A variable attenuator is a circuit that decreases the strength of the input signal either continuously or step by step without appreciable signal distortion while substantially maintaining constant impedance match.

Mechanically variable attenuators are usually adjusted with a tuning screw or control knob. Electronically controlled variable attenuators are available in many forms. Nowadays there are integrated chips that implement adjustable RF attenuator. One commonly seen such IC has been PE4302 (end of life product that is replaced with PE4312). The PE4302 is a high linearity, 6-bit RF Digital Step Attenuator (DSA) covering a 31.5 dB attenuation range in 0.5 dB steps, and I bought a circuit board with PE4302 chip in with plans to build my own adjustable RF attenuator. There are also other boards available with similar functionality based on PE43703 and HMC472 chips.

I planned to add my own controls to the board to make is easy to use. Due lack of time I never finished that project. While I still had need for adjustable RF attenuator, saw 6G Digital Programmable Attenuator 30DB Step 0.25DB OLED Display CNC Shell RF Module for sale at attractive price (below 30 Euros). This looked like time saver compared to building my own controls.

6G Digital Programmable Attenuator 30DB Step 0.25DB OLED Display CNC Shell RF Module is a digital attenuator can adjust the RF signal level of the circuit in 0.25dB steps without interrupting the circuit. The manufacturer advertises OLED display for attenuation, high accuracy, stability and reliability and even option to control the module from computer. This looked like a high quality attenuator built in a solid aluminum case at attractive price point.

Technical data from product page:

1. Working frequency: LF-6GHz
2. Attenuation adjustment range: 0-31.75dB
3. Attenuation step: 0.25 (dB)
4. Insertion loss: ≤1.5dB (the insertion loss at the high frequency end will be a little larger)
5. Standing wave ratio: ≤1.4
6. Attenuation accuracy: ± 0.25dB Max
7. Rated power: ≤1W
8. Connector form: SMA (female, outer screw inner hole)
9. Temperature range: -10 ℃ ~ + 50 ℃ (operation), -40 ℃ ~ + 70 ℃ (not operation)
10. Dimensions: 55X40X16.5mm (excluding SMA interface protruding part, SMA protruding part 9mm)
11. Weight: 57g
12. Input and output impedance: 50 ohms

After few weeks of waiting, I finally received the package. I was happy that the packet finally came, but what I was very disappointed that what I received was broken. One of the control buttons needed to operate it was completely broken, quite probably during postal handling because it was not packaged well (just put to a plastic bag without any package or padding).

I contacted Banggood customer service on the problem. They promised to send me a new one, and they did not want me to send the broken one back. Because there was still weeks waiting, I tried if I could fix the one I have on the mean time when waiting for it. Trying to glue the existing button was out of luck. Best would be just change the button to a new one. Unfortunately I did not have any exactly right size button, so I had to make a “hack” of soldering a bigger button in place. After the soldering the unit worked well.

After waiting I received the new one. This time it was still packaged in the same bad way, but fortunately the buttons or display did not get damaged on the transit. Looked good. But when I tried to power the device with USB cable, I could not plug in the supplied USB cable because the microUSB connector on the module has taken some hit becoming too flat.

I fixed this connector myself and got the unit working.

This product fells like a high quality attenuator built in a solid aluminum case, but there seems to be some problems in getting the unit in good condition from factory to the customers.

When I got the module to work, I found it worked well (tested the attenuation working well with NanoVNA). The module was easy to use. The attenuation was displayed on OLED screen and can be controlled with control buttons. The device remembers the set attenuation over device power down and power up cycles. This module needs 5V to operate, and this 5V is designed to be supplied through the microUSB connector.

There product page also gave download link for a PC control software. I did not try to run it, because after download the PC virus scanner listed the software package suspicious. There is also said to be option to control the attenuation of the device through Python code rather than an application. There is some Python example code at https://github.com/emptemp/att6000_control

Now an Israeli researcher has demonstrated that LAN cables’ radio frequency emissions can be read by using a $30 off-the-shelf setup. Mordechai Guri of Israel’s Ben Gurion University of the Negev described the disarmingly simple technique to The Register, which consists of putting an ordinary radio antenna up to four metres from a category 6A Ethernet cable and using an off-the-shelf software defined radio (SDR) to listen around 250MHz.

