Category Archives: Ham Radio

Southgate ARC: What Is a Balun and How to Make One Cheaply

(Source: Southgate ARC)

Ham Radio – What Is a Balun and How to Make One Cheaply

A Balun is a transformer which allows coaxial cable, which is an unbalanced lead to be connected to a balanced load, for example a resonant aerial.

The 1:1 balun is often called a choke balun, it works by eliminating Radio Frequency currents flowing on the outside of your coaxial cable, this is important because it prevents the pattern of the dipole becoming distorted and prevents the braid of the coaxial cable radiating.

Connecting coax to your resonant dipole which can be configured in a V shape or in a sloping fashion, however serious power loss and feeder radiation can occur without the use of a balun transformer. No one wants to induce Radio Frequency currents into Television receivers or Broadcast equipment as it may result in disputes with neighbours and could possibly lead to your station having to close down. Try to keep the centre of your aerial away from buildings as it may induce Radio currents into the mains wiring.

Building a choke is not difficult all you need is some plastic pipe available from many Do It Yourself outlets and warehouses. I use a length of about 1 foot of plastic pipe and 21 feet of coaxial cable, the length of the pipe and diameter is chosen because it works well if using R-G-5-8 coax the ends of the pipe can be sealed after placing a SO-239 connector for your coaxial lead. I use two bolts and solder tags at the other end of the pipe to connect the ends of the dipole to the choke.

When wrapping your coax around the pipe don’t use too much force as it may damage the inner braid and space the turns away from each other by a millimetre or two. R-G-2-1-3 coax around 21 feet used with 5 inch pipe will handle 400 watts pf power. Wire ties can be used to hold the turns together along the length of the pipe. Using these measurements your choke will cover all of the ham radio bands from 1.8 Megahertz through to 28 Megahertz and will keep the radiation pattern.

Using a dummy load connected to the choke and transmitting 100 watts from my transmitter indicated an S.W.R. readings of around 1.5 to 1 at 3.5 Megahertz when testing 28 Megahertz the S.W.R. reading came down to 1.1 to 1 which is an excellent match. Using the choke as it should be at the feed point of a dipole cut for 40 metres give an S.W.R. reading of 1.2 to 1. The highest reading was 1.5 to 1 when using 18 Megahertz but the rest of the High frequency bands gave me very acceptable matching.

John Allsopp G4YDM

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Cloud-SDR: a remote access system for a number of popular SDRs

Many thanks to SWLing Post reader, Sylvain (F4GKR), who writes:

I am Sylvain, from Cloud-SDR, a new company selling software to get remote access to your existing SDR receivers through the Internet.


  • currently supports : SDRPlay, Perseus, BladeRF and AirSpy. LimeSDR to come when received and tested.
  • client software is free (can be used as standard SDR receiving software with locally connected devices),
  • server software starts at 110 Euros, VAT may be added depending on customer location,
    easy to use

From the Cloud-SDR website:

The Cloud-SDR Concept

You need a way to remotely access your existing SDR receiver? To stream your IQ samples to another remote computer over the network?

Cloud-SDR is a commercial software solution to enable real time RF data sharing or processing through the cloud.

Cloud-SDR can collect real-time IQ complex samples from an SDR hardware device connected on one machine, stream the samples to a second machine for demodulation or analysis, then send the resulting stream to third machine for storage.

In standalone mode, Cloud-SDR can execute signal processing tasks described with embedded JavaScript DSP engine.

Because network bandwidth is limited compared to SDR receiving bandwidth, the core concept of Cloud-SDR is to move the processing along the cloud to where it is required or possible : the DSP chain is divided in sub-tasks that are spread between computers interconnected through Internet.

Very cool, Sylvain!

I like the fact your system supports popular affordable SDRs like the SDRplay RSP & AirSpy and that you can stream your IQ samples.

Click here to read more on the Cloud-SDR website.

