Category Archives: How To

How to Build a Simple Linear-Loaded Dipole for Low-Noise Shortwave Radio Listening

Many thanks to SWLing Post contributor and RX antenna guru, Grayhat, for another excellent guest post focusing on compact, low-profile urban antennas:

A linear loaded dipole for the SWL

by Grayhat

What follows is the description of an antenna which may allow to obtain good performances even in limited space, the antenna which I’m about to describe is a “linearl loaded dipole”(LLD) which some call the “cobra” antenna due to the “snaking” of its wires
The arms of the antenna are built using 3-conductors wire (which may be flat or round) and the 3 conductors are connected this way:

That is, connected “in series”, this means that, the electrical length of the antenna will be three times its physical one; this does NOT mean that the antenna will perform like a single wire of the same (total) length, yet it allows to “virtually” make it longer, which in turn gives it good performance even with relatively short sizes. Plus, the distributed inductance/capacitance between the wires not only gives it a number of “sub” resonance points, but also helps keeping the noise down (in my experience below the noise you’d expect from a regular dipole). At the same time it offers better performances than what one may expect from a “coil loaded” dipole. Plus, building it is easy and cheap and the antenna will fit into even (relatively) limited spaces (a balcony, a small yard and so on…).

Interested–? If so, read on and let me start by showing my (short – 9mt total) LLD installed on a balcony:

Here it is in all its “glory”–well, not exactly–I fiddled with it lately since I’m considering some mods so the tape isn’t correctly stuck and it has been raised and lowered quite some times, but in any case that’s it.

Bill of Materials

Here’s what you’ll need to build it (the links are just indicative, you may pick different stuff or buy it locally or elsewhere).

Some length of 3-conductors electrical wire which will fit your available space (pick it a bit longer to stay on the safe side), it may be flat or round, in my case I used the round type since it was easily available and cheap: https://amzn.to/3g2eZX3
A NooElec V2 9:1 BalUn–or, if you prefer you may try winding your own and trying other ratios. I tested some homebuilt 1:1, 1:4 and 1:6 and found that the tiny and cheap NooElec was the best fitting one): https://amzn.to/3fNnvce
A small weatherproof box to host the BalUn: https://amzn.to/33vjZy3
A center support which may be bought or built. In the latter case, a piece of PCV pipe with some holes to hold the wires should suffice. In my case I picked this one (can’t find it on amazon.com outside of Italy): https://www.amazon.it/gp/product/B07NKCYT5Z
A pair of SMA to BNC adapters: https://amzn.to/37krHwj
A run of RG-58 coax with BNC connectors: https://amzn.to/2JckHcR

Plus some additional bits and pieces like some rope to hang the antenna, some nylon cable ties, a bit of insulated wire, duct tape and some tools. Notice that the above list can be shortened if you already have some of the needed stuff and this, in turn will lower (the already low) cost of the antenna.

Putting the pieces together

Ok, let’s move on to the build phase. The first thing to do will be measuring your available space to find out how much wire we’ll be able to put on the air; in doing so, consider that (as in my case), the antenna could be mounted in “inverted Vee” configuration which will allow to fit the antenna even in limited space.

In any case, after measuring the available space, let’s subtract at least 1m (50cm at each end) to avoid placing the antenna ends too near to the supports. Also, if in “inverted Vee” config, we’ll need to subtract another 50cm to keep the feedpoint (center/box) away from the central support.

Once we’ve measured, we may start by cutting two equal lengths of 3-conductor wire. Next, we’ll remove a bit of the external sleeve to expose the three conductors and then we’ll remove the insulator from the ends of the three exposed wire (and repeat this at the other end of the cable and for both arms).

The resulting ends of each arm should look somewhat like in the example image below

Now we’ll need to connect the wires in series. We’ll pick one of the cables which will be the two arms of our antenna and, assuming we have the same colors as in the above image, we’ll connect the green and white together at one end and the black and green together at the other end. Repeat the same operation for the second arm and the cables will be ready.

Now, to have a reference, let’s assume that the ends of each arm with the black “free” (not connected) wire will go to the center of our dipole.

