Using the Ultimate3

I have dusted off the Ultimate3 QRSS beacon kit that I built earlier in the year while a foundation licensee. Having progressed to a intermediate licence I can now operate something I’ve constructed.

Until now it has been attached it to a dummy load with the FUNCube Dongle Pro+ SDR in close proximity as a receiver for experimental purposes.

One unresolved issue was it being consistently off frequency. The DDS modules used are prone to temperature fluctuations and component variances so the Ultimate 3 has the option of using a GPS module to provide both an accurate time source and an accurate 1PPS input which can be used to self calibrate. Except in my case it had proved to be unreliable.

I am using one of the inexpensive GY-GPS6MV2 modules containing the U-Blox chipset I posted about previously with the additional tap off to provide the 1PPS TTL signal.

Initially the GPS module was connected in close proximity to the Ultimate3 but struggled to maintain lock probably due to interference from the DDS module. Even when lock was achieved the calibration never seemed to work. I posted a question on the yahoo support group and from the answers I verified the calibration setting were correct so the only likely culprit was the quality of the 1PPS signal.

The serial NMEA sentences and the 1PPS signal from the GPS are likely to be required in other planned projects, such as an ‘shack clock’ and a GPS disciplined frequency standard. So I decided to put the GPS module  into a waterproof housing that can fitted on the shack roof in clear view of the sky and away from any potential interference. A multi-cored cable supplies power and the TTL RX/1PPS signals being fed back to the bench.

Sourcing an inexpensive weatherproof enclosure (£2) and waterproof cable gland were straightforward enough. I mounted the GPS module on a piece of strip board and replaced the on board LED with one mounted in the enclosure so I easily determine if the GPS had achieved lock, since it only flashes when it has. The LED is sealed with epoxy resin. It should be noted that the outputs of the U-BLOX chip are only rated at 10mA so bear it mind when selecting an LED and calculating the current limiting resistor. The connecting cable is some surplus unscreened alarm cable fitted with a couple of ferrite clamps.

The GPS now has no trouble achieving lock and quickly sets the Ultimate3 clock. Researching the 1PPS problem I hadn’t come up with anything definite, as the signal looked okay on the oscilloscope. But I decided to fit a 10K resistor pull up resistor between the 1PPS output and the 3.3V supply on the GPS module. If this actually made the difference I have no idea but the Ulimate3 now successfully calibrates the DDS using the GPS.

At the moment I have configured the beacon to run WSPR and I have been spotted by other operators. Initially I wasn’t getting much RF out of the device and it turned out to be a combination of poor connection caused by me not removing the enamel properly on a toroid winding and an iffy antenna connector. Both have been corrected and now get a measurable deflection on the SWR/Power meter. With the additional of a second power amplifier FET it is around 200-250mW.

I purchased the Ultimate3 with a low pass filter for the 40M band and while I have had some European spots the results have been a little disappointing. 40M has turned out to be almost unusable at my QTH due to QRN/M so not sure if that is having an effect, also the antenna I have isn’t naturally resonant on 40M so is going through a tuner which will certainly be introducing some losses, without the tuner the FETs get very warm!

With this in mind I have purchased some additional LPFs for the 30M and 20M bands and the LPF relay switching board for the Ultimate 3 so can try/run multiple bands.

Cheap GPS module

Several of the Arduino projects I have been experimenting with have used a GPS module to provide accurate time and/or location information and in the case of the QRSS/WSRP QRP beacon a highly accurate GPS derived 1 second pulse is used for frequency calibration. A number of people have enquired about the GPS module I am using.

Most GPS devices have a limit on the altitude they work at, normally 60,000 feet or less. This is a legacy of the now defunct CoCom (Coordinating Committee for Multilateral Export Controls) restrictions. For my HAB project this restriction needs to be disabled and the GPS must be switched into ‘flight mode’ In the HAB community the favoured devices are made by U-BLOX

Therefore when I was sourcing a GPS I had search specifically for a inexpensive device using a U-BLOX.