The research paper says:
“The computers are equipped with 10/100/1000 Mbps Gigabit Ethernet
card. We tested three types of widely used Cat 5e and Cat
6A Ethernet cables listed in Table V. We also tested a laptop
computer and an embedded device (Raspberry Pi) to evaluate
the attack on these types of devices.”

“For the reception we used two types of
software-defined radio (SDR) receivers, as specified in Table
III. The R820T2 RTL-SDR is capable of sampling up to 16bit
at narrow band and has RF coverage from 30 MHz to 1.8 GHz
or more. The HackRF device has 1 MHz to 6 GHz operating
frequency and 8-bit quadrature samples (8-bit I and 8-bit Q)”

LANTENNA ATTACK: Leaking Data from Air-Gapped Networks via Ethernet Cables

Ethernet cables emit electromagnetic waves in the frequency bands of 125 MHz and its harmonics (e.g., 250 MHz and 375 MHz). “Ethernet cable emits electromagnetic waves in the frequency bands of 125 MHz. Changing the adapter speed or turning it on and off makes it possible to regulate the electromagnetic radiation and its amplitude,” says Guri. This can potentially opening the door to fully developed cable-sniffing attacks because “From an engineering perspective, these cables can be used as antennas and used for RF transmission to attack the air-gap,” said Guri. LAN cables sniffing can reveal details from network traffic. In one test data could be transmitted from an air-gapped computer through its Ethernet cable and received 200 cm apart.

In experiment UDP packets with single letters were sent over the target cable to a very low speed and, via a simple algorithm, be turned back from received RF signal back into human-readable characters. Nicknamed LANtenna, Guri’s technique is an academic proof of concept and not a fully fledged attack that could be deployed today. So RF noise from un-shielded LAN cables can be used to lead information air-gapped networks. The experts explained that often air-gapped networks are wired with Ethernet cables since wireless connections are strictly prohibited to avoid data leaks. But clearly even wired networks can leak information when you can get near to them with an SDR radio hardware.

The researchers proposed several defensive measures that can be adopted against the LANTENNA attack such as:

• implementing zone separation banning radio receiver from the area of air-gapped networks;
• monitoring the network interface card link activity at the user and kernel levels. Any change of the link state should trigger an alert;
• using RF monitoring hardware equipment to identify anomalies in the LANETNNA frequency bands;
• blocking the covert channel by jamming the LANTENNA frequency bands;
• Cable Shielding;

Paper:

LANTENNA: Exfiltrating Data from Air-Gapped Networks via Ethernet Cables

Sources:

https://nakedsecurity.sophos.com/2021/10/15/lantenna-hack-spies-on-your-data-from-across-the-room-sort-of/

https://www.theregister.com/2021/10/14/lantenna_ethernet_cable_rf_emissions/

https://securityaffairs.co/wordpress/123008/hacking/lantenna-attack-exfiltration-technique.html

https://www.bankinfosecurity.com/lantenna-attacks-exploit-air-gapped-networks-via-ethernet-cables-a-17688

https://arxiv.org/pdf/2110.00104.pdf

EMC stands for electromagnetic compatibility, which means that different electrical products must work well together. Our homes are filled with more and more electronics and then it is important that our products work together. Much attention is paid to EMC issues in the electronics industry, for example, because disturbances that exceed the limit values ​​directly cause financial damage to production. In homes, however, no attention is paid to EMC limits and we are apparently accustomed to accepting interference. Within EN 55032 it requires Radiated Emissions measurements to be performed from 30MHz to 6GHz.

There are EMC requirements for electrical products that they must meet. There are EU specifications for antenna and HDMI cables, most of the tested cables do not meet them. The Swedish Electrical Safety Agency is the authority in Sweden that handles the EMC directive. The Swedish Electrical Safety Board’s mission is not only to ensure that the products are safe to use, but also that they meet other quality requirements. One of these is the requirement for electromagnetic compatibility (EMC), which among other things ensures that different electrical products or electrical installations do not interfere with one another. EMC requirements are regulated both in Swedish law and at EU level with the EMC Directive.

HDMI cable is a very common product in our homes between TV and different devices connected to it. Of the 30 HDMI cables that were tested, 27 failed. The four groups tested 30 coaxial antenna cables and 30 HDMI cables, of which only 11 percent of the antenna cables met the manufacturers declared attenuation and and only 10 percent of the HDMI cables met an acceptable EMC quality of at least 50 dB coupling attenuation. The test was performed on retail cables and not cables that were supplied with TVs or monitors.

