Posts Tagged ‘homebrew’
FabLab first
May 2nd, 2014 | 
Author: After some cautious first steps my first laser cut parts have been made. The case for the clubs upcoming WSPR kit build prototype has been, well, lasered.
There’s a couple of minor points to address but for a first effort I’m pretty pleased.
The idea was to cut for a single sheet a ‘desktop’ case for the U3 WSPR transmitter that could display a callsign or something similar on the front as a customisation as well as being simple and space efficient. Yep, you can buy a case but its quite nice to be able to make one in Cumbria rather than China. I should be able to get 4 and a half of them out of a single 300mmx600mm sheet.
All I have to do now is fix the faults and make it right next time.
Datamode Interface built
To transmit and receive digital/data modes you need to connect the radio audio in/out to the computers sound card in/out, the computer then runs the necessary software to encode/decode the signals. I want to try out WSPR, PSK, JT65 and some SSTV for starters I have spent too long just receiving and decoding...
There are a number of inexpensive commercial interfaces available, but many of them use the same basic design originally intended for eQSO/Echolink operation. I nearly succumbed but I had built an eQSO interface many years ago when using PMR446 and had most of the parts to build another.
I nearly took the easy route and got a commercial one since connecting up some home built circuitry to a £20 hand held is slightly less daunting than plugging it into an expensive rig! My original interface has been modified and reused over the years and was a bit of a mess, but being brave I decided I could tidy it up and I couldn't really damage anything if I took my time... actually the truth was I discovered I didn't have the necessary optocoupler IC so couldn't build a new one just yet...
A simple internet search for digital/data mode interfaces will bring up a great deal of information, schematics and ideas for home brew solutions. The basics can be found here for example.
The simplest form of interface is just a simple direct lead with the transmitter operating in VOX mode. However levels can be a problem as the line/speaker output from a computer can be too high for a transmitters microphone input. Also connecting a radio to a computer directly can lead to problems with ground loops and interference.
The computer can be made to control the Push-To-Talk (PTT) on the transmitter using a serial port with the software controlling one of the handshake lines (RTS/DTR) Some data mode software support CAT to allow control of the PTT as well as tuning the transmitter, but the serial port method is more universal.
The preferred interface, and the one I had built isolates the computer from the radio by using two audio transformers and an optocoupler. There is no direct connection between the two devices so keeps interference to a minimum.
I could have used the microphone and speaker output on the radio, but the FT-857D has a convenient data connector on the back. This is a 6-pin DIN socket as used by older (PS/2) computer keyboards/mice. Note the diagram shown in the FT-857D manual (as below) is the view as you look at the socket.
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| FT-857D Data connector as in the manual |
Like many people I initially thought I could cut a lead off a mouse/keyboard and repurpose it, however I discovered most only use four wires and they don't use the necessary pins! You might be lucky especially with older keyboards or alternatively if you have an old keyboard extender cable they usually have all six wires present. Alternatively the plugs are readily available from the likes of CPC/Farnell.
I had a hunt around in a junk box and located a suitable keyboard extender cable. I chopped off the useless end and metered out the pins to identify the appropriate wires. Remember when looking at the plug the pins are swapped left-to-right compared to the diagram which is the socket view.
Well here is the insides of the interface.. and as you can see I completely failed to tidy it up! Not my best work, but I did put it in a new box and I did tape up all those unused wires!
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| The messy internals of the interface |
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| It looks better with the lid on.. |
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| Computer, radio and interface |
It was straight forward setting up WSPR to use a combination of CAT for tuning and the RTS PTT control and soon had some encouraging results, in fact these are some of the spots of my 5W signal on 10m/20m and 30m, I was grinning from ear to ear!
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| 10M Spots |
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| 20M Spots |
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| 30M Spots |
Looking forward to spending some more time experimenting with the data modes.
Show off your project in a clear top tin
I first learnt about these tins from the 4 State QRP Group. They advertised them as “Clear Top Enclosure – An Altoids On Steroids. Do you need an enclosure slightly larger than an Altoids tin? Would you like to see your project after building it, instead of hiding it? If so, this enclosure is for you!”
The rectangular hinged tins are no longer sold by the 4 State QRP Group, but I was able to buy them from Specialty Bottle via a friend of mine in the US (their minimum order for export was too high for me).
My projects from left to right and top to bottom are:
- Component tester (transistors, capacitors, resistors, inductors, equivalent series resistance) from Ebay based on this open source design.
- Direct digital synthesis (DDS) generator that generates RF from 0 to 20 MHz
- Ultimate2 QRSS kit transmitter from G0UPL
- 3.5 MHz Pixie transceiver
- AVR Butterfly Morse keyer from KD1JV
- Softrock Lite 6.2 SDR (Software Defined Receiver) in an enclosure which originally housed a 4.5″ USB flash disk.
Welcome new readers
I was very surprised, shocked even, to be asked to syndicate my postings to the site. Hopefully my posts will be of interest to a wider audience.
I have been a licensed amateur operator for six months currently on the bottom of the UK licence structure, the so called Foundation licence, but am hoping to take the Intermediate licence soon.
