Sunday, April 24, 2016

TA7642 / ZN414 / MK484

All 3 references in the title are small, 3 pin, AM receivers in a chip with minimal external components.

I remember seeing then in schematics at electronics magazines many years ago, somehow expensive (the Ferranti ZN414) at that time, so, never got one. Until now, the equivalent TA7642:

... previous image is the testing board, run with the following schematics and it worked: small changes in red. During the night with this it was possible to get some stations and also a beacon, I guest the cap/coil tuning range was going inside the LW band. The coil, don't remember where I got it, probably from some scavenged radio.

Tested also with variable capacitor to ground:
..was about to try with the varicap in place when I "fried" the TA7642 by touching the input with the soldering iron while powered on, bad luck and crappy iron, pretty sure the varicap version will work too!

Anyhow it's a funning litle device, good enough for a very simple AM receiver.

Have a nice week!

Saturday, April 23, 2016

FV-107 External VFO for the Yaesu FT-107 and Sommerkamp FT-307

Since I got the Sommerkamp FT-307 ,

might get also the companion FV-107, external VFO, not the "same" brand but with the same schematic, so last week scored one on an auction site and received yesterday.

Today did a light on test and all fine, I'm sure the oscillator works also, if not will be an easy fix:

I previous had one FV-107 in grey colour that I sold and at that time made an adapter/converter circuit so an FV-107 could be used on the FT-102 because the external VFO for the FT-102 line it's hard to find, here's mine:

Have a nice weekend!

Monday, April 18, 2016

World Amateur Radio Day - 2016

It's today!

Have a nice day if you enjoy this hobby! If not, have also a nice day!

Saturday, April 16, 2016

Stand-alone Arduino RTTY Decoder

Having build the LM567 tone decoder and the Arduino video out part. It was just a question of "gluing" with an RTTY decoder (download here or from the previous link) for a complete standalone decoder.

On top of the FT-707 decoding "meteo" on 30m:

 ..some "garbage" was due to initial VFO drift.

It works this way:

Audio from the radio headphones goes in to an audio isolation transformer, from there goes to an LM567 tone decoder:

..the output of the LM567 goes to a level shifer:
The "RX Input" on the previous image goes to the Arduino running ji3bnb RTTY decoder code (thank's OM). I modified the code to output also to the serial line (the original code is for an LCD which I didn't connected)... with this two lines:

The serial TX from the decoder looked like this on first test using a terminal for monitoring. provision for CR/LF on the added code since the next module will do that automatically.

 The previous Arduino (RTTY decoder) serial TX port connects to the serial RX of another Arduino that does the TV/video out to the display from the charecters received:

  In the midle you can see references to the station frequency (10.100.0) and the call sign mixed in the garbage DDK9.
using this code:

// Video/tvout from serial port reading / char by char
// module for the rtty decoder arduino
// read from serial and output on video
// Ricardo / CT2GQV / 2016
//p.s. fontall had to be include as a lib on the IDE to get the font to work...(normaly not needed...)
TVout TV;
// serial receive
String inputString = "";         // a string to hold incoming data
boolean stringComplete = false;  // whether the string is complete
// end serial receive
// serial events
void serialEvent() {
  while (Serial.available()) {
    // get the new byte:
    char inChar = (char);
    // add it to the inputString:
    inputString += inChar;
    if (inChar == '\n') { TV.println("\n");  stringComplete = true;  };
    if (inChar == '\r') { TV.println("\n");  stringComplete = true;  };

void setup() {
  TV.select_font(font6x8); // 19 chars by line
//  TV.select_font(font4x6); // more space but less font resolution
  TV.println(">"); // the starting prompt just to let know that it started.
} // end setup

void loop() {
 if (stringComplete) {
    inputString = "";
    stringComplete = false;
} // end loop

And basicaly that's it.. still need to include a "tuning" indicator using another LM567 for the "space".... or include CW decoding, adding the code to the RTTY decoder.

Here, assembled inside the box:

...nd just the decoder board, still space for audio monitoring amplifier since the headphones plug disconnects audio on the radio:

Audio transformer on lower left, level converter near the green LED, decoder Arduino on the lower right and the video output Arduino on the top right. Right of the audio transformer there's a second LM567 for the "space" decode, not implemented yet.

So... have a nice weekend!

Sunday, April 10, 2016

Sommerkamp FT-307 ... again

Some time ago I had a Sommerkamp FT-307, basically the Yaesu FT-107M re-branded by Sommerkamp for some markets.

It was this one and had the usual CB mod's: on (picture taken by me)

I think I swapped by an FT-817 and some accessories at that time.

In my last journey to Portugal I bought another one...

...according to the description, unit was not functioning after some magic smoke going out during transmit.

I didn't had the chance of testing or even seeing the radio, in any case made the deal and asked a friend to collect this previous week and keep it until my return. Today, after some persuasion, he powered on the unit just for fun, would it explode? No, it powered on and had noise (no antenna connected),  so in worst/best case scenario I will have to fix the  transmission part or the radio.

I think the final unit is similar to the FT-707, so, since I have two of them, will see if it fits. This radio it's modular in construction so should be easier to fix than the two FT-707 I already sorted.

Have a nice week!