Leave the two arms alone for a moment, and let’s install the balun inside the waterproof box. To do so, we’ll start by cutting a (small) hole through the single rubber cap found at one side of the box, then insert the cap reversed, so that it will protrude to the inside of the box and not to the outside. Slide the balun SMA connector through the hole so that it will protrude outside the box.

Now use a marker to mark the balun position and remove the balun from the box. Pick a piece of wood/plastic or other insulating material, cut it to size (refer to marking and to balun size) and drill four holes matching the one found on the balun board. Slide four screws through the holes and lock them with nuts, the screws should be long enough to extrude for some mm. Now insert the balun in the screws using the holes present on the balun board and lock it with nuts (be gentle to avoid damaging the balun). At this point, add some “superglue” to the bottom of the support we just built, slide the balun SMA connector through the rubber cap hole we already practiced, and glue the support to the bottom of the waterproof box. Wait for the glue to dry.

Just to give you a better idea, see the photo above. That’s a photo of the early assembly of my balun. Later on, I rebuilt it as described above (but took no pics!), the image should help you understanding how it’s seated inside the box–by the way in our case it will be locked by the screws to the plastic support we glued to the box.

While waiting for the glue to dry, we may work on the dipole centerpiece.

If you bought one like I did, connecting the arm “black” (see above) wires should be pretty straightforward. If instead you choose to use a PVC pipe you’ll have to drill some holes to pass and lock the wire so that the strain will be supported by the pipe and not by the wire going to the balun box. In either case, connect a pair of short runs of insulated wire to the end (black) wire coming from each end. Those wires should be long enough to reach the balun wire terminal block inside the box.

Assuming the glue dried, it’s time to complete the feedpoint connection.

Bring the two wires coming from the centerpoint inside the waterproof box. Pick one of the wire terminal blocks which came with the balun (the “L” shaped one should be a good choice) and connect the wires to it. Then, slide the block in place until it locks firmly. After doing so, close the box and screw the SMA-BNC adapter onto the SMA connector coming from the balun. Our centerpiece and arms will now be ready, and will be time to put our antenna up!

I’ll skip the instructions about holding the arm ends and the centerpiece up, since I believe it should be pretty straightforward. Just ensure to put the antenna as high as possible and, if you have room make the arms as long as possible. In my case, due to my (self-imposed) limitations, the antenna was installed on a balcony. The arms have a length of about 3.5m each and the feedpoint (in the image above) sits at about 9m off the ground.

The more acute readers probably noticed those “blobs” on the coax, they are snap-on ferrite chokes I added to the coax (there are more of them at the rx end) to help tame common mode noise. I omitted them from the “BoM” since they may be added later on.

Anyhow, now that you have your LLD up it will be time to give it a test! In my case, I decided to start by running an FT8 session to see what the antenna could pick up during 8 hours, and the result, on the 20 meters band, is shown on the following map (click to enlarge):

Later, that same antenna allowed me to pick up signals from the Neumayer station in Antarctica–not bad, I think!

Some final notes

While running my “balcony experiment”, I built and tested several antennas, including a vanilla “randomwire”, a dipole, and a T2FD.

Compared to those, the LLD offers much less noise and better reception on a wide frequency range. By the way, it won’t perform miracles, but it’s serving me well on the LW band, on most ham bands, and even up to the Aircraft bands–indeed, was able to pick up several conversations between aircraft and ground air traffic control.

All I can suggest is that given a linear-loaded dipole is so simple, quite cheap, and may fit many locations, why don’t you give it a spin–? 🙂

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A True Treasure Trove: International Radio Club of America Free Reprints

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Many thanks to SWLing Post contributor, Nick Hall-Patch, who writes:

Since 1964, the International Radio Club of America has been documenting medium wave DXing and DXers’ efforts to improve their understanding of radio reception and to develop better listening techniques. During that time, over 900 articles have been written, that have furthered the art of DXing. Many of these continue to be relevant to the more general radio hobbyist, including articles about antennas, radio propagation, receivers and accessories, plus general technical information.

