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:

amppic1

ampic4amppic

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.

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50W QRP Amplifier – Schematic, PCB ver 1

The 5W-to-50W QRP HF Amplifier project is rolling along nicely  – I received the first PCB draft in the male this week and am 90% of the way through assembling it, with only heatsink-placement left to sort out.

I’ve made a couple of additions to the schematic since the original layout, including a relay-activated indicator (R27 and its LED) and an RF-output sensing LED (from C14 to its associated LED to ground) along the the lines of VK3YE’s recent project. There’s also a space on the PCB now for a low pass filter with the same footprint as Hans Summers’ LPFs over at QRP-Labs. Not that you’d necessarily want to reuse a QRP LPF for a 50W amp, you’d be in danger of putting too much voltage on the caps, but that would be a simple change.

Here’s the schematic as it exists now:
qrp_amp_schematic_1-1

 

And here’s the current boards (layout, unpopulated, populated):

qrp_amp_board_1-1

FullSizeRender (1)

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I’ve already got a little laundry list of things to modify for a second rev of this board, including, in no particular order:

  • Swap the Diode placements the vertical to preserve board space
  • Add footprints for alternate relay packages
  • Add footprints for alternate trim-pot packages
  • Re-think component designators for clarity
  • Add bypass jumpers for the 3dB input pad and the LPF.
  • For some reason, the none of the component values printed on the silkscreen, will need to sort that out
  • I’m not sure if I screwed up how to designate a cutout or if JLCPCB doesn’t do them for its bare-bones PCB service, but I’d like not to do the next set with a drill press and a nibbler.

Hoping to put this on the air soon for some signal tests. Hear you there!

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

A Portable 20/30/40m Vertical Antenna

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

Following the Forth of July, I took a few days off of work to recuperate from a grueling work project that we pushed over the finish line on the third. And what better way to relax in the wake of a heatwave than getting out in the beautiful, low-70’s weather and working on a new portable HF antenna.

Pole.jpg
From eBay listing

The heart of the antenna is an inexpensive ‘7.2m’ telescoping fishing pole, which can be had for less than $30 with Prime shipping or for less than $10 if you don’t mind waiting. The pole weighs about 10 ounces, comes with a small fabric sheath, and collapses down to about 24″. I’ve been wanting to try out something like this since I stumbled across VK3YE and his squid-pole setups awhile back – Peter’s also featured these particular poles in another video. Be aware, a pole called “7.2m” may not actually be 7.2 meters from end to end: check the listings carefully:

rod
Note the difference between the “stretch” column and the “specification” column.

The length of the pole is enough for a quarter-wave vertical for 20m with some room to spare on either end. To allow for multi-band operation, I added a QRPGuys Tri-Band Vertical accessory to the bottom of the antenna. The piece is essentially just two loading-coils (in this case, iron-powder toroids) with slide-switches to short them out. The 20m configuration is a true quarter-wave vertical; one of the toroids is switched in series for 30m, and both are placed in series for 40m. Ultimately, not a complicated setup. While it would be easy enough to homebrew, the ergonomics of the switches, the hardware to attach the antenna wire and radials, and the clever PCB setup are enough to make it worth the $15 to just buy the darn thing. It even has little notches on the edges of the PCB for straps/ties/rubberbands to attach it to the vertical.

triband
From QRPGuys.com

Tuning the antenna is straightforward: you cut a piece of wire (a bit long) for a 20m quarter-wave, and lay out four 10′ radials. Then, you bit-by-bit trim down the vertical element to resonate at the desired point in the 20m band. Then you switch in the 30m coil and compress/expand its turns without changing the antenna length to resonate on 30m. Finally, switch in both coils and adjust the second coil to resonate on 40m without changing either the antenna length or the first coil. Voila, a tri-band, base-loaded antenna.

