Category Archives: How To

HF Signal Enhancer for SDR: A Hands-On Build by Steve Allen (KZ4TN)

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Many thanks to SWLing Post contributor Steve Allen (KZ4TN), who shares the following guest post:

SDR Signal Enhancer

by Steve Allen

I came across this HF Signal Enhancer for SDR on the RTL-SDR.com website. It was designed and built by Peter Parker, VK3YE from Melbourne, Australia. Below is the link to the video of the signal enhancer in action using an RTL-SDR V4 Software Designed Radio;

www.youtube.com/watch?v=W6OXc_wZTXU

It was very easy to see and listen to the improvement to the signal reception the signal enhancer made. Having been a life-long shortwave listener and current SDR user, I had to build one.

I did a screen capture of the schematic, re-drew it using MS Word, and built the bill of materials. In Peter’s original design he included a T-R relay so you could use the SDR along with a transmitter, which I opted to leave out. I had the passive components in my “junk box” but had to source the enclosure, controls, and antenna connectors. I have used these clam shell extruded enclosures with previous projects and love the build quality and the fact that they incorporate a slot in the sides which let me insert a sheet of PCB material on which I can do the assembly.

Referring to the schematic drawing in Peter’s video, you can see that the variable capacitor “floats” above ground, which is not the usual application for these devices. To do that I mounted the vari-cap on a piece of non-plated PCB material that I cut to the width of the enclosure and it fit nicely within the slot. The vari-cap had three pins on the side of the frame that allowed me to force fit it into three holes I drilled in the PCB material. I was very careful to drill the holes undersize and then slowly open them up until the vari-cap press fit on to the board. For good measure I ran UV curing adhesive down into each hole, letting it flow all the way through before I set it with a UV light source.

I then drilled an oversized hole in the front panel for the vari-cap shaft to pass through.

I then mounted the RF gain and band switch. The next step was the assembly of the AM broadcast filter. As SDRs can be overpowered by local AM radio stations Peter choose to include an internal band pass filter that is configured for around 3.5 MHz. The intent of this filter is to attenuate the signals below 3.5 MHz. Strong AM stations will still be heard but there is much less chance of them bleeding through on the higher frequencies.

I assembled the filter on a piece of perf board and connected the component leads on the bottom. I passed leads back up through the perf board for the signal path and ground. I mounted it on the main board with a standoff.

The next step was the wiring of the inductors to the rotary switch. Simple, and I tied them to the vari-cap frame.

For the back panel I chose an SO-239 and a BNC for the antenna input, and for the radio connection an SMA and another BNC. I sanded off the coating on the enclosure at the antenna mounts as well as the four corners where the back panel screws into the top and bottom of the clam shell enclosure to provide good grounding of the enclosure. I wired the 1N4148 diodes on the antenna connectors, and attached the RG-174 coax. As Peter suggested, I grounded the long (relatively speaking) runs to and from the back panel with coax and grounded it at the back panel.

The last step was to apply a bit of epoxy adhesive to the fiberglass board and the slot it runs in to hold it in place. Once the epoxy set, I did the final wiring of the front and rear panel components. You can see how I sanded the corners of the back panel in the above photo.

I connected it to my inverted L antenna and an SDR Play RSP2 and gave it a test run. I like the fact that I can visually see the changes to the signal strength on the SDR software as well as audibly. It makes a noticeable improvement to the reception.

Thank you Peter. I enjoyed the build.

Steve Allen, KZ4TN

Giuseppe’s Multi-Band Milk Crate Loop Antenna

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

Dear Thomas and Friends of SWLing Post,

I am Giuseppe Morlè from Formia, a town in central Italy on the Tyrrhenian Sea.

I have built a new “Multiloop” antenna using a 40 cm diameter milk crate. The crate is very sturdy and shockproof, making it an excellent base for this project.

Construction Details

I wound three different loops on the crate:
1. A single shortwave coil
2. Two shortwave coils
3. Twelve medium-wave coils

The design includes a single coil placed between the two shortwave coils, which picks up the signal by induction and transfers it to the receiver via an RG58 cable.

The heart of this system is a 2,100 pF variable capacitor with sockets connected to the rotors. Inside the crate, I added another 18 cm diameter loop positioned just below the two main coils.

