RF Analyser (Work in progress)

I found this project from the work of JA2NKD, an RF Analyser built around an Arduino Nano, AD8307 log detector, AD9850 DDS and 2.8" LCD/TFT display, and features an inbuilt calibration routine.
 I made some changes to the Arduino sketch to accomodate the larger display (2.8”) and built the project on Vero style strip board.
A special thanks to Jaques VK6KDX for his help with getting the programming procedure into my thick skull.
Tuning range is from 1 - 55MHz and includes a signal generator (DDS) with selectable step size, an RF power meter, Scalar network analyser and antenna analyser (with external directional coupler)
A calibration routine for the power meter function is included in the Arduino sketch and once set up, holds good to within 0.1 dB to beyond 148 MHz as compared against my HP8648B signal generator.

It’s important for an instrument of this type to have a clearly defined output impedance of 50 ohms and an output level as close as possible to 0dBm.
The AD9850 DDS evaluation board as standard, comes with an output impedance of 200 ohms with an on board anti alias filter designed around 200 ohms, it has a cut off frequency of around 70 MHz. Another shortcoming of the original module is due to the poor output filter performance, significant 125mhz clock frequency leak through is apparent on the DDS output spoiling the output waveform.

 The DDS reference clock is calibrated so that the DDS output is exactly 10 MHz as measured on a frequency counter connected to the output as part of the calibration process and the resulting math is stored within the Arduino EEPROM.
Unfortunately, the sketch uses just about all the included memory capacity in the Arduino NANO


leaving no space to include the usual ‘normalisation’ function to flatten the output frequency response, however, by modifying the AD9850 DDS with a replacement anti alias filter and impedance matching to 50 ohms it is possible to acheive a response that is within +/- 1dB from 100 kHz to 55Mhz.
As an improvement to the original JA2NKD design I have implemented these changes as originally described by Jim Giammanco (N5IB) in his PHSNA design, these changes also result in a gain of some 6db in output level, the new filter is followed by a Pi attenuator that trims to output level to 0dBm. and the 125mhz signal has gone from the output.

Here’s a few photos of the project

Building an AD8307 RF Power Meter

Power Meter shown measuring the output signal of a Rig Expert Analyser (-10dBm )  at 100mHz
VSWR 1.08 indicates a nice 50 ohm input impedance.

Connected to a home brew 40dB tap to allow higher power measurements,
no signal noise floor is -74dBm…near enough for a backyard project.

AD8307 power head, this assembly is enclosed in a brass screen to improve noise figures. 

Home Brew AD8307 Power Meter

Home Brew Linear Power Amplifier.

RF Deck

A few Pictures during construction of my Linear Amplifier, it uses 2 GI7BT Russian triodes set up in grounded grid configuration, forced air cooling from a repurposed microwave oven cooling fan together with teflon chimneys, Power supply is 2300 VDC from a toroidal HV power transformer. Each band has a separate input tuning network to ensure low input SWR for solid state transceivers. Built mainly from bits and pieces collected from Hamfests

etc., it is very predictable in operation with no nasty sup prises…So Far!.

About Me

Wayne Johnson

Born in Dargaville in the north of New Zealand in 1946, my family soon moved to Auckland where I grew up, I have an older sister Raewyn and a younger brother ( Murray now sadly deceased,) When leaving school in 1963 I joined the Post and Telegraph department that has now become the Telecom Corporation of New Zealand and began a career in telecomunications, and, in what seemed like a lifetime, advanced to Manager Network operations Field in Auckland.

In 1988 my family and I moved to Perth, Western Australia and I was employed in the role of Field Service Technician installing and servicing office equipment. I am now widowed with 2 grown up sons and enjoy a comfortable lifestyle in sunny Perth.

I have had an interest in radio for as long as I can recall and started as so many others by building a crystal set and then a 1 valve regenerative receiver with which I could receive the 'Hams' on 80 metres and so it went, up went numerous antenna arrays around my parents home much to my mothers dismay!

My interest is now mainly DX and I currently have some 280 countries confirmed. I am a member of the Northern Corridor Radio Group (Perth) and am active in contesting and various club activities.
Antenna wise my station is rather modest as council restrictions limit the erection of antennas and I have a 3 element yagi by TET Emtron on a crank up mast to 10 metres, radios include an Icom IC7800, A SUNsdr2DX, an Icom IC910H and Icom IC7300
I am a keen home builder of equipment including my LDMOS linear amplifier, and numerous other  Ham related gear

Other interests include woodwork and home renovation. I love working with Jarrah timber which was plentiful here but has become very expensive in recent times. Over the years my latewife and I owned 6 homes, 3 in New Zealand and 3 in Perth, we have both had an interest in home renovation for many years.

I also have an interest in Geneology and are currently researching my family tree, very hard work, should have started years ago when my parents were still alive but a very interesting pastime.
View my complete profile