Driven by the explosion in portable consumer electronics several chip manufacturers are now offering integrated VCO and PLL chipsets that are capable of generating a programmable frequency across a wide frequency range. There are several designs available using the Silicon Labs Si4133 chipset, and recently Analog Devices have improved the specs on their previous designs and released the ADF4350 and ADF4351 which offers significantly better specs over the Si4133 for small increase in unit price.
- 137MHz to 4400MHz
- Fractional-N synthesizer capable of 1KHz (or better) frequency resolution
- 2 x RF outputs @ 5dBm
- 4 software programmable output levels at 2dB increments
- No Tuning required
- Frequency selection to one of 16 preset values (optional)
- RS232 interface for programing of frequency and power levels
- Frequency offset for TX
- Several reference frequency options:
- Internal OCXO or VCXO reference
- External Reference
- Automatically switch from internal to external frequency reference
Having 2 high level outputs is useful for applications sharing the e same LO module between 2 transverters.
The use of 0603 components and the 32 pin 0.5mm pitch leadless package means construction should only be attempted by those with previous experience in SMD construction.
The PLL chip requires several decoupling capacitors on each of its supply pins in order to achieve is low noise specification. As a result most of the decoupling capacitors are placed on the underside of the board to ensure they are as close to the chip as possible.
Comparing against the Si4133 the results speak for themselves. Note that the VK3XDK Agile PLL (Blue) is 3dB worse than indicated as it was fed using the same 10MHz reference from the spectrum analyser which causes the phase noise to be correlated resulting in a 3dB advantage. For comparison my personal design using a Si4133 with a low noise supply is in green
It can also be seen that the ADF4350 PN (violet) is close to the noise floor of the SA (red) used for the measurement so the results may be slightly better than indicated.
Documentation is available from ADF4350 PLL Manual
A small batch was built in October for several interested Hams in Australia and NZ and based on the interest future batches will be made. Due to specialist equipment required for working with the SMD components this is currently being offered in fully built and tested.
The Blank PCB’s have arrived and I will be starting to build a batch for shipment in early Janurary 2013.
Price is expected to be US$115 + US$15 for international shipment
To register interest please email w.knowles (at) xtra.co.nz and I will advise when the PayPal checkout has been setup on this site.