Category Archives: Test equipment

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.

 

The SDRPlay RSP1A-a momentary lapse

At the RSGB Convention last week I broke my pledge to have a 100% homebrew station. There was a demonstration of an SDRPlay RSP1A right next to the Martin Lynch stand with a small pile of boxes on sale! Not only is it a wide band receiver there is also spectrum analyser software available and all this for just less than £90.

The justification was simple; I build transmitters and need to be able to check the harmonics and other spurious signals to conform to licence regulations. It does not have to be an absolute measurement just the level of the spurious emissions compared to the carrier. And spectrum analysers are expensive.

Then there is the imminent launch of Es’hail, so I need a 10Ghz receiver to listen to it. The conscience clincher was a demo by the microwave group of a modern satellite TV LNA connected to an SDR receiver. Simple. Another reason to get the RSP1A.

And then there is 630m. You get the message, justification for the temptation and I must confess I had a moment of weakness and succumbed. I am trying to atone by finishing the remote tuner.

Not had much time to play but what I have seen is impressive. SDR receivers are incredible, amazing etc. This morning I listened at the top end of 80m for the transatlantic DX spot, 3.798Mhz and was astonished to hear AA8KB at 5-7 on the meter. This is on an untuned inverted L sloper with the high end at about 10m and low end at 6m.

This is a short recording of AA8KB holding the recorder close the the PC speaker.

I can only confess to this lapse and argue that this was a one-off purchase of an extremely useful piece of kit!

The usual disclaimer, no connection with the company and these are my own views.

Update a half hour later. Just gone back to the SDRPlay and found the RF gain was almost turned to minimum.

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.

The radio shack, workshop man cave

This is where I spend a lot of time. It is part of an old converted barn that was a coaching stop between Manchester and Sheffield. It built into a bank with walls 2-3 feet thick which makes it very quiet and cool all year round.

Next project on the bench will be a remote antenna tuner using a couple of Arduinos with an RS485 link. See this F4GOH web page


The construction area. Note the solder fume extract pipe.


The fume extractor is an inline ventilation fan bought from a hydroponics shop. It has a variable speed control and works very well.


The SMD rework area. The heated tweezers will soon be joined by a hot air gun.

The mechanical workshop!

 

What is a redpitaya?

Doing a lot of home construction is helped by having a heap of test equipment. There are several ways of getting that; take a risk on eBay and buy old stuff, build your own or get a redpitaya.

It claims to be able to work as an oscilloscope, signal generator, spectrum analyser, Bode analyser, logic analyser basic, LCR meter and vector network analyser.

If it can do all then it is truly revolutionary, and I want one! It is not cheap but if you add up the costs of the single instruments it replaces then it is definitely NOT expensive.