Soundcard Interface for APRS/Packet - Part 2

Well, I finally got the PTT part of the soundcard interface working.  This was fun, and sometimes frustrating, but very educational.  I am lacking in my understanding of component level electronics engineering.  As a network engineer, I would be comfortable designing and implementing an enterprise network for a new hospital (that's a different story), but understanding why a transistor works the way it does is beyond me at this point.  So I kind of fumbled my way through this.  One thing that is very important in network engineering is attention to detail, and solid planning.  For some reason I didn't carry this over to this project, and it bit me..lol

Let me state, for the record, plan your work, and work your plan.  Don't just wing it.

Okay, on that note, on to the project.  Once again, soundcardpacket.org was a great source of information on getting this part working.  I used this schematic from their site (click on the image to see more details):

R1 = Resistor, e.g. 1K2, to reduce voltage on the IC pin 1

IC =  Integrated Circuit; this sketch shows an IC, such as a 4N33

        or PS2603 Optocoupler, which uses a Darlington pair transistor.

        (Note: to identify pin #1, look for a small embossed circle on

         the top of the IC above pin 1; or looking into the notch in one

         side of the IC with the pins down, pin #1 is to the right of the notch.)

D1 = Diode, e.g. IN4001, would shunt any potential reverse voltage

        that might damage the sensitive diode/emitter in the IC.

        (Note: the band printed on the diode marks the cathode end,

        which attaches to the Serial Port/IC Pin 1 line in the sketch above.

        The opposite/anode end attaches to Ground.)

In the last post about this project, I built the receive and transmit cables that connect the output of the radio to the input on the soundcard, and the output on the soundcard to the input on the radio.  This worked well for listening to APRS and packet conversations, but I couldn't join in without manually keying the mic, which works okay if you're doing PSK31 or other HF digital modes, but isn't as easy with packet or APRS.  With this addition, a signal is sent via the PC's comm port to key the PTT circuit on the radio.  This allows the radio to be keyed via software instead of manually.  This allows things like APRS beacons to work normally.

This particular design uses an optocoupler to isolate the radio and the PC, while still allowing communications to flow.  This, along with the audio transformers used in the last post, helps to eliminate ground loops and voltage differentials, which are a source of hum in your transmission audio.

While building my version, I found that I didn't have the required 1.2K Ohm resistor, so I substituted a 1K and a 220 Ohm resistor in series.  This took a little additional space, which was at a premium in the tiny project box that I used, but ended up working well.  As you'll recall, in the last post, I decided to build this in a project box, instead of as a set of cables.  I think that in the long run my way will be more durable since there will be less movement of the internal solder joints due to cables wiggling around.  Time will tell.

A couple of issues that I ran into:

1. On Windows XP (need to upgrade my shack PC), the serial mouse driver keeps the RTS pin HIGH, which causes the mic to key if nothing has taken ownership of the comm port that you are using (AGWPE, Digipan, etc) to bring it LOW.
2. The pinout of the IC that I used was different than the one pictured in the schematic, don't blindly trust any schematic, do your homework first.  It saves solder (and frustration)
3. Don't use too small of a project box, it is easier to do things if you have the room to do them in.

A couple of lessons that I learned:

1. When if doubt, check solder joints.
2. Follow the voltage, step through the circuit with a multimeter and make sure that you are seeing what you expect to see.
3. Amperage kills...  This applies to ICs and other components as well as people.
4. Be sure that the part is installed correctly BEFORE soldering...  

My Parts List:

• 1 x 4N33 Optoisolator
• 1 x 1K Ohm resistor
• 1 x 220 Ohm resistor
• 1 x IN4001 diode
• 2 x 1/8" mono audio jacks
• 1 x 6-pin mic connector to interface with my TR-7730

Time to Completion:

• This part took me about eight hours due to lack of understanding and being too trigger happy with the soldering gun.  Next time should go smoother as hopefully I have learned my lesson on this.