The failed cables caused too much EMC interference when in use. EMC interference means that unwanted signals are leaked which can interfere with other devices in the vicinity where the cable is connected.

A total of 30 HDMI cables and 30 antenna cables were tested in the study. Of these, only 3 HDMI cables held the line, the remaining 27 cables leaked unwanted signals.
It was not revealed which brands were tested, but according to the study high price does not guarantee quality: In some cases, even the most expensive cables performed worst. It should be noted that all cables tested were of quite short lengths of between 1.5 to 3 meters, so longer cables could perform even worse. HDMI cables are said to potentially cause radio interference, like interfere with 2.4 GHz radios, such as Wi-Fi, Bluetooth, wireless mice and headphones etc.

It seems that people chasing cheap-ass products don’t get what the marketing material says. Since their manufacturers race to the bottom price point, the quality of products suffers. HDMI cables are often very cheap, and very crap. Because there was no significant difference when it comes to how interference prone or not the cables were based on price, it seems that everybody is chasing for cheapest production and some just sell their cheaply/badly cables at higher price. For any product incorporating HDMI 1.0 or above it is most likely that the frequency range in the cable will be at least 30MHz to 2GHz. For some models it could be something to do with the fact that older HDMI cables weren’t designed for current standards. The HDMI connection standard has reached version 2.1. As a result, the data transfer capacity of the bus increased from 18 gigabits in the 2.0 standard to 48 gigabits per second.

Use a good quality HDMI cable to start off with including a cable shield well-bonded to the metal connector shell in multiple places. A good quality HDMI cable also has a tight weave with very small openings. For Radiated Emissions the problem is the common-mode noise i.e. the common mode current flowing on the outside of the shield, thus you may require some filtering. Poor quality (usually the cheap ones) with loose shield weaves or cables with pigtail connections to the connector shell, will allow interior signals or common-mode currents, respectively, on the outside of the shield.

In poorly made HDMI cables the wire ends are often exposed. The main culprits of causing problems are the connectors itself and their design. Wires are soldered on PCB, then glue and then the shell. Good cables encapsulate the PCB and cable with copper foil and the cable shield is worn very high up, leaving no exposed places and then the case (metal same that goes in to the end device). The cable core itself often is made from who ever knows and somewhat shielded. Some problems might be solved making a loop or two through a ferrite ring or using the clamp on ones.

Buying anything has become more and more annoying. You have to do research all the time, because reliable brands, price brackets or shops actually sourcing quality products more or less are dying out.

The antenna cables also showed similar results: These were also tested against the quality classes used on the market, with only four of the antenna cables meeting the “Class A” requirements (quality of antenna cables shows that they have deteriorated since last test done in 2012). One of the main issues that was pointed out in the briefing is that if poor quality antenna cables are being used to connect set-top boxes or TVs to cable TV networks can cause system wide problems. A somewhat unexpected side effect from this is that it can also cause problems with radio reception in an unspecified area near the poor quality antenna cable, due to interference coming from the cable.

NOTE: Keep in mind that the antenna cables in the EU are different from the cables that are used for cable modems and most other uses in the US. Instead of using F-type screw-in connectors, European antenna cables use Belling-Lee connectors, which are simple push-in connectors.

The Top Five Reasons Products Fail EMI Testing article at https://passive-components.eu/the-top-five-reasons-products-fail-emi-testing/ list reasons why products fail in EMC testing:

PC Board Design—Poor layout and layer stack-up
Cable Shield Termination and Pigtails—Cable shields are not terminated to enclosure or lack of common mode filtering for unshielded products, plus shield pigtails used
Gaps in the Return Path—High frequency clocks or signals crossing gaps in the return path
Power Distribution Design—Poor power distribution network (PDN) design
Shielding Design—Apertures or slots in the shielded enclosure that are too long

Sources:

9 av 10 HDMI- och antennkablar uppfyller inte kraven
https://www.elsakerhetsverket.se/om-oss/press/nyhetsbrev/2021/september/nyhetsbrev-fran-elsakerhetsverket-september-2021/9-av-10-hdmi-och-antennkablar-uppfyller-inte-kraven/

