Category Archives: Antennas

Dan compares the Chameleon CHA RXL to the Wellbrook and W6LVP Loops

Many thanks to SWLing Post contributor, Dan Robinson, for the following guest post and review:

Chameleon CHA-RXL: Is This Pro-level Loop A Worthy Competitor To Wellbrook and W6LVP?

by Dan Robinson

At the end of summer 2021, I took up an offer from Chameleon to test and review their CHA – RXL loop antenna. The company describes this as a “new design high-performance” LF, MF, and HF receive-only loop perfect for mobile RV and apartment situations and with low noise characteristics.

This is not a cheap antenna, like the Chinese-made MLA-30, but a heavy duty professionally-built unit designed to, as the old TIMEX watch commercial said, “take a licking and keep on ticking”.

Price for the CHA RXL is around $500, though the company dropped the price at to $382 – but only for the two section loop rather than the single piece antenna advertised on its site.

You can see the Chameleon on the company’s website here, but it’s also sold by Gigaparts, DX Engineering and other radio suppliers. Chameleon lists features as:

Highly directional, balanced input preamplifier to eliminate environmental noise and ground loops, receives on new 2200m and 630m ham bands, flexible mounting and power options, and a stealthy [36 inch] Navy gray loop [that] fades into the background sky.

The built-in preamplifier, says Chameleon, “will enable clearer reception than many large horizontal wire or vertical antennas.” Weight of the amplifier is given as 7 lbs. The large pre-amp box is made of heavy metal, with a rubber gasket seal. Continue reading →

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Giuseppe’s Homemade “Magic Tablet” Antenna System

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Many thanks to SWLing Post contributor, Giuseppe Morlè, who writes:

Dear Thomas,

This is Giuseppe Morlè, from Formia central Italy on the Tyrrhenian Sea,

I built this “Magic Tablet. during a rainy afternoon to test various portables I have.

The tablet is composed of 2 separate circuits: one for the short waves, a single coil along the entire perimeter of the tablet, and another with 2 ferrites wrapped around 36 turns of telephone cable for the medium waves.

The heart of the system is a 1050 pf variable capacitor with its old wheel.

To listen to medium wave I have to exclude the short wave loop with a switch on the loop.

I also added another small switch to connect it to a capacitor for more or less capacity, but this I will do later.

I can test my portables like this because the tablet tunes very well from 500 kHz to 18 MHz. I spent very little to make all this as it is all recycled stuff.

You can see the first tests on the balcony of my house with a Tecsun H-501 via my YouTube channel:

Note: this video is in Italian, but you can turn on closed captions and have it translate into the language of your choice.

As I always say, I am not a technician and I have little manual skills in building things, not having a proper laboratory. When I get an idea, I put it on paper and I start to find all the materials and then see if they work. Not all of us are of the experts in electronics–what drives me is a passion for radio listening. Now being retired, I have more time to devote to it.

Thanks to you and hello to the whole SWLing Post community …

73. Giuseppe Morlè (IZ0GZW)

I love this, Giuseppe! What a clever all-in-one portable antenna system for your shortwave radios. I especially love the fact you were able to create all of this from parts you have at your home. You’ve got a winning attitude, too: build and experiment! Thank you for sharing.

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Video: Dave sets up the Chameleon CHA-RXL

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Many thanks to SWLing Post contributor, Mike, who shares the following video from David Casler featurin the CHA RXL amplified loop antenna:

Click here to view on YouTube.

Thank you for the tip, Mike!

I just checked out the loop at Chameleon and discovered that they’re currently offering a sale on the “two sections” version of the CHA-RXL. Click here to check it out.

Also, if you live in Switzerland or Europe, Lutz Electronics is now a distributor of Chameleon products.

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Ham Radio Workbench episode explores Diversity Reception

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The SDRplay RSPduo

I just finished listening to the most recent episode of the Ham Radio Workbench with John Fallows (VE6EY) as a guest.

John is an SWL and Ham Radio operator and speaks at length about how he uses diversity reception to mitigate persistent local RFI (radio frequency interference).