Here are a couple of pics:

The IC and diode on the bottom right, and the two resistors on the bottom are all that make up this part of this circuit.  The other two resistors and the two transformers are for the rx and tx circuits.  You can also see the two audio jacks that I used to connect the PC and Radio.

This shows the completed and closed project box.  Again, while I at first thought that smaller would be better, after building it, I should have used a slightly larger box.  The next one that I build will be a bit bigger.

These are the cables that I built to connect the computer to the project box, and then on to the radio.  The gray DB9 connector attaches to the comm port for RTS based PTT.  The other end of that cable is an 1/8" mono connector that attaches to the project box.  The 6-pin cable actually has two pig-tales, one 1/8" mono for audio, and another 1/8" mono for the PTT signal.

And here is a shot of the APRS terminal showing me sending and receiving traffic.  I need a better antenna to hit more than one or two stations directly, but thankfully, one of the stations that I can hit is a digipeater/IGate.

All in all this project was a lot of fun and extremely educational.  It is also a LOT cheaper than buying another SignaLink.  I think that I have around $20 invested in this, plus my time.

73,

Richard, KK4JDO

Soundcard Interface for APRS/Packet

Happy 4th of July to all of my American visitors (and also to everyone else, although I don't imagine that it is quite the same).  Not that I have that many visitors from anywhere, but it's the thought that counts.  It's been a few days since I posted anything, so I wanted to get this up on the site.  I've been enjoying my SignaLink USB soundcard interface for digital modes on HF, but I would like to run APRS on the same PC, and running two SignaLinks with APRS can be problematic.  Besides that, I didn't want to spend another $70 to $100.  So I decided to build my own interface.  There is a great resource for this at: http://www.soundcardpacket.org/.  They walk you through the build options and troubleshooting if needed.  That being said, I've borrowed their schematics to post here (full credit for the schematics goes to them).

For this interface, you will need three connections, one for receive, one for transmit and one to activate the PTT switch on your radio to allow the transmission.  I am 2/3 of the way there.  I have the send/receive portions complete, and am waiting on the parts for the PTT circuit (it requires an opto-isolator, which I couldn't get from Radio Shack).

I tested the receive and transmit using DM780, which is part of the Ham Radio Deluxe suite, and was able have a QSO via PSK31 on 14.070MHz (manually keying the mic, which is annoying).  That being said, it seems to work well, and hopefully the parts will be in soon for the PTT portion.

Here is the schematic for the receive cable.  The radio that I am using (old Kenwood TR-7730) does not support audio out via the MIC at line-level, so I opted for the 1000:8 transformer to allow me to use the speaker out jack on the back of the radio:

And here is the schematic for the transmit cable:

These are fairly basic circuits and do not require a lot of time or effort to build out.

My Parts List:

• 1 x 1:1 audio transformer (transmit cable - RS Part #274-1374 - these are getting scarce)
• 1 x 1000:8 audio transformer (receive cable - RS Part #274-1380)
• 1 x 100K Resistor
• 1 x 1K Resistor
• 2 x mono audio jack
• 2 x stereo audio jack

Time to Completion:

• This one took a few hours to put together, but quite a bit of time finding the right transformer.

Here are some pics:

(I nabbed the TR-7730 pic off of the net, but it looks identical to mine)

I decided to build this out as a stand-alone box with audio jacks instead of as a set of cables for neatness.  I'm an engineer by trade, and am rather stuffy about how wiring looks.  Stay tuned for the next installment in this post when I get the parts in the complete the PTT circuitry. 

73,

Richard, KK4JDO

Update to the PTT Mic via USB Project

So since I've gotten into trying to learn Morse code, I needed some type of oscillator, so that I can hear my key as I practice.  You can purchase an oscillator from companies like MFJ, or you can make the on the cheap with a piezoelectric buzzer and a 9v battery.  I chose a slightly different route.