9 av 10 HDMI- och antennkablar släpper igenom strålning som kan störa radio
https://www.hamnews.se/2021/09/29/9-av-10-hdmi-och-antennkablar-slapper-igenom-stralning-som-kan-stora-radio/

“9 out of 10 HDMI cables do not meet the requirements”
https://newsbeezer.com/swedeneng/9-out-of-10-hdmi-cables-do-not-meet-the-requirements/

Many HDMI and Coaxial Antenna Cables in the Market Don’t Meet EU EMC Regulations
https://www.techpowerup.com/287381/many-hdmi-and-coaxial-antenna-cables-in-the-market-dont-meet-eu-emc-regulations

EU testasi HDMI-kaapelit: lähes kaikki reputtivat testissä
https://etn.fi/index.php/13-news/12638-eu-testasi-hdmi-kaapelit-laehes-kaikki-reputtivat-testissae

The Top Five Reasons Products Fail EMI Testing
https://passive-components.eu/the-top-five-reasons-products-fail-emi-testing/

Nytt nummer av Elsäkerhetsverkets nyhetsbrev
https://www.elsakerhetsverket.se/om-oss/press/nyheter/2021/nytt-nummer-av-elsakerhetsverkets-nyhetsbrev3/

Links on HDMI cable EMC design and testing:

https://interferencetechnology.com/hdmi-cables-emi/

https://www.element.com/nucleus/2020/what-you-need-to-know-about-en-55032-and-55035-cispr-32-and-35

https://incompliancemag.com/article/emc-testing-the-eu-experience/

https://www.emcbayswater.com.au/blog/emc-testing/commercial-emc-testing/emc-compliance-hdmi-radiated-emissions-testing-emi/

https://www.unit3compliance.co.uk/hdmi-more-like-hdm-why-thoughts-on-cable-shield-grounding/

https://community.altair.com/community?id=community_blog&sys_id=9124723cdbb57c90e8863978f4961924

https://www.murata.com/en-global/products/emc/emifil/library/pickup/hdmi2

Antenna isolator is very convient way to solve antenna connection related ground loop problems. Unfortuantely isolator has some drawbacks: attenuation and possible poor suscpectibility to RF interference.

Here is the picture of one commercial antenna isolator:

The circuit inside main details pretty much resembles the simple circuit shown at Building your own antenna isolators page with some RF filter added to the center:

Another type of antenna signal isolator is RF transformer based antenna isolator as shown at Building your own antenna isolators page:

Read more at https://www.epanorama.net/documents/groundloop/antenna_isolator.html and https://www.epanorama.net/documents/groundloop/antenna_isolator_building.html

“When 802.11bf will be finalized and introduced as an IEEE standard in September 2024, Wi-Fi will cease to be a communication-only standard and will legitimately become a full-fledged sensing paradigm,” explains Francesco Restuccia, assistant professor of electrical and computer engineering at Northeastern University, in a paper summarizing the state of the Wi-Fi Sensing project (SENS) currently being developed by the Institute of Electrical and Electronics Engineers (IEEE).

For some more information read the following article:

Wi-Fi devices set to become object sensors by 2024 under planned 802.11bf standard
Security and privacy still left to fix, preferably before launch
https://www.theregister.com/2021/03/31/wifi_devices_monitoring/

I have myself written about Bletooth location features:
https://www.epanorama.net/blog/2019/01/30/bluetooth-enhances-support-for-location-services-with-new-direction-finding-feature/
https://www.epanorama.net/blog/2019/05/27/bluetooth-5-1-location-technology-demo/

TINYSA IS A $49 SPECTRUM ANALYZER that I got from Banggood. The tinySA is a small spectrum analyzer, primarily intended for 0.1MHz to 350MHz input but can be used with higher frequencies up to 900 MHz.

The tinySA is a small spectrum analyzer having dual inputs. One of the input enables working frequencies over the MF/HF/VHF bands of 100KHz to 350MHz and the second input enables a lower quality frequency measurements over the UHF band of 240MHz to 960MHz. Really neat what could be done with the cheap SI4432 modules, the variety of cheap MCU’s,

The tinySA is aimed at radio amateurs, students, and electronic enthusiasts. The primary use is to measure the power of the spectrum of known and unknown signals. Spectrum analyzers are widely used to measure the frequency response, noise and distortion characteristics of all kinds of radio-frequency (RF) circuitry.