Unfortunately, my antenna analyzer is old school, and doesn’t have a frequency readout. It’s an old MFJ-207 that I scooped up at the SMCC Hamfest in 2016, and while it does have a port to attach a portable frequency counter, I couldn’t find my cheapie one on the day. But I do have a nice Heathkit IM-2420 Frequency Counter with an internal OXCO that I scored an amazing deal on at a hamfest last year (it had an intermittent power switch). So, I attached the MFJ to the antenna, tuned its analog VFO for lowest SWR, walked inside without touching the dail and hooked it up to the frequency counter to see where the center frequency was. Repeat for say the upper and lower 2:1 SWR ranges. Trim the antenna a little, and repeat measurements. Once 20m is tuned, repeat with adjusting the coils for 30m and 40m. A fairly cumbersome process, but for three frequency ranges on one antenna, it was a half-hour project at most.

IMG_4804

In the end, the antenna is less than 2:1 SWR across all of the 20m band, all of the 30m band, and all but the top 50 Khz of the 40m band.

I’ve glossed over the mechanical details of the antenna to this point – the base of the telescoping pole fits snugly-yet-easily into the a piece of 1″ schedule-40 PVC pipe. I bought a 5′ section from the local big-box store and cut off a ~10″ section to hold the antenna. I strapped two ground-stakes that I got at Hamvention this year to the bottom with a couple zip-ties and a couple rubber-bands. Finally,  I threaded a long 3/8″ eye-bolt though a matching hole about 2″ from the bottom of the pipe and secured it with a nut on either side – this acts as both a stop for the pole so it doesn’t fall out the bottom, and provides an easy hand- or foot-hold for pressing the stakes into the ground.

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The finished antenna mount. It may be getting a coat of high-vis paint in the near future.

The setup for the radials was something I stumbled across by chance while buying the PVC pipe. Our local big-box hardware store was having a sale on these RECOIL Brand cable winders that are meant for headphones or charging cables or similar. I’ve found that they can almost hold four 10′, 24-guage speaker wire radials. This is solving the problem of wires-getting-tangled-in-a-bag that I’ve had with all my antennas to date. Thank goodness!

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A few loose ends are worth it for the assurance that the wires won’t get tangled in transit.

It takes about 6 minutes to setup or tear down the antenna:

  • The stakes are driven into the ground with a firm foot.
  • The telescoping pole is unwrapped and placed in the base
  • The antenna wire is unwound from the QRPGuys winder and tied to the tip of the telescoping pole with a small bit of cotton-wrapped nylon line (what we’d call tie line). The top section the pole is very flimsy, so I add a second tie to the next-largest section.
  • The pole is pushed up to full height, taking the antenna wire with it, which leaves the QRPGuys rig hanging about 2′ off the ground.
  • The QRPGuys rig is tied to the pole with another bit of tieline.
  • The radials are unstrung from their winder, pinched to the ground terminal on the QRPGuys rig, and spread out.
  • Run coax to a nearby table/seat/rock.
  • Set up radio, battery, key, antenna, and logbook.
IMG_4810
The antenna fully set up and freestanding.

Of course, my very first time away from home with the antenna… I forgot the radial wires. D’oh! I was way out in the suburbs, too. I wasn’t about to drive an hour home and an hour back for 4 bits of wire, so I first tried out the antenna with no radials (just the coax as a counterpoise). This worked alright – I picked up K2D in CT in the 13 Colonies event on the second call (this at 5W QRP with the ATS-4), but was having trouble with other contacts.

Since I planned to swing by the local Fry’s Electronics on this adventure, I decided to pause operating for a while and make that run. Mostly I was picking up parts for an amplifier project (more on that to come), but while I was there, I looked for solutions to my radial problem. I found a 10′ section of RJ11 phone cord with 4 wires for $1.69 – perfect! Back out in a new park, I stripped the wires out of their jacket, spread them on the ground, and tied them to the antenna’s ground terminal. Instant radials!

IMG_4814
And such colorful radials too!

With the antenna back to spec, things really picked up – surely, being on 20m at sundown didn’t hurt either. I scooped K2A (NY), K2B (VA), K2H (MA), K2L (SC), and K2M (PA), as well as the 13-cols bonus station WM3PEN in Philly. Many of these I got on the first or second call, though K2L was a real struggle. There was a very patient operator on the other end though.