If you have persistent issues with radio interference or if you’ve been curious about using diversity reception for mediumwave and shortwave DXing, I highly recommend listening to this episode. John has been known to frequent the SWLing Post and actually comes into the discussion primarily from an SWL’s perspective.

If you’ve tried diversity reception or a noise-cancelling system like the Timewave ANC-4+ in the past with mixed results, you’ll definitely benefit from listening to John’s best practices.

In addition, John points out that the excellent SDRplay RSPduo is a very affordable way to explore proper diversity reception.

How effectively can you mitigate RFI with diversity reception? Check out this video on YouTube queued up to the point where John does a live demo with his Anan SDR and loop antennas: https://youtu.be/vu8D87aVUTQ?t=2011 (I also recommend watching to full video presentation for even more detail.)

I’ve embedded the audio for the Ham Radio Workbench podcast below, but you can also find it along with show notes on the Ham Radio Workbench website.

Ham Radio Workbench is one of my favorite podcasts; if you like exploring a wide variety of technical topics, I highly recommend checking it out. It’s available on all podcasting platforms.

Also, check out John VE6EY’s YouTube channel and web site/blog.

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Bob’s Updated Passive, Resonant, Transformer-Coupled Loop Antenna for Shortwave

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Figure 1. A Passive, Resonant, Transformer?Coupled Loop Antenna for Shortwave

Many thanks to SWLing Post contributor, Bob Colegrove, for the following guest post:

A Passive, Resonant, Transformer?Coupled Loop Antenna for Shortwave

By Bob Colegrove

Over the years I have resisted the level?of?effort necessary to construct and maintain outdoor antennas. Rather, I have focused on squeezing out all of the microvolts I could get inside the house. Many years ago I had access to a well?stocked engineering library, and used my advantage to gather information about the theory and development of loop antennas – a daunting undertaking for an English major. Ultimately, by adhering to a few basic rules, some of them dating back 100 years, I found quite acceptable performance can be had with an indoor passive antenna intersecting just a few square feet of electromagnetic energy.

Theory

There are a couple of advantages of resonant loops as opposed to non?resonant ones. The first is the fact that the signal dramatically increases when you reach the point of resonance. The second follows from the first in that resonance provides a natural bandpass which suppresses higher and lower frequencies. This gives the receiver a head start reducing intermodulation or other spurious responses. The downside of all this is that the resonant loop is, by design, a narrow?band antenna, which must be retuned every time the receiver frequency is changed by a few kHz. On the other hand, there is nothing quite as rewarding as the sight (S?meter) and sound you get when you peak up one of these antennas – you know when you are tuned in.

There is nothing new about the loop antenna described here. It’s just the distillation of the information I was able to collect and apply. There are a number of recurring points throughout the literature, one of which is the equation for “effective height” of a loop antenna. It basically comes down to the “NA product,” where N is the number of turns in the loop and A is the area they bound. In other words, provide the coil with as much inductance as possible.

Unfortunately, for resonant loops, the maximum coil size diminishes with frequency.
With this limitation on inductance, the challenge becomes minimizing unusable capacitance in the resonant frequency formula in order to get the highest inductance?to?capacitance (L/C) ratio possible. Some of the unusable capacitance is built into the coil itself in the form of distributed capacitance, or self?capacitance between the coil turns. This cannot be totally eliminated, but can be minimized by winding the coil as a flat spiral rather than a solenoid, and keeping the turns well separated.

The second trick is with the variable capacitor. Even with the plates fully open, there is residual capacitance on the order of 10 to 20 picofarads which can’t be used for tuning purposes. A simple solution is to insert a capacitor in series, about 1?4 the maximum value of the variable capacitor. This effectively decreases the minimum capacity and extends the upper frequency range. In order to restore the full operating range of the variable capacitor, the fixed capacitor can be bypassed with a ‘band switch.’ With the series capacitor shorted, the variable capacitor operates at its normal range and extends coverage to the lower frequencies. Continue reading →

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Guest Post: Jock explores the Tecsun PL-880’s ATS system

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

Oh, no, it’s broken – NOT! And other observations on the PL-880

by Jock Elliott, KB2GOM

Okay, okay, I’ll admit it: I’m an oldster, currently enjoying well over 70 trips around that Big Orange Ball in the sky. Further, I’ve been out of SWLing for a while.

