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

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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.

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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