The tinySA is a small spectrum analyzer, primarily intended for 0.1MHz to 350MHz input but it has some nice other capabilities:

Spectrum Analyzer with two inputs, high quality MF/HF/VHF input for 0.1MHZ-350MHz, lesser quality UHF input for 240MHz-960MHz.
Switchable resolution bandpass filters for both ranges between 2.6kHz and 640kHz
Color display showing 290 scan points covering up to the full low or high frequency range.
Input Step attenuator from 0dB to 31dB for the MF/HF/VHF input.
When not used as Spectrum Analyzer it can be used as Signal Generator, MF/HF/VHF sinus output between 0.1MHZ-350MHz, UHF square wave output between 240MHz-960MHz.
A built-in calibration signal generator that is used for automatic self test and low input calibration.
Connected to a PC via USB it becomes a PC controlled Spectrum Analyzer
Rechargeable battery allowing a minimum of at least 2 hours portable use
Due to the low cost and very small form factor there are certain relevant limitations.

The product comes in quite nice looking box that contains pretty much everything needed to get started to use the device:

The device is ready to be tested when you take the tinySA and antenna from the box.

Testing to see the radio signals around me.

Device information from the back of the tinySA.

The tinySA also features a 2.8” color display screen showing 290 scan points covering up to the full low or high-frequency range. It Input Step attenuator can be set from 0dB to 31dB for the MF/HF/VHF input, but the UHF input cannot exceed 10dBm. TinySA has a switchable resolution bandpass filters between 2.6kHz and 640kHz. The tinySA can be connected to a PC via USB it becomes a PC controlled Spectrum Analyzer. You can view the tinySA output on your PC if you use tinySA-saver (multi-platform) or the tinySA PC software (only runs on Windows). . Rechargeable battery allows a minimum of at least 2 hours portable use.

The tinySA also features a built-in calibration signal generator that is used for automatic self-test and low input calibration. When not used as Spectrum Analyzer it can be used as Signal Generator, MF/HF/VHF sinus output between 0.1MHZ-350MHz, UHF square wave output between 240MHz-960MHz. Signal Generator offers MF/HF/VHF sinus output between 0.1MHZ-350MHz, it can output a sinusoid with harmonics lower than -40dB of fundamental at an output point that is pickable in 1 dB steps between -76dBm and -6dBm. It also features an optional AM and FM module or a moderate brush over the selective frequency range (UHF square wave output between 240MHz-960MHz).

There are many features in tinySA, but there are also some limitations. Due to the low cost and very small form factor there are certain relevant limitations. As the internal components of the tinySA where selected with a careful balance between performance and cost there are certain limitations that experienced users of much more expensive spectrum analyzers must be aware of:

The internal phase noise sets a clear lower limit for phase noise measurements.
The minimum resolution bandwidth of 2.4kHz makes it impossible to see more spectral detail
The high input (240MHz to 960MHz) has very limited image suppression and only one level optional built in attenuator which makes it difficult to interpret complex signals.
The high input optional input attenuator is frequency dependent and varies between 25dB and 40dB
At lower resolution bandwidths (below 30kHz) the measurement time per point starts to increase due to the resolution filter implementation. Careful use of the FAST sweeping mode may reduce this time increase
The performance limitations of the shielding and the filters may lead to certain images and spurs being visible but certain functions like spur suppression and switching to below IF may help detect and/or reduce these spurs and images
Below 0.1MHz the sensitivity starts to reduce.
Below 1MHz it is recommended to disable the AGC and possibly enable the LNA to get best measurement quality
When using the supplied telescopic antenna or a low RBW one should be aware of the radiation from the tinySA MCU on 48MHz and its harmonics

There is currently no clone of tinySA. All are genuine and manufactured by Huyen.

#535b​ TinySA Tiny Spectrum Analyzer for $49

tinySA Spectrum Analyzer review (Banggood)

Excellent work, it’s amazing that so much functionality can be brought into such a small unit and at such a low cost. This will be a very useful piece of test equipment.

