Last Edited 14 September, 2007 Links open a new window.
Chirpview http://www.dcs.lancs.ac.uk/~senior/chirpview.html Chirpsounder monitoring. (I use the "Public Beta" version.)
I have been playing with "Chirpview", a program that records
signals from chirpsounders. These use transmitters that smoothly move frequency
according to an accurately defined schedule. Everyone must have heard them as
they swish past a frequency, a typical one starts at 2MHz and moves up at the
rate of 100KHz per second to 20MHz or more. A receiver synchronised to the
transmitter records signals from the transmitter. They are often used to
determine the best frequency to use over a particular path, or maybe just for
research.
If, starting at the correct second, a receiver is stepped at the rate of 100KHz
per second the sounder can be followed and Chirpview" will record the
strength of pulses received, an ionogram can be plotted.
My initial thought was to use the "Ham Radio Deluxe" (HRD, See below) direct entry feature, "highlight"
the 100KHz digit and press the "up" arrow each second. (One of the
many frequency control features of HRD)
However, I thought of the risk of RSI or, more likely, boredom and came up with
a solution.
I opened up an old keyboard and connected the contacts of a reed relay across
the "up" key contacts, actuated the relay from the "one pulse per
second" signal from the GPS used to synchronise "Chirpview". The
HRD window needs to be kept active during this process.
Ionogram
of propagation between Preston, Lancs and Cowes at 0845 on 19 March. Horizontal
axis is frequency MHz. Propagation present between 3MHz to 8MHz. Vertical is
propagation delay in mS, this is not accurate, the technique introduced an
error? Or was the frequency not precise? Not sure what happened, later
trials gave reasonable results.
I now have a 500mS pulse delay using a 74123 so the 100KHz step occurs between each whole second, the frequency may then be multiples of 100KHz and no correction to the "Chirp Time" is required.
GPS units
Modules to provide a "one pulse per second" (1PPS) are available on ebay. I first got a Motorola Oncore. Recently I found a Rockwell Jupiter, this, in addition, has a 10KHz output. I have seen a claim that the long term accuracy of this signal is one micro hertz! It should not be difficult to produce a good frequency standard. See below.
With these units it is necessary to monitor with a computer when initialising. At http://www.gpskit.nl/index-en.htm which gives details of the Jupiter is a link to the software "CSI GPS Command Center" [ Dead link- I've put it here - CsiGps (Zip File) ] this works with Rockwell, Motorola and others. It is mentioned that many serial "com" ports are compatible with TTL signals. To read from the Jupiter so I used a single transistor inverter to feed the NMEA data to pin 2 of the com port. This has worked on all four computers I have tried. A simple resistor/zener arrangement can be used to transmit to the GPS. A 7404 can be used with the other inverters used as buffers for the 1PPS/10KHz. Two for the 1PPS, to keep it a rising edge pulse. (Chirpview did not seem to work properly using the falling edge option.)
GPS modules I have seen on Ebay. There are Trimble units available from Ebay USA, these are often in a box with connections already made. The bare Oncore or Rockwell modules might need some care when making connections, the Oncore has a small plug, the Rockwell unusual pin spacing. A supply of 5 Volts is required. The antenna may be an active commercial unit, often with a small MCX connector. Most are said to work with a passive antenna, make sure that any current feed is isolated. As noted above a simple computer interface is required, various softwares eg "Visual GPS" and CSI as above.. All these units have a "One Pulse per Second" output accurate to better than one microsecond, the Oncore VT is to 100nS. There are circuits available that employ a PIC microcontroller that use this pulse for a frequency standard output. These modules are well documented, just use Google or your favourite.
Rockwell and "Chirpview":- Chirpview does not recognise the NMEA string from the Rockwell if all the outputs are selected. All that is needed is the "RMC" message. This can be configured with CsiGps (Zip File) (I have put the csigps.exe here as it is no longer offered by CSI.) NOTE if you use a USB/Serial adaptor GSIGPS only has the option of 4 COM ports. If the adaptor is assigned a higher number it may be changed (with warnings) in Device Manager. If the offset is set at -1 on my computer the time is set automatically.