My option was to add a 1/4" jack to my PTT desk mic via USB project box.  I did keep the piezo buzzer in case I wanted to practice without interacting with the PC, but I am currently using a program called MorseRabbit, which can accept input from the keyboard spacebar.  Only, in this instance, the input is coming from my straight key, which in turn is connected to the Teensy USB microcontroller, which is emulating a keyboard.

My Parts List:

• 1/4" mono audio jack (panel mount)
• 5v piezo buzzer
• bit of wire and solder

Time to Completion:

• 30 minutes, including adding the necessary code to the "sketch"

Here is a pic:

Here is a copy of the code "sketch" that I am using:

#include <Bounce.h>

Bounce button0 = Bounce(0, 10);

Bounce button1 = Bounce(1, 10);

void setup() {

  pinMode(0, INPUT_PULLUP);

  pinMode(1, INPUT_PULLUP);

  pinMode(12, OUTPUT);

  pinMode(14, OUTPUT);

}

void loop() {

  // Update all the buttons.  There should not be any long

  // delays in loop(), so this runs repetitively at a rate

  // faster than the buttons could be pressed and released.

  button0.update();

  button1.update();

if (button0.fallingEdge()) {

   // press and release CTRL

   Keyboard.set_key1(KEYPAD_PLUS);

   Keyboard.send_now();

   Keyboard.set_key1(0);

   Keyboard.send_now();

   analogWrite(12, 200);

  }

 if (button0.risingEdge()) {

   // press and release CTRL

   Keyboard.set_key1(KEYPAD_PLUS);

   Keyboard.send_now();

   Keyboard.set_key1(0);

   Keyboard.send_now();

   analogWrite(12, 0);

  }

  

if (button1.fallingEdge()) {

   // press and hold space

   Keyboard.set_key1(KEY_SPACE);

   Keyboard.send_now();

   analogWrite(12, 200);

   //analogWrite(14, 255);

  }

 if (button1.risingEdge()) {

   // release space

   Keyboard.set_key1(KEY_SPACE);

   Keyboard.set_key1(0);

   Keyboard.send_now();

   analogWrite(12, 0);

   //analogWrite(14, 0);

  }  

}

You have to forgive the sloppy wiring, it was too much hassle for this project to etch a pc board.  Now I have the ability to practice CW on my PC, both sending and copying!

73,

Richard, KK4JDO

CW aka Morse Code

So, I want to venture into the land of CW and become a true ham.  When I first attempted getting into Amateur Radio over 20 years ago, in order to gain Novice privileges, you had to demonstrate proficiency in receiving (copying) Morse Code at five words per minute.  This turned out to be my biggest challenge, and the reason that I didn't earn my license back in the late 80s.  Fast forward to today, and I still want to master this.  So, I went to my local ham shop and picked up a straight key, which of course needs to be mounted on something so that it doesn't move all over while you are trying to use it.  This lead to a small project, and the topic of today's post.  This is a quick and easy project, and didn't cost much.  I went to Home Depot to see what I could find, figuring that a block of wood would work.  Well, I found that, and then something even better.  A chunk of base molding was the exact right size, and cost around a buck.  A quick coat of paint, and two screws later, and I had a functional straight key.  Now all I need to do it learn to use it!

My Parts List:

• 1 x Chunk of base molding
• 1 x Straight Key
• 2 x Wood Screws
• 1 x Some old spray paint.  ;-)

Time to Completion:

• It only took a few minutes to mount the key once the paint dried, and only a few minutes to paint it.  The longest part was waiting for the paint to dry!

Here is a pic:

All in all, a simple, fun little project that hopefully will open up a whole new world for me!

73,

Richard, KK4JDO

Intermod and Spurious Emissions!

So, as I was scanning the 10m band, I noticed that I was receiving occasional bursts of static on my 2m radio.  These were occurring as I crossed fairly strong carriers, which means that these carriers were interacting with my rig in receive mode, and causing what is called intermodulation, which was resulting in a spurious emission.