13cols
The 13 Colonies special operating event runs each year for a week around the 4th of July in the US.

I picked up a couple of other interesting stations along the way: PJ2/KB7Q out of Curacao (though the license gives away that he’s either an ex-pat or visiting), and CQ918FWC from Madeira Island (!) off the coast of Portugal. There were a number of these World Cup special stations on the bands this week as we close in on the finals. At 3800+ miles away, this was my best DX of the day, and a great proof of concept for the new antenna.

ord fnc
At QRP wattage ,this 3800 mile contact was made at 760 miles/watt.

Hear you on the air!

73

Dayton Hamvention 2018

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

While I’m still exhausted from the travel and the good times, I wanted to put up a little note from this year’s Hamvention, the largest annual gathering of ham radio operators in North America. I only decided a week ago that I was going – I left Friday after work, drove 5 hours to Dayton OH (well, Xenia), and crashed at a hotel. Up bright and early, spent the day at the convention and checked out some local beer and grub in Dayton. Sunday, caught an early breakfest with some friends new and old, then got on the road back to Chicago. What a ride!

Others are doing fuller summaries of the convention – SWL-ing post always does a photo wrap-up of both the indoor and outdoor experience, and the Ham Radio Workbench podcast from the event is now up.

Hamvention is a great place for meeting the hams you’ve yet to meet, and seeing again those you already know. I spent most of Saturday hanging out with the Workbench crew, but I also ran into hams that I knew from elsewhere. Plus this guy, who falls into both categories:

It’s wild that 15 years after I accidentally introduced the future W6KWF to ham radio we hung out together at giant swapmeet in the middle of Ohio. Totally wild.

The flea market was certainly the biggest radio swapmeet I’ve ever been to – it’s probably bigger than that De Anza flea market by a good 300% – but it wasn’t all that special. I would say there was the usual assortment of used radios, test year, bits and parts, old tools… nothing super intriguing. Of course, I did get there on Saturday, so perhaps all the interesting things were just scooped on Friday.

It was neat to see a lot of the vendor products in person that I’d only heard about, but since I wasn’t in the market for anything in particular, I didn’t linger too long at any of the booths. Except Elecraft – those are some very, very attractive radios. I chatted with Wayne N6KR (one of Elecraft’s founders) for about 15 minutes about the KX2 and its SDR structure, which, not to be a fanboy, was pretty exciting.

In the end, I don’t know if I would go back the very next year – it was a really neat experience, and I’d go to see the people, but in this age of eBay, Amazon, and vendor websites, seeing everything in person and picking through the fleamarket feel just a little bit like a relic of the days when everything had to be done in person.

That said, I did find a few treasures… here’s this year’s haul:

Roughly from left to right:

  • Some panel-mount SMA connectors
  • An old automatic shutter trigger/timer
  • A tube of TFM-2LH Level 10 2Mhz-1000Mhz mixers from Minicircuits ($15 for 20, a steal!)
  • Six interesting potentiometers (dual with concentric controls or dual with concentric switch)
  • A bag of assorted HF/VHF H49 Crystals
  • An old Collins 250Khz crystal filter
  • A ZUMspot DMR hotspot/raspberry pi kit
  • A pair of QRP-Labs filters, both a low-pass and a bandpass filter for 40 meters.

Sometimes, you get back from a big trip or conference or meetup thinking Boy, am I worn out, I don’t need to do any more of that thing for awhile. This time, I came how itching to get back to work, revive some projects that had been dormant for awhile, and make things. So for that, at least, Hamvention 2018 was worth it.

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

Hamfesters’ Hamfest 2017; Homebrew RF Power Meter

This morning, I trekked out to the Hamfesters’ Hamfest in Peotone, IL for the second year in a row. Though the rain threatened to put a damper on the day, the sun had burned through by 10am and left everyone alone.