Build a Raspberry Pi-powered SDR

Many thanks to SWLing Post contributor, Jeremy Clark (VE3PKC), who writes:

I have developed an SDR receiver that may be of interest to your readers. It can be used directly with the Raspberry Pi2B/3B. It comes in several versions DIP/SMD.

Check out this MP4 movie:

I have two eBooks which are basically design manuals for the DIP and SMD version of my SDR receiver. Each eBook has an Internet linked parts list, so that the reader can get their own parts to keep costs down. The DIP eBook is $7.90 CAD and the SMD book is $14.90 CAD.

Click here to view Jeremy’s website.

Thank you, Jeremy–this looks like a fascinating construction project!

Readers: just to be clear, Jeremy is selling eBooks detailing construction–not kits. He did mention if you’re interested in obtaining the PCB, he can sell this as well.

Klaus demonstrates his folding mag loop antenna

Many thanks to SWLing Post contributor, Klaus Boecker, who follows up after our recent post showcasing his homebrew magnetic loop antenna.

One of the cool things about Klaus’ antenna is that he can easily position it vertically (see above), or fold it over into a horizontal position (see below).

While one would think Klaus would get optimal performance from his loop while vertically-oriented, it’s not always the case. Klaus has discovered that on some frequencies, placing the antenna in the horizontal position lowers the noise level and increases the target signal’s strength.

To demonstrate, Klaus made the following short video for us:

Click here to view on YouTube.

That’s a pretty amazing difference, Klaus! I’m no antenna expert, but perhaps what’s happening is you’re eliminating noise that is polarized in the plane of your antenna, thus the signal “pops out” much better when oriented horizontally?

I’m curious if any readers can explain this.   I know very little about loop antennas–especially small loops since so much of their surroundings affect their performance.

Thanks for sharing, Klaus!

GigaParts opens new distribution center in Las Vegas

(Source: Southgate ARC)

GigaParts opens new distribution center in Las Vegas

After Amateur Electronic Supply went out of business in July, GigaParts began hiring the AES staff in Las Vegas and working on moving the operation to a new location less than 5 minutes from the famous Las Vegas Strip and just 3 miles from the former AES building.

Although the retail showroom won’t be ready for visitors for another few months, starting today, the Las Vegas store becomes the primary distribution center for GigaParts shipments to the western half of the US. That means fast, affordable shipping to the huge population of hams in California and other western states, without sales tax!

Former AES customers will see some familiar faces at GigaParts Las Vegas, including AES’s former shipping manager, Terry Spaulding, and store manager, Julio Suarez. “I’m excited to be back and I’m looking forward to helping all of my old friends again,” said Julio. “AES was iconic in ham radio and it was sad to see it die off, but we have an opportunity with GigaParts to do things better than we ever could before,” he continued.

In addition to the new and improved facility, another improvement over the AES business model will be a single toll free number for customers wishing to place orders by telephone: (866) 535-4442. Sue Stephens, Customer Service Manager for GigaParts: “Technology has come a long way in the 70 years since AES first opened. Our state-of-the-art call center in Huntsville handles calls and online chats from all over the world. The guys in Las Vegas are going to be a huge asset to us by helping with employee training, adding new product lines and even backing up our reps on the phones during peak call times.”

Jeff Sinclair, the e-Commerce Division Manager at GigaParts, states, “This is a significant move forward for GigaParts as we continue to expand our distribution capabilities in North America. The new facility in Las Vegas doesn’t just mean faster shipping to our west coast customers, but the employees there add decades of experience in customer service and ham radio product knowledge.”

Initially, the Las Vegas store will carry the complete lines of amateur radio and maker equipment with more product lines being added later. Understanding that hams come to Las Vegas from all over the country and all over the world, GigaParts plans on making the retail showroom more of an interactive showcase of the latest equipment rather than a self-service shopping experience common amongst other amateur radio outlets. Today, GigaParts Las Vegas is stocked with ham radio gear and is ready to fill your order! To welcome AES customers, GigaParts is offering a $25 gift certificate to every former AES customer.

See for details