Tag Archives: Homebrew Mag Loop Antenna

Larry’s variation of the W6LVP amplified magnetic loop antenna

Many thanks to SWLing Post contributor, Larry Thompson (WPE8EKM), who writes:

I’ve just finished building a variation of the W6LVP amplified magnetic loop antenna. I was able to purchase the preamplifier, power inserter, and the power supply separately. I then created my own loop antenna using LMR400Max coax and designed my own knock-down PVC support. I wanted something extremely compact and portable to take on sae-kayaking expeditions and to DXpeditions to Africa.

I spent many years teaching in the DRC Congo and hope to return.

I’ve used a 6’ loop, a 9’ loop, a 12’ loop, and an 18’ loop. All do very well, but the 6’ and the 9’ seem to do the best. I’ve been using the 9’ length of coax doubled into two loops and that seems be be doing extremely well.

The signal strength from the W6LVP variation is equal to my Parr EF-SWL End-Fedz 45’ dipole, but the reduced noise level on the bands is amazing. I live in a central city high-rise with no possibility of an exterior antenna. The EF-SWL is strung out a 5th floor window down the side of the building. It performs well, but with a high degree of noise. My QTH is rampant with QRM and RFI noise. The W6LVP amplified magnetic loop has really resolved that in a big way.

The bands are horrible at the moment, so evaluating the loop antenna is difficult. But the cleaner, stronger signals of CHU Canada on 3339 kHz and 7850 kHz, as well as WWV on 10,000 kHz is impressive.

I’m impressed with the reduced noise level on the bands tuning across them, as well as the noise-free signal once you lock into a station. I’ve heard hams on the 17 mb for the very first time.

So far, I’m very impressed with the performance of this amplified magnetic loop.

Very cool Larry! You’ve build a compact loop that can bring the RFI down to a tolerable level–I’d say that’s a complete success. Thanks for sharing!

Click here to read our previous article about the W6LVP loop.

Guest Post: Backpack-Shack radio listening

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Many thanks to SWLing Post contributor TomL, who shares the following guest post:

Illustration 1: Main contents

Backpack-Shack radio listening

by TomL

So, the Car Shack idea was good, but I felt constrained by lack of access to better locations to listen to shortwave radio. I took most of the original equipment and stuffed it into a photo backpack I was not using and now I have a portable listening station. Now I can listen in my car or in the field fairly easily.

LowePro350AW – The backpack has three main compartments, integrated carry handles, nice padded waist belt, and a couple of ways to stick a 3/4-inch PVC pipe into external tripod or water bottle pouches. My homemade 14-inch loop antenna with Wellbrook amplifier is light enough to be attached to a 3-foot PVC pipe attached to the backpack. The Palstar preselector (active antenna) and KIWA BCB filter are still part of the portable setup. I added a Daiwa two-position switch to cut out the KIWA BCB filter so I can listen to mediumwave. Power for all these devices are Powerex AA’s for the Sony 2010 and two 12V power packs made from three sets of XTAR 14500 lithium batteries + one dummy AA. I have mounted the electronics and wires using large cable tie-wraps to a 14×10 inch polypropylene kitchen cutting board (sturdy and easy to drill through).

Illustration 2: The electronics board fits neatly into the laptop section of the backpack

Illustration 3: Backpack Shack in operation

Here are some recordings from two test outings around 2100-2200 hours UTC. A local county park (“Forest Preserve”) purposely has few man-made structures (just a trail, picnic shelter made of wood and an outhouse). It is about 15 minutes drive from where I live; the reception is notably clear of local noise. There is an occasional wide-band noise that comes and goes but nothing else I can identify as detrimental noise and it is mostly just a nuisance.

Cuban Numbers station on 11635 kHz:

Click here to download.

VOA from Santa Maria di Galeria, Italy in French on 12075 kHz:

Click here to download.

All India Radio on 11670 kHz:

Click here to download.

BBC Ascension I. on 11810 kHz:

Click here to download.

R. Guinea with music and announcer on 9650 kHz:

Click here to download.

A big downside of the Forest Preserve, like most parks now, is that it is ONLY open from sunrise to sunset and strictly enforced. So, my personal quest for nighttime access to an RF-quiet location continues (I guess I will have to buy/build my own)! It begs for an even more portable setup than this one. That means buying an SDR (with control via a tablet), miniaturizing the antenna, and modifying the lithium power packs to fit in a very small backpack or fanny pack.

If I can miniaturize it enough, I will be able to use common parts of this setup at home, in the car, and at field locations for either mediumwave or shortwave listening. I could then pre-install the unique parts in those situations and just plug-and-play, so-to-speak!

It could be that the continuing tech wave of small, powerful, wide-band equipment is causing a revolution in general. A type of radio revival may be at hand where regional radio starts to take a foothold, catering to a multi-state area and not just to one local metro area – with its one-city mindset and control (Do I really care that the Big City is installing a downtown-only, 12 million dollar bike and jogging connection + hearing endless whining about how bankrupt pensions are putting that County at risk when I never go there and don’t care to?). Portable wide-band radios allow for hours of listening to various types of broadcasts!

An example could be to use digital broadcasts over longwave (somewhere from 150 kHz-500 kHz) which allows ground wave signals to travel hundreds of miles reliably during the day or night without depending on variable skywave propagation. Digital would enhance the listener experience in stereo. It would probably need a narrower type of digital modulation since the current “HD Radio” standard is really too wide and splatters everything at adjacent frequencies. Pure wishful thinking but the technology is available to make something NEW happen!!

Cheers from NoiZey Illinoiz,
TomL

Thank you, Tom! You certainly have the right idea: taking your radio to the field! Keep us informed about your progress and updates. No doubt, over time you will discover a year-round spot to play radio in the field!

Guest Post: Building a magnetic loop antenna & broadband amplifier for your SDR

9 Replies

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.

The LZ1AQ broad band Amp solves all these problems. http://active-antenna.eu/amplifier-kit/.

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:

http://active-antenna.eu/tech-docs/2_ActiveAA_Mount_20.pdf

http://active-antenna.eu/tech-docs/1_ActiveAA_DandS_20.pdf

http://active-antenna.eu/tech-docs/3_ActiveAA_Antena_11.pdf

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!

Tony’s homebrew mag loop antenna and amplifier

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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].

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!