Category Archives: Digital

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.

Can we talk?

After 6 years away from the radio what is different? Everything and nothing. Still the same camaraderie and immense kindness in the hobby. That has not changed. The difference is there seems to be a growing reluctance to actually talk to each other on the air.

What has become apparent is the reliance of the internet. I saw a message on the net recently from a VHF op who said he had spent a long time calling CQ with no response. The reply was that he needed a ‘spot’ on the ON4KST site and then people would know he was there. I assume from that nobody turns on the radio and tunes around anymore.

Then there is ‘the HF bands are dead’ mantra usually followed by it’s not worth turning on the radio as there is nothing much on the DX cluster. Again, it looks as if ops are sitting in front of their computers waiting for to see something happen instead of using their radios.

And the automated digital QSOs, jt8? And digital propagation checking where you don’t even need to contact another human being to know how far you signal has travelled.

Is that what it is all about now? Only operate when there is DX around? Never call CQ because nobody is listening?  But what gets me most is never ‘talk’ (voice or CW) to another human being? Have radio amateurs lost the ability/desire to speak to each other?

Don’t get me wrong, I am all for using the latest technology and moving with the times but if we insist on removing the human element or reducing it to the shortest possible exchange for the points or to bag another country then we lose the very basis of the hobby. There must still be a place to rag chew on 160m or 80m or 2m, I want to talk to another human being and not a computer.

Using SMD – part 1

Why do I like using SMD? Let me explain, I began making radios using valves, it was all there was at the time. When I started work in the industry the first training courses were on valves and how they worked. Then the transistor came, then integrated circuits followed by surface mount devices, SMD. I guess I have followed the technology.

It is easy to be overwhelmed by progress and stick with what you know but there are many advantages to using SMD:

  • individual components, resistors and capacitors, are very cheap
  • many older devices are no longer available as wire ended e.g. the SA612
  • PCBs are smaller due to high packing density
  • high frequency boards are easier and cheaper
SI5351 board

An SMD VFO module

Above is an SI5351 board (ready made apart from soldering the SMA connectors) it is just 30mm wide and can used with an Arduino to make VFO with 3 programmable sine wave outputs. Current cost is less than £5 on ebay plus the Arduino.

You might need some new tools like a magnifier, fine tipped soldering iron and good quality tweezers. There are more including heated tweezers and a hot air gun for component removal but they can wait for a while.

So, my advice is do not be put off and have a go. Find a simple kit to practice with and then progress to more complex circuits. It helps if you know something about how SMD components are sized. Srat with the larger sizes and work down.

1206 and 0805 are popular SMD sizes

This is another good one to print out.

Over the coming month I will add to this series of posts and share some of the projects I am working on which include: a remote tuner, vector network analyser (VNA), wide range VFO/signal generator, a switched attenuator.

To talk or not to talk?

After being away from the hobby for around 5 years I am surprised by the uptake of digital modes. I wonder what this means and where it is going.

It is not that I have not used them in the past, in the early 1970s I had a Creed 7B teleprinter connected to a home brew terminal unit taking audio from a modified Pye base station on 2m. It was part of a local net and was left on standby a lot of the time. I would come home from work and find a few feet of paper on the floor. RTTY using the computer is not the same. No smell of 3in1 oil or the noise of the motors and clatter of the mechanics.

Video of a Creed 7B

 

I also found WSPR to be useful to test antennas and tried a few other data modes but frankly I found them to be boring. Yes, they can establish a 2 way connection where other modes cannot but so what? It is machines talking to machines. There is no experience of making contact with a human being, no suppleties of voice or ‘fist’ in CW. Nothing to personalise the contact and gain some idea of who you are connected to.

For me radio is about connecting, communicating with another person using voice or Morse. It is about recognising that there is a human being operating the equipment, making the connection, the contact. And I mean ‘contact’ in both the human communication sense as well as the technical sense.

I fear that digital modes are being pushed hard as a way of interesting younger people in the hobby. I must ask why? Why do something in a more expensive and complicated way that can be and is done by Snapchat, Facebook, Instagram etc?

A few years back when Internet linked repeaters started I remember having a conversation with a newcomer who was excited about ‘working’ a VK via the local repeater. In fact, he worked the repeater a couple from miles from his house but was under the impression he could get DXCC and other awards easily. That is the problem, the quick and easy fix appealed but took him nowhere.

I still believe that if you show a real contact on a radio with someone in a far-off place it will be more exciting and more attractive than dangling the instant hook of digital communication. Kids do that on their phones every day, why would they bother doing it via radio?