TinySA works as pretty nice spectrum analyzer. Like any spectrum analyzer, it is possible – easy, even – to overload the front end and generate harmonics and spurs. If you are aware of the tinySA’s limitations, it works surprisingly well. If you can keep signals below -35 dBm and most of spurs disappear. The issue in keeping signal levels low is that -35 dBm is pretty low so thiscuts way into the usable dynamic range. The TinySA doesn’t have a front end tracking filter, so strong out of band signals can cause problems. The attenuator helps. Nobody expects a low NF for a spectrum analyzer, so that’s not a big deal.

How tinySA compares to NanoVNA? They are different things designed for different tasks although they have quite similar looking form factors. While there are similarities, the tinySA is NOT NanoVNA hardware. The NanoVNA is a VNA, for measuring S-parameters for reflection, transmission, and impedance properties of a system. You might use it to measure SWR, filter frequency response, transmission line velocity factor, input impedance, etc. A spectrum analyzer measures the frequency content of rf signals into its port. It’s good to testing things like harmonic suppression, spectral purity, intermodulation, etc. The hardware on tinySA is in many ways different from NanoVNA. What differentiates TinySA from Nano VNA is the TinySA includes switchable input attenuators. To get the best measurement performance, it is important to pre-scale the input signal to the level where the detector has its best trade-off of linearity and sensitivity. There are also other Spectrum Analyzer factors such as resolution bandwidth, IF bandwidth and type of detector (peak/average/log/minimum) that are not as important considerations to a vector network analyzer that is generating its own controlled stimulus signal. IMSAI Guy did a video teardown so you can see that it is not the same as the NanoVNA design at all. TinySA – Spectrum analyzer with tracking generator (Reincarnation of nanoVNA) is develeperd by hugen79 (of NanoVNA-H, -H4, v2.2N) and Erik Kaashoek. TinySA uses different analog hardware for the Spectrum Analyzer and Signal Generator functions. Same screen and case. Some of the NanoVNA code has been used for the screen and user interface. There was an attempt to write different firmware to turn the NanoVNA into a Spectrum Analyzer but the analog hardware is just not suitable.

If you are doing RF experimenting it might be a good idea to have both gadgets. By having both tinySA and the NanoVNA (which can also work as a signal generator) you’ve basically got $100-120 to get the RF equivalent of a DMM.

“How does it compare to the RTL-SDR?” Apples to oranges. The tinySA is a spectrum analyzer. The RTL-SDR is a receiver. tinySA offers significantly better bandwidth and a lower noise floor ~100dB for the frequency range spec. Works well below -30dB so consider using with attenuation or signals of interest. tinySA offers small and stand alone operation. RTL-SDR needs to have a computer and has ~-70db noise floor, has more limited dynamic range and slow frequency scanning. On the other hand, the RTL-SDR gives you real time I and Q samples at 2 megasample/sec or more over USB, making it a very flexible receiver when used with a computer. You can build almost arbitrarily complex virtual receivers the GNU Radio software and an RTL-SDR. One of the bigger problems with the RTL-SDR is that there are no pre-selector filters, making it susceptible to overload and intermodulation of out-of-band signals with the signal you want. The RTL-SDR is OK but not great for 1.0 MHz – 30 MHz.

For more information:

tinySA.org website

HUGEN LAUNCHES PORTABLE TINYSA SPECTRUM ANALYSER

TinySa article is in 3 languages: English, Danish and German

TinySA spectrum analyzer 0.1MHz to 350MHz video and videos noting how to use for better performance

The tinySA firmware code is available on github because parts of it are based on open source NanoVNA (and other) code, it had to be open source: https://github.com/erikkaashoek/tinySA

https://hackaday.com/2020/09/01/tinysa-is-a-49-spectrum-analyzer/

How to Test EMP Proof Container with tinySA. Let’s Test The Tactical Trash CanErik Kaashoek Youtube with new tinySA videos

TinySA spectrum analyzer 0.1MHz to 350MHz

Reincarnation of nanoVNA

#558b TinySA High Port Calibration (It’s not easy)

#537b TinySA Mode Changes

#537c TinySA Don’t use AUTO settings

Conspiracy Theorists Buy Faraday Cages To “Protect” Themselves Then Complain When They Work
https://www.iflscience.com/technology/conspiracy-theorists-buy-faraday-cages-to-protect-themselves-then-complain-when-they-work/

Crackpots are buying Faraday cages for routers then bemoaning bad Wi-Fi
Buyers are enraged that it’s ruining their Wi-Fi signal. Amazon doesn’t care and continues to sell the devices conspiracy theorists claim “protect” against 5G.
https://www.inputmag.com/tech/crackpots-buying-faraday-cages-for-their-routers-on-amazon-then-bemoan-bad-wi-fi?utm_content=bufferf171a&utm_medium=social&utm_source=facebook&

75 Ohm is primary used for video and audio. 75 Ohm cables are the standard coax cable you find everywhere inside your home and office from the back of the tv to cable & satellite tv boxes and cable internet router. They are commonly used and are often pre-wired in many homes and businesses.

