(A 2007 ZS1I EXPERIMENTAL RESEARCH AND DEVELOPMENT PROJECT)
NOTE: This 2007 ZS1I project is not an ARDF (Fox Hunting) transmitter. However it can easily be modified to be used as a very interesting fox. All you need to do is to remove the TX unit and replace it with a 2m HT. You can then use the correct fox hunting frequencies. This was one of the most enjoyable projects I ever constructed. Great fun and interesting to see how far 10mW can get you on UHF.
I always had this crazy idea of in sending “something” up in the sky with an amateur radio payload on board. I had a look at several helium balloon and rocket projects but due to various Governmental and Aviation “red tape” in this country, I decided the next best option for the time being would be to use a kite to carry the payload. You might say what a waste of time but did you know that a World Kite Altitude Record of 14,509Ft (4422 meters) was set by Richard Synergy in Kincardine, Ontario, August 12, 2000 for a single kite. Needless to say I am not currently interest to better the record. I am more interested in constructing a useful and simple amateur radio payload that can be built and used by fellow radio amateurs in model rockets, model aircraft, balloon flights, kite flights, foxhunting, tracking animals and even tracking whatever needs to be tracked.
OVERVIEW:
There are many problems to overcome when designing an amateur radio payload. The main “obstacles” being size, weight, expense and versatility. Size and weight are obvious problems although not such a big problem as some kites can carry several grams if not up to half a kilogram, but the lighter the payload the better. Also important is the expense. Like it or not I alone carry the budget and flights can go wrong, horribly wrong. Versatility in the field is another prime consideration, including consideration of multiple sensor configurations (both analog and digital), and compatibility with standard receivers, antennas and transmission modes. Having said that, I decided to start small and then add-on as the project develops. What started off as a payload for a kite suddenly changes to a tracking transmitter or some kind of ARDF. I envisage that the payload will be constructed in several stages:
Stage 1: UHF Tracking Transmitter.
Stage 2: APRS Module and Transmitter
Stage 3: Simplex Repeater
Stage 4: Cross Band Repeater
Stage 5: Meteorological Sensor Board
Stage 6: Who knows? Imagination is the key to several more stages
What started off as a payload for a kite suddenly changes to a stationary tracking transmitter. Be as it may it gave us great pleasure and insight into UHF low power (QRPP) operation and will the experience gained be used to complete the Kite Payload at a later stage. (Below: Picture of the UHF Tracking Transmitter.)
The “brain-module” (PIC Microprocessor) was designed to send morse code telemetry to a FM transmitter and then into a 50-ohm antenna load. The “brain” consists of a PIC12F675 flash micro controller. The “brain-module” PCB also accommodates a 3 volt battery power source, two resistors, J- Adapters, link, IC Socket and other connector blocks.
The 433 Mhz transmitter is tone modulated by the microprocessor approximately every two seconds. A Morse code call sign ID (ZS1I) is transmitted approximately every 30 seconds. The microprocessor generates “beep” tones approximately every 1 to 2 seconds and a call sign ID every 16 “beeps”. A piezo buzzer can be used to produce sound from pin 5 of the PIC. This is useful if you want to have an outside audible tone in locating the payload after flight.
Space does not permit me to explain the PIC12F675 chip operation and programming to the full. Please note I did not write the ASM file for the PIC, as I did not deem it necessary to “re-invent the wheel” again. Recognition will be given to the appropriate developers and sources at the end of this article.
I chose a 433 Mhz transmitter to avoid “clashing” of transmitters at a later stage.
Technical Features of the Transmitter:
· SAW resonator stability
· Carrier frequency: 433.75 Mhz but adjustable
· Supply: 12 Volts
· 15 mA consumption with TX enabled
· RF output impedance: 50 Ohm
· Output power: 10mW (Hey, QRPP here we come!)
· Dimensions: 40.6 x 19 x 3.5 mm
· Construction: Surface Mount Components.
