The sample program running on a
Micromite LCD BackPack. These
are the only two screens the software
uses: one to enter a specific frequency
for the module to output and another
to display the current frequency.
Spectrum analysis of the ADF4351 module’s output performance at 275MHz (left) and 4.2GHz (right). The RF output
performance over the full range was good, with only a few visible spurs outside the programmed frequency. These
normally correspond to beat frequencies or integer-multiples of the reference and oscillator frequency.
Fig.6: CON1 has been
changed completely on
the newer version of
the ADF4351 module.
Every signal, except
for CLK, is connected
to a different pin
location.When you’re happy with the new
figure, simply touch the OK button and
the module jumps to the new frequen-
cy. The program returns to the main
screen, displaying the new frequency.
So for those who would like to team
up the module with a Micromite, this
program (Simple ADF4351 driver
program.bas) should get you off to a
good start. Like the Arduino sketch,
it’s available from the Practical Elec-
tronics website.
Performance
I checked the module’s RF output
performance at quite a few different
frequencies, using my Signal Hound
USB-SA44B spectrum analyser, which
was controlled by Signal Hound’s
‘Spike’ software.
The results were quite impressive,
as you can see from the two spectrum
plots. One plot shows the output at
275MHz, with the only significant
spurs visible being at ±50MHz with
an amplitude of –57dBm.
The other plot shows the output at
4.200GHz, with two spurs again visible
but this time both on the low side: one
at 4.150GHz (far left) with an ampli-
tude of about –53dBm and the other
at 4.175GHz with an amplitude of
–61dBm. In both cases, the amplitude
of the main output carrier is very close
to 0dBm. This turned out to be the case
over most of the range, in fact.
The only region where the carrier
level did drop (to around –20dBm) was
in the vicinity of 2.45GHz – perhaps by
design, to minimise interference with
Wi-Fi and Bluetooth systems.
Overall, the ADF4351 frequency
synthesiser module is very impressive,
especially when you consider its fre-
quency range and price.
It could even be used to make your
own VHF/UHF signal and sweep gen-
erator, teamed up with a Micromite and
a 4GHz digital attenuator module that
we will describe in next month’s issue.A new version of the ADF4351
synthesiser module
Just recently we received a second
ADF4351 Synthesiser module and
discovered that it was a ‘V2’ module
which had been changed in a numberof ways compared with the original
version (‘V1’).
These changes will be critical to
successfully connect the module to
a micro, so here are the main details
listed below:- Many of the connections to the
10-way pin header (CON1) have
changed, as shown in Fig.6. - There is now no on-board pull-up
resistor connecting IC1’s CE pin to
the +3.3V (DVDD) line, nor are there
pull-down resistors connected be-
tween the CLK, DATA and LE pins
and ground.
To ensure normal operation of the
module with either an Arduino or a
Micromite, an external 10kΩ resistor
must be connected between the CE and
+3.3V pins of CON1.
To ensure maximum stability, it’s a
good idea to also connect an external
10kΩ resistors between the LE pin and
the ground.
Once the above changes are made,
version 2 of the module performs just
as well as the earlier version.
Useful links
The module, available from AliExpress:
http://bit.ly/pe-may19-ali
The module from eBay – at the time
of going to press, item 143041004110
Analog Devices ADF4351 data sheet:
http://bit.ly/pe-may19-ad
Fundamentals of PLLs from Analog
Devices: http://bit.ly/pe-may19-pll