Things I Learned: Forward Diode Drop Limits RF QRPp Power Meter Sensitivity

How to measure ham radio QRPp using a device from my past. How to jailbreak your thesis. Gudermanians?

Measuring QRP Power

I haven't seen a lot of QRP, (low power amatuer radio transmitter), power meter projects. The ones I have found, usually mention that it's difficult to measure low powers, (the Rockmite nominally outputs 500 mW aka QRPp.) This has been a bit of a mystery to me until today when I found this video from Mark Smith, N6MTS:

In short, Mark explains that the issue is the drop across the rectifying diode used to generate the DC-ish current used to drive the meter. If the RF peak voltage is too low to forward bias the diode, then there's no measurement. A bias voltage can be applied to the diode to make it just-ready-to-go all the time, but that is difficult per N6MTS, (I haven't learned why yet.)

Mark's solution is to use an Analog Devices logarithmeic amplifier. The amplifier has an output indicating peak RF power at the input. Mark's plan (as of the video) is to then load that output into a microcontroller for measurement purposes.

I can't find the exact part number I used, but I've used these, (logarithmeic amplifiers), in the past for building particle acclerator beam position monitor circuits. I'm excited to see them again.

Moving a Thesis to Open Access:

If you've written a thesis at Texas A&M, you can request that it be made open access!

Check out the thesis link below for an example of the above banner, (at least until it becomes open access I suppose.)

YouTube APIs:

There's an API for the YouTube video embeds so you can add snazzy (annoying?) features like video previews when a page loads the player. Here's a demo.

Anyway:

In the future, look up Gudermanian work elsewhere on this blog.
Also, here's the inspiration for the Anyway section.

References:

N6MTS's QRP monitor project on github

Ham Radio Workbench Podcast Episode: QRP Service Monitor Design

My thesis utilizing logarithmic amplifiers for proton beam position monitoring at Los Alamos Meson Physics Facility.

Logarithmic Ampliier Product Page

Gudermanians and beam position processing, and at the lab (pdf)

Comments

More Cowbell! Record Production using Google Forms and Charts

First, the what : This article shows how to embed a new Google Form into any web page. To demonstrate ths, a chart and form that allow blog readers to control the recording levels of each instrument in Blue Oyster Cult's "(Don't Fear) The Reaper" is used. HTML code from the Google version of the form included on this page is shown and the parts that need to be modified are highlighted. Next, the why : Google recently released an e-mail form feature that allows users of Google Documents to create an e-mail a form that automatically places each user's input into an associated spreadsheet. As it turns out, with a little bit of work, the forms that are created by Google Docs can be embedded into any web page. Now, The Goods: Click on the instrument you want turned up, click the submit button and then refresh the page. Through the magic of Google Forms as soon as you click on submit and refresh this web page, the data chart will update immediately. Turn up the:

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

Now available as a Kindle ebook for 99 cents ! Get a spiffy ebook, and fund more physics The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems , there seem to be fewer explanations of the procedure for deriving the conversion, so here goes! What do we actually want? To convert the Cartesian nabla to the nabla for another coordinate system, say… cylindrical coordinates. What we’ll need: 1. The Cartesian Nabla: 2. A set of equations relating the Cartesian coordinates to cylindrical coordinates: 3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system: How to do it: Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables. The chain

The Valentine's Day Magnetic Monopole

There's an assymetry to the form of the two Maxwell's equations shown in picture 1. While the divergence of the electric field is proportional to the electric charge density at a given point, the divergence of the magnetic field is equal to zero. This is typically explained in the following way. While we know that electrons, the fundamental electric charge carriers exist, evidence seems to indicate that magnetic monopoles, the particles that would carry magnetic 'charge', either don't exist, or, the energies required to create them are so high that they are exceedingly rare. That doesn't stop us from looking for them though! Keeping with the theme of Fairbank[1] and his academic progeny over the semester break, today's post is about the discovery of a magnetic monopole candidate event by one of the Fairbank's graduate students, Blas Cabrera[2]. Cabrera was utilizing a loop type of magnetic monopole detector. Its operation is in concept very sim

Copasetic Flow

Search This Blog