Measuring SDR noise figure


David has written an article on measuring SDR noise figure:

One number I wanted to know was the Noise Figure (NF) of the SDR. Mark has a bunch of SDRs so we got on a roll and checked out the NF on all of them.

Now there are a lot of people playing with SDRs, but very few tutorials on HowTo engineer radio systems. For example, how to answer questions like “can I send this many bit/s over X km with SDR hardware Y?” So I thought it might be useful to explain how we measured Noise Figure (NF) and present the results for a bunch of SDRs.

More details at Rowetel site.

How do I FPGA?


TC-Engineering writes:

I’ve been thinking about building stuff with FPGA’s for a while, and usually get turned away because FPGA’s are considerably harder to implement than microcontrollers since they have no on-chip memory. It is necessary to re-program the gates every time they power up, which requires an external flash memory chip. There aren’t great references online for the DIY community, so I figured I’d post how to get this working. Not using dev boards opens a world of opportunities, so I’m a proponent of not using Arduino’s and their FPGA equivalent for too long (sure, they’re good to get started with, but don’t become dependent)
Not wanting to screw up an expensive complex board by being a first-timer at putting an FPGA into a circuit, I figured I’d build a little test board with the cheapest Spartan 6 you can get (about $10), which comes in a solderable TQFP144 package. Sadly, most high end FPGA’s are BGA and therefore quite hard to solder as a DIY project.

More details at TC-Engineering blog.

Using “Ultracapacitors” as a power conditioner and ballast for transient high-power loads (or “How to run your HF rig from D-cells” – sort of…)


KA7OEI writes:

An advantage of Lead-Acid, NiCd, Lithium Ion and some NiMH cell types is that they have quite low internal resistance compared Alkaline cells: Even an aging lead acid battery that is near the end of its useful life may seem to be “OK” based on a load test as its internal resistance can remain comparatively low even though it may have lost most of its storage capacity!
One could ask, then, why now simply parallel Alkaline cells, with their ready availability, long life and high storage capacity with one of these other cell types and get the best of both worlds? In theory you could – if you had some sort of charge control circuitry that was capable of efficiently meting out the energy from the alkaline pack and using it to supplement the “other” storage medium (e.g. lead-acid, lithium-ion, etc.) but you cannot simply connect the two types in parallel and expect to efficiently utilize the available power capacity of both types of storage cell – this, due to the wildly different voltage and charge requirements.
Even if you do use a fairly small-ish (e.g. 7-10 amp-hour) lead-acid or lithium-ion battery pack, even though its internal resistance may be low compared to that of alkaline packs, it likely cannot source the 15-20 amp current peaks of, say, a 100 watt SSB transceiver without excess voltage drop, particularly if it isn’t brand new.

This is where the use of “Ultracapacitors” come in.

Details at KA7OEI’s blog.

Output voltage control of DC/DC converters


Thomas Fischl writes:

Some applications needs to control the output voltage of a dc/dc converter instead using a fixed output voltage. For example battery chargers has to adjust the output voltage to the current battery level. This page shows how to add such a control function to a buck converter circuit.

Control output via external voltage source
Typically a voltage divider is used in dc converters to adjust the output voltage to the needed feedback voltage. To control the feedback signal by an external voltage source, a third resistor is added to the circuit.

More info at Fischl’s site.

ESP8266 troubleshooting guide


Rui Santos has written an article on SP8266 troubleshooting guide:

The ESP8266 has a few common issues, specially when you are trying to flash a new firmware or uploading scripts.
This is a companion guide to the Home Automation using ESP8266 and Password Protected Web Server eBooks.

Here’s a compilation with some of the most common problems with the ESP8266 and how to fix them.

More details at

Building a tracking generator


A how-to on building a tracking generator using off-the-shelf components by Kerry Wong:

In this blog post, I will show you how to build a 0 to 5.8 GHz tracking generator for the HP 8566B 100 Hz to 22 GHz spectrum analyzer using off-the-shelf components for under $100. Although this tracking generator is specifically designed for my HP 8566B spectrum analyzer, the method discussed below is applicable to pretty much any spectrum analyzer that has an LO output (typically the 1st LO).
A tracking generator, as its name implies, tracks the frequency of the spectrum analyzer’s sweeping oscillator (typically 1st LO) so that the tracking generator’s frequency output matches the center frequency of the bandpass filter in spectrum analyzer’s IF stage. Thus at any given moment, the spectrum analyzer sees the same frequency input as what it is currently sweeping at. The combination of a spectrum analyzer and a tracking generator is often referred to as a scalar network analyzer (SNA).

More details at Kerry Wong blog.

Check out the video after the break.