Boat Anchor Twins Get A Little Digital Help Staying On Frequency

March 11, 2022 by Dan Maloney 9 Comments

In the ham radio trade, gear such as the old Drake units [Dr. Scott M. Baker] has in his radio shack are often referred to as “boat anchors.” It refers to big, heavy radios that were perhaps a bit overengineered compared to the state of the art at the time they were designed, and it’s actually a shame that the name has taken on something of a pejorative connotation, since some of this gear is rock solid half a century or more after it was built.

But older gear is often harder to use, at least compared to the newer radios with microcontrollers and more stable oscillators inside. To make his 1970s-era Drake “Twins” setup of separate but linked receiver and transmitter a little more fun to use, [Scott] came up with this neat Raspberry Pi-based DDS-VFO project to keep his boat anchors afloat. Compared to the original mechanically tuned variable frequency oscillator in the Drake receiver, the direct-digital synthesis method promises more stability, meaning less knob-nudging to stay on frequency.

The hardware used for the DDS-VFO is actually pretty simple — just a Raspberry Pi Zero W driving an AD9850-based signal-generator module. Sending the signal to the Twins was another matter. That was done by tapping into the injection cable linking both units, which meant a few circuit complications to deal with signal attenuation. [Scott] also added amenities like a digital frequency display, optical encoder with crank-style knob to change frequency, and a host of Cherry MX keyswitches for quick access to different features.

From the look of the video below, the Twins are now rock-solid and a lot easier to use. This project is loosely based on a recent panadapter project [Scott] undertook for the receiver side of the Twins.

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Radio Shack Shortwave Goes Digital

May 20, 2020 by Al Williams 25 Comments

If you spent the 1970s obsessively browsing through the Radio Shack catalog, you probably remember the DX-160 shortwave receiver. You might have even had one. The radio looked suspiciously like the less expensive Eico of the same era, but it had that amazing-looking bandspread dial, instead of the Eico’s uncalibrated single turn knob number 1 to 10. Finding an exact frequency was an artful process of using both knobs, but [Frank] decided to refit his with a digital frequency display.

Even if you don’t have a DX-160, the techniques [Frank] uses are pretty applicable to old receivers like this. In this case, the radio is a single conversion superhet with a variable frequency oscillator (VFO), so you need only read that frequency and then add or subtract the IF before display. If you can find a place to tap the VFO without perturbing it too much, you should be able to pull the same stunt.

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EBay Modules And Custom PCBs Make A Plug And Play Ham Transceiver

March 17, 2019 by Dan Maloney 9 Comments

Many of us have fond memories of our introduction to electronics through the “200-in-1” sets that Radio Shack once sold, or even the more recent “Snap Circuits”-style kits. Most of eventually us move beyond these kits to design our circuits; still, there’s something to be said for modular designs. This complete amateur radio transceiver is a great example of that kind of plug and play construction.

The rig is the brainchild of [jmhrvy1947], who set out to build a complete transceiver using mostly eBay-sourced modules. Some custom PCBs are used, but those are simple boards that can be etched and drilled easily. The transceiver is only for continuous-wave (CW) use, which would normally mean you’d need to know Morse, but thanks to some clever modifications to open-source apps like Quisk and FLDigi, Morse can be received and sent directly from the desktop. That will no doubt raise some hackles, but we think it’s a great way to learn code. The rig is QRP, or low power, transmitting only 100 mW with the small power amp shown. Adding eBay modules can jack that up to a full 100 Watts, which also requires adding a 12-volt power supply, switchable low-pass filters, a buck-boost converter, and some bandpass filters for band selection. It ends up looking very experimental, but it works well enough to make contacts.

We really like the approach here, and the fact that the rig can be built in stages. That makes it a perfect project for our $50 Ham series, which just kicked off. Perhaps we’ll be seeing it again soon.

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Teensy 3.1 Controlled VFO

March 5, 2016 by Rud Merriam 27 Comments

[Tom Hall], along with many hams around the world, have been hacking the Silicon Labs Si5351 to create VFOs (variable frequency oscillators) to control receivers and transmitters. You can see the results of his work in a video after the break.

[Tom] used a Teensy 3.1 Arduino compatible board, to control the Si5351 mounted on an Adafruit breakout board. An LCD display shows the current frequency and provides a simple interface display for changing the output. A dial encoder allows for direct adjustment of the frequency. The ham frequency band and the frequency increment for each encoder step are controlled by a joystick. When you get into the 10 meter band you definitely want to be able to jump by kHz increments, at least, since the band ranges from 28 MHz to 29.7 MHz.

So what is the Si5351? The data sheet calls it an I2C-Programmable Any-Frequency CMOS Clock Generator + VCXO. Phew! Let’s break that down a bit. The chip can be controlled from a microprocessor over an I2C bus. The purpose of the chip is to generate clock outputs from 8 kHz to 160 MHz. Not quite any frequency but a pretty good range. The VCXO means voltage controlled crystal oscillator. The crystal is 25 MHz and provides a very stable frequency source for the chip. In addition, the Si5351 will generate three separate clock outputs.

[Tom] walks through the code for his VFO and provides it via GitHub. An interesting project with a lot of the details explained for someone who wants to do their own hacks. His work is based on work done by others that we’ve published before, which is what hacking is all about.

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