13cm Project
I came across some older equipment and decided to see if it could be converted into a usable transverter for the 13 cm band. The unit is a DB6NT 2.3 GHz Transverter MK2. Since 2320 MHz is no longer available for normal amateur use in Sweden, some modification was needed.
The original 120.889 MHz crystal and the crystal heater were removed. The external OCXO input can then be used instead. For 2.4 GHz operation, a 125.333333 MHz signal at 0 dBm is required. After multiplication, this gives a 2256 MHz LO signal, which is fed to the mixer. One NEOSID filter also has to be replaced: F3, originally 2176 MHz, should be changed to a 2450 filter.
One possible LO source is an RFzero, since it is GPS-locked and easy to use. However, it is based on the Si5351A, which is a programmable CMOS clock generator rather than a dedicated low phase-noise microwave LO source.
The Si5351A can perform well enough for many HF and VHF applications, but its phase noise becomes more critical when the signal is multiplied up to microwave frequencies. In this case, 125.333333 MHz is multiplied by 18 to produce 2256 MHz. Phase noise increases by 20 × log10(N), so multiplication by 18 worsens the phase noise by about 25 dB.
RFzero has an RF output network and transformer after the Si5351A, so it is better than a bare Si5351 module. However, the Si5351A phase noise still remains the limiting factor, especially after frequency multiplication. Therefore, RFzero is acceptable for testing and simple operation, but it may not be ideal as a permanent LO for a high-performance microwave transverter.
Since I already had an RFzero available, I decided to use it anyway. Everything is built into a small 120 × 200 mm enclosure, with the GPS antenna mounted on top. It will be interesting to see if there is any activity during NAC. I will also try to use it for satellite work.
Hardware is completed and working. No antenna is installed yet.
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