Category Archives: Guest Posts

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

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.


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: Simple Android Database Part 2

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

Simple Android Database-PART 2

by Billy Hemphill, WD9EQD

In the first part, I showed how you could easily take a spreadsheet and create a simple database for viewing on an Android phone/tablet. The examples used in that article was two spreadsheets of radio schedules – one for Shortwave and one for FM Radio Programs. See the following link to the original article:

There are many lists on the internet of various radio databases. If the database can be downloaded as either a CVS file or a spreadsheet, then it is possible to load it into the PortoDB app on the phone tablet. I’ll show how this can be done with two popular databases that I reference all the time.

EIBI Data Base

Most of you are probably familiar with the EIBI database of shortwave schedules. Many of the Shortwave Schedule apps on the Phones reference this database. For example, I use the Skywave Schedules on my phone. While it does allow for me to search by many parameters, I thought it might be fun to have it in a PortoDB database. Plus it would be interesting to see how PortoDB performs with a large data set. Continue reading

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Guest Post: Radio Schedules in a Simple Android Database

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

Radio Schedules in a Simple Android Database

by Bill Hemphill

I am a program listener. I really enjoy listening to various radio stations direct and by internet streaming. Over time, I have come up with a couple of spread sheets that lists the program, station, time, date, etc. For example, following is the spreadsheet for the shortwave radio programs/stations that I enjoy:

As the program schedules change, I update the spreadsheet. This has worked quite well for me. I usually sort on the weekday and then print out the spreadsheet as a list by time and frequency for each day.

While this method works, it does mean that I have these multiple page printouts that I have to refer to. This got me thinking that it would be great to have this on my Android phone/tablet. Then I could refer to it no matter where I was located.

At first, I tried to use Google Sheets, but found that using a spreadsheet on the phone or even a tablet to be a pain. I then tried entering it into a calendar program, but also found that very cumbersome. Continue reading

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Guest Post: A synchronous detector crash course!

Many thanks to SWLing Post contributor, 13dka, who shares the following guest post:

Revisiting the Belka’s “pseudo-sync detector”: A sync detector crash course!

by 13dka

“It’s usually hard to assess whether or not a sync detector helped with a particular dip in the signal or not, unless you have 2 samples of the same radio to record their output simultaneously and compare.”*

That’s what I wrote about the “pseudo sync detector” in my review of the Belka DSP last year.

Since I was recently upgrading to the Belka DX in order to pass on the Belka DSP to a friend, I had briefly two examples of almost the same radio on the table at the dike. I tuned them to the same stations and recorded some audio clips with one radio on sync detector, the other in regular AM mode, to answer the question whether or not sync has “helped with a particular dip in the signal”. Then I thought that demonstration would be an opportunity to try an explanation on what exactly (I think) sync detectors are all about anyway, hoping to find a middle ground between “technical” and “dumbed down beyond recognition”.

The trouble with sync detectors

Perhaps no component of a shortwave receiver is surrounded by so much misconception and confusion as sync detectors. Full disclosure: Until quite recently, I had an, at best, vague concept on what they do myself. It seems it’s not so much that people don’t know how they work, what they actually do when they work is where the ideas often diverge. Continue reading

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HFDY vs. Fire Brothers: Dan compares two Chinese Malahit SDR clones

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

Two Chinese Clones:   A Look at Noise Levels

Arriving recently here in the radio shack, were a Chinese clone under the name of “Fire Brothers” and another under the name HFDY.  I thought it would be constructive to note the key differences between these two clones, both of which are running Malahit 1.10c firmware, and post some video of a brief comparison.

A note in advance of any comments – I am primarily a HF listener so these comparisons do not cover frequencies above 30 MHz.  For those whose focus is on higher frequencies I recommend looking through the many comments on the Malahit Facebook group and Telegram by those who use these receivers in those ranges.