There was an interesting mix of vendors at this year’s Hamfesters – lots of assorted “hardware” (tool, dental picks, kitchen sink), but also a good number of radios new and old. There was a table absolutely stacked with older 2M gear, mostly Heathkit. A couple newer ICOM rigs, the usual FT-101e’s… nothing too exciting. I scooped up a handful of beefy heatsinks meant for CPU’s, but will be re-purposing them as LED heatsinks in future projects.

I did find two real scores at the Hamfest today. First, from Patrick-J, a secondhand, gov’t-surplus Tektronix TDS644a. It’s a 4-channel digitizing scope, with 500MHz bandwidth at 2GS/s, and I got it for a song.

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Not unexpectedly, when I got it home and opened it up, it’s in need of a good re-cap-ing (see, for example, W6KWF’s recent video on this subject.) I’ve already got two packs of electrolytics on their way from the wide wide eBay, so I’ll pick this project back up on a future weekend.

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The second find was a small, slant-top box with a 1mA DC meter movement already built into the top. It was configured originally to be a shunt ammeter, but I really just wanted the nice box and meter. Instead of measuring AC current, it’s now set up to measure RF power.

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The original unmodified meter – something out of some other amateur’s homebrew shack.

The only external sign that the box has been altered is the presence of a small SMA jack, but the internals are entirely different. I populated and installed one of the AD8307-based power meter PCB’s that I cooked up back in March, fed directly from the external SMA connector. The output feeds the mA meter through an op-amp buffer – I started with a direct connection, but the AD8307, with its 10k-15K output impedance, wasn’t up to the task. The voltage output from the AD8307 is also directly fed to the red external binding post, for measurement with a DMM. I added a little green power LED to remind me to turn the darn thing off. I left the original switch in place, just because it feels right.

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The final meter, with an SMA/BNC adapter hanging off it.

The schematic for this project is essentially the same as W7ZOI’s Power Meter published in QST – see that article for details, as well as Wes’ further errata. The meter covers the range of the AD8307’s output voltage, from about -70dBm to +20dBm. As I’ve been working on putting together my BITX homebuild (more on that soon!), I’ve been thinking that having an RF power meter with an analog movement would be very helpful in peaking filters and looking at relative input and output power. And now, I have one!

See you at the ‘fest!

73

ARRL Field Day 2017 – QRP Portable

In contrast to my field day adventures last year, in which I hung out with the folks from the North Shore Radio Club and ran 100W on a K3S, this year I opted for a decided more small-scale approach. Using my ATS-4 receiver, I ran 3.5W CW on 15m, 20m, and 40m for about four hours Saturday afternoon in the lakefront park here in Chicago.

My antenna was a single 40-some-odd-foot wire hung from a tree, fed by my ZM-2 antenna tuner. I think when I built the ZM-2 last year, I goofed something up in the SWR circuitry – the built-in LED should go out at minimum SWR, but mine seems to be brightest at low SWR. To compensate for this, I brought along the MFJ-207 Antenna Analyzer I got at the SMCC Hamfest last year and used that to adjust the antenna tuner.

With the big analog, multi-octave dial on the front of the 207, I found it useful to first tuner the ATS to the desired frequency (say, 14.030) while attached to the antenna and adjust the analyzer until I heard the “WHOOP” of its signal generator in my headphones. With the frequency of the analyzer and receiver close to matching, I’d move the coax back from the tuner to the analyzer and adjust the ATU until the 207 showed lowest SWR. Reconnect the ATS, and away we go!

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The MFJ-207 Antenna Analyzer covers up to an octave with a half-turn of the variable cap. Listening for its signal on a receiver made it much easier to find a specific frequency.

I used a new battery setup for this outing – a 12V, 6000mAh TalentCell lithium-ion pack that I borrowed from work. I love this pack – a little less than a pound, charges from a wall-wart, and has a built-in barrel connector and on-off switch. There are also models with a built-in 5V USB charging port, for topping off cell phones and other devices on the go. While the ATS is designed to run at 12V MAX (not 13.8V), I found that the 12.2V the pack was putting out proved to be fine – it seems the limitation is in the heat dissapation from the BS170 finals, and running relatively low duty-cycle search and pounce that wasn’t an issue. I’ll be ordering one for my own use soon. (Or perhaps the even more compact 3000mAh version – the size of a deck of cards!)

