Tagged: antennas

Tech Minds: Building a Low Cost VHF/UHF Antenna from Copper Tape

In his latest YouTube video Matt from Tech Minds shows how to build extremely low cost antennas out of copper tape. Rolls of copper tape are commonly found very cheaply in garden stores as slug barrier tape as garden slugs will not travel over copper.

After using a dipole calculator Matt solders coax to two strips of copper tape, resulting in a rudimentary dipole (without balun or choke). His first test with a UHF sized dipole showed poor SWR and yielded poor results on an actual radio/SDR. But his second test with a VHF sized dipole actually yielded decent results. 

VHF / UHF ANTENNA MADE FROM COPPER TAPE

DEF CON 30 RF Talks: Biohacking, Designing Antennas, Tracking Military Ghost Helicopters and More

DEF CON is a yearly conference with a focus on information security. At this years DEF CON 30 conference various talks on RF related topics were presented. In the past few weeks talks have been uploaded to YouTube for all to watch. Below we highlight a few we found interesting. The list of all main talks can be found on the Defcon YouTube channel, and talks from the RF Village can be found on the RF Hackers Sanctuary YouTube page

J9 - Biohacking Using SDR When You Don’t Know What You’re Doing

Security Researcher and BioHacker J9 presented an interesting and entertaining talk about how she used an SDR to listen in and decode a wireless pH sensor pill she ingested as part of a medical test.

What would you do if you were implanted with a medical device that broadcasts every 12 seconds?

Starting with loads of curiosity and very little knowledge about RF, how to use a software defined radio (SDR), and no knowledge of how to decode captured RF signals, I embarked on an adventure to teach myself something new. Jumping head first into the RF CTF helped greatly!

This presentation starts with cocaine and ketamine (in a controlled medical setting) and includes a near-death experience and new skills attained by building on the work of those who came before me. The end result of this adventure led me to the US Capitol to sit down with Senate staffers about the security and exploitability of medical devices.

DEF CON 30 RF Village - J9 - Biohacking Using SDR When You Don’t Know What You’re Doing

Erwin Karincic - Have a SDR? - Design and make your own antennas

In this talk Erwin Karincic explains how to design and make custom PCB antennas using home based or low cost techniques.

Most Software Defined Radios (SDRs) process a wide range of frequencies usually ranging from few MHz to multiple GHz where different antennas are used to pick up signals in a specific subset of that range. All applications using SDR require antennas to operate efficiently at very specific frequencies. Most inexpensive commercial antennas are designed either for wider ranges with lower gain over the entire range or very specific known frequencies with higher gain. The problem occurs when the researcher performs an assessment of a device and requires the use of specific frequency for which an antenna with high gain is not readily available. Most security researchers within wireless domain have outlined that their specific attack or exploit could be executed at higher range if antenna had better gain at that specific frequency. This talk focuses on bridging that gap by providing a way for researchers to create their own patch antennas without deep electrical engineering experience.

DEF CON 30 RF Village - Erwin Karincic - Have a SDR? - Design and make your own antennas

Andrew Logan - Tracking Military Ghost Helicopters over Washington DC

In this talk Andrew explains how ADS-B receivers, combined with ATC communications, public announcements and crowd sourced visual identification have helped track the activity of military helicopters operating over the Washington DC area.  

There's a running joke around Washington D.C. that the "State Bird" is the helicopter. Yet 96% of helicopter noise complaints from 2018-2021 went unattributed: D.C. Residents can not tell a news helicopter from a black hawk. Flight tracking sites remove flights as a paid service to aircraft owners and government agencies; even in the best case these sites do not receive tracking information from most military helicopters due to a Code of Federal Regulations exemption for "sensitive government mission for national defense, homeland security, intelligence or law enforcement." This makes an enormous amount of helicopter flights untraceable even for the FAA and leaves residents in the dark.

What if we could help residents identify helicopters? What if we could crowd source helicopter tracking? What if we could collect images to identify helicopters using computer vision? What if we could make aircraft radio as accessible as reading a map? What if we could make spotting helicopters a game that appeals to the competitive spirit of Washingtonians? And what if we could do all of this... on Twitter?

DEF CON 30 - Andrew Logan - Tracking Military Ghost Helicopters over Washington DC

CENOS Antenna Design and Simulation Software Looking for Testers

Back in March 2020 we posted about CENOS, a company creating a new antenna modelling and simulation design package. Back then they were offering applications to beta test the software for free. CENOS has now reached V1.0 status, and they are now wanting to enroll another 300 testers. The benefit to the testers is that they will receive a 90% lifetime discount on the software, and testers who provide lots of active feedback will be granted free licenses.

CENOS Antenna Design version 1.0 will be available for closed testing starting from March 17, 2021.

During the free 14-day testing trial, users are expected to share their feedback about the software and usability, thus making an impact on further software development. 

In reward, they will get a generous discount or lifetime-free-licenses (for best contribution), once the software is available for public use (we expect to launch it shortly after rigorous testing completes).