FREQUENCY MEASUREMENT.
The Rockwell Jupiter has a 10KHz output. This can be used as a basis of a
frequency source, it has an impressive long term accuracy. There are circuits similar to
the one I have used that use the 10KHz to lock a crystal oscillator of
10MHz.. A good one here:- http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm
I do not use a MAX233 and my 10MHz OCXO is homemade using a Khune (http://www.kuhne-electronic.de/english/special/crystalheater.htm)
crystal heater. Sept 07 I now use a Philips VTCXO, better than my effort -
It does not have the range to lock when the GPS is not locked.
Also for a GPS that does not have a 10KHZ output there are circuits that use the 1PPS signal as a basis for a
standard, but are more involved. There is a "T" version of the Jupiter that is
designed for timing applications but is not very common.
http://www.gpskit.nl/index-en.htm
details a kit, and gives useful information and links.
A simple application:- http://aprs.gids.nl/gpskit/gps-readme.html
gives info, links and shows this circuit.
I based mine on a similar circuit. The 7404 can be used to buffer the 10KHz and
1 Hz output. The simple interface has worked on all serial ports I have tried.
All that is needed is 5 volts, the simple computer interface (to set it up and check it is working), and an antenna. It will work with a home made dipole. The 10KHz output could be divided down, for example a 74390 would divide by 2,2,5,5 giving 100Hz minimum frequency. This can be applied to the antenna socket of the RX via an attenuator (just a variable potentiometer). SpecLab ( http://www.qsl.net/dl4yhf/spectra1.html ) would then show a marker every 100Hz.
Harmonics of the basic 10KHz are useful on HF. For absolute accuracy the 10KHz should be used to lock an OXCO but I suspect the raw signal may well be adequate except for the most exacting requirements.
It is possible to power this unit from a USB port (about 200mA). One way could be to use a USB/Serial adaptor, if it is the type with the control electronics at the far end of the cable the power could be taken by breaking the cable. UPDATE:- ON SOME SYSTEMS USB POWER WILL NOT WORK, I HAVE SEEN THE USB VOLTAGE AT LESS THAN 5.0, SOMETIMES TOO LOW TO SATISFACTORILY POWER THE GPS. For the experimenter, USB mobile telephone connectors usually contain a USB/Serial converter. These are available cheaply, or unwanted ones may be free. It MAY be possible to open one up and adapt it. I managed this with an Ericsson DCU-11 adapter. The Cygnal CP2101 inside runs on 3V0 so needs a simple interface to the 5V0 of the Rockwell. As with many components, a "Google" will often find details of the ICs.
Incidently the Khune crystal heater CAN transform a receiver, my old ICR70 is stable within +/- 1 Hz for days with two of these fitted.
Ham Radio Deluxe (HRD) http://hrd.ham-radio.ch/
This is a free Program. Nearly every HF rig with CAT is supported. It is in development, and final touches are being added. The forum gives details of what may/may not be included.
It is a comprehensive rig control program incorporating a super PSK31 application with a mapping facility. For the SWL it has an ILG database included. A Logger facility is integrated. For satellite operators there is a tracking program with doppler shift compensation. When finished rigs like the FT847 should be fully supported. HRD can be "Bridged" to the DXLab http://www.qsl.net/dxlab/ suite. It is easy to find it's features by playing with it. The F8 button and right click help a lot. Look at Documentation particularly http://www.ham-radio.ch/guides/hrd/hrd.html by VK3CKC, and the Forum available on the site.
DXLab http://www.dxlabsuite.com/download.htm
Another free Amateur Radio program.
Logging, Dx spots, Propagation, Winwarbler, QSL info, Rotator
control, links with HRD.
This is a large collection or programs, needs a modern computer preferably with Windows XP (does not work with my W98SE)
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