Previously, those articles were available only to club members, but they are now available to all. Go to www.ircaonline.org, and click on the “Free IRCA Reprints” button to download your own copies.

Oh wow! What an amazing and deep treasure trove of articles! Thank you so much for the tip, Nick!

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Paolo warns of persistent classifieds scams targeting radio collectors and advises how you can be scam savvy!

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Many thanks to SWLing Post contributor, Paolo Viappiani (SWL I1-11437), who shares the following guest post:

A recent resurgence of Internet scams involving quality radios

by Paolo Viappiani (SWL I1-11437)

After my previous post on this subject, I found on the Internet other very dangerous fraud attempts concerning high-quality radios offered at very convenient prices. Below, you’ll find the details of a recent attempt concerning the highly-desirable SONY CRF-V21 receiver.

The methods are always the same, but the scammers greatly refine their fraudulent techniques, even going so far as to carry out real identity thefts, as in this case.

Of course, I knew from the beginning that it was a fraud (I don’t let myself be fooled anymore!), but I tried to continue corresponding with the scammer in order to get as much data on his real identity as possible. At the same time, however, I reported the fraudulent advertisement to the site webmaster in order to prevent other users from falling into the trap. The ad was promptly removed, but the scammer noticed it and immediately he slipped away…

Here is the story…

I have been trying to detect and report Internet scams from some time (since I was scammed!), and recently I found an advertisement for a SONY CRF-V21 radio, described as working and in good cosmetic conditions, on the Italian website “Clasf”, look at the picture below:

The radio was offered for Euro 2.600 from a seller who supposedly resided in Rome, Italy.

I sent him a message through the “Clasf” site and almost immediately I received a reply from someone who claimed to reside in Reichertshofen, Germany.

Déjà vu… Germany, Spain or Portugal always seems to be the same story…

But this time the very serious thing is the fact that the scammer identified himself as an “implantology dentist”–a fake identity–also providing a counterfeit website:

From my investigation it appears that both the picture and the website were stolen from a true professional from Hamburg, Dr. Bernhard Brinkmann, look at the websites (here and here).

Of course I tried to contact Dr. Brinkmann and I still make all the documents available to him, in case he wants to prosecute the thief.

About the pictures I received from the scammer (you’ll find some of them below):

All photos were stolen from a Canadian eBay advertiser instead:

So, buyer beware! The number of frauds in the radio market on the Internet is growing day after day, and it always advisable to keep your eyes wide open, even in the rush to purchase a much desired item at an affordable price.

Today scam techniques are increasingly refined, as shown in the example reported above.
Sincerely I don’t know if this user has something to do with the other European scammers (supposedly from Spain and Portugal) I quoted in my former post. The Italian Postal Police, after having examined the headers of the e-mails that I received along with other documents, believe that such scammers can reside anywhere in the world.

Most scammed

Anyway, the three “most scammed” radios are currently the Panasonic RF-8000, the Panasonic RF- 9000 and the Sony CRF-V21 (pictures below):

Please also notice that a number of advertisements on the most popular classifieds sites (Quoka.de and ebay-kleinanzeigen.de in Germany, Subito.it, Clasf and AAAnnunci.it in Italy, Le Bon Coin in France, ComoFicho in Spain, etc.) still are mirrors for larks only, and you have to pay a great attention in order not to be scammed.

A recent trip over all the mentioned sites revealed that only a few ads are really true…

Red Flags

I repeat some notes about scammers and their usual techniques:

A.) The scammer advertises a very rare radio in like-new conditions at an unbelievably low price. The buyer does not want to miss the bargain, so he contacts the seller and promptly transfers the money to him without further ado, but after that he waits in vain for the delivery of his item.

B.) If you contact the seller, the item is always abroad. The alleged seller then proposes to handle the purchase through a “trust company”. The radio should be paid in advance and the amount sent via cash transfer, but after that you never hear anything from the seller again.

C.) Alternatively, the buyer is requested to to deposit the money to the eBay company account to get the product. But the account is fake (eBay HAS NO “Company Account” and never handles private transactions!), so the buyer loses his money and receives nothing in return. Please also notice that often the fraudulent sellers offer a free period for evaluating the item, saying that if you do not like the device you can send it back. Please don’t fall into this trap, it is only one of the means the scammers use to entice you to purchase, but IT IS NOT TRUE AT ALL!

