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September 2023 Long time between drinks, but not much happening on the tech front at the moment. Added another couple of rants to the rant page.

January 2023 Updated the AD9833 VFO code to use a 12F1840.

December 2022 Added rant about todays useless (internet) search engines.

November 2022 NEW Project An AD9833 Based Simple VFO. FT101ZD VFO project updated.

October 2022 A replacement internal DDS VFO for FT101Z/ZD rigs. Because the worlds postage system has gone totally bonkers and it is not possible to send a small pcb anywhere except at extreme cost, I am slowly making available the option to purchase pcb's from Pcbway. First up is the Simple DDS VFO 2017 project pcb. Others will be added over time. Noise Canceller kits available again- see Noise Canceller page.

Privacy Policy uploaded. GPDR and all that stuff In accordance with various bits of legislation around the world, either currently in force, about to come into force or proposed, you will now find that annoying "We use cookies" notice at the top of this website. The full Privacy Policy is available at the Privacy Policy link in the footer at the bottom of the page. (If you don't know what GPDR is, Google it. Real scary shit for ANYBODY with a web presence.)

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. Please see notes at the bottom re software and using the Simple DDS VFO project for this mod.

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.

Notes

Normally I have been emailing the PIC software for this mod to those requesting it. However, despite the schematic at the top of this page, some confusion has ensued when I mention you can use the Simple VFO pcb to build this mod. This confusion arises because the software was written for the older Simple VFO project and uses different connections for the encoder and switch. I have updated the software so that it is now directly compatible with the updated Simple DDS VFO project schematic and pcb, i.e. - you follow the Simple DDS VFO 2017 update project details and use the software posted at the bottom of that page for the PM5326 mod. Also, the pcb may be slightly too wide depending on how you fit it, so you may need to shave a couple of mm off two of the opposite sides or build it on a piece of strip board as in Stefans build above.

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