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Many thanks to SWLing Post reader, Klaus Boecker, who originally posted these images of his homebrew magnetic loop antenna on the Shortwave Radio Station Listening Facebook page.
I love the design of his mag loop which easily allows for a vertical or horizontal orientation. Kaus has discovered, in certain cases, places the loop in a horizontal position dramatically decreases the noise level.
Having a little fun with what I call “urban camouflage” Klaus recently decorated his antennas to match the neighborhood flower boxes!
I’m sure more than one neighbor may be wondering what sort of creative floral arrangement Klaus has planted!
Klaus notes that the vertical to the left of the loop is a a 2m / 70cm J-Antenna.
Thank you again, Kalus, for allowing me to share your images here on the SWLing Post. I imagine your modest home-grown antenna farm works some serious DX on occasion!
Thanks again for sharing!
Readers: Have you camouflaged or decorated your antenna(s)? Please share your photos!
Over the past year, a number of SWLing Post readers have asked me to review the PK Loop portable magnetic loop antenna produced by Paul Karlstrand in Australia.
I finally caved in and purchased one.
I ordered the shortwave version of the loop, the C-LOOP-HDSW6-18 in early November and received it about one week later.
The Sony SW100 tuned to WBCQ.
I was first introduced to this antenna by SWLing Post contributor, Mark Fahey, who brought it to the SWL Fest and our 2015 PARI DXpedition.
Mark has taken his PK Loops (both the shortwave and mediumwave models) on his numerous travels around the world. He finds that they’re relatively effective portable antennas in RFI-dense environments like hotels and guest houses. They’re better at mitigating RFI than, say, portable wire antennas or telescopic whips.
Mark hooks up his portable SDR to the PK Loop and makes spectrum recordings (wideband recordings)–from, say, his hotel room in Kuala Lumpur–then takes the recording back home to listen and tune at his leisure via his laptop or tablet PC. While I’ve certainly made spectrum recordings while travelling in the past, the appeal of such a portable loop antenna is what finally caused me to pull the trigger.
Overview
The PK Loop is a small loop antenna–measuring about 12″ in diameter. It’s encased in UV-stabilized PVC conduit and the matching box also seems to be made of PVC. It feels very durable and can, no doubt, even survive the wildest of luggage handling.
The PK Loop has an attached battery 9V battery holder, but can actually be powered by any 9-18 volt DC supply. Current consumption is less than 15 mA. On the matching box, you’ll find a tuning knob, a BNC connector, DC power in port and a HI/LOW gain switch. My loop shipped with a 2 meter BNC-BNC Cable, 3.5mm adapter, and DC Power lead to open ends.
Operation
Operating the loop is very simple:
Power the antenna with a 9V battery or other DC source
Chose either the high or low gain setting
Place it on a stable surface (height from the ground is not a critical issue, but you should avoid placing it next to noisy electronics or mobile phones)
Connect the PK Loop to your receiver’s antenna jack with the supplied cable
Turn on your receiver to the desired meter band, then adjust the loop’s tuning knob until you hear the signal level peak
Start listening, keeping in mind that as you tune around the band you may need to adjust the loop’s tuning knob for maximum gain
Loop antennas, in general, are fairly narrow-band and–unlike a Wellbrook or Pixel Loop–manual adjustments need to be made with the tuning knob to match the PK Loop as you scan across bands.
Still, I see why Mark favors the PK Loop for spectrum recordings: the bandwidth is wide enough that if I tune the loop to the middle of the 31 meter band, for example, it does a fine job covering the entire band.
On the air
My free time has been very limited since receiving the PK Loop earlier this month, but over Thanksgiving holiday, I took it to my family’s home that has relatively high RFI levels.
The following are a couple of videos I made with my Moto X smartphone. I’ll be the first to admit that these are not the best videos–I had no tripod and the Moto’s microphone leaves much to be desired–but I think you’ll still get the idea of how well the PK Loop works.
