
You’re on the right track with a PK Loop if you live in an apartment and have no way of putting an antenna outdoors. Being a small magnetic loop antenna, the PK Loop should help mitigate a bit of the noise in your apartment building.
What I love about the PK Loop is it’s small enough that you can re-position and rotate it to tweak noise rejection and find the quietest spot in your listening room. When I travel by car and even by air, the PK Loop is a welcome companion.
Before we talk about investing in a better indoor antenna, let’s make sure we cover a more affordable option first…
External wire antennas
If you have operable windows in your apartment, even fishing a thin-gauged wire out of your window–allowing it to simply hang along the outside of the building–could improve your reception significantly. Of course, if there’s a source of noise outside of your apartment it might only make things worse, but this is at least an inexpensive experiment and the results might impress you.
I had a fantastic opportunity to evaluate how well the PK Loop would perform in a typical hotel room. My buddies Eric (WD8RIF), Miles (KD8KNC) and I stayed overnight in a hotel on Wright-Patterson Air Force Base during our mini National Parks On The Air DXpedition.
The hotel room was indeed dense with RFI.
We hooked my Electraft KX2 to both the PK Loop and to a simple random wire antenna.
Without a doubt, the PK Loop was much better at mitigating radio noise than the wire antenna we hung on the inside of the hotel window.
Unlike most modern hotels, however, this one actually had operable windows, so we tossed the random wire out the window and made another comparison. In this case, the external wire antenna consistently outperformed the PK Loop, no doubt because it had the advantage of being outside the radio noise cloud within the hotel’s walls. It goes to show that outdoor antennas–even if simply hanging from a room window–will almost always outperform comparable indoor antennas.
So, if you have a way to dangle a wire out one of your window, give this a try.
How long should the wire be? I suppose it depends on how much vertical space you have below your window. For starters, I’d try to suspend at least eight feet of wire outside. If I had the vertical space, I’d try as much as 31 feet.
Important: First you must check to make sure your wire couldn’t possibly touch electrical lines. Never lower a wire outdoors if the wind could blow it into an electric service entry point, power line or any other type of line or cable. You should do a thorough inspection of the site first.
With that said, keep in mind: Stealth is key!
Can you spot the wire antenna in this photo? Of course not.
Use a thin wire with a black or dark jacket/insulation. Only lower it when using it–don’t leave it out all day long. Check to make sure your antenna isn’t going to interfere with your neighbors below (like landing in their outdoor grill or flower pots!). One strong complaint from neighbors could shut down your operation permanently.
Now back to loops…
If you don’t have operable windows or a way to deploy a wire antenna outside–or you’ve tried a wire antenna and results were unsatisfactory–then you will be forced to stick with indoor antennas which almost always leads you down the path of larger amplified wideband magnetic loop antennas.
This is a topic I covered extensively earlier this year.
I’m plotting to write a more in-depth article about antennas in the coming months, but it will focus on external antennas and methods of mounting them. When you have no means of mounting an antenna outdoors, in my opinion, your best options are the ones mentioned above.
Post readers: Have I overlooked an indoor antenna option? Please comment if you have experience with indoor antennas!
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!
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