SDR transmit and clean signals

If you have a transmit capable SDR, you may have heard that you need to filter its output, before transmitting to the world. Certainly before amplifying the signal.

I have a TinySA Ultra spectrum analyzer, and will here show you some screenshots about just how true that is.

I tested this with my USRP B200, transmitting a pure carrier around 145MHz and 435MHz.

Oh, and a word of caution: If you want to replicate this, make sure to add an inline attenuator, to not damage your spectrum analyzer. I had a cheap 40dB one, but the values in the graphs have been adjusted to show the real signal strength, as if I hadn’t.

tl;dr

  1. Harmonics can be almost as strong as the fundamental. You need to filter these.
  2. Transmitting at maximum output gain may cause lots of unwanted signals right around your fundamental. You cannot filter these. You need to not generate them.

Harmonics

Harmonics for 145MHz Harmonics for 435MHz

Reducing the output gain did not meaningfully fix the problem. The best I saw from using half output gain was to make the strongest harmonic 9dB less than the fundamental. That’s way too strong.

I added a cheap band pass filter (FBP-144), which made Continue reading

AX.25 and 9600bps G3RUH decoding

I’ve been coding more on my rust SDR framework, and want to improve my ability to send/receive data packets efficiently and reliably.

There are two main ways I use learn to do this better: designing a new protocol, and making the best implementation possible for an existing one. This post is about refining the latter.

AX.25 and APRS

First a detour, or background.

AX.25 is the standard amateur radio data protocol. It’s mostly an OSI layer 2-4 protocol, mashing the layers together into one. Contrast this with IP, which just encapsulates the next layer.

Layer 3 (IP stack equivalent: IP itself) consists of the ability to add, in addition to source and destination, a variable number of intermediate repeaters. This allows limited source routing. In APRS the repeaters are usually not named, but instead uses “virtual” hops like WIDE1-1.

Layer 4 (IP stack equivalent: TCP and UDP) allows both connected and disconnected communication channels. In my experience connected AX.25 works better over slow simplex radio than TCP. If TCP was ever optimized for high delay low bandwidth, it’s not anymore.

For the physical layer, there are three main “modems”:

  1. 300 baud bell 103, used Continue reading

Pushing The Limits Of HPC And AI Is Becoming A Sustainability Headache

As Moore’s law continues to slow, delivering more powerful HPC and AI clusters means building larger, more power hungry facilities. …

The post Pushing The Limits Of HPC And AI Is Becoming A Sustainability Headache first appeared on The Next Platform.

Pushing The Limits Of HPC And AI Is Becoming A Sustainability Headache was written by Timothy Prickett Morgan at The Next Platform.

SC23 Over 6 Terabits per Second of WAN Traffic

The world’s fastest temporary internet service gets turned on in Denver for one week only describes the SCinet temporary network built to support the The International Conference for High Performance Computing, Networking, Storage, and Analysis (SC23) this week in Denver. The SC23 WAN Stress Test chart demonstrates that the provisioned 6.71 terabits bits per second capacity was pushed to the limits.
SC23 SCinet traffic describes the architecture of the real-time monitoring system used to comprehensively monitor the SCinet network and generate these charts. This chart shows that over 175 Petabytes of data were transfered during the show.
SC23 Dropped packet visibility demonstration describes a joint demonstration by InMon Corp and Arista Networks of one of newest developments in sFlow telemetry, identifying every dropped packet, the reason it was dropped, and the location it was dropped across all the switches in real-time.
SC23 WiFi Traffic Heatmap shows a real-time view of WiFi usage at the conference displayed on a conference floorplan.
Finally, SC23 Data Transfer Node TCP Metrics demonstrates how standard metrics maintained by the Linux kernel can be used to augment sFlow telemetry and track the performance of large science data transfers.

How to execute an object file: Part 4, AArch64 edition

How to execute an object file: Part 4, AArch64 edition

Translating source code written in a high-level programming language into an executable binary typically involves a series of steps, namely compiling and assembling the code into object files, and then linking those object files into the final executable. However, there are certain scenarios where it can be useful to apply an alternate approach that involves executing object files directly, bypassing the linker. For example, we might use it for malware analysis or when part of the code requires an incompatible compiler. We’ll be focusing on the latter scenario: when one of our libraries needed to be compiled differently from the rest of the code. Learning how to execute an object file directly will give you a much better sense of how code is compiled and linked together.

To demonstrate how this was done, we have previously published a series of posts on executing an object file:

The initial posts are dedicated to the x86 architecture. Since then the fleet of our working machines has expanded to include a large and growing number of ARM CPUs. This Continue reading

Saying Goodbye to the Full Stack Journey

In January 2016, I published the first-ever episode of the Full Stack Journey podcast. In October 2023, the last-ever episode of the Full Stack Journey podcast was published. After almost seven years and 83 episodes, it was time to end my quirky, eclectic, and unusual podcast that explored career journeys alongside various technologies, products, and open source projects. In this post, I wanted to share a few thoughts about saying goodbye to the Full Stack Journey.