So far, I’m very pleased with the PK Loop. It does seem to mitigate noise better than other portable antennas I’ve used in the past and certainly improves my SW100’s reception. It makes SWLing with the Elecraft KX2 or KX3 easy and convenient.
One word of caution: if you use the PK Loop with a transceiver like the KX2, please turn off the ATU, and set the power level to 0W before using. The PK Loop is receive-only and will not handle any RF power.
Note that with the SW100, I have only used the PK Loop’s low gain setting. I’m a little nervous about overloading the SW100, so do not plan to use the high gain setting. The Elecraft KX2 seems happy to handle either gain setting: I imagine this will be the case with most general coverage transceivers and tabletop receivers.
More to come!
In a couple of weeks, I’ll be staying in a hotel room (likely with inoperable windows and heavy RFI) so I will attempt to put the loop through its paces and compare it with my radio’s built-in antenna. Stay tuned!
Many thanks to SWLing Post contributor, Troy Riedel, who shares the following guest post:
Review: DoxyTronics Portable HF Magnetic Loop 8020CA
-by Troy Riedel
Before I purchased the DoxyTronics 8020CA antenna, I emailed the owner/manufacturer and asked if he felt this antenna would be a good choice with the radios that I own. He promptly and courteously answered my question and I purchased the antenna on September 30th. I received the antenna approximately 6-days after I ordered it.
The DoxyTronics 8020CA magnetic loop antenna
I have been evaluating the antenna for 5-6 weeks mostly on my Grundig Satellit 750 and my Grundig G3. I have used other portables but the two aforementioned Grundigs were the radios I used most.
The antenna control box has a ¼-20 hole on the bottom so it can be mounted to a video camera tripod. The assembled antenna weighs 3 lbs. I tried using a light duty DSLR tripod that I own, however that was nowhere near sturdy enough. I had to use a heavier duty tripod (Ravelli AVT) that I use for astronomical purposes. This Ravelli has a weight capacity of 16 lbs and it easily supported the antenna. I’m confident a much smaller and lighter duty tripod than the Ravelli could be used, I simply don’t own anything in-between as my astronomical binoculars and binocular telescopes weigh 5 – 14 lbs.
The 8020CA Antenna consists of a large tuning knob and control box. The control box has switch settings of 3-5 Mhz and 5-15 Mhz. In testing, I found that I could “tune” up to 17.840 MHz. No batteries are needed to operate.
The antenna worked equally well with all of the “portable” radios that I tested (I am a SWL’er, not a ham).
I can summarize the antenna’s performance as this: it is not a magic elixir that will allow you to capture signals too faint to recognize without the antenna attached, but it definitely enhances the signal and “stabilizes” it to the point where the level of the signal remains relatively constant (less peaks & troughs in signal strength).
Hopefully you can hear what I have summarized and concluded. I have included a two and one-half minute recording of the following:
Radio: Grundig Satellit 750 Recorder: RadioShack 140-214 Freq: 7.310 MHz BW: Wide Broadcaster: Radio Romania International Date of Recording: 15NOV2016 Time: 2309 – 2313 UTC
00:00 – 00:30: 8020CA Antenna Attached 00:30 – 01:00: Radio’s Whip Antenna 01:00 – 01:30: 8020CA Antenna Attached 01:30 – 02:00: Radio’s Whip Antenna 02:00 – 02:30: This last 30-second segment is with the 8020CA attached, however I am panning the Ravelli tripod 360-degrees in the horizontal. You will hopefully notice that there is a “sweet spot” where the signal and reception is the best of the entire 2:30 recording. I had set-up the antenna and I completed a quick, test recording of Radio Romania. But conditions changed slightly and the best signal during the recoding was approximately 50-60-degrees away from where the best reception was earlier. This is a positive for the antenna: you can pan the tripod head where the antenna sits to null and/or find the best signal.
Note: this is my first shortwave and radio-related review I have ever done. I have done many astronomical reviews – where I have much more experience – so please be kind towards this first attempt.
