Programming AD9850 & AD9851 DDS

🔘I previously posted about using the AD9850 & AD9851 DDS chip evaluation modules in 2018 and again in 2023. To recap, before these devices can be used as a signal source they require programming with 5 bytes of data related to frequency and phase, which form a 'tuning word'.

A µ-controller and a smart phone🖁 App could be used to upload 🠝 the tuning word ( see 16 July 2023 ), or a USB dongle and pc💻 interface software, ( see 4 January 2018 ).  As I have recently updated that software it would now be a good time to give a description.

My dedicated pc 💻 software, called "DdsModTerm", is the user interface which I started developing in about 2015. Since then I have updated it 15 times; the latest revision appearing this month.

DdsModTerm user window

The clock 🕰 frequency and the required output frequency ∿ & phase are entered either manually or by recall from memory. By clicking 'Confirm' the software generates the 5 configuration bytes required from the user input data. In the example in the image above the output frequency is 137700Hz* & bytes hex 00C88AC604. The pc 💻 is connected to the serial data interface of the DDS module via a COM port and a USB-SPI protocol converter dongle.

(L) USB-SPI dongle (R) AD9851 DDS module on adaptor

Clicking 'Update DDS' then uploads the bytes to the registers of the DDS chip using SPI and a voltage having an amplitude 1V peak to peak at the programmed frequency ∿ is then present on the output.

DDS output signal, 1Vp-p, 137.7KHz

Other features of the software include up/down step 🪜tuning, slider tuning control, view of 255 byte eeprom addresses E0-FF, 3 memories for storing frequency, saving custom clock🕓, alias frequencies calculated, and general purpose output ( GPO ) toggling on/off.

The dongle and software are available from me. Post a comment to receive more information. Note that both AD9850 & AD9851 DDS devices are supported.🔘

( Click on images to enlarge detail. )

* 137.7KHz is a calling frequency on the radio amateur 2190m long-wave band, 135.7-137.8KHz.

SPI = Serial Peripheral Interface, 3-wire bus.

AD9850, AD9851 : 🔗Analog Devices Inc. parts, 32-bit CMOS Direct Digital Synthesiser (DDS) chips.

My low power LF radio signal is received in Germany

🔘 Almost 11 years 🗓 have passed since I last used my low-power transmitter power amplifier ( see 08.05.2013 ) based on the TDA2030 class AB audio 🔉 amplifier i.c. ( see 22.02.2013 ). Since then several data 💾 transmission modes, e.g., FST4W,  have become popular among radio amateurs who are active transmitting on the LF 2190m/136KHz 〰 ( longwave ) 📻 band. I also have high power transmitting equipment for that frequency band. However I wanted to conduct a simple test by transmitting a very low power beacon signal using FST4W to determine at what distance it might be received.

My setup for the test was the phasing exciter ( see 02.11.2017 ) as the signal source driving the low power amplifier. The antenna 🗼 was my usual one for the 2190m band; a 47m  long x 13.5m tall base and end-loaded inverted 'L' ( Ꞁ ) ;  see 19.02.2010 et al.  The transmit frequency ∿ was 136.13KHz, transmitter output power only 3.5 watts, ( similar to the power consumption of a small LED lamp 💡 ), and beacon transmission, consisting of my callsign, location and power level, sent at 5 minute intervals.

Equipment used for the low power test on 2190m band

I began sending beacon transmissions during the evening of  21.01.2024. Previously, during the tests on 8 May 2013, ( albeit using a different mode ), the reception distance had been only 17 kms. I was doubtful if anyone beyond that range would receive my signal. So I was very surprised, when, at 2120 utc 🕤, a reception report was posted 📮 on wspr rocks  ☁ that my beacon signal had been received 📶  near Chemnitz in Germany, at a distance of 582 kms. Incredible and amazing 😀 !

 

LF = Low Frequency.

135.7-137.8KHz ( 2190m band ) is the lowest frequency band allocated to radio amateurs.   

3-D Printed Holders, Clips & Formers

🔘I've designed and printed a selection of parts some of which are intended for use in the transmitter power amplifier I am currently building for the 472KHz∿/630m wavelength radio 📻 band. So far I've made holders for some large foil capacitors, mounting clips for toroidal cores and coil formers ➿. Both PETG (grey) & PLA (blue or yellow) plastic filaments were used

Toroidal core clips, coil formers & capacitor holders

The toroidal core clip is for a T150-26 core which has an external diameter of 1.5". The coil fomers are ribbed for a close-spaced winding with 1.6mm diameter enameled copper wire. One side of the capacitor holder is open so that the value and voltage rating are visible. Where required, the parts can be panel-mounted using M2.5 nuts and bolts 🔩.

One benefit is that all dimensions and the style can be customised for a 'tailor-made' solution. I am no longer restricted to using PVC tube or pipe fixings for example, in only a few sizes bought from the shop.