More details will be announced on March 17!
 
Sign up here:
Software benefits
 
​CENOS is fast-to-learn and easy-to-use specialized antenna design simulation software for budget-sensitive customers.

CENOS integrates FreeCAD geometry editor to handle geometry of any complexity, provides built-in utilities for handy design of microstrip antennas and arrays, feed networks, wire antennas (including import of NEC files), and arbitrary 3D structures. FreeCAD also allows to import CAD files from external editors like Autodesk Inventor or similar.

CENOS ensures automatic meshing, as well as allows building manual mesh of any detalization level in the specially designed FreeCAD workspace.

For antenna calculation, the current software version utilizes FEM solver to provide accurate simulation for geometries of any complexity, including multi-port, high Q and other cases. Already now, CENOS R&D is pointing to combining the FEM solver with MoM and FDTD methods to provide a unique, optimized (fast and accurate) solution for any particular case.

CENOS provides very powerful visualization capabilities that includes full visualization of fields and graphs powered by Paraview, spreadsheet for data like S11, VSWR, reflection coefficient, etc, and pdf report.

That all makes CENOS a good alternative to well-known general purpose software like HFSS, CST, FEKO and Comsol for budget-sensitive customers looking for specialized antenna design simulation software.
Software functionality
• One-stop software: from CAD geometry to full visualization of results and analysis
• Desktop (on-premises) installation for Windows 7-10
• CENOS leverages open-source tools to ensure full stack of CAD/CAE software: FreeCAD, GetDP, ParaView
• User experience optimized for RF antenna design
• Supports the use of CAD geometry files prepared by any design program (.step or .iges formats)
• Pre-defined templates for basic antenna geometries
• Full-stack geometry editor powered by FreeCAD
• Material database, possibility to add and save custom materials

Simulation capabilities
• Wide range of antennas, antenna arrays, geometries of any complexity, inhomogeneous structure
• Finite element method (FEM) solver optimized for high frequencies
• Lumped port type, multiple ports (feeds) with phase shifts
• Frequency diapason (wide, multiband) 
• Ports: S11, VSWR, power, reflection coefficient, impedance, reactance, and resistance
• Fairfield pattern: directivity (gain), radiation intensity
• Antenna: Electric field, magnetic field, vector plots 
• Frequency-dependent dielectric constant and loss tangent
 
… all you need for antenna design in an easy-to-use way, because this is the software specialized on RF antenna design with full spectrum of necessary functionality. And we are constantly working to add more value.
 
Hardware requirements
You don’t need a supercomputer to run antenna design simulations with CENOS. Intel i5 or i7 (or similar) are good enough. The faster processor you have, the faster calculation will go.

We recommend to have at least 16Gb RAM to calculate 3D cases, 32Gb is better. Actually, the more RAM you have, the bigger (more complex) 3D geometries you can simulate. Some of our customers use 128 Gb machines and that’s like for rocket-science-cases. MS Windows OS.
CENOS Antenna Simulation
 

Comparing Shortwave Antennas with an RTL-SDR and FT8 Monitoring

Eric had an inverted L and T3FD antenna set up in his backyard and he wanted to test both at the same time to see which received HF better overall. Rather than relying on subjective 'by ear' measurements he decided to use the digital FT8 mode as his comparison signal. FT8 is quite useful for this purpose as the decoded data includes a calculated signal-to-noise (SNR) reading which is a non subjective measure that can be used for comparisons. It also contains information about the location of the signal which can be used for determining the DX capability of the antenna. 

To perform the comparison he used two or our RTL-SDR Blog V3 dongles running in direct sampling mode, and also added an additional low pass filter to prevent excessively strong TV and FM signals from overloading the input. Each antenna is connected to it's own RTL-SDR, and a modified version of GQRX with remote UDP control is used to switch between multiple FT8 frequencies so that multiple bands can be covered in the experiment. WSJT-X is used for decoding the FT8 packets.

After logging SNR values for several days he was able to plot and compare the number of packets received by each antenna, the maximum distance received by each antenna. His results showed that his inverted L antenna was best in both regards. He then performed a relative comparison with the SNR readings and found that the inverted L performed best apart from at 14 MHz, where the T3FD performed better.

In further tests he also compared the antennas on which signal headings they were receiving best from. The results showed that Erics inverted L was receiving best from one direction only, whereas the T3FD received signals from more headings.

Eric's post includes full instructions on the software setup and also Python code which can be used to replicate his experiments. We think that this is a great way to objectively compare two types of antennas.

Antenna directionality measurements via FT8 received headings

Building an Underground Earth Probe Antenna for 0 – 14 MHz TX/RX

Thank you to Jean-Marie Polard (F5VLB) for letting us know about his work in creating underground "earth probe" antennas that work for both RX and TX between 0 - 14 MHz, and are especially good at VLF and below. He writes:

Can't install an antenna at home? Madame refuses the masts, taut son? One solution, The Earth probes antenna.

