Pic A Star

G4NVH Pic-A-Star Project

Welcome to G4NVH.net!

Here you will find a brief record of my construction of the excellent Software Transmitter And Receiver designed by Peter Rhodes G3XJP. The transceiver design has been considerably developed over the past few years with numerous contributions from members of the Pic-A-Star group, without whose help I would never have got this far. I would especially like to thank Ian GW8OGI who purchased many of the components for me. And of course Peter G3XJP for the design.

One Case - Three Radios. Pic-A-Star has been a long time in the making for me!!

	Like many other constructors my first concern was producing the bare PCB's. The recommended way of producing these was to use an Iron-on process using artwork transferred onto laser film. Although I did have to touch up some areas, and in some cases remove a short between adjacent tracks, I found this process entirely repeatable and managed a 100% success rate.

	After many years of using the laborious indelible pen and a complete disaster with the Paint & Scratch method, this was a revelation in terms of the speed and quality that can be achieved. I found three key variables for producing consistent results. Firstly, absolute cleanliness. Secondly, the time/temp ratio of the Ironing process. And thirdly, keeping the boards in the etchant only just long enough to remove the exposed copper.

	First up was the DDS assembly. I used the G6AK boards which included the Pic-Adaptor components. It uses the AD9851 DDS chip with a 160Mhz reference oscillator. After many hours spent in front of the Spectrum Analyser I am happy that I have got it's performance as good as I can get it .

	I originally had plans to build the rig into an old Kenwood TS930S carcass. Included in this picture is the DSP/IF assembly, DDS, Key Pad and the old 930 PSU and Final Amplifier. This approach was soon abandoned in favour of a much smaller unit. However, I did decide to use the old 'S' meter and display Perspex in a similar fashion to Bob 5B4AGN (www.5B4AGN.net). Also, the old rig donated a very nice 8.83MHz 8 pole Xtal filter which is now mounted on the IF board.

	This picture shows the first On-Air trial of the basic transceiver. The DSP monitor indicates the status of many of the stages in the transceiver. The thrill of tuning into the first QSO, and hearing the lovely audio emanating from the dual Hi/Fi speakers was quite amazing. I decided to use the TDA2005 20W Audio amplifier and this has worked out very nicely. The rig was in a very raw state here. No front end filtering, calibration or any other setting up. Still, a great feeling of accomplishment.

	Now it's beginning to look like a real transceiver. The case I've used was originally double the height shown here. Everything, including the handles and side panels, had to be cut in half to produce a unit that matched the proportions of the rest of the transceiver. This picture shows the trial fitting of the front panel components, all held in place by masking tape and gravity.

	This picture shows the status of the screening as of the 17th May 2006. I have easily spent as much time on the mechanical layout and the screening as I have on building the PCB's. Each functional unit is in its own screened compartment and there is only one cable duct, which itself is screened. The space on the left hand side is for the Band Pass Filter unit.

	October 2006. Top View The Band Pass Filter block (LHS) and G6ALU PA have been added. Because of the mechanical constraints, I've used a different interconnection arrangement for the BPF lines.

	Bottom view In this view you can see the AF amplifier mounted between the BPF unit and the IF board.

	BPF Side view To allow easy alignment I drilled holes corresponding to the inductor positions. This method of mounting the BPF unit certainly fitted in with the rest of the overall mechanical layout, but was a real pain to work on when I blew several of the IC's.

	Rear Panel view Here you can see the PA and Low Pass Filter module. As well as the rear screening partition and screened cables, I decided to fit the PA & LPF into a screened compartment. The final installation has a brass cover. The Black module next to the BPF unit and the regulator on the screening partition are components of the LPF relay driver circuit.

	Here is my version of the TX/RX switching unit. Connections are LHS: Aerial In. Linear GND. RHS: Star TX. RX in. GND. +12V.

	Just for interest, here is a picture of my construction bench. Under the microscope is the Magic Roundabout board. The test gear comprises of a Marconi Spectrum Analyser + Tracking Generator, 60Mhz Dig & 20Mhz Analog scopes, RF & Audio signal generators, Frequency counter and PSU's etc. All pretty basic stuff, mostly picked up at rallies for a fraction of the new cost.