Here are some links for more reading on these phenomena: 

http://en.wikipedia.org/wiki/Intermodulation

http://en.wikipedia.org/wiki/Spurious_emission

I recorded a quick video of it to show folks that just because you are using a receiver, it does NOT mean that you are not also broadcasting a signal!  Something to be mindful of, especially if you are in an area that is sensitive to RF fields (thinking of mining sites that use an RF signal to detonate explosives, among other scenarios).

I should probably point out that the volume on the radio that I am adjusting is completely down, the only radio that has its volume turned up is my Yaesu FT-2200 2m radio.  The sounds that you are hearing are the spurious emissions generated by my TS-440S tuned to ~28.5MHz being received by my FT-2200 on 147.120MHz.  I should also point out that these are extremely localized and can not be picked up beyond my shack.  I tried with an HT in the yard under the dipole and got nothing.  Also, I apologize for the poor quality of the video, I shot it with my iPhone 3GS, which has a pretty lousy camera.

73,

Richard, KK4JDO

Using a PTT desk mic on a PC

So in this post, I'm going to talk about a cool project that I finished a few weeks ago.  I like to use EchoLink (http://www.echolink.org/) to chat with people all over the world.  One of the uses for EchoLink, and the only thing that I use it for, is to connect to a repeater that you are too far away to hit using RF alone.  This software connects you to that repeater, and broadcasts what you say into your PC mic as if you were using a radio.  That being said, I like to feel like I am talking into a real rig, instead of talking on Skype or some other VoIP application when I am using EchoLink, especially since it is only accessible by other licensed Hams.  To that end, I had an old mic laying around, so I decided to connect it to the computer.  There were several obstacles that needed to be surmounted, the first being that the mic used an 8-pin connector for Kenwood HF radios, and the second being that you needed the press the PTT (Push-To-Talk) button in order for your audio to be sent out of the mic's audio pins.  The final issue was that the EchoLink software needs to be "keyed" as well by pushing down the space bar on your PC.  Here is how I solved these issues:

To convert from 8-pin to something that the PC could accept, I wired up the audio pins from an 8-pin male connector (the mic has a female, although it seems as though the names should be reversed) to an 1/8" female audio jack.  I mounted both in a small project box to make the assemblage a little easier to use.  This took care of getting the audio into the PC, but I still had to hit the space bar to "key" EchoLink, and at the same time hit the PTT button on the mic to connect the mic element to the audio pins inside the mic.  This was annoying to say the least.  Enter the Teensy USB Development Board:

This board connects to the PC and is recognized as one of several devices, a keyboard, a flash device, a MIDI device, etc.  The main one that I am concerned with was the ability to emulate a USB keyboard.  I soldered a connection from the PTT pins in the mic jack to one of the digital pins on the Teensy board, and another one to the ground pin.  This allows me to detect when the PTT button is depressed on the mic.  I then took this detection, and triggered a key press event to key EchoLink!  Now I can use EchoLink just like a normal radio, via the desk mic, without keyboard input.  Just for fun, I added a red LED to know when the mic PTT key is depressed (to hopefully avoid "hot-mic" issues).

My Parts List:

• 1 x Teensy USB Board ( http://www.pjrc.com/teensy/)
• 1 x Project Box
• 1 x 8-pin male mic connector
• 1 x 1/8" (3.5mm) audio connector
• 1 x Red LED
• 1 x 220-Ohm resistor

Time to Completion:

• About four hours including figuring out the code for the "sketch" on the Teensy board.

Here is the simple schematic:

Here are a few pics:

Here is the code that I used on the Teensy board (which uses the Arduino IDE environment):


#include <Bounce.h>


Bounce button0 = Bounce(0, 10);


void setup() {
  pinMode(0, INPUT_PULLUP);
   pinMode(12, OUTPUT);
}


void loop() {
  // Update all the buttons.  There should not be any long
  // delays in loop(), so this runs repetitively at a rate
  // faster than the buttons could be pressed and released.
  button0.update();


if (button0.fallingEdge()) {
   // press and release CTRL
   Keyboard.set_key1(KEYPAD_PLUS);
   Keyboard.send_now();
   Keyboard.set_key1(0);
   Keyboard.send_now();
   analogWrite(12, 200);
  }


 if (button0.risingEdge()) {
   // press and release CTRL
   Keyboard.set_key1(KEYPAD_PLUS);
   Keyboard.send_now();
   Keyboard.set_key1(0);
   Keyboard.send_now();
   analogWrite(12, 0);
  }
}

Well, that's all for this post, I hope that you have enjoyed it, I certainly enjoyed making it!

