SCARC Projects and Kits
VK5JST AERIAL ANALYSER
Page information sourced from Jim Tregellas VK5JST's Website. (Thanks Jim!)
HARDWARE
This project was published in the May 2005 issue of the Australian magazine "Amateur Radio", and has been designed using parts which are very readily available (see the circuit and parts list). There is little point in supplying a kit of parts to amateurs who have been around a while - most will be in your junk box. However, the printed circuit board (double sided and hot air solder reflow coated) is another matter, and is available here.
Payment can be made by either:
1. Posting Cheque or Money Order to SCARC - PO Box 333 Morphett Vale, SA 5162
2. PayPal
3. Direct Bank Deposit. (contact kits@scarc.org.au for details)
To purchase the kits via PayPal, please select the "Add to Basket" button below.
Complete Kits.........A$135.00 Incl. post and packing (within Australia).
Complete Kits.........A$150.00 Incl. post and packing (International Buyers).
To View your PayPal Purchase Basket, click below
** Purchasers: Please email Name, Callsign, Postal Address & PayPal Reference Number to kits@scarc.org.au **
*NB Regarding Cost increase*
Unfortunately, increases in postal charges have meant we have had to raise the kit price slightly to cover the increased postage cost.
While this is regrettable, it is unavoidable.
*OVERSEAS BUYERS*
Overseas buyers, please use paypal only.
*POSTAGE*
An alternate delivery option is available though Australia Post's
Express Courier International, which includes track and trace [www.auspost.com/track]. For
further details and prices, please email kits@scarc.org.au
before making payment.
DATA
You can Download ALL the files for the "Aerial Analyser", by clicking here (Zipped File).
The code for the PICAXE 28X was prepared using the Revolution Education Programme Editor and is in BASIC format. This will program any PICAXE chip, by Revolution Education.
Note that since submission of the article for publication, a battery voltage monitoring modification has been included at the suggestion of Barry Williams VK5ZBQ. To add this feature to MK1 printed circuit boards, cut the PCB connection between AN3 (microprocessor pin 5) and ground. Then add a 16K resistor between the +12volt rail and AN3, and 3K9 between AN3 and ground. At switch on the battery voltage is displayed for 1.5 seconds.
To obtain the correct voltage indication, simply vary the division ratio in the line "w0=w0/100" in the "battery:" subroutine of the microprocessor code. The divider should lie in the range 94-106, and compensates for the 5% component tolerances. This modication ( and other minor layout and circuit mods ) have been included on the Mk2 version of Analyser detailed below
DOWNLOADS
ARTICLE
*
The article text (Word 2000
format).
* The parts list for the
analyser (Word 2000 format).
* A
diagram showing the maths on which the analyser is based
(JPEG).
* The component overlay
for the MK2 PCB (JPEG).
* The
first half of the analyser circuit (JPEG).
* The
second half of the analyser circuit (JPEG).
* A
sketch of the cable used to download data to the PICAXE (JPEG).
PHOTOS
*
The front view of the analyser (JPEG).
* An
interior view of analyser- MK1 PCB!! (JPEG).
* The
MK1 PCB - included for early constructors- note that the MK2 PCB
is very similar, but constructors should follow the MK2 component
overlay (JPEG).
* An adapter for ununs, baluns
and stubs etc, as well as adapters for BNC, N type and similar
connectors (JPEG).
PICAXE CODE
*
Original PICAXE 28X code (including battery
monitor) by VK5JST.
* Original PICAXE 28X code
(including battery monitor) with leading zero suppression routine
added by Keith Gooley VK5OQ.
* Original PICAXE
28X code (including battery monitor) modified by Lee De Vries
VK3PK for firmware versions 4.6 to 7.3 (support for 16 gosubs only
rather than 256). Also a serial output to a PC, providing speech
output.
* Completely rewritten PICAXE 28X code
(including battery monitor) much greater accuracy of calculations by
VK5JST. For leading zero suppression on your displays, is turned on
by deleting a few REM statements in the display routines. The code is
extensively commented, allowing easy customizing (include your own
call sign at switch on for example). Change a multiplier in the
battery measurement routine to trim out all component tolerances, as
well as an exact display of battery voltage. For PICAXE 28X chips
firmware versions 7.4 or later.
* The new code
above with further refinements, like trailing zero suppression
added by David VK3DPM.
* David Milne's (VK3DPM)
new code, complete with explanatory notes, that allows L & C
to be measured with the analyser.
* Looking at
the results produced by the Analyser!! by John (ZL2TTM) has
ingeniously modified the software to display load impedance in both
polar form (magnitude and phase angle) as well as the more
conventional form (resistance plus impedance magnitude). He can be
e-mailed at zl2ttm@nzart.org.nz
TRY WRITING YOUR OWN CODE FOR THE AERIAL ANALYSER!! ADD YOUR OWN DESIRABLE FEATURES, AND HAVE THE CODE DISPLAYED HERE TOGETHER WITH YOUR NAME AND CALLSIGN.
Further Information
If you wish to contact the South Coast Amateur Radio Club Inc. you can e-mail us kits@scarc.org.au
WARTS, PROBLEMS AND COMMENTS
At the time of writing, around 500 units have been built, and apart from the odd dry joint, only 3 units have given serious trouble. For two of these units, the trouble was identical and involved the upper frequency range of the oscillator.
Instead of producing a good sinusoidal output, the generator produces a near sawtooth waveform of about half normal amplitude. This is caused by the 1uH RF choke in the oscillator tank having much lower losses than normal,and consequently causing much higher than normal gain around the oscillator loop. The oscillator consequently "squeggs" producing a weird output, and to overcome the problem, simply reduce the tank Q by paralleling the 1uH RFC with a damping resistor. Both of the troublesome units produced good flat sine outputs when the 1uH choke was paralleled with a 3k3 resistor, but depending on your choke characteristics, it may be necessary to go as low as 1k5. Keep an eye on the waveform purity when you are experimenting.
The remaining unit gave trouble simply because it would not oscillate on the two highest frequency ranges, and had odd looking waveforms on the remaining ranges (flat topped sines etc). This was traced to the use of ordinary standard 100nF disc ceramic bypass capacitors, which being physically large single plate devices, have relatively high losses and low self resonant frequencies.
There is no place in a wide band power circuit (which this instrument is) for such components. Use only miniature multilayer MONOLITHIC bypass (and coupling) capacitors in this circuit with lead lengths of as near to zero as possible, or you WILL end in trouble.
The bypass capacitor at T3 base is particularly important. Minimizing stray capacitance in the test circuit is important, as it appears in parallel with the load and can upset measurement accuracy at high frequencies and high SWRs. It can be minimised by mounting the following components away from the ground plane by 1-2mm. (a) D5 and the associated 100pF and 47K (b) D6 and the associated 100pF and 47K. (c) The 2 X 100 ohm test cct series resistors.
Warning:
This kit is of an Advanced standard,and assembly requires good
soldering and hand skills. The club takes NO responsibility with problems
associated with construction, but will provide reasonable assistance to the
purchaser to get the kit operational . However, the purchaser should keep
clearly in mind that this is a volunteer organisation with limited resources,
and that politeness in correspondence is much appreciated. As the technical
article makes clear, access to an oscilloscope is highly desireable but not
strictly mandatory.