The main driving force for wanting to progress is I want to build things, to experiment and learn.
In a natural extension/diversion from my day job I have already been experimenting with the Arduino platform, initially with the intention of developing a High Altitude Balloon tracker but more recently with other radio related projects including a satellite tracker and using it in conjunction with DDS modules for WSPR/QRSS purposes. I have just built a dedicated Ultimate 3 QRSS kit from Hans Summers (G0UPL)
The DDS module are particularly interesting and I have some tentative plans for an Antenna Analyser and a Power/SWR meter capable of working down in the mW range which I stumbled across on the website of Loftur E. Jónasson - TF3LJ / VE2LJX. This is of particular interested to low power QRP operating. Did I mention that I have joined the GQRP Club?
Progressing from a couple of Baofeng VHF/UHF handhelds (which I hardly use) to a proper rig last month with the purchase of a Yaesu FT-857D I have been dipping my toe into the frightening world of operating!
It is common for new amateurs to be "Mike Shy" and I admit to suffering terribly. Not being the most outgoing or confident person being confronted by a barrage of rapid fire abbreviations, codes and etiquette it took a while before I had the courage to key up.
I plucked up the courage to have an attempt at some of the RSGB UKAC VHF evening contests and after gaining a bit of confidence I ventured properly onto the HF bands this weekend making a few simple signal report QSOs.
I should like to thank all those who have been patient with me as I fumble along.
Because of the shyness the use of data 'digital' modes is a strong draw since it uses computers and you don't have to talk! I am salvaged some suitable connectors to build a new computer data interface for the FT-857D, I built one several years ago but it got slightly cannibalised when experimenting with an ARPS gateway.
I can afford a commercial interface but why should I pay over the odds for something I can easily build myself? The desire to homebrew isn't just driven by cost, but lets be frank this can be an expensive hobby! Nothing gives more satisfaction when something you built works.. and yes they may be famous last words.
Ultimate3 QRSS Beacon kit built!
My current licence restrictions prevent me using anything home-brew for transmitting except for commercial kits. So I ordered an Ultimate3 QRSS beacon kit from Hans Summers (G0UPL) thinking that it would be okay. I subsequently learned that any commercially available kit must satisfy IR 2028 which is all a bit vague and unclear but sadly I don't believe this particular kit does.
All was not lost, building this kit should more than satisfy one of the practical assessments of the intermediate examination, which will get me around this problem.
The Ultimate3 kit is extremely popular and so I had to wait a little for delivery and it arrived on Friday. After the last few weekends of non-radio activities I had planned to get my antennas backup and do some proper operating. Like many people I had been forced to take everything down due to the barrage of storms and high winds the UK has been experiencing recently.
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| A tidy workbench |
Saturday saw no let up in the wind, so I decided to spend a few hours building the kit instead.
The instructions were extremely clear and straight forward and soon had it built up, though it is high time I invested in new soldering station. I have a basic Antex 25W iron. I cannot remember exactly when I brought it but it is well over 10 years ago. It was more than adequate to build this kit and for soldering connectors but I could do with something adjustable and more comfortable.
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| Taking shape |
I also made the mistake of not scraping the enamel off the toroid wire and tried the heat it and bubble it off method, except I think my iron just isn't hot enough so ended up using a piece of wire wool to remove the enamel.
Lessons learned I soon had the other three toroids correctly wound and wire prepared for the low-pass filter board.
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| Close up of the LPF |
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| All built |
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| It works! |
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| Setting it up |
Pressing the button I occasionally got some random characters and a flashing cursor! I de-soldered the GPS and still nothing. I suspected the display was faulty but trying it on the HAB prototype board confirmed it was okay. I checked the display connector continuity and everything appeared okay.
Out with the oscilloscope I started probing, everything checked out. Crystal was oscillating and data pulses on the display control lines. Then I checked the supply pin on the display and it was only reading 4.1V, this under-voltage would explain the odd display behaviour.
PSU output was 5V, micro-controller was 5V, DDS module had 5V. All very puzzling till I removed the DDS module and spotted a discoloured track on the PCB, touching it with a screwdriver and the lacquer fell away revealing a tell tale scorch mark, somehow I had made a nice resistor!
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| Burnt track to right of micro-controller |
What caused it? Checking the de-soldered GPS connecting wire I spotted a stray single strand of wire on the ground wire. I suspect this must have shorted to the adjacent 5V line and since I was using a nice beefy ex-PC PSU as a bench supply it had popped the track without the hint of a flicker. The GPS has been rewired properly and is working nicely, now to connect a dummy load and experiment some more.
Sunday was a lovely day, wind dropped so antennas have been put back up and I took the opportunity to tidy up the installation a bit. I also dug out an old fibreglass pole to put the M0CVO HW-20HP back up. I didn't get to do any operating in the end as by the time I had done this and made up a couple of decent patch leads it was time for roast beef and all the trimmings and an evening in front of the TV.
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| The HW-20HP back up |
The simplest possible AM transmitter
Here’s a design for a 1 MHz amplitude modulated (AM) transmitter. I’ve been looking a while for something like this, a simple short range AM transmitter for the medium wave band, as I needed something for demonstration of my collection of old radios.
