Tag Archives: GPS

Low cost frequency standard

I have been looking for a low cost frequency standard for a while to replace one I once had about 10 years ago. The only way to do it then was to build a GPS locked oscillator. I chose the extreme overkill route and locked a doubtful rubidium standard to GPS. It worked for a while and then the rubidium kit stopped working.

The next solution was to lock a temperature-controlled 10Mhz crystal oscillator. It worked well enough as along as it was left on all the time. Recently I have been looking for a cheaper and less complex way of providing a 10Mhz standard signal for test equipment and radios.

Things have moved on and the GPS modules that used to be relatively cheaply available on ebay are no longer there. Ditto oven-controlled oscillators. Then I found the ideal solution on the QRP Labs web site; a “ProgRock – triple GPS-disciplined programmable crystal” which is basically a Si5351A chip programmed for a single frequency. It can be GPS locked via a 1PPs signal from a GPS receiver, the “QLG1 GPS Receiver kit.” An order was placed.

The kits arrived, and I spent a few hours yesterday building them. As usual with QRP Labs kits they all worked first time. The first check was my £17 ebay counter, a Racal-Dana 9918. It was 5.2Hz low at 10Mhz! I could try adjusting the internal 10Mhz oscillator but it might take a while to get it to read 10,000,000!

The better option is to complete the project by building a small distribution amplifier which will give 3, 10Mhz sine wave outputs from the ProgRock and use one of them as an external timebase for the counter.

The PrgRock with scope probe attached

GPS board with patch antenna.

The kits, parts for the distribution amp and a case will cost around £35 in total. That is probably about one tenth the cost of the previous project!

Is this all overkill? Well yes and no. Modern transceivers are accurate but when you build your own you never know. Also, the move to VHF, UHF and microwave for satellites means I want to be sure that the frequencies are correct. This crucial when multiplying up free running crystal oscillators as any error will also be multiplied.

The usual disclaimer, I have no connection with QRP Labs other than being a satisfied customer. This review/article was not solicited by them and they had no knowledge I was doing it.

 

Next project-GPS locked 10Mhz source

Work is progressing well on the remote antenna tuner, more pics to follow soon. I am already thinking of the next project and decided I need an accurate 10Mhz frequency source for my counter and other stuff. In the past I have used a surplus rubidium standard and when that popped a GPS locked crystal oscillator.

That was over 10 years ago and things have changed. Used Racal Rubidium boxes are on ebay for between, £550 – £811. Bare bones Rubidium standards which need control circuits are priced at £157. These are often units removed from cell phone installations with an unknown lifespan remaining.

There are also lots of ready built Chinese boxes using 1PPS GPS sync for around £100 but in the spirit of making everything myself either from kits or self sourced components I decided to make my own.

QRP Labs have the QLG1 GPS Receiver kit and the ProgRock kit which makes a very cost effective combination. I have no connection with them except being a satisfied customer. Adding a box, power supply and other bits and pieces the estimated the overall cost will be below £40. The kits are ordered and I will share the build here soon.

See my build of a QRP Labs 20m QCX transceiver here

An Extron ADA4 300MX video distribution amplifier can make a cheap way of distributing the 10Mhz signal around the shack/workshop. See this page.