I repeat also some useful advices in order to make secure and safe purchases on the Internet:

1.) Always beware whenever the item is in a place (or a country) different from the one that was specified in the advertisement; also there is a valid reason for suspicion when the name or the address of the advertiser does not match the seller’s ones;

2.) Do not completely trust the pictures sent by the seller (they could be stolen from the Internet) and don’t forget to proceed to a “Google Reverse Image Search” in order to find the sources of similar ones;

3.) Always ask the seller for some specific pictures or videos (radio precisely tuned to various frequencies and/or modes) and do not accept any runarounds about it (“you can try the radio for some days”, etc.);

4.) Never pay the item in advance by rechargeable credit cards, Western Union or other non-secured/guaranteed ways of payment. Also Bank Transfer (Wire Transfer) is not a secure form of payment in order to avoid frauds;

5.) Always ask the seller for paying by PayPal “Goods and Services” (NOT “Send money to friends”); via “Goods and Services”, your purchase will be fully covered by the PayPal warranty.

In the case you are a victim of a scam anyway, please always report the incident to the Police or the Judiciary of your Country, and don’t forget to also warn the site where the announcement was found.

Best regards!
Paolo Viappiani – SWL I1-11437

Thank you so much for sharing this, Paolo! All very solid advice for avoiding scams.

If you think about it, scammers want to optimize their scam profits per transaction–in other words, go for the “low-hanging fruit.” This is why quality, rare radios are their bait of choice. They know there are motivated collectors and buyers who need to act quickly in order to secure a deal. The stakes are very high if you’re purchasing a rare/vintage radio via online classifieds sites.

Bookmark this article. Before making a radio purchase, re-read this post and follow Paolo’s advice. I promise: real vintage/rare radio sellers will happy take specific photos and videos in order to prove that the radio is indeed in their possession and that it functions as specified. If you receive an excuse–any excuse–from the seller, consider that a major read flag and do not proceed.

Thank you again, Paolo! I hereby name you an honorary SWLing Post Investigative Reporter!

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Steve builds a simple SWL antenna tuner that pairs brilliantly with the Belka-DX

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

A Simple Antenna Tuner for SWL Radios

by Steve Allen, KZ4TN

After reading 13DKA’s excellent review of the Belka-DSP on SWLing.com a few weeks ago I knew I had to have one! The size, features, and performance of the Belka-DX (latest version of the Belka-DSP) is phenomenal. I won’t go into reviewing the radio as I couldn’t come close to 13DKA extensive review. If you are considering this SWL receiver his review is a must read.

I love bedtime SWLing and have been putting off setting up an outside antenna specifically to feed into the bedroom for too long. Given that the resonant frequency of the antenna would not be broad enough for the tuning range of the Belka-DX I decided to build a small antenna tuner just for SWLing.

After a couple of hours searching the internet for a simple tuner I found just what I was looking for on http://www.hard-core-dx.com/nordicdx/antenna/lab/tuner.html. It’s a simple L match using a single variable capacitor and coil.

For the coil I wound ~100 turns of 26 Ga wire on a one inch diameter wooden dowel. The wire size can be whatever you have on hand. I twisted a tap every 10 turns. I drilled a hole in each end and glued in a machine screw to mount the coil to the bottom of the enclosure. I’ve had this enclosure in my junk box for a long time and have been waiting for just the right project. The variable capacitor I used was one I found on EBay a few years ago that had two sections, 330 pF and 120 pF. I tied them together for 450 pF. For the rotary switch I had to scratch around on eBay for a while until I found a 12 position single pole.

The plans for the tuner suggested adding a fixed value capacitor with a toggle switch to increase the lower end of the tuning range. I found a 510 pF silver mica and wired it into the circuit.

The antenna I put up is a sloper about 30 feet long.The high end is up about 40 feet and the low end is at about 12 feet. I put the antenna and tuner to the test last evening and the reception on the Belka-DX was superb. With the tuner the strength of the signal would peak about 2-3 units when I found the sweet spot.