Coming back into the hobby after more than a decade’s absence, has been eye-opening. Back when I wrote for Passport To World Band Radio, my main interest, equipment-wise, was tabletop communications receivers hooked to serious outdoor antennas.

Today, however, tabletop communications receivers are hard to come by (there are few new offerings), and, in my situation, serious outdoor antennas present a series of logistical problems that aren’t going to get solved quickly.

So that has brought me to today’s crop of portable shortwave receivers, and – bottom line – they are pretty darn cool, offering worthy performance on a number of levels. My latest acquisition is the Tecsun PL-880.

Like many of the current SW portables, it offers a system for scanning the SW bands and automatically storing the stations it finds into memory. On the PL-880, it’s called ATS (for Auto Tuning Storage.) Oh, you knew that. Yeah, but did you know that the PL-880 has, essentially, two ATS systems?

The down arrow activates ATS Mode A, and the up arrow activates ATS Mode B.

Check it out: If you press the DOWN arrow button (in the SW-METER BAND rectangle), the ATS Mode A system searches the band you are in (FM, MW/LW or SW, including ALL the SW meter bands), automatically stores stations it finds, and “previously stored radio stations will be replaced automatically by the newly found stations.” Each band has its own set of memories, so that SW stations will be stored in SW memories, FM stations will be stored in FM memories, and so forth.

ATS Mode B, however, behaves differently. You can activate it by pressing the UP arrow (in the SW-METER BAND rectangle). If you are in SW frequencies, ATS Mode B will search and store stations only within the current SW meter band. Further, it will NOT overwrite memories, but will start storing stations it finds, starting with the first available unused memory. Pretty neat.

You can, however, fool yourself. I ran ATS Mode A on SW frequencies one night and found a station that was broadcasting unusual stuff (Kennedy assassination, UFOs, and the like). A couple of nights later, I wanted to see what the night’s topic was on that station, so I punched the button to access memories and found . . . nothing! Oh, no, it’s broken!

Then I realized I was in SSB mode, and, it turns out, the PL-880 has a separate set of memories for SSB. (And the manual says that explicitly.) I switched off the SSB mode, and – tah-dah! – the SW memories reappeared. Sometimes it really does pay handsome dividends to read the manual.

One of the slick things about the PL-880’s memory setup is that, when you are in memory mode for a particular band, you can easily scroll through the memories simply by turning the tuning knob.

Wire antenna reels come in different styles. PL-880 (left) and CCrane Skywave SSB. But both improve performance for their respective radios.

The PL-880 has a nice long whip antenna (nearly twice as long as the CCrane Skywave SSB’s antenna), and it seems to be quite sensitive operating off the whip. But if you take the time to deploy the external wire antenna that comes with the PL-880, there is a considerable gain in sensitivity. Tuning around the 40-meter ham band, with the external wire antenna plugged into its socket, I could hear two stations in conversation, one louder than the other, but both copyable. When I tried to listen to the same pair of stations with just the PL-880’s whip antenna, the fainter station disappeared entirely, and the louder station was “down in the mud” but copyable. So the external wire antenna is clearly worth using.

So far, I am well pleased with the PL-880.

PS: Here’s a link to a really good article on extending the wire length of the reel-up antenna that came with the PL-880: https://www.hamuniverse.com/shortwavereelantenna.html

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GRAHN Spezialantennen currently closed

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Many thanks to SWLing Post contributor, Dan Robinson, who notes that Grahn Spezialantennen is currently closed due to the fact that Mr. Grahn is undergoing extended medical treatment.

Dan received this message from Christine Grahn who did not indicate if/when the business might re-open. We certainly wish him all of the best in recovery.

Click here to view the Grahn Spezialantennen website.

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