Interfacing the transmitter is simple. Finally the antenna is the single most important item that will determine the range and audio quality of the project. Imagination and exploration is the key elements here. The test quarter wave antenna (16,4cm) I used is made from brazing rod and is connected directly to the transmitter with a short piece of RG174 coax cable. My homebrew 4-element 70 cm Yagi antenna gives the gain I need for longer distances, but will be very difficult to use in flight. A simple wire antenna work well (range restricted) and can be coiled to save space.
CONSTRUCTION:
The “brain-module” is constructed on a standard size single-sided printed circuit board. The PIC is inserted in a 8 Pin IC Socket and the rest of the brain- module components are directly installed onto the PCB. Soldering is straight forward and to the point. Keep the power leads as short as possible.
The FM audio transmitter is a ready to install module with a LF section and Modulator. Two AC-coupled amplifiers with voltage gains of: AMP 1 = 20 and AMP 2 = 5 and have a LF bandwidth of 20 Hz to 30 Khz. The FM modulator is an oscillator stabilized by means of a SAW resonator and modulated by a varicap diode. In order to improve the signal-to-noise ratio and the dynamics of the demodulated signal it’s advisable to fit a pre-emphasis network between the 1st and 2nd LF amplifier stages. The pre-emphasis network shown in the block diagram, lowers the bass tones by about 6 times with respect to the trebles, makes the FM modulation index approximately constant over all the audio bandwidth and increases the available dynamics for the bass tones.
Pin 2 of the transmitter makes it possible to enable or disable the FM transmitter simply by interfacing it with TTL or CMOS logic families supplying output logic levels of 0 to 5V and 0 to 12V respectively. I installed the transmitter module with the pre-emphasis network on a small piece of perfboard. The few connections required are pretty simple and straightforward. Power to the transmitter is supplied by a small 12V alkaline battery, which is normally used in lighters, camera flashes and pagers. Data is sent from the PIC into the transmitter at pin 4.
The single most important component that controls the system range and frequency is the antenna. Three antennas are described by the manufacturer of the transmitter module nl. Helical, Loop and Whip. I used a whip for testing purposes with a length of 16.5 cm from antenna pin 2 and later successfully used a 4 element Yagi and a 8 element Quagi in field operation.
INITIAL TESTING:
Inspect all solder joints on the PCB and Perfboard for solder-bridges and bad joints. Install the 3V Lithium battery for the PIC and then the small 12V battery for the transmitter. Confirm operation of the transmitter. If the transmitter function then it is ready for use. I tested the transmitter on the workbench with the whip antenna. This antenna yielded a ground-to-ground distance of well over 1000m. But the big test was yet to come.
OPERATION AND TEST RESULTS:
A first “formal” testing schedule was held on Saturday 28 April 2007 as part of “Marcony Day” activities in the Southern Cape. Francois ZS1Q contacted me early on Saturday morning to make final testing arrangements. I could feel the excitement building while one question keeps coming up “Will 10mW RF power on FM (No line of sight) be enough over a distance of 45.5km of which 23.7 km runs over the ocean?” Time will tell. The first test was done on the workbench at the QTH of ZS1I with the whip antenna. Batteries were installed and 145.550 Mhz Simplex was used to co-ordinate the 70cm FM QRPP tests between ZS1Q and ZS1I. The transmitter was left standing upright on the workbench and ZS1Q was given the green light to monitor the 70 cm frequency for the QRPP FM signal. After 15 minutes it was clear that no audible signal was heard and it was decided to get mobile to a high point and test again. This time using two different antennas, the 16,5mm whip and a 4 element portable Yagi. Yet no success over the distance and from the high point. Enthusiasm soon turns to disappointment and on my return to the QTH it was decided to connect the fixed (No rotator) 8-element quagi antenna to the transmitter. Yet again no success. I then decided to leave the transmitter in the shack with the quagi antenna attached and to get mobile with the 4-element yagi and Yaesu FT817.
