|
My build history
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.
Like many other constructors my first concern was producing the
bare PCBs. 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 its performance as good as I can get it. (I have subsequently upgraded
the DDS chip to a AD9951)
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 its 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 PCBs.
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 ICs.
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.
The final result! This picture was taken in May 2007 and
shows the finished transceiver along with a Drake L7 Amplifier and home brew balanced ATU. The power meter sitting on top
of Picastar was a club project I designed for the Stafford & Districts Amateur Radio Society. www.sadars.net
|