The ends of this small loop are attached with crocodile clips to the external ends of the rotor. This small loop allows me to exploit induction and, by turning the capacitor, access all decametric bands from 160 to 10 meters.

Tuning Ranges

The variable capacitor enables tuning as follows:

      • In the lower ranges, it covers 80 to 20 meters.
      • When reversed, it tunes all higher ranges from 10 to 20 meters.

This works because the small loop and capacitor couple inductively with the primary turns. By increasing capacity with cables on the rotors, the antenna can even tune up to 160 meters.

The medium-wave turns cover frequencies from 300 kHz to 1,900 kHz. Essentially, this Loop Milk Crate antenna can access a wide range from 300 kHz to 30 MHz.

Testing and Comparisons

I tested the antenna using the Tecsun PL-660 and the Tecsun S-8800 receivers. I also compared the Loop Milk Crate with my “Ferritona” antenna and found surprising results!

Some of the videos were filmed in my shack because it was too cold to work on the balcony. Other videos were shot outside, either on my balcony or on the beach in Formia.

Videos

Final Thoughts

I hope you enjoy my “crazy” constructions. Always remember, I’m not a technician—just a passionate listener who loves building with recycled materials.

Wishing everyone a year full of happiness and satisfaction!

Best wishes to all,
Giuseppe Morlè

A File Worth Having: Bob’s guide to building an Electrically Small Resonant Loop Antenna for Mediumwave Reception

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Screenshot

This post is short and sweet.

If you click here–Electrically Small Resonant Loop Antenna for Mediumwave Reception (PDF)–you can download a copy of Bob Colegrove’s excellent paper on the Electrically Small Resonant Loop Antenna for Mediumwave Reception.

He has actually built this antenna; it works; and he uses it often. Perhaps you might want to build one for yourself. As an added bonus, Bob is an excellent writer (in my not-so-humble opinion). What’s not to like?

— Jock Elliott, KB2GOM

Compact Antenna, Big Results: Giuseppe’s DICA 2 Redesign

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

Dear Thomas and Friends of the SWLing Post,

I am Giuseppe Morlè, IZ0GZW, writing to you from Formia, in central Italy, on the Tyrrhenian Sea.

Do you remember the DICA 2 antenna? It was a small, shortened antenna with three ferrite cores inside, capable of tuning across all shortwave bands. Unfortunately, it no longer exists in its original form.

I have completely reworked the windings to enable the ferrites to also function for medium wave (MW) reception. Now, the antenna features:
• 35 turns for medium waves,
• 4 turns for shortwaves, and
• the same variable capacitor of over 1000 pF remains in use.

For medium waves, the antenna works wonderfully by induction. You simply place the ferrite core near the tube and turn the variable capacitor to achieve perfect tuning across the entire MW range.

I was genuinely amazed by its performance on shortwaves. Despite its small size, the antenna provides excellent gain, especially when a ground cable is connected to the variable capacitor’s casing.

I conducted several tests on my balcony. Initially, I thought the random ground wire simply improved the rotor’s tuning capability, but I discovered the antenna works equally well even when placed on a metal surface.

During a recent outing to Monte Orlando Park in Gaeta, I observed how the ground cable significantly enhanced both the signal strength and audio modulation. You can see this in my latest video, where I received Australian operators Greg and Grant on 20 meters with excellent signals.

The antenna’s two windings are separated and connected to the stator and rotor of the variable capacitor. On one end of the shortwave winding (the 4 turns), I’ve added a crocodile clip that can be attached or detached to switch between shortwave and medium wave operation. All of this functionality is achieved with a single variable capacitor.

I will soon share videos demonstrating all of these details and performances.

Thank you, Thomas, for your incredible activations—I follow them regularly on your channel, and they are a constant source of inspiration for me.

Greetings to you and all the Friends of SWLing Post!

73,
Giuseppe Morlè, IZ0GZW

Videos:

Pavel’s Practical Electronics Homebrew Mediumwave Ferrite Antenna

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

Mediumwave Ferrite Antenna

by Pavel Kraus

This antenna for MW was made according to the instructions from Everyday Practical Electronics magazine, September 2000. The author of the Active Ferrite Loop Aerial construction project is Raymond Haigh.

