Category Archives: How To

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.

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 →

Guest Post: Simple Android Database Part 2

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: https://swling.com/blog/2021/10/guest-post-radio-schedules-in-a-simple-android-database/

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 →

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

Guest Post: Radio Schedules in a Simple Android Database

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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 →

Gary DeBock’s XHDATA D-808 loopstick model

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Many thanks to SWLing Post contributor, Gary DeBock, who shares the following:

The 7.5 inch (19cm) loopstick XHDATA D-808 model was designed to be the ultimate AM-DXing (or Longwave DXing) travel portable, and can be built for a construction cost of around $30 US. It has already been used by numerous DXers to track down transcontinental and transoceanic AM-DX during overseas travel, and the orange plastic loopstick frame allows full operation of the whip antenna for FM and Shortwave reception.

The modification procedure isn’t difficult, and the full construction article is posted at

https://dreamcrafts.app.box.com/s/5d0pi85jfptgmrj4pd0jsmaybgb6gteh

A video demonstration of its daytime DX performance (compared to the stock model) has been posted on YouTube:

Build one, and join the fun! 🙂

Many thanks for sharing this, Gary! Your ultralight DXing creations are simply amazing!

Guest Post: A synchronous detector crash course!

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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 →

“Anatomy of a Field Radio Kit” series on QRPer.com

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If interested, I’ve now published both parts of my Anatomy of a Field Radio Kit series over on QRPer.com. This series was originally featured in the June and July 2021 issues of The Spectrum Monitor magazine. Here are links to both articles:

These articles primarily focuses on portable amateur radio field kits, but many of the concepts are ones I also use for my field portable receiving setups like this one.

I hope you enjoy!