VK5TM


News, Updates and Other Minutiae

I have, for quite a while, provided modified versions of the code for my projects free of charge. However, the cost of webhosting for this site has tripled in the last couple of years and the little I make out of the pcbs I sell goes nowhere near covering this cost.

As of October 2017, I will be asking for a donation in exchange for providing custom modified code for my projects to help keep this site available.

November 2017

A modification plus software to allow the Simple DDS VFO to be re-calibrated as often as you want without having to re-program the PIC has been added to the Simple DDS VFO page. Simple DDS VFO bug problem fixed. Code uploaded to webpage as version 'c'.

October 2017

There is a bug in the Simple DDS VFO code. See Simple DDS VFO page for the problem and updated code. Included an add-on for the Simple VFO project to indicate which step size has been selected. Simple DDS VFO project updated and software file uploaded. The pushbutton on the encoder is used to change step size (step sizes 10Hz, 1kHz and 10kHz).

September 2017

Noise Canceller kits now available.

July 2017

Updated both the DDS Xtal Substitute and DDS Xtal Substitute Mark 2 projects into one project. The original webpages are available to download as PDF's.

May 2017

New project added - my version of the X-Phase noise canceller. PCB available and a kit of parts to follow soon

This is a mod using a DDS module to repair a drifty Philips PM 5326 RF generator. Stefan has done a marvellous job, not only of the mod, but also in providing the write-up and pictures presented below.

Philips PM 5326 RF generator DDS mod

Starting point for this project was a constant frequency drift of my Philips PM 5326 RF generator. Even after hours of warming up it doesn't come to a full stop. Furthermore tuning to a specific frequency was a touchy thing because no fine tuning was possible with the build in tuning capacitor. The RF section of the generator is based on the PLL principle. The reference frequency is generated by a VFO, comprising a simple transistor LC oscillator. This reference frequency determines the frequency of a VCO as the active element of the generator. It generates the RF frequency between 100 KHz and 125 MHz via several range coils and divider chains for the phase comparator. Every slight deviation in frequency of the VFO results in a relatively higher deviation of the VCO and therefore of the RF frequency. So, the weak point was the VFO, which was state of the art in the late 70's, early 80's. It was as good as was possible in those days. So, I decided to replace the "analog" VFO with a modern DDS-VFO. An additional requirement was, that the generator shoud remain in its original state. I never wanted to drill any holes to the case for adding any switches etc. The modification should not be seen from outside and it should be reversible. Browsing through the internet I found the "Simple DDS VFO" from Terry (VK5TM) which fits all my needs, except for the step size switch. But Terry thankfully updated the software for the microcontroller, so that the step size could be toggled with a push switch on a suitable encoder. The following pictures show how the project was realised: Pic_00: The circuit diagram, modified for my project. Power supply was altered and 100n cap fitted across the step switch. dds modified schematic Pic_01 + Pic_02: The DDS-VFO circuit build on a Veroboard. DDS-VFO circuit DDS-VFO circuit Pic_03 + Pic_04: Aluminium die-cast case, ready to mount. Aluminium die-cast case Aluminium die-cast case Pic_05 + Pic_06: A look into the Philips PM5326 RF Generator. You can see the RF-section opened with the VCO (0,1-125 MHz) and the VFO (498-1255 KHz) parts. On the right side the tuning capacitor for the VFO. It has to be removed. RF-section RF-section Pic_07: The tuning capacitor removed. A lot of work to do that. The side panel has to be removed as well as the front plate of the generator. tuning capacitor removed Pic_08: The empty space where the case for the DDS-VFO will be installed. space for DDS Pic_09 - Pic_11: The rotary encoder all ready in place with a new bracket. rotary encoder rotary encoder rotary encoder Pic_12 + Pic_13: The generator's front and side panel taken apart. front and side front and side Pic_14 + Pic_15: The new die-cast case in place and the side panel mounted. new die-cast case new die-cast case Pic_16: All the knobs fitted on the front plate. knobs fitted on the front plate Pic_17: The circuit built into the aluminium case. circuit built in the aluminium case Pic_18 + Pic_19 : The microcontroller 12F629 and the new wiring harness installed. 12F629 and the new wiring harness 12F629 and the new wiring harness Pic_20: Finally the AD9850 DDS-module on top of the veroboard. AD9850 DDS-module Pic_21 + Pic_22: Alignment of the DDS-VFO to the center frequency 876 KHz with my Racal Dana 1991 frequency counter (with OCXO option). Frequency is spot on after 30 min. warm up time). Alignment of the DDS-VFO Alignment of the DDS-VFO Pic_23: Fit the cover and tighten the screws of the DDS-VFO case. Fit the DDS cover Pic_24: The same for the RF section of the generator. Fit the RF cover Pic_25: Wire harness of the encoder instead of the tuning capacitor's shaft. encoder Pic_26: The generator completely assembled and in its case. No optical changes visible. But the frequency setting knob now has a push button (built within the encoder). generator assembled Pic_27 + Pic_28: The generator turned on and tuned to the FM and AM IF frequencies 10,7 MHz and 455 KHz repectively. 10,7 MHz 455 KHz Frequencies now are absolutely stable and precise (tolerances of only a few hertz). A huge improvement to the former state ! The modification was worth all the efforts. I am very grateful to Terry for all his support and help making this project a great success.