  • Constructed of metal-like material (a correction from my previous articles that this is fiberglass of the kind used in printed circuit boards – thanks to Georgiy of Malahiteam for pointing this out)
  • Front speaker grille is gold color and appears to be metal but may be fiberglass as well – audio is quite good
  • Two top-mounted antenna jacks, one 50 ohm, the other Hi-Z (makes switching between HF and FM/VHF reception easier) with in-use LED indicators
  • Two high quality right side mounted black metal encoder knobs with large power button (clear printed Frequency/STDBY/Volume printed on panel)
  • Cabinet held together with TORX screws
  • 1.10c firmware
  • Receiver is elongated left to right to accommodate left side front-firing speaker, but is thinner overall and could be easily placed in a pocket though not recommended to prevent damage
  • Like every one of these SDRs, suffers from body sensitivity to touch which reduces signal levels unless some sort of additional ground is attached to cabinet
  • Internal flat-type Lithium battery of 3300 mAh though apparently capable of fitting up to 8000 mAh

Continue reading

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Guest Post: A “Horizontal DXer” explores the CC Skywave SSB and PL-880

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

Confessions of a horizontal DXer and some initial impressions of the Tecsun PL-880

by Jock Elliott

Back in the day when I wrote for Passport To World Band Radio, one of my favorite things to do, while my better half drifted off to sleep, was to clamp on a pair of headphones, lean back against the pillows, and mess around with a Sony 6800W shortwave receiver.

It wasn’t a radio that was built for band scanning: you had to rotate a dial to select the megahertz segment of the bands that you wanted, tune a built-in preselector to the appropriate area, and then dial in the frequency with a tuning knob. And memories? Ha! You want memories?!! There were no stinking memories . . . you had to remember what frequencies you wanted or at least what portions of the bands you wanted to tune. The memories were between your ears.

But it was a receiver with an extraordinarily low noise floor, and many a happy evening I enjoyed programming from half a world away. Drifting off to sleep with headphones piping in a signal from a distant land was not without its dangers, though. One night I fell asleep listening to the news from Radio Australia beamed, in English, to Papua, New Guinea. I woke a while later to the same newscast beamed to Papua, New Guinea, but this time in Pidgin English. I heard some English words, but the rest did not make sense. I panicked, thinking some neurologic event had scrambled my brain, but a crisp voice rescued me: “This has been the news in Pidgin English, from Radio Australia.” Thank God!

When Passport ceased publication, I neglected shortwave radio for over a decade, busy with freelance writing and running the Commuter Assistance Net on two meter ham radio.

Earlier this year, the SWLing bug bit me again, and I fired up a long-neglected Grundig Satellit 800 and started cruising around the HF frequencies. Many of the big-gun shortwave stations were gone, or they weren’t aiming programming at North America, but there was plenty to listen to, including shortwave stations, HF ham bands, and some utility stations.

Gee, I thought, it might be great to have a radio for a little horizontal in-bed DXing before shutting off the lights for the night . . . something I could hold in my lap, turn the tuning knob, and discover hidden treasures. The Satellit 800, emphatically, was not the answer. It is a large radio, roughly the size of the vaunted Zenith Transoceanic radios, and definitely not suited for laps.

So, based on a great reputation and excellent reviews, I bought a CCrane Skywave SSB. The Skywave SSB is a powerhouse, offering AM, FM, Weather, Air, SW, and SSB in a package roughly the size of a deck of cards and perhaps twice as thick. And it delivers the goods, offering worthy performance on every band, although SW performance is greatly enhanced by attaching the wire antenna that is included with the Skywave SSB.

Two factors, I discovered, reduced the suitability of the Skywave SSB for bedside DXing. First, the tuning knob is really small, so you can’t just twirl your finger to traverse the bands. It also has click-detents on the tuning knob and muting between tuning steps, so the tuning is non-continuous, which diminishes the pleasure for me. So the drill becomes: use the automatic tuning system (ATS) to search the bands and store stations in memory and then use the keypad buttons to jump from stored station to stored station. Further, each keypad key makes a distinct “click” sound when properly depressed. And that brings us to the second factor: one night, I am attempting to explore the stations stored by the ATS when my bride, who was trying to doze off, taps me. “What?” I say. “Too much clicky-clicky,” she says. Oh, I thought; now I need to find a radio that is quiet, so long as I am wearing headphones.