Our group (https://www.facebook.com/groups/earthprobes/) started in January 2019. At first everyone made fun of me, the professionals called me crazy and today with more than seven hundred members, we installed underground antenna systems and the results are there.

Between 0 and 14MHz, in transmission and reception, it works!

This system dates from 1914/1918 but has been brought up to date.

It doesn't take much to get started, just the urge to try.

Mad of vlf - elf - ulf ? come here https://www.facebook.com/groups/VLF.ULF.ELF/ nearly 1000 members are waiting for you.

So when? Welcome everyone.

To access the Earth Probes and VLF.ULF.ELF groups you'll need a Facebook account. The groups contain a number of research papers documenting the concept, and the photos section. From the photos, an earth probe antenna appears to consist of two long grounding rods spread over a distance, or a grounding rod and long buried wire, combined with a balun.

An example of an underground antenna setup from a 1935 shortwave magazine.
An example of an underground antenna setup from a 1935 shortwave magazine.

Sign up to be an Early Beta Tester of CENOS Antenna Design and Simulation Software

CENOS are a company specializing in 3D modelling and simulation software for induction heating applications. However, they are now branching out and are creating software for antenna design and simulation. Final pricing of the software is not yet advertised, but they write that it has been made affordable thanks to "open source algorithms". Hopefully it will be affordable to hobbyists, but judging by the heat simulation software pricing it may not be (although they offer to software free to students, researchers and teachers).

However, it appears that they will soon be running a beta testing program that should hopefully be free to use during the testing phase. You can sign up to their email list and wait for their announcement on their website.

CENOS Antenna Design Program Screenshots
CENOS Antenna Design Program Screenshots

A Discone Antenna Made from 3D Printed Parts and Aluminum Tape

A Discone is a type of antenna that is designed to be resonant over a wide range of frequencies. Most antenna designs only really receive well on a few resonant frequencies, but a Discone is resonant over a much wider frequency range. This makes it a good partner for RTL-SDR and other SDR units as many SDRs tend to have wide tunable frequency ranges. With a wideband antenna like a Discone connected to an RTL-SDR one can scan over the almost entire tunable frequency range without needing to change antennas for each band. The drawbacks to a Discone however is that the antenna gain is not very high, and that it makes the SDR more susceptible to out of band interference. They also tend to be fairly expensive and difficult to build.

However now over on Thingiverse, mkarliner (aka Mike) has a remedy for the difficulty in building a Discone with his 3D printable Discone design. To construct it you simply need the 3D printed parts, some .3mm and 2mm plastic sheets, a 25mm plastic conduit and some aluminium tape. Mike's design works from 400 MHz and up, but the design could be easily enlarged for better performance on the lower frequencies. He writes:

The Discone antenna is remarkable in that it is capable of receiving and transmitting over a wide range of frequencies with good matching. Because of this, it is a good match for SDR receivers such as the popular RTL-SDR sticks.

The only really tricking thing about making a discone is that the disc has to be balanced at the very top of the cone, which is mechanically awkward.

The two parts here allow the cone to be solidly clamped and provide an adequate base for the disk. There also two holes for bring the coax centre and braid out to the disc and cone.
The base part has a socket at the bottom for 25mm (1 inch) plastic conduit for mounting

This antenna illustrated is designed for 400MHz and up, and as such transmits well on the 70cms amateur band, US and UK PMR channels and 23cms. It also receives aircraft ADS-B signals very well. I used .3mm plastic sheet for the cone and 2mm plastic for the disc, and then covered them with aluminium weatherproof tape. Be sure to check for continuity across the tape stripes.

The screenshot is of a calculator by VE3SQB which can be downloaded from http://www.ve3sqb.com/ if you want to make attenna's for other ranges.

A 3D Printed Discone
A 3D Printed Discone

If you're interested in building wideband antenna there is also the planar disk antenna (pdf) which can be built out of pizza pans.

The K9AY Loop Antenna: A Directional E-H Antenna for HF

Thank you to Frank Sessink (PA0FSB) for submitting to us his document describing the K9AY loop antenna (pdf), which is the antenna that he successfully uses with his RTL-SDR for HF reception. The antenna combines magnetic (H) and electric (E) field reception in order to create a directive radiation pattern. Frank extends the idea by showing a method that can adjust the directivity electrically with some simple resistor switching.

The antenna that I use is for medium wave DX, specially to receive MW from USA here in Europe/The Netherlands. The antenna is a combination of a magnetic loop and a sense antenna for the E-field. The magnetic loop is directive, but has no front-rear ratio. The E-field antenna has omnidirectional sensitivity. The combination, in correct phase and amplitude, results in a front-rear ratio of more than 25 dB over the frequency range from 500 kHz to around 3 MHz. Higher frequency makes no sense, since skywave signals distort the ground wave directivity pattern.

A simple modification is used as directional antenna with remote control: two orthogonal loops that combine E and H-field in a simple way. I can make 8 selectable directions.

The full document is available here in PDF format.

The K9AY E-H HF Antenna
The K9AY E-H HF Antenna