CDV-720 3A High Range Radiation Meter

This post is cross-posted to my general blog, jeff.glass/blog

I went to the WCRA Hamfest in St. Charles this weekend in search of test gear (I had been fortunate to find a working Heathkit IM-2420 Frequency Counter there a couple years ago). I didn’t come away with anything of that sort, but I did scoop up this yellow beauty:

This beaut is a CDV-720 3A High Range Radiation Meter. It’s a remnant of the early cold war, the beginning of the atomic age – thousands were produced in the late fifties and early sixties by the Victoreen Company out of Cleveland Ohio. It’s got a cast aluminum case that feels like it’s made to survive a bomb, and maybe it was. The manual notes that:

It is designed to be used by radiological Civil Defense personnel in determining radioactive contamination levels that may result form an enemy attack or other nuclear disaster.

The really staggering thing about this meter is the range it covers: up to 500 Roentgens/hr. At that rate, your goose is cooked in a matter of minutes (first metaphorically, then literally).

Here’s a brief video overview of the meter, its circuitry, and the scary-high levels of radiation that it’s meant to measure:

Stay safe and non-irradiated out there!

50W QRP Amplifier – 3D Printed Case Design and Livestream

With the 50W QRP amplifier project coming along nicely, I felt it was time to start thinking about a reproducible case for the project. And for custom, reproducible cases, 3D printing is my current tool of choice.

I ended up designing the case on a YouTube Livestream on Saturday night, to which a few great colleagues stopped by to ask questions and offer advice. The full video is below.

The case is in two parts – a box with standoffs for the PCB and holes for connectors, and a lid with labels. The standoffs and the attachment holes for the lid are meant to connect with M3 threaded-inserts and be held down with M3 machine screws.

This was my first time using Fusion 360’s Eagle Sync function – since Eagle was acquired by AutoDesk in 2016, it makes sense that they’ve been working to integrate PCB design workflows into their other products. The sync was fair straightforward – open Fusion360, select Eagle Sync, select your board file in Eagle, and after a minute or two of importing, up pops your PCB in Fusion360. Neat! I’m still struggling with how to handle board cutouts in eagle, and I’m not sure how well they’ll be supported in Fusion, but that’s a project for another day.

Here’s the final design as it turned out in Fusion360:

The PowerPole model was provided by Chris Wych, a theatrical propmaster who’s done some really interesting work with Fusion360, including using it to model some 2d-printable geodesic designs which then folded up into geometric shapes. Very cool!

First print of this design coming soon!

73

This post is cross-posted to my more general-purpose nerdery blog, jeff.glass/blog.

50W QRP Amplifier – PCB Layout Video

This past weekend, I started on the process of laying out the 50W QRP Amplifier project as a PCB. Small PCBs can be remarkably inexpensive these days – $10-$15 for 5 pieces of say 4″x4″, shipped in 2-3 weeks. I’m treating this amplifier project as a chance to experiment with different, similar FETs to learn about critical power MOSFET properties, and also as an opportunity to brush up my layout skills that I haven’t used in awhile.

As the first step of PCB design, I captured the schematic of the amplifier as built in AutoDesk Eagle. I did this on a livestream on YouTube, the first time I’ve tried such a thing. It was great fun! Kenneth W6KWF stopped by to lend advice – he deals with prototype PCBs as part of his day job, though he has team members to do most of the actual layouts when needed. We’ve had a great deal of fun over the years, including building a cloud chamber for seeing charged ions in high school.

Here’s the full (2h45m!) livestream in all its glory! There’s a recap and full-circuit overview at 2h41m for those who want to see the final circuit.

Hear you on the air!

73

This post is cross-posted to my more general-purpose nerdery blog, jeff.glass/blog.

50W QRP Amplifier – First Demonstration

This post is cross-posted to my more general-purpose nerdery blog, jeff.glass/blog.

As I alluded to last week, I’ve been working on a simple “QRP Amplifier” to kick my power up from 5W to something a little more punchy. Specifically, an amp I can still use when portable. There’s something wonderful about achieving a contact with only 5W, but there’s also the frustration of getting into the field and having band conditions just wreck your day. It’d be nice to have the power to crank up the juice for special occasions.

While I have awhile to go before this project is wrapped up with a bow and ready for field use, here’s a brief video about my first successful test. 5W in, 50-60W out when run off two 13.8V sources in series:

More technical details to come, but for now, I consider this a really successful validation of the idea! Like I say, a few more critical steps to come, including an input 50-ohm pad, a low pass filter, and a case, but this is enough of a proof of concept to move forward.

Hear you on the air!

73

Video – Introduction to Termination Insensitive Amplifiers

As I’ve alluded to previously, I’m currently working on a BITX-style transceiver, using bi-directional termination insensitive amplifiers in the vein of N6QWs ZIA rig and N2CQR’s BITX DIGI-TIA, with the added challenge of implementing a variable-bandwidth crystal filter. In the process of putting this thing together, I’ve been learning about and experimenting with these so-called termination insensitive amplifiers, and I’ve put together a little video about their characteristics and uses:

This is my first foray into video-making, and I had a great time putting it together. Looking forward to making a few more down the road.

See you on the air!

73