Now, just to be clear: I would highly recommend the CCrane Skywave SSB (except for use next to a spouse who is attempting to sleep), particularly for traveling because it is so small and performs so well. To underscore the value of a shortwave-capable travel radio, some years ago, I spoke with a journalist who was in Russia when the Chernobyl nuclear disaster took place. Russian media were not reporting on it at all; he found out about Chernobyl by listening to the BBC on a shortwave radio he had tucked into his luggage, and he rapidly made plans to leave Russia.

A bunch of research eventually led me to the Tecsun PL-880, which is about the size of a trade paperback book. According to some reviewers (including Dan Robinson), the 880 is a bit more sensitive and shortwave than the PL-990. The 880 offers a bunch of bandwidths on both AM and SSB, and the tuning is butter smooth with no muting or detents. The smallish tuning knob has a bit of knurling on the edge, which make it possible to twirl the knob with one finger; you can fine-tune SSB with another knob, and, with one button-press, use the tuning knob to select filter bandwidths or memory channels. In short, if you avoid the keypad, this is a radio that can be operated in near silence next to a better half who wishes to snooze.

The performance, so far, is exemplary; using the PL-880 whip antenna, I could readily hear Gander, Newfoundland, broadcasting aeronautical weather as well as Shannon, Ireland, air traffic controllers directing aircraft crossing the Atlantic Ocean. Yes! I haven’t yet begun to explore all that the PL-880 can do, but it promises to be a lot of fun.

Click here to read more posts by Jock Elliott.

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Sam found where genealogy and radio meet

Many thanks to SWLing Post contributor, Sam Alcom (KB3DFJ), who shares the following guest post:

Genealogy and radio meet

by Sam Alcom (KB3DFJ)

Who knew two of my hobbies – genealogy and radio – would joyfully collide in such an unexpected way?

My grandfather died in the 1950s when I was just a few months old, so I didn’t know him, let alone have some misty recollection of him. Seemingly, our only connection was the DNA bloodline though my father.

But as I dove into my family’s history, one web search led me to William H. Alcorn and 3ADJ. What the heck was 3ADJ? I dug deeper and found Amateur Radio Stations of the United States, U.S. Department of Commerce, Radio Division from June 30, 1924. Both of us were hams!

He was licensed as amateur radio station 3ADJ in Port Norris, N.J. with authorization to operate up to 50 watts.

I found him and his 3ADJ callsign again listed in 1925 in the Department of Commerce, Bureau of Navigation, Radio Service publication. The “3” in his sign threw me for a brief loop, but I learned that in the early days of radio Southern New Jersey was part of the third call district along with Delaware, Maryland, Virginia, certain counties of Pennsylvania and the District of Columbia.

The website, a goldmine for anyone delving into all aspects of broadcasting’s past, led me to more publications where I spied my grandfather in the late fall 1925 edition of Radio Listeners’ Guide and Call Book and the 1926 edition of Citizens’ Radio Call Book and Complete Radio Cyclopedia.

The last radio trace I find was in the June 30, 1927, edition of the Amateur Callbook.

It was around this time that the U.S.  began using “W” to start callsigns and I wondered if my grandfather continued with his radio hobby under the new designation. I looked up W2ADJ and found William Czak of West Brighton, N.Y., owning that sign. Likewise, W3ADJ belonged to the University of Maryland in College Park, Md. Both were from 1929.

I dug a little deeper to learn if he possibly had been an amateur prior to 1924, but I saw 3ADJ licensed to Horace Derby of Norfolk, VA., 1920 through 1923.

His amateur radio interest appears to have started sometime after 1921 and a stint in U.S. Navy as a Seaman Second Class and then seems to have waned – at least license-wise – as marriage and the first of my aunts, uncles and my dad were being born.  I wonder if my dad had known about his dad’s radio hobby. In all the years I’ve been a licensed ham and bono fide radio nerd, he never mentioned it.

Of course, learning on this radio connection to my grandfather raised a host of other questions. Did he enjoy CW as much as I do? What kind of contacts was he making with 50 watts? Would he have admired the WAS and DXCC award certificates hanging on my wall? Would my hefty binder of shortwave QSL cards impressed him?

So, I’ll keep poking, looking for more radio connections. Who knows, maybe, somewhere, there’s a 3ADJ QSL signed by my grandfather.

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