The rest of the pack list included:

  • A HamKey brand iambic paddle
  • A golfball and a kite-string winder for getting the antenna wire into a tree
  • A pair of Koss UR-20 headphones
  • A small battery-powered speaker with 1/8″ aux input
  • Variable DC and Coax jumpers
  • A notebook and pen
  • A folding camp chair.

All of the above fit into a small laptop bag, along with a few other tools and bits I didn’t end up needing.

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The full field day setup, minus the antenna.

I managed 69 contacts, all QRP CW hunt-and-pounce, during my operating time – no tremendous DX, but I did hit a couple of rocky-mountain states and a plethora of sections up and down the East Coast. Final score was just over 1000 pts – that QRP multiplier really stacks up!

I also couldn’t have asked for better weather on the day – 72 degrees and slightly cloudy with a pleasant breeze. Simply stupendous.

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Hear you on the air!

73

SI5351 Signal Generator

As I alluded to in my March bench report, I’ve been working on packaging up my old SI5351 VFO that sat on a breadboard for two years into a functional signal generator for the bench. That project is now essentially complete, though there are a couple of planned improvements in the works.

IMG_2249

The heart of this project is a Silicon Labs Si5351 clock-generator IC, on a little interface module from Adafruit.  With an I2C interface, it can output square-wave signals at roughly 6dBm anywhere from 8Khz to 160 MHz. This nifty little chip has been around for a few years, and has been used in many a homebrew radio rig, including the work of N6QW, N2CQR, M0XPD, and other. Jason NT7S was essentially in building some of the earlier Arduino-friendly libraries for controlling the Si5351. With such a wide frequency range and the confidence that comes from XTAL-derived, PLL frequency generation, this little chip has breathed life into rigs both new and old.

With the hardest part of building a SigGen (actually producing the darn frequency) neatly packed away in silicon, what remains for a builder is to wrap the thing in packaging to promote ease of use and flexibility. That’s where the fun of this project lay. The parts list ended up like so:

The project box and the LCD display were the most expensive parts of this build by a wide margin, although both would be available for quite a bit less with a longer lead time from oversees.

The SigGen has 4 different software modes:

  • VFO – The primary output frequency matched the displayed frequency. Frequency steps are 10kHz, 1kHz, 100Hz, and 10Hz.
  • Test – Same as VFO, but steps are 10MHz, 5 MHz, 1 MHz, 500kHz, 100kHz, 10kHz, 1kHz, 100Hz, 10Hz, and 1Hz.
  • Polyakov – Primary output frequency is half of the displayed frequency, for experimenting with half-frequency-driven mixers. Step size is the same as VFO mode.
  • BFO – Adjusts the secondary output frequency, for using the SigGen to drive a Superhet directly. Steps are the same as in Test mode.

The SigGen’s three pushbuttons (one built into the rotary encoder and two next to the LCD screen) do essentially the same thing in each mode:

  • Encoder: Changes the frequency step size, per the step options above.
  • Mode: Changes through the software modes, per above.
  • Band: Advances to the next highest Amateur band frequency, to aid with band-changes especially in VFO mode. For example, if the current frequency is 5.72MHz, pressing the Band button sets the frequency to 7.0Mhz, the bottom of the 40m band.

There are still a couple improvements I’d like to make, namely replacing the cheapo detent-based rotary encoder with a nice smooth continuous one, which can be had for about $10 on eBay – using a detent-based encoder as a VFO is a pain in the patoot. I’d also like to implement a sweep functionality to sweep through various filters, but that would require a bit more UI work as well.

This gadget has been complete on my bench for a month of so, and has already been useful in working on my variable-bandwidth superhet… but that’s a story for another post.

Hear you on the air!

73