BNC (Bayonet Neill-Concelman) RF connectors make it easy to connect coaxial cables with radio-frequency equipment like radios and TVs, composite video on commercial video devices, and ethernet networks. They are available in 50 and 75 ohms models. Physically, the main differences can be found in the center pins and dialectric insulators. 75-ohm BNC connectors feature Teflon as a dialectric, and surround the outer spring fingers with air. Its center pin maintains a consistent diameter in both the front and rear areas (this is important—read on to find out why). 50-ohm connectors, on the other hand, use Delrin to surround the spring fingers, and its center pin is larger in the crimp area. You’ll need different crimp tools for each type of center pin.

If the connectors are 50 ohm, you are introducing impedance matching problems on your instalaltions, as if the impedance of cameras, DVRs and cables is 75 ohms. But most of DVRs and cameras in the market are manufactured with BNC connectors of 50 ohm impedance.

Sometimes there is need to convert between 50 ohms and 75 ohms systems. The web page https://electronics.stackexchange.com/questions/36168/how-to-build-a-75-ohm-to-50-ohm-converter/36186 gives some useful tips for impedance conversion:

A twelfth-wave transformer can match 50Ω to 75Ω with negligible loss and no adjustment (but at limited frequency range). It is a special case of a series-section transformer.
The Twelfth-Wave Transformer is often a more convenient alternative to the more well-known quarter-wave transformer
Choose Coax and calculate 1/12 λ of 50Ω coax. and 1/12 λ of 75Ω coax. for chosen frequency.. This works from DC to 1.5 x center F chosen. These two cables will transform the impedance for maximal power transfer. Choose the lowest loss cable you have avail. and best connectors to achieve less than 0.1dB loss for these short lengths.
For calibrated voltage output, set the generator to 0.83 times the desired output level in microvolts.

Convenient calculator: http://vk1od.net/calc/tl/tllc.php#NoteModellingLoss
Choose F, coax , 50 Ω load 1/12 λ option enter 0.083333 [wavelength], then calculate. Repeat for both 50Ω & 75Ω coax choosing type of coax as 1st entry.

Web page https://electronics.stackexchange.com/questions/234914/diy-75ohm-to-50ohm-impedance-matching-circuit-to-work-at-uhf-frequencies-around gives the simplest solution is to accept some signal (power) loss by using a two resistor solution like this:

But a better solution (less signal power loss) would be to use a transformer based impedance adapter. However these are more difficult to make.

Web page http://ham-radio.com/k6sti/match.htm gives the following advice:

Matching 50Ω to 75Ω
Most signal generators have an output impedance of 50Ω. To align an FM tuner or measure its performance, it’s best to match this to the tuner’s 75Ω input impedance. Mismatch loss is only 0.2 dB, but a source impedance that differs from the design value may alter the RF input circuit bandwidth or resonant frequency. This can degrade front-end tracking and affect intermod or desensitization measurements.

Minimum-Loss Pad

A simple minimum-loss pad provides a broadband match. Use chip resistors or the shortest possible lead lengths to minimize stray inductance and pickup of local broadcast signals. Loss is 5.6 dB for the 5% values shown. For calibrated voltage output, set the signal generator to 1.55 times the desired output level in microvolts. (For 1% resistors, use 43.2Ω and 86.6Ω. Loss is 5.7 dB.)

L-Network

An L-network is nearly lossless. This circuit isn’t broadband like a minimum-loss pad
The L-network loss measured 0.05 dB. For calibrated voltage output, set the generator to 0.83 times the desired output level in microvolts.

Spectrum analyzers used to be very expensive special instruments, but nowadays cheap electronics components and cheap software defined radio hardware has made this tool affordable. TINYSA IS A $49 SPECTRUM ANALYZER. The tinySA is a small spectrum analyzer, primarily intended for 0.1MHz to 350MHz input but can be used with higher frequencies up to 900 MHz.