No worries, Troy! We’re kind and appreciative here–especially since guest posts are all about sharing our experiences and experimentation!
I must say, the DoxyTronics loop is doing a fine job mitigating the local QRM/interference that is easily heard when only the telescopic whip is being used. I’m also impressed that a passive loop this modest in size has so much gain without amplification.
I recently stumbled upon the Active Antenna Amplifier (model AAA-1C) by LZ1AQ. At 87.00 EUR, it’s a pretty affordable and flexible solution for those who would like to design or use a loop antenna.
According to the website, it packs a lot of features:
4 remotely switched modes (Loop A, Loop B, crossed parallel loops A&B and dipole)
Each mode can be switched immediately
Good sensitivity and a flat frequency response
High dynamic range
Protected input from strong signals
High immunity to local noise with balanced amplifiers and balanced feed line
Balun transformer coupling for common mode noise reduction
Extensive documentation manuals with detailed description how to build your own small antennas
The amplifier is described as a kit because you must mount the board, wire up the antenna and set up remote switching yourself. It appears the SMT board comes pre-populated, though so I’m not sure if any actually soldering is required (perhaps someone can verify).
Many thanks to SWLing Post reader, Larry Caracciolo, who comments:
I bought the AN-200 in the spring of 2015 off of eBay. I was favorably impressed with the product. Comparing it to my old 9′ diameter tuned/shielded loop from 1992, there are some similarities and differences.
The Hallicrafters SX-96 (Image: Universal Radio)
I live in an apartment complex so plenty of radiated electromagnetic noise is present. I use a modified [Hallicrafters] SX-96 (AVC ckt was modified for improved modulation acceptance). The AN-200 does null out local static sources, somewhat, but not well enough to dig out weak stations. The tuning range for the loop is just at the bottom of the AM band (about 535 khz) to just over 1700 kcs.
On a whim, I wrapped aluminum foil around the loop and grounded it to the SX-96 chassis – in wistful hope of achieving some shielding from the RF has. As soon as I connected the aluminum foil ground clip to the rx chassis, all RF noise ceased and signals appeared from the mud. However, the tuning range is attenuated above 1200 kcs.
My favorite frequency on the AM band is 590 kcs. During the night, as many as seven different stations rose from the noise and provided station IDs at just the right moment. My best catch here in Everett, WA is KCSJ, a 1KW station in Colorado Springs.
From time to time, stations on the low portion of the AM band are accompanied with echoes – what I took for two stations and a small time delay between the same broadcast was actually multi-path to the degree that nearly 1/2 second separated the arriving signals. Short-delayed echoes, anyone? I’ve not observed this on frequencies above 1000 kcs.
Other sources of RF noise can come from the laptop, the cable modem, and even CFBs in other rooms. For truly noise-free listening environment, I place the laptop in sleep mode and unplug the cable modem. I’m quite happy with the AN-200 loop. Affordable, easy to use, easy to tune.
Thanks so much for sharing your experience with the AN200 loop antenna, Larry!
As anyone who grew up in the era of TV rabbit ears knows, aluminum foil can simply work magic in a pinch! There is no easier material to work with either!
As I pointed out in previous posts, the AN200 loop antenna is quite affordable. I just did a quick price search:
Many thanks to SWLing Post contributor, Dave Gahimer (K9ZCE) for the following guest post:
Small Magnetic Loop Antenna with Broadband Amplifier for SDR Reception
by Dave Gahimer (K9ZCE)
Those with limited space, or antenna restrictions, might find a small 1 meter loop antenna a solution.
My son lives in an apartment. One Loop leaning against a wall gives him acceptable reception with the SDRPlay RSP on the ground floor–2nd or 3rd level flats should have very good reception.
Ten meters off the ground outside should give reception equal to any SWL antenna. We all with SDRs fight the image problem. Normal resonate ham band antennas show too strong reception of unwanted bands/stations. Did I mention noise? Loops are well known for –6 db noise reduction.