The GY-GPS6MV2 as supplied

I soon found something called a GY-GPS6MV2, it appears to be a generic design and is readily available on eBay from suppliers in China, Hong Kong and Singapore and can be purchased at the moment for around than £10 (approx $15) including postage!

It is also available from domestic suppliers but often at a much more inflated price, but you don’t have to wait several weeks for them to be delivered.

There are many other GPS modules available but this module seems to be one of the cheapest available. it is often listed as a NEO6MV2 GPS Module Aircraft Flight Controller.

The module consists of a small PCB 25mm x 35 mm size with a separate ceramic antenna connected by a small lead which is 25mm x 25mm in size. The Antenna is quite heavy and isn’t suited to Pico HAB payloads but for other uses is more than satisfactory.

On the board is a small button-cell battery to provide backup to the GPS chip and a small EEPROM connected to the GPS chip which I believe can store configuration(s). I haven’t used it myself just using the module in it’s default set up at the moment. For a schematic click here

The board has four connectors VCC, GND, TX (Transmit) and RX (Receive) and can be powered by the 5V supply on Arduino boards since it has a small regulator to provide the 3.3V needed. 

In most projects all that is required is data out of the GPS. The GPS TX (data out) being connected directly to the microcontrollers RX (data in) The (0V and 3.3V) level shift of the signal is compatible with the TTL input of the microcontroller.

The GPS by default will start up and output standard NMEA sentences at 9600 Baud, until GPS position lock is achieved the NMEA sentences won’t have a long/lat location. The module also has an LED which will start flashing once a lock is achieved.

There is no direct connection for the highly accurate 1PPS (pulse per second) signal that can be used for frequency calibration, but the flashing LED is driven by pin 3 of the GPS module which is the 1PPS (pulse per second) signal required.

The 1PSS signal, like the TX is either 0V and 3.3V, in order to use it a small lead will need to be soldered onto the board, either directly onto Pin3 of the GPS chip, or alternatively on to the small current limiting resistor used by the LED, as indicated below.

Showing the GPS 1pps points

FUNCube Decode Issues

I had a pleasant surprise last week at the AGM/Prize giving evening of the South Kestevan Amateur Radio Society (SKARS) being awarded the Most Promising Newcomer!

I also had a small write up in Tim Kirby’s (G4VXE) VHF/UHF section of the February issue of Practical Wireless about my I-Cube1 reception which I have mentioned on here before.

I haven’t progressed very far with my Arduino projects. There has been a set back in the plans to build and use an Ultimate3 QRSS kit. I had incorrectly assumed as it was a kit being sold commercially that it would satisfy my foundation conditions. However I have been advised that Foundation license holders may use radio equipment constructed using commercially available kits which satisfy IR 2028 which is all a bit vague and woolly, but I don’t believe this particular kit does.

There is a simple solution, I will just have to take my intermediate assessment and exam at the first opportunity!

I have been doing a little WSPR spotting, getting some nice spots.

Over the Christmas/New Year period I have neglected the FUNCube-1(A073) satellite and was slipping down the telemetry upload rankings, sad I know!

Now I have got back the upstairs ‘shack’ I set up my original FUNCube Dongle on the laptop running the dashboard application continually to capture/decode the telemetry using the loft mounted discone. I took the opportunity to upgrade to the latest version 8.14 of the dashboard software, however something was amiss when checking the statistics I was only adding the odd frame here and there, sometimes not making a single decode during the high power daylight passes.

I switched back over to the newer FUNCube Dongle PRO+ running my main PC, which I had also updated to the version 8.14 dashboard and saw the same behaviour, rather than getting daylight decodes of 30+ frames I was just getting the odd 1 or 2.

My first thought it was an antenna or interference issue, but checking the SDR waterfall the signal is still very strong with little QRM. Suspecting a software issue introduced by the update I checked the FUNCube forum and found a thread which appeared to confirm my suspicions.