I got myself tinySA from Bangggood and it seems to be a nice tool for RF testing.

For more details read the PRODUCT REVIEW: THE TINYSA, A SHIRT-POCKET SIZED SPECTRUM ANALYZER and view the following videos.

#535b TinySA Tiny Spectrum Analyzer for $49

TinySA spectrum analyzer 0.1MHz to 350MHz

tinySA first use

tinySA Marker Menu and Marker positioning

#557b TinySA Power Levels (don’t kill your tiny)

tinySA Config and Expert Config Menu

#546b TinySA Measuring Filter with Noise Source

#551b TinySA Wireless Measurements

#563c TinySA RF Sniffing Around the House

553b TinySA Inside the Microwave

#072 tinySA , Just in! Review.

#584b TinySA Ref Level and Attn Setting Hunting

#543b TinySA Measuring Noise Floor

#537c TinySA Don’t use AUTO settings

#551C TinySA On air FM broadcast band modulation

#552b TinySA Measuring with a Coupler

#551b TinySA Wireless Measurements

#538b TinySA Measuring FM Modulation

#550b TinySA Zero Span Mode

Using zero span to look at modulation waveforms
#542b TinySA as an RF Generator

Testing the output modes of the TinySA. Spectral quality and modulations
#561b TinySA Tracking Generator using External Mixer

By using the LO output, a mixer, and fixed frequency oscillator, a tracking generator is created
#562b TinySA Low Frequencies Down to 10 KHz

The TinySA seems to work much lower than the datasheet
#545b TinySA Using Attenuators

#536c TinySA Update: Works well below -30dbm

The TinySA needs to have low input levels to keep mixer harmonics low. If used in this range the performance is quite good

#557b TinySA Power Levels (don’t kill your tiny)

Make sure you don’t over power your TinySA. Check all frequencies and total power.
datasheet: maximum +10dBm input power either port less than 15VDC offset
My recommendation: maximum 0dBm (1mW) input power 0VDC offset

#540b TinySA and NanoVNA Fight

tinySA and NanoVNA measuring each other

#536 TinySA Testing Against an Expensive Spectrum Analyzer (see update for more)

Some initial tests of the TinySA comparing against HP8921a spectrum analyzer. RF signal is sent through a power splitter to both instruments for direct comparison.
The problems I was seeing was do to high input levels. The TinySA will only operate nicely at signal levels below -30dbm.

Accurately measuring cable length with NanoVNA article will go through some mathematics on deriving TDR response with VNA data. Remember that the VNA does its measurements in the frequency domain. If we transform the frequency domain data into the time domain, we should see the time domain nature of our measurement (with certain limitations though). By using the magnitude and phase of the signal measured throughout the frequency sweep, we can compute the distance from where reflection occurred.

NanoVNA To Test The Loss & Length Of Coax Cables by Jim W6LG YouTube Elmer for Ham Radio Basics

The NanoVNA does many things. Two of which are testing coax cables for loss and length. Jim W6LG shows how to do both in this first video about the NanoVNA. In a subsequent video, Jim will show how the NanoVNA can be used to check antennas for resonance, impedance and reactance. The software that Jim uses is NanoVNA Saver. That software is free and easy to use.
Here is the link to the software : https://github.com/mihtjel/nanovna-saver

#316: Use NanoVNA to measure coax length – BONUS Transmission Lines and Smith Charts, SWR and more

nanoVNA – Coaxial Cable Measurement Methods (Characteristic Impedance and Cable Loss) – VE6WGM

1. Calibrating the nanoVNA
2. The Smith Chart – Briefly (Begins at 8:24)
3. Measuring the characteristic impedance of coax cable. (Begins at 11:46)
4. Measuring coax cable loss. (Begins at 22:34) *Correction: At 23:34 I stated that the nanoVNA has a directional coupler. I have since discovered that this is not accurate information. The nanoVNA actually uses a bridge to make it’s measurements. My apologies. For more information on how this works, please see this excellent video here: https://youtu.be/yGKWBpgN8PU

#502 NANOVNA Demystified

#37: Use a scope to measure the length and impedance of coax

Cable Basics; Transmission, Reflection, Impedance Matching, TDR

Reflected waves on a cable