Then there is the possibility of SDR chip damage from your 1.5 KW station! In researching Loops we came across LZ1AQ. A Brilliant design /engineer (http://www.lz1aq.signacor.com/). Deep reading sometimes, but a great understanding of what makes a good receiving loop antenna.
Those who chase DX know that sometimes fading is caused by the signals’ polarization changing in the Ionosphere. Having both vertical and horizontal loops, and the ability to combine both signals diminishes this fading problem. Being able to filter the powerful, commercial FM transmitters diminishes image problems. Clipping strong signals at the antenna from very near powerful antennas/transmitters could save the SDR receiver from damage.
My son Ted and I built three, one meter loops from soft ½ inch copper plumbing tubing. One for his apartment, two for my crossed loops antenna. We weather proofed the Copper from corrosion by coating with outdoor clear spar varnish. We shaped the circle by drawing the tubing around a round glass top patio table.
The soft copper loop in held by white PCV plastic plumbing pipe. 1” or 1.25 inch schedule 40. Be careful to check that the PVC is schedule 40, thick wall. The thin wall pipe is not strong in the wind and will crack when you try to drill it.
Drill up to a 3/8 hole for the ½” copper tube to go through, then file out to fit. Here are some photos (click to enlarge):
Check out these links (all courtesy of LZ1AQ) to acquaint yourself with the loop construction and amplifier installation:
Many SDR receiver owners have seen improved noise and Image reduction by placing the plastic cased SDR unit on a small shielded/ grounded case.
The Amp needs 12VDC from in the shack. The Amp has two relays that you can switch, from in the shack, to select Vertical or Horizontal loops, or a dipole. The loop amp connects back to the shack via a shielded Cat 5 cable, Make sure you get shielded CAT 5 to reduce noise pickup. Make sure you provide an adequate good Ground below the antenna, less noise pickup and lightening protection.
Have fun!
Dave, K9ZCE
Retired from EE Dept @ Rose-Hulman Institute of Technology
Terre Haute, Indiana
Thank you so much, Dave!
Readers: yesterday I saw Dave’s loop antenna photos on the SDRplay RSP Facebook page. I was fascinated by his horizontally/vertically oriented loops and asked if he would write up a short guest post. He kindly obliged in a matter of hours!
If you have an antenna project you’d like to share, please contact me. So many SWLs and ham radio operators live in areas with restrictions and pervasive RFI–projects like Dave’s can revive one’s radio life!
Yesterday, Tony (K3DY), shared a video (via Twitter) demonstrating his new home brew loop antenna and amplifier.
This is actually a great demonstration of how even a relatively simple, inexpensive loop antenna can improve reception in locations with heavy radio interference. Tony includes the following notes with his video:
“Testing a new receiving loop antenna that I built today. It uses a pre amplifier based on deferential setup of two 2N5109 transistors. Loop is made out of coaxial cable, only the shield is connected to the circuit.
Quick demo on 31 meters, lots of stations at sunset time. No time for further testing but I observed a pronounced directivity below 7 MHz. 75 meters is so quiet that it makes me forget I live in a townhouse. As a comparison, my noise level on 75 meters is at S8 on an end fed [antenna].
https://www.youtube.com/watch?v=bq_gKNQSVeA
I will use this loop primarily for SWLing purposes but I may use it as a separate receiving antenna with my amateur radio equipment.
A lot of fun, loops are fascinating and efficient!
Indeed, Tony! And perhaps the icing on the cake is that loop antennas are so portable, low-profile and easy to deploy. They’re ideal for those living in restricted areas and with picky home owners’ associations.
Inspired by my buddy Vlado (N3CZ), I’ve actually been collecting the pieces to build my own mag loop antenna this winter. I doubt the parts for my loop will exceed ten dollars as I plan to use the shield of some heavy coax for the primary loop and a little PVC for support (much like Tony’s loop).
Tony’s video is inspiring me to go a step further and also build a simple amplifier. Any suggestions or schematics for doing so are most welcome!
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