The signal was clearly audible for up to a distance of 3.4 km where after I ran out of ground. Alternatively I had the option to charter a boat to trace the signal over the ocean, which was impossible at such short notice.
The back to the shack option where chosen where a on air meeting was held to discuss the operations of the morning. A unanimous decision was taken that despite the lack of success, this is definitely not the end of the road. A decision was taken to evaluate all receiving and transmitting equipment before future tests are carried out.
TESTS: 1 MAY 2007:
Round about 07h30 after a cup or two coffee I received an SMS from Francois ZS1Q instructing me to switch the 70CM UHF TRACKING TRANSMITTER on around 08h00, as he was ready to hunt the 10mW FM signal. His equipment consisted of a Yaesu FT857 and an 8-element 70CM Quagi antenna. He decided to mobile towards the Outeniqua Mountains to an area where he thought would be the best to receive the signal. We used 145.550 Mhz Simplex to keep in constant contact during the “searching” process. Round about 8h12 ZS1Q contacted me to confirm his position. After setting up his equipment he realized that there was an obstacle (mountain) between him and me and that this position would turn out to be unsuitable. He did listen but receive no signal and decided to move to an area lower down the roadside. ZS1Q stopped alongside the Outeniqua Pass, Blanco and George intersection. A few minutes later at 9h25 the audio of the tracking transmitter could be clearly heard on 145.550 Mhz. Francois voice suddenly interrupted the audio with confirmation that he is receiving the signal. The air went silent for a couple of seconds and then we both realized that the 10mW signal was audible over a longer distance than before. A record distance of 41.6Km. (for now) Francois copied the signal (S4 to S9) with fading at times.
The location was fixed at 33.55.38S, 22.24.50E with a height of 362m above sea level.
The signal could be heard for several minutes and ZS1Q decided that with the good conditions at hand that he would like to move towards his QTH to investigate the possibility that he might hear the signal from his shack. Francois and myself expressed great satisfaction with the distance achieved and it was clear that when conditions are favorable, a 10mW FM signal would be heard over long distances on the 70CM band. Unfortunately Francois could not hear the signal at his QTH but he is of the opinion that he will copy it in future. Congratulations Francois, you are the new Record Holder!!
Test results for 1 MAY 2007:
Establish a “one-way” contact on 70CM between Francois ZS1Q and Johan ZS1I with 10mW FM modulated signal over a distance of 41.6Km. (No line of sight)
ZS1Q POSITION:
Portable at George roadside crossing
33.55.38S, 22.24.50E, 362m above sea level
Receiving Radio: Yaesu FT857
Antenna: 8 element 70cm Quagi (Horizontal polarized)
Distance from ZS1I: 41.6 Km
228 Degrees Celsius
ZS1I FIXED POSITION:
Mossel Bay KF15BT
34.11.54S, 22.06.10E
Transmitter: AUREL 70CM MODULE
Antenna: 8 element 70CM Quagi (Vertical polarized)
Output Power 10mW
FM Modulated
Distance from ZS1Q: 41.6 Km
WEATHER:
Misty conditions (Low level mist covering several hillsides and valleys) Francois ZS1Q indicated that he could not see Mossel Bay at all from his location. I am convinced that the weather played a big role in setting the distance of 41.6 Km. The conditions were as follow:
No Rain
Early morning dew.
Temp: 18 Degrees Celsius
Bar: 1016 Mb
Wind : None
The question that now comes to mind is: “Will this distance be extended? From those who participated a clear message: “This is only the beginning!” I have heard roamers of long antennas, pre-amps and “terrain searching”. Bottom-line don’t miss the excitement if you live in the Southern Cape and who knows even up-country radio amateurs. You never know what might happen. Join in and have some fun. Until next time. Keep those soldering irons smoking!!
Above: Inside view of the UHF Tracking Transmitter. The PCB's are a real "Mixed Grill" variation....really ugly.
Above: Picture of the signal received on the 28 May 2007 at 9h23 SAST.
