I have all of the major components I need to finish the tuner project. The roller inductors from Palstar arrived yesterday as did the high current relays that I’m going to use to switch between high / low impedance matching and high / low capacitance ranges. The plan is to assemble the RF deck and prove it operates manually before attaching the stepper motors. Tasks that remain are to sort out the end travel limit switches for the capacitor and inductors and to assemble a relay driver circuit for the PIC micro-controller so that it can switch the relays.
After lengthy delays I’ve finally sourced the components I need to finish the tuner.
Scouring the web for a pair of matching roller inductors has lead me up a number of blind alleys and finally Palstar in the US have come to the rescue. Paul at Palstar was very helpful and I trust his products – I have one of his tuners in the shack here and it is bombproof. I’ve gone for 20uH inductors which should be plenty big enough:
The remaining task is to decide how I lay out the tuner. I can either mount the inductors parallel to one another and use a toothed belt to couple them, or mount them end to end with an insulated coupling between the shafts. Either way I can maintain mechanical symmetry so I might try both to see if there are any advantages. I also need to arrange end of travel limit switches for the rollers which should be straightforward.
Hopefully progress will pick up now and I’ll get the job done before winter is out.
It is a Comet CV05C-500XIH/5, 16 turns 5 – 500pF rated at 3KV. Now I need to couple it to the stepper motor and arrange the end of travel limit switches. This should be fairly straightforward as the cap has a position marker that travels along a slot in the drive mechanism. It looks like the cap originally had a fibre optic end travel sensor and I may use a similar technique as it would keep the switching devices away from the RF in the tuner.
Apologies to any readers for the lack of recent updates. I’ve been busy sourcing components for the tuner RF deck and I’m just about there. I’m waiting for a pair of matched roller inductors to arrive and unfortunately they are about 8 weeks away. I’ve been trying to avoid paying the earth for them and although I’ve found some cheaper possibilities I either wasn’t happy with the condition of them (very well used) or they were not a matched pair. I considered butchering my Palstar balanced tuner (AT1500BAL) but decided against that as I might want it or may sell it to fund this project.
I decided to go with a vacuum variable cap for a number of reasons. Firstly they are available with very low minimum capacitance (5pF) and secondly they are multi-turn devices (the one I’m using is 16 turns minimum to maximum capacitance) giving me an easier time with the stepper motor drive arrangement i.e. no need for a reduction drive. All I need to do now is work out the end travel limit switch arrangements which will probably use a threaded bar with a travelling nut that operates a couple of micro switches.
I’ve been bringing my HPSDR transciever to life over the last few days so the tuner project has paused temporarily. Now I have the HPSDR running I’ll get back to the tuner, but in the mean time I have posted an audio recording of the Mercury HPSDR receiver on my file library page – happy listening.
This weekend I’m working on the metalwork for the front panel. In the pictures below you can see the bare front panel with the holes drilled and the cutout for the LCD display, and another pic with the buttons fitted. I’ve test fitted the LCD display and everything lines up but I’m not quite happy with my handiwork for the LCD cutout – it needs a little more filing. Incidentally, in case you missed this from previous posts the enclosure is an EC2 from Elecraft and it’s pre-painted a dark grey colour – the pictures don’t accurately represent the colour.
I considered buying a hobby milling machine to make the LCD cutout as it would have many more uses, but in the end I decided that it was a luxury I can do without for a while.
I’ve also realised that the encoders that I have will need replacing as the shaft is only 1/8″ diameter and I can’t get large enough knobs to fit that size of shaft. No problem as they will get used on another project.
After some careful measuring I’ve had to adjust the front panel layout. This is primarily due to the depth available behind the front panel in the corners. The Elecraft EC2 enclosure uses some small aluminium blocks that Elecraft call D fasteners to attach the front panel to the body of the enclosure and these reduce the available depth at the corners of the front panel. To accommodate these I’ve had to move the front panel components slightly to the right and reduce the spacing between the LCD display and the other components.
The revised layout is shown below and this has replaced the previous version referenced in other posts. Click on the image for a link to the PDF file that is dimensionally accurate.
I’ve had a productive day and finished the code that sets up the serial communications. I’ve implemented this as a menu only accessible at power up, by holding the mode and Z buttons. The pictures below show all of the screens that the controller uses together with (hopefully) a short video showing the controller in action. Apologies for the slightly blurred pictures but I don’t have a tripod and using the flash on the camera is a non starter.
This is the main screen and shows the controller in automatic mode. In this case the radio frequency is 3.602MHz and the controller is showing that the current L and C values will be used from 3.600MHz to 3.620MHz. Low impedance matching is selected and the capacitor in the balanced L network is switched to the low range position.
This picture shows the controller in manual mode and high impedance matching has been selected.
Here, you can see that the radio frequency (3.810MHz) is outside of the amateur band so the tuner will not attempt to set the L and C values. I’ve done this to keep the number of memories high within the amateur bands so that antennas with a high Q can be used without a problem.
This is the main setup menu with 2 options – set up the serial communications to the radio or clear all of the L and C settings from the tuner (this will usually only be used once on first power up).
This is the communications setup menu, again with 2 options to either change the baud rate or switch between master and slave modes. Slave mode will be useful if you are using a computer with the radio and wan’t to “snoop” the serial port with a Y cable.
Fairly self explanatory, currently supports 4800 or 38400 baud but others could be added.
Screen to select master or slave mode for the serial port.
This is the only setup screen that will ask for confirmation as it cannot be undone. As the tuner may take quite a while to initially set up I thought it wise to get confirmation that the memories really do need clearing.
The video clip below should show the controller in operation:
The noise you can hear in the background of the video clip is the stepper motors moving. I need to start boxing the controller up now and sort out the RF end of the tuner.
Quick update – the master comms mode code is now working but I have an issue to resolve with detecting communication timeouts. I know where the problem lies and hopefully will have it resolved before the weekend. All that’ s left to do then is to provide a power up otion to select the mode and baud rate.
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