I have a number of discussions on twitter with various people including David Johnson (G4DPZ)  an AMSAT-UK Committee Member and one of the developers of the FUNcube ground segment. David kindly performed an analysis of one of the passes yesterday where I managed just 2 frames, and from the results it does appear to be an issue at this end, rather than issue with the spacecraft.

I have uninstalled v8.14 and put back on an earlier version of the dashboard (v8.09) and thanks to a windows update last night have also performed a full reboot!

There was a good pass this morning at 62 degrees maximum elevation (to the east), followed by a lower pass at 22 degrees elevation (to the west so not so good) and it seems things have improved managing 68 and 17 frames respectively. So could this be an issue with the latest dashboard?

If anyone has suffered similar performance fall-off, or indeed not suffered any issues then please add some feedback to the FUNCube forum.

My copy of Radcom arrived but didn’t have much time to read it..

The culprit! 😉

Arduino, WSPR and AD9850 DDS experiments

Happy New Year!

Christmas is thankfully behind us so I can get back to what I enjoy doing once I have reorganised my workshop.

As you know I am currently developing a potential High Altitude Balloon (HAB) project and have been experimenting with the Arduino microprocessor platform and have constructed a basic prototype.

With the arrival of the GPS module(s) I have had it successfully working and even took it out for a test walk in the local area, receiving the data and uploading it to the UKHAS habitat system.

NERD-1 and Boris have just been for a walk, first time NERD-1 has had proper GPS and running on batteries. #hab
— Andrew Garratt M6GTG (@nerdsville) November 23, 2013

This project has revitalised my interest in ‘hobby electronics’ and I have ideas for a number of other Arduino based projects and have been splashing out on components from eBay. Just before Christmas I purchased an Arduino Mega board, this has more I/O pins than the current Uno and specifically some extra hardware serial ports.

Do any internet search for Arduino based amateur radio projects and it will results in numerous mentions of projects using ultra cheap DDS modules based on the Analog Devices AD9850/AD9851 chipsets.

DDS means Direct digital synthesiser and is a type of frequency generation which can be used for creating arbitrary waveforms from a single, fixed-frequency reference clock. Read the Wikipedia page for more details.

In a nutshell the AD9850 is a chip that under microprocessor control can produce a sinusoidal wave from about 1hz to 40mhz. In other words it is an accurate microprocessor controlled VFO (Variable Frequency Oscillator) or signal generator.

VFOs are the main building blocks of radio receivers and transmitters, so not surprisingly a lot of projects have utilised these modules, rather than the traditional means. Intrigued I ordered a couple of these modules for the pricey sum of £3.50 each!

Using information on George Smart’s (M1GEO) website and Simon Kennedy’s (G0FCU) blog  I quickly had a simple WSPR beacon running!

Experimenting with Arduino and AD9850 DDS and GPS unit..
— Andrew Garratt M6GTG (@nerdsville) December 29, 2013

The Arduino uses the GPS module borrowed from NERD-1 for accurate time and then controls the output of the AD9850 DDS to generate the WSPR signal.

Before anyone panics I know at the moment I only hold a Foundation Amateur Licence so the construction of homebrew transmitters isn’t allowed. This ‘beacon’ has no power amplifier and the antenna consisted of an inch or so of wire on the DDS output. I was able to verify the operation using my SDR receiver in the same room.

Construction of commercial kits is allowed under my licence so I have ordered a Ultimate3 QRSS kit from Hans Summers for the pricely sum of £17.50! This uses the same DDS module and same microcontroller as the Arduino.

In the meantime there is also more information and ideas on Eugenr Marcus’ (W3PM) webpage about the use of these DDS modules, including making frequency reference sources and calibration using the GPS module.

My new year resolution is to get my Intermediate Licence as soon as possible..  but it has been great to get down to some proper experimenting…

Cannot beat a picture of an oscilloscope to look techy.. my DDS experiments continue…
— Andrew Garratt M6GTG (@nerdsville) January 1, 2014