The tuner also does double duty as an attenuator for very strong signals.

One mod I made to the Belka-DX was the addition of some grip tape to the tuning knob. It makes fine tuning much easier.

I believe we will continue to see a number of innovative receivers coming to market in the near term utilizing SDR technology. The ratio of performance to size of the Belka-DX is truly amazing in my opinion.

Thank you, Steve, for sharing this brilliant weekend project! As always, brilliant craftsmanship!

Click here to read Steve’s other posts and projects.

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How to find the Tecsun PL-330’s firmware version

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Many thanks to SWLing Post contributor, Jaap de Goede, who shares the following note:

Thanks for posting the hidden feature table to the Tecscun PL-330.

I see more and more videos of the PL-330 popping up on YouTube. I’m wondering what firmware they run. It’s easy to identify the firmware version.

Press and hold the VM/VF button when the radio is off. Release the button when all icons are displayed. Next, the display will briefly show the firmware version in the upper right corner. As you can see in the picture (above), mine has version 3302.

Thanks so much for the tip, Jaap! I am curious, too, if Tecsun is updating the firmware version with each release/update of the PL-330. With the PL-880, there were a number of iterations all carrying the same version number (8820, if memory serves).

It would be great for comparison purposes to check the firmware number.

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Help using crystal calibration on the Toshiba RP-2000F

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Many thanks to SWLing Post contributor, Darren Davies, who writes:

Hello Thomas,

I was gifted the Toshiba BCL receiver by an old work colleague. It’s an absolute beauty, in excellent condition and is unusual in that in comes with UK FM band and not the more popular Japanese one. It wipes the floor with newer radios on MW.

I writing to ask if any of your readers have any idea how to use the crystal calibration system. There’s very little information about the radio online and I’d like to get it into tip top condition.

Absolutely love your site and look forward to your daily emails. Keep up the good work.

Cheers Darren

First of all–wow! I love the design of this Toshiba. It’s brilliant that it even has built-in rails to protect the front panel. Obviously a radio that beckons to be taken to the field! Thanks for sharing your photos, Darren.

Post readers: If you know how to calibrate this Toshiba RP-2000F, please comment!

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How to properly install a Mini Whip antenna in an noisy urban environment

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

Setting up a Mini Whip antenna

by Grayhat

I’ve been fiddling with my “balcony antenna” experiment for quite a while now, and I settled with a Linear Loaded Dipole (LLD, also known as “Cobra”) which, in my case, due to self-imposed limitations was a short one (about 9m total).

Since I mentioned it, here is a pic of the antenna showing its installation:

Click images to enlarge.

In the above image you can see the overall setup of the LLD, the modification I did, by adding additional wires to the end of the arms and also the Mini Whip location

The LLD served me well, from LW up to around 200MHz allowing me to listen to broadcasters, hams, aircraft communications, time signals and then more, and it’s definitely a keeper, but I wanted to give a try to the “Mini Whip” antenna, even if a lot of people discard it saying it’s a noisy antenna and not worth it; keep in mind the Utwente SDR uses it and it seems to work fine, so I had to give it a try !

Anyhow, after searching the internet for a suitable whip, I finally found this one:

I bought the antenna on Amazon, but it’s also available on eBay and while the price isn’t the lowest one, I chose it since it uses BNC connectors only (some models use a mix of UHF/BNC or the like). This one had a top wing nut allowing to connect an additional (optional) external whip (may be useful on lower bands) and, last but not least, its color; being gray, it is quite stealth, which may be useful for some people (not my case, luckily). So I went on and ordered the antenna, the delivery took about 10 days and the package contents were exactly as shown above. The supplied coax is thin (RG-174 I believe) and it would be a good idea replacing it with some runs of RG-58, but for the sake of the experiment, I used the original wire.

So, having the antenna, I looked around for informations about the correct installation for the “Mini Whip” and found that in most cases, the reported poor performances of the Mini Whip are due to people installing it the wrong way. For reference and information about how the whip works and about how to properly install it, please refer to the information from PA3FWM found here and here.