The result is the AM transmitter shown here in an Altoids tin on top of a Radionette Kurér radio. This is a portable tube radio from the 1950’s. Several hundred thousands were produced, and it was exported from Norway to 60 countries. It is still popular among collectors.
The transmitter is as simple as it gets. The heart of it is a 1 MHz crystal oscillator in a can. Its 5 Volt power is modulated via an audio transformer, one taken from the output of a transistor amplifier (primary 147 ohms – secondary 3 ohms). I drive the modulator from my cell phone into the low resistance side of the transformer and get good audio when the phone’s volume is set to maximum.
The design was inspired by one from Instructables, but mine also has a 78L05 5 Volt voltage regulator and a red LED in series with the power supply. It indicates that the battery is plugged in. In total the transmitter draws 4.4 mA at 9 Volts. The input power to the oscillator is less than 5 Volts * 4.4 mA or in the order of 20 mW. The power output is just a fraction of that. I have tested it with a 1.5 m wire hanging down behind the built-in frame antenna in the back of the radio with good results.
This is really just a modulated marker transmitter as I have briefly described on this blog before, and the square wave will have harmonics of 1 MHz over the entire short wave band. Some of these frequencies may propagate really well, so if used with a longer antenna, it should really have an output low pass filter to prevent that.
I’m not totally happy with this design, despite its simplicity, though. If I could, I would rather like to transmit in the long wave band at 216 kHz. This is the old frequency of the Oslo transmitter which ceased operation in 1995. As a member of the Norwegian Radio Historical Society, I am allowed to use that frequency with a transmitter input of 0.5 W for demonstration purposes.
For other frequencies, one simple alternative is a standard canned oscillator at 1.288 MHz. I also believe some of the Silicon Labs oscillators can be used in order to get an adjustable frequency, but I haven’t tried that myself.
But until I find a suitable frequency source at 216 kHz, I’ll stay with the 1 MHz alternative at a mere 20 mW. It is in line with the best principles of KISS (keep it simple stupid) or with Occam’s principle : “It is vain to do with more what can be done with less“, i.e. the QRP philosophy.
The advantage of the single-lever paddle
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| My single-lever PCB keyer KI6SN/NB6M-style |
It may seem like a bad idea to downgrade from a dual-lever paddle and iambic keyer to a single-lever paddle. It must be inefficient since each individual dash and dot has to be generated by a right or left movement of the paddle. Despite this, many of the champions in the High Speed Telegraphy competitions use single-lever paddles, often home-made ones. How can that be?
K7QO, Chuck Adams, wrote “Using an Iambic Paddle” and compared the dual-lever paddle with the single-lever with respect to number of movements. If all 26 letters of the English alphabet and the numbers from 0 to 9 are sent, the single-lever paddle requires 73 strokes while a dual-lever and an iambic keyer requires 65. This is 11% less.
But when N1FN, Marshall G. Emm, wrote “Iambic Keying – Debunking the Myth” he analyzed the 7 letters that are faster to send with an iambic keyer – C, F, K, L, Y, Q, and R – and found that only one of them, the L, is among the 12 most frequent ones in English. He illustrated it this way:
Guess what’t wrong with this figure? He didn’t see the R and forgot that it is also among the most frequent letters!
So two of the faster letters are among the most frequent ones, not just one. I guess that N1FN’s estimate of only a 5% increase in efficiency when letter frequencies are taken into account is a bit too small then. In addition comes the fact that CQ, and all Q-codes use letters that are more efficient with the iambic keyer, so in radio amateur use the efficiency advantage of the iambic keyer is probably even more than 11%.
So this doesn’t explain the fact that many of the high speed champions do so well on single-lever paddles. My experience is based on learning to send Morse code at the age of 47. Somehow I feel that this was 20-30 years too late in order to master all the finer movements involved in iambic keying.
The issue must be tolerance to errors, not just efficiency. The high-speed champions value that and increasingly the producers of morse paddles are including single-lever paddles in their assortment.
A single-lever paddle is also easy to make yourself, much easier than a dual-lever paddle. I made one from printed circuit board based on the paddles of KI6SN. That design was a modified version of the miniature single-lever paddle of NB6M. I made it just to try the concept before I move on and eventually buy one. But the homemade one was surprisingly good to use, so I might stay with it for a while. The nice thing is that the single-lever couldn’t care less if your keyer is set up for iambic A og B. Neither if the keyer does the ultimatic mode which I promoted recently (Is the ultimatic Morse keyer really that efficient?)
There should be freedom in choice of paddle, so everyone should find what suits best regardless of what is the current fashion or what it is that is considered to be ‘best’. So whether you are a newcomer who struggle with learning to send properly with an iambic keyer, or an oldtimer who keep using the dual-lever as if it is a single-lever paddle, feel free to change to a single-lever paddle. I am sure you will notice a reduced error rate.
The question for me is what “real” single-lever key I should upgrade to, they all look attractive: Begali, Bencher, Bushwhacker, Hi-Mound, Kent, K8RA, N3ZN, Scheunemann, UR5CDX, Vibroplex, …
