Even better low-pass filters for transmitters

The last issues of QEX have featured two interesting articles by Gary Cobb, G3TMG. He outlines the advantage of using Zolotarev designs for the harmonic suppression filters of transmitters, giving even better suppression of the second harmonic than the more common Chebyshev or quasi-elliptic filters.

Chebyshev low-pass filter from the GQRP data sheet (issue 1)

My interest in this was triggered by the test of the Ultimate 3 QRSS/WSPR kit from QRP Labs in the Nov 2016 QST. The review was positive overall, but it was remarked that the harmonic suppression does not meet FCC requirements (-43 dBc or better). I am not sure whether this is due to PCB layout issues, or if better filters can alleviate it, but I note that the design uses the simplest filter of the ones I have listed here.

The evolution of filters for use for harmonic suppression follows at least these three steps:

Yet another Arduino clock

Does the world need more Arduino clocks? Maybe not.

But I needed another Arduino project as I had made a K3NG morse keyer. I love this keyer because it is unique in supporting a display where you can see what you send. But I wasn't using the morse keyer all the time, so I wanted the hardware to serve two purposes. That's the excuse for also making a clock.

Its main features are:

• Controlled by a GPS module outputting data over a serial interface, and handled with the TinyGPS++ library
• Shows raw GPS data such as UTC time and date, position, altitude, and number of satellites
• Shows derived GPS data such as 6-digit locator
• Finds local time and handles daylight saving automatically using the Timezone library
• Finds local sunset and sunrise, either actual value, or civil, nautical, or astronomical. The library is Sunrise.
• The clock also gives local solar height based on the Sunpos library from the K3NG rotator controller. 
• Finally, the clock also provides the lunar phase based on ideas found here.

The hardware for the K3NG keyer includes a speed pot and a memory bank selector (to the right) as well as four push buttons on top for selecting memories. The pot now controls the intensity of the display, but the bank selector switch is not used. Of the four push buttons, only button 1 is used (later two are used). With it one can toggle the clock through various displays as shown below.

Local time, solar and lunar state

Line 1: Local day, date, time

Line 2: Sunrise, maximum solar elevation (actual solar angle during the day), sunset

Line 3: Civil dawn, local time at maximum solar elevation, civil dusk

Line 4: Lunar phase, arrow showing that it is rising, days since new moon