The antenna was only adjusted mechanically according to my capabilities. Reception on this antenna was tested with receivers Malahite DSP 2 – original, Belka, Qodosen DX 286, AOR 7030+, Eton E1 XM and other receivers. Of course, the antenna does not replace a long wire antenna, but in limited urban conditions its performance is sufficient. I compared the antenna to Garry Thomas’ factory Quantum Loop.

Both antennas work similarly, Quantum Loop has a shielded ferrite rod, it is less susceptible to elmg. interference. Raymond Haigh’s antenna shows a bit more gain, the ferrite antenna is made up of 7 pieces of ferrite rods 20 cm long and 1 cm in diameter. The antenna is not shielded.

The construction of the antenna according to the instructions is not difficult. A Raimond Haigh antenna will definitely improve MW reception, especially for radios without an internal ferrite antenna. Instructions can be found at https://www.worldradiohistory.com/UK/Practical-Electronics/00s/Everyday-Practical-Electronics-2000-09.pdf

Belka Test

https://www.youtube.com/watch?v=Yk-ngCQ8TFc

Qodosen DX286 Test

https://www.youtube.com/watch?v=F77HOJSmu_4

Malahite DSP2 Test

https://www.youtube.com/watch?v=C2dvaCT9z6Y

Steffen shares some XHDATA D-220 tricks

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XHDATA D-220 PortableMany thanks to SWLing Post contributor, Steffen Schultz, who writes:

Hello Thomas,

As a regular reader of your blog, I was fascinated by the reports on the XHDATA D-220 [affiliate link] and ordered a black one. I was not disappointed. Of course it’s not a DXing machine, but finally we have a device wich reaches the reception quality of the old pocket radios again I used to carry around in my childhood. I still have a Philips D1220 from the 80s, which is even less sensitive than the XHDATA D-220.

This reminded me of my early radio days, when I would try to use the simplest methods to manipulate analog radios to do things that were not intended by the manufacturer. For example, by moving the band selector switch to an intermediate position, it was possible to get some radios to receive frequencies outside the intended range. Of course, I couldn’t resist and experimented with the D-220. It takes a bit of patience and sensitivity, but the radio really does hold some secrets.

Medium wave reception with the telescopic antenna

When I was listening to a weak station on medium wave and slowly moved the switch to short wave, the medium wave station got louder for a moment before the slide switch clicked into the correct position. In fact, the radio seems to switch to the telescopic antenna when you move the band selector a little toward short wave. A finger test on the antenna confirmed my suspicion. I also tried connecting a long wire, but that was counterproductive with all the men-made noise inside my house. Extended shortwave reception

A similar trick can be used to change the shortwave frequencies. If you slightly move the band selector from the shortwave position towards medium wave, the receiver switches to a different shortwave frequency range, covering between about 3000 and 7000 kHz. Now I was able to receive shortwave radio from Germany on 3975 kHz without any problems, and of course South Korea via England on 3955 kHz was no problem either.

I have not yet found out if the two FM bands can also be manipulated in this way, an intermediate position of the band selector seems to have no effect here. Perhaps one of the readers has discovered something?

73 and best regards
Steffen
Wittstock/Germany

Thank you for sharing these D-220 tips/hacks, Steffen!

A Band Aid for the XHDATA D-220

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

A Band Aid for the XHDATA D-220

By Bob Colegrove

In the olden days of analog radios, we would have generated a graph plotting frequency against a 0 to 100 linear bandspread scale. That permitted determination of a station’s frequency with varying degrees of accuracy.

The case of the charming little D-220 requires a simpler approach. The dial covers 5.6 MHz to 22 MHz in less than two inches. They could have cut off coverage at 18 MHz and gained a precious half inch of dial.

With the shortwave scale well below the pointer, I needed some additional guidance indicating where I was. Best not to get too fancy. I cut a strip off a sticky-back label and attached it to the dial right below the pointer. Using the left edge of the pointer as a guide, I marked off the location of each international broadcast band and a couple time stations. The width of each band isn’t much more than the point of a sharp No. 2 pencil. Any further resolution is hopeless, but at least you know what part of the spectrum you are in.

Red lettering is not part of the band aid.

Again, going by the old logarithmic analog dials you would expect the frequencies to be increasingly mashed together as you go higher. This is not the case with the D-220, nor do the increments appear to be very linear. At any rate, it is now relatively easy to tune from band to band.

The sensitivity and clarity of the D-220 is amazing. Perhaps it’s the green one.