Homebrew radio projects and FlashForth - OH2AUN

Updated 30th of August 2007. Release of FlashForth V2.1 and move to SourceForge.

FLASHFORTH

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Navtex receiver and NMEA monitor.

Version 1.5

The NMEA time display is now parsed correctly.

Source : navtex1_5.txt

Version 1.4

Some bugfixes have been made.

1. The FSK decoder decoded wrongly about 15 percent of the bitsamples.
   This fix should increase the sensitivity and range of the receiver slightly.
   
2. The reception of NMEA messages during mode adjustment corrupted
   the LCD display.

Version 1.3

Since I had some 16F870’s lying around, I had to make version for that PIC.
In the process some new features were introduced.

1. The LCD display is now optional. The output of the Navtex messages can now be made
   to the serial line with 4800 baud, 8 bits, 1 stop, bit no parity.
2. The Navtex filter parameters can now be freely controlled from the serial line and from the
   mode/up/down keys. For example:
   ‘msg_a=y’ command orders the reception of all ‘a’ (navigational warning) messages.
   ‘stid1=*’ command orders the reception of messages from all stations.
   ‘stid1=u’ command orders the reception of all messages from ‘u’ (Tallinn) stations.
   
   The Navtex filter parameters are stored in EEPROM, so the settings are remembered
   after a power break.
   There are 3 station id message filters.
   There is a help and a print command.
3. The new board supports both 16f870 and 16f876. Since the 16f870 does not have any
   pulse width modulator, a 74hc93 is used to generate the local oscillator signal.
4. The same hex file can be used both for the 16f870 and the 16f876.
5. The new board supports in circuit programming, by isolating the programming pins
   from the rest of the circuit.
6. The power supply to the MAX232 and the LCD display is filtered, to reduce interference
   and further improve sensitivity and dynamic range.

Building note: The version of the HW with the 6 kHz intermediate frequency has better selectivity and sensitivity.

schema1_3.gif board1_3.gif place1_3.gif navtex1_3.txt navtex1_3.hex

Some low quality pictures.

Navtex1.JPG Navmode.JPG

Version 1 .1

For Toshiba controller T6963 based LCD displays, with 240x64 pixels, which gives 8 rows of text with 40 characters per line.
Example of a suitable display module: http://www.hantronix.com/down/64gs242p.pdf

Reception frequency 518 KHz FSK
Intermediate frequency about 6 KHz or 18 KHz depending on the exact crystal frequency.
IF Audio output, which can be used to trim the RF stages and IF stages,
by using a PC audio spectrum analyzer.
Local Oscillator signal generated by the PIC Pulse Width Modulator.
FSK demodulator using the PIC capture function.

Note that the CRYSTAL constant in the program may need to be changed
depending on the real crystal frequency. I use a serial resonant mode 18432 KHz crystal.
It resonates on 18439 KHz.

NMEA display decodes GLL, VTG and APB messages.
NMEA serial speed is 4800 baud

This circuit is currently in use aboard my boat,
it has worked now continously for 3 summers.
Current consumption is 35-40 mA

Version 1.2

Version 1.1 has the opamp and the comparator switched with eachother.
The 1.1 version was found to have bad sensitivity, and bad dynamic range.
It was due R13 having the value 0.
This caused wideband noise from the comparator output to be coupled to the mixer input.
With R13 = 10K, the sensitivity is so good that the RF amplifier can be removed.
To ensure good performance, the top side of the PCB should be used as a ground plane.
A new improved version 1.2, with the RF amplifier removed, is introduced below.
This will reduce possible overloading problems.
Also the opamp and comparator are now correctly used.
The inductors are standard chokes, available ready made from for example ELFA.
No need to wind anything :-)
The pin out of the LCD control lines and the keyboard lines have changed,
therefore a new software version is provided.

schema1_2.gif board1_2.gif place1_2.gif navtex1_2.txt

Single conversion SW receiver.

Very nice small radio for listening to shortwave broadcasts
5,9 - 18 MHz.
455 kHz IF.
TCA440.
Uses dual gang capacitor and a 1:36 geared reduction drive.
This circuit has been built and debugged 27.11.2001

TCA440 SW radio

Frequency counter.

Fits the above SW receiver.
455 KHz IF offset.
0-19999 kHz.
This circuit has been built and debugged 27.11.2001.

Frequency counter

0 - 30 Mhz up conversion HF receiver.

The first intermediate frequency is 45 MHz.

1. Preselector
2. First Mixer
3. Second Mixer
4. IF amplifier and demodulator
5. DDS Synthesiser
6. DDS BFO
7. Control PIC and display.

0 - 30 Mhz HF receiver with 10.7 MHz first intermediate frequency.

This is a project I actually have built, and it is in use all the time.

Picture: hf1.jpg

50 MHz SSB tranceiver.

This is another project which actually is ready and working.

Picture: 6m.jpg

Grundig Satellite 700 modifications.

I have made some modifications to my Sat 700.
These have mainly to do with improved sensitivity,
and strong signal tolerance of the whip antenna amplifier,
and a proper AGC which works with SSB.

Comments & Questions to: oh2aun-at-flashforth.com