gpsdo

All posts tagged gpsdo

After the antenna work I did in my previous post, my GPSDO MKII had stopped working.
Reason was that I had been a little too rough with the small coax going to the rooftop GPS antenna.
The coax had shorted and this being an active antenna the RF-choke on the Jupiter GPS board feeding the antenna with 5VDC was fried. Having no idea on what value the original inductor has I had to substitute it with something, I chose a 33nH inductor with a self-resonate frequency around 1.7GHz.

20160713_180137 (Large)

Jupiter TU30-D140 GPS board

 

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GPSDO working again.

 

Here is a small update regarding my band hopping picaxe controlled wspr beacon.
I took the beacon of air the other day to do some revisions to it’s circuitry. And in this context figured out that I was in need for a filter to clean up the square wave shaped signal from the 10MHz reference oscillator, the GPSDO MKII. I did a little googling and found an interesting circuitry drawn by Jerry Mulchin – N7EME. The reason for needing this filter is that I have a passive frequency trippler for clocking the DDS-60 @ 30MHz, and this tripler need a sine wave to work right.

There is still some work to be done before I can put the beacon back on air. But as they say in broadcasting; Stay tuned, will be right back after….

PCB measures 60x20 mm and parts are SMT

Schematics

Measuring reflection (S11) with the minivna. Return loss is more than 26dB @ 10MHz.

Measuring transmission (S21) with the minivna. 1dB insertion loss @ 10MHz and cout-off at 12MHz.

Here are some pictures of my second GPSDO.
This one, like my first GPSDO is based on the G3RUH James Miller desing.
Whats new with this is that I have added a Picaxe controller and a display unit for decoding the GPS NMEA-0183 sentences.
The display show various information decoded of the gps sentences.
But the main reason for building the MKII was that I needed it for controlling my DDS based WSPR Beacon.
GPSDO 10Mhz output drives the DDS and the micro-controller which steers the DDS.
The picaxe gps decoder take care of the keying of the beacon at the start of every tx period.

Ii’l will come back with a separate post regarding details of the wspr beacon.