Now, if you can place the whip in a garden or yard, using a pole, the correct installation of the whip is the one shown in this pic:

If you carefully look at the image you will notice that the whip sits above the supporting (metallic) pole and that the ground of the connector is electrically connected to the pole (through the clamp). Plus, the pole is then grounded (at the bottom) and the coax (which has chokes) runs away from the metallic pole.

What does the above mean ? Well, the Mini Whip antenna needs a “counterpoise” (ground) to work, and installing it as above, instead of using the coax braid as its counterpoise, the Mini Whip will use the supporting pole, this helps a lot minimizing the noise and it’s one of the tricks for a proper setup, the other one is placing the whip as far away from the “noise cloud” of your home as possible. In my case, I choose the far end of the balcony–also since I had a nice support there, the image below shows the whip installation using a piece of PVC pipe I bought at a nearby home improvement store:

At first, I just installed the antenna without the ground wire and with the coax coming down vertically from the connector. When I compared the whip to my LLD, the results were discouraging: the noise floor was much higher and a lot of signals, which the LLD received without problems, totally disappeared inside the noise floor.

Being the kind of hard-headed guy I am (and having read the documentation about proper setup) I went on and made further modifications.

Let me detail the installation a bit better with this first image (click to enlarge):

As you can see in the above image, the whip is supported by a piece of PVC pipe which keeps it above the metal fencing of the balcony (or a support pole if you’ll use it) and I also connected a short run of insulated wire to the ground of BNC plug at the bottom of the whip. This short run goes to a wire clamp which allows it to connect to the “counterpoise” (ground) wire.

In my case, since the balcony was at 2nd floor, I didn’t have a way to give to the antenna a real ground, so I decided to run a length of wire (AWG #11) down the pipe and then along my balcony fencing (10m total). An alternative, which will also work for roof installations, would be using chicken wire (fencing). In such a case, you may lay as much chicken wire as you can on the floor/roof and connect the wire coming down from the whip ground to it. I haven’t that that (yet!) but I think it may further lower the noise and improve performances.

Notice that in the case of the Utwente Mini Whip, the antenna support pole is connected to metallic roofing so it has plenty of (virtual) ground.

Later on, I improved the setup by raising the antenna a bit more and routing the wire (almost) horizontally from the feedpoint to reduce coupling with the vertical “counterpoise” wire.

The image below shows the final setup:

While not visible in the above image, I also wrapped the coax wire in a loop at the point where it’s held by the fencing and added some snap-on chokes to the coax at the point where it enters the building.

With all the modifications in place, the antenna started performing as it was designed to. The noise floor is still a bit higher than the one of the LLD, but given that it’s an active antenna, that’s to be expected

To give you an idea of the signals and noise floor, here are a couple of images taken from the screen of my laptop while running SDRuno. The first one shows the waterfall for the 40m band

While the second one, below, shows the one for the 80m band:

At any rate, my usual way of testing antenna performance (and modifications effects), aside from some band scanning/listening, is to run an FT8 session for some hours (and optionally repeat it over some days) and then check the received spots.

In the case of the Mini Whip, after all the modification to the setup, I ran an FT8 session using JTDX for some hours and the images below show the received spots. The first image shows the whole map of the received stations:

While the second one below is a zoom into the European region to show the various spots picked up there; the different colors indicate the 20m (yellow), 40m (blue/violet) and 80m (violet) bands:

As you can see, the Mini Whip performed quite well despite the “not exactly good” propagation.

While some time ago I’d have discarded the Mini Whip as a “noise magnet”, as of today, with a proper installation, I think it’s a keeper. While it can’t be compared to bigger antennas, I believe it may be a viable antenna for space-constrained situations. The only thing it needs is a bit of care when setting it up to allow it to work as it has been designed to.

Brilliant job, Grayhat! Thank you so much for sharing your experience setting up the Mini Whip antenna. As you stated, so many SWLs dismiss the Mini Whip as “noisy”–but with a proper ground, it seems to perform rather well. The benchmark example of a Mini Whip’s performance must be the U Twente Web SDR.

Thank you again, Grayhat!

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