First and foremost, let me say that I really enjoyed being the host of the Full Stack Journey podcast—far more than I expected I would, if I’m honest. While I didn’t love the logistics of producing a podcast, I did love getting to talk with folks, hear their stories, and learn about new things. So, while part of me is thankful to have a little less work to do, another part—a larger part—is sad to see it end.

That being said, some of you are probably wondering why it ended. I mentioned that I didn’t enjoy the logistics of producing a podcast; specifically, I didn’t enjoy audio editing. Some folks like it, but I didn’t. It was truly a chore for me. That was Continue reading

Video: Outages Caused by Bugs in BGP Implementations

The previous BGP-related videos described how fat fingers and malicious actors cause Internet outages.

Today, we’ll focus on the impact of bugs in BGP implementations, from malformed AS paths to mishandled transitive attributes. The examples in the video are a few years old, but you can see similar things in the wild in 2023.

Watch the video
You need at least free ipSpace.net subscription to watch videos in this webinar.

Video: Outages Caused by Bugs in BGP Implementations

The previous BGP-related videos described how fat fingers and malicious actors cause Internet outages.

Today, we’ll focus on the impact of bugs in BGP implementations, from malformed AS paths to mishandled transitive attributes. The examples in the video are a few years old, but you can see similar things in the wild in 2023.

Watch the video
You need at least free ipSpace.net subscription to watch videos in this webinar.

What To Do When You Can’t Get Nvidia H100 GPUs

In a world where allocations of “Hopper” H100 GPUs coming out of Nvidia’s factories are going out well into 2024, and the allocations for the impending “Antares” MI300X and MI300A GPUs are probably long since spoken for, anyone trying to build a GPU cluster to power a large language model for training or inference has to think outside of the box. …

The post What To Do When You Can’t Get Nvidia H100 GPUs first appeared on The Next Platform.

What To Do When You Can’t Get Nvidia H100 GPUs was written by Timothy Prickett Morgan at The Next Platform.

KU041: Running Kubernetes On Nomad

In this episode, Michael, Kristina, and Adriana Villela discuss the challenges and benefits of running Kubernetes on Nomad. Adriana shares her experience of using Nomad in a data center, highlighting its simplicity and ease of deployment compared to Kubernetes. The speakers also discuss the differences between the two platforms, the concept of vendor lock-in, and... Read more »

KU041: Running Kubernetes On Nomad

In this episode, Michael, Kristina, and Adriana Villela discuss the challenges and benefits of running Kubernetes on Nomad. Adriana shares her experience of using Nomad in a data center, highlighting its simplicity and ease of deployment compared to Kubernetes. The speakers also discuss the differences between the two platforms, the concept of vendor lock-in, and […]

The post KU041: Running Kubernetes On Nomad appeared first on Packet Pushers.

SC23 Data Transfer Node TCP Metrics

The dashboard shown above is based on the open source sflow-rt/dtn project. The dashboard shows data captured from The International Conference for High Performance Computing, Networking, Storage, and Analysis (SC23) being held this week in Denver.

The dashboard displays data gathered from open source Host sFlow agents installed on Data Transfer Nodes (DTNs) run by the Caltech High Energy Physics Department and used for handling transfer of large scientific data sets (for example, accessing experiment data from the CERN particle accelerator). Network performance monitoring describes how the Host sFlow agents augment standard sFlow telemetry with measurements that the Linux kernel maintains as part of the normal operation of the TCP protocol stack.

The dashboard shows 5 large flows (greater than 50 Gigabits per Second). For each large flow being tracked, additional TCP performance metrics are displayed:

  • RTT The round trip time observed between DTNs
  • RTT Wait The amount of time that data waits on sender before it can be sent.
  • RTT Sdev The standard deviation on observed RTT. This variation is a measure of jitter.
  • Avg. Packet Size The average packet size used to send data.
  • Packets in Flight The number of unacknowledged packets.

See Defining Flows for full range of Continue reading

Introducing advanced session audit capabilities in Cloudflare One

The basis of Zero Trust is defining granular controls and authorization policies per application, user, and device. Having a system with a sufficient level of granularity to do this is crucial to meet both regulatory and security requirements. But there is a potential downside to so many controls: in order to troubleshoot user issues, an administrator has to consider a complex combination of variables across applications, user identity, and device information, which may require painstakingly sifting through logs.

We think there’s a better way — which is why, starting today, administrators can easily audit all active user sessions and associated data used by their Cloudflare One policies. This enables the best of both worlds: extremely granular controls, while maintaining an improved ability to troubleshoot and diagnose Zero Trust deployments in a single, simple control panel. Information that previously lived in a user’s browser or changed dynamically is now available to administrators without the need to bother an end user or dig into logs.

A quick primer on application authentication and authorization

Authentication and Authorization are the two components that a Zero Trust policy evaluates before allowing a user access to a resource.

Authentication is the process of verifying the identity Continue reading

IPB139: Avoiding Typical IPv6 Pitfalls

Network engineers and architects considering IPv6 can benefit from the experiences of those who have gone before them by avoiding the problems that have bedeviled other deployments. On today’s show, your hosts discuss three typical pitfalls and how to get over or around them without falling in. Those IPv6 pitfalls include: IPv4 thinking Deploying ULA... Read more »
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