73,

Richard, KK4JDO

The Obligatory Shack Pic

So now I can show you what all of those antenna are used with!  This is a quick overall shot of my "shack" as it stands right now.  I am considering some upgrade options in the near future, so stay tuned to see what kind of rig takes center stage (thinking TS-2000 for the shack and IC-7000 or FT-857D for the truck).

Included in this pic are:

Kenwood TS-440S, 20 years old and still talking around the world!  (just talked to Russia and Ukraine!)
Yaesu FT-2200 (look for an upcoming post on lessons learned about eBay)
MFJ-941D Antenna Tuner
Heath 3A power supply for testing purposes
Kenwood PS-30 for powering the TS-440S
SignaLink USB for APRS and other digital modes (trying to talk to the ISS, but need higher gain antenna)
Wouxun UV3D HT
Kenwood TS-120S (not feeling so well these days)
Homebrew PTT Mic to USB adapter to allow me to use my desk-mic with EchoLink (look for a future post)
Shure 256T desk mic
Kenwood MC-50 desk mic
El-cheapo CW straight-key (again, look for an upcoming post)
Radio Shack SWR/Power meter


Here are some more pics:

So that sums up my current shack.  More details as things change!

73,

Richard, KK4JDO

Last antenna post for now... ;-)

Okay, last one for now.  So the j-pole works pretty well, but I was still staticy when transmitting.  What I needed was a directional antenna for maximum gain.  Again, purchasing one at the Candy Store would have been $50 or more.  But for less than $8 at Home Depot, I was off and running.  When I use this antenna, I am full-quieting on the repeater.  The downside for me right now is that I cannot permanently mount this one outside, as I need to be in the front of the house to point at the repeater that I like to use (147.120MHz,+600,PL-103.5).

My Parts List:

• 10' of 8AWG copper wire (enough for about three antenna like this, I want to make one for 70cm also)
• 10' of 3/4 PVC pipe (again, enough for multiple antenna)
• 50' of RG-58 coax

Time to Completion:

• About four hours

Here is a pic:

More information on this type of antenna can be found at:

http://www.moxonantennaproject.com/

I have to say that I am impressed with how well this antenna functions!  The one thing that I do need to add is a balun at the feed-point, that is on the project list!  ;-)

73,

Richard, KK4JDO

And another antenna!

Alright, this is almost the last one for now, I promise.  I needed something to get better reception on my little handheld Wouxun HT, but didn't feel like spending $25 or so for one from the local ham store (referred to by other hams as the Candy Store).  My solution was to build a roll-up j-pole antenna out of left-over twinlead from my dipole.  Again, before I was not able to use my HT from home as the repeater is clear across town from where I live, and 5W wasn't going to cut it with the little rubber-duck that came with the HT.

My Parts List:

• 6' of 300-Ohm twinlead
• 10' of RG-58 coax with a PL-259
• 1 PL-259 to Reverse-SMA adapter (had to buy this one, too much of a pain to make it)

Time to Completion:

• 30 minutes or so

Here is a pic:

So admittedly I need a better pic of this one.  I'll work on that...

73,

Richard, KK4JDO

First Antenna, 1/2 wavelength 10m dipole

Hi All,

So, since this is about Ham Radio, you had to have guessed that there would be talk about various types of antenna.  I have a terrible dislike of spending money, so instead of buying my first antenna, I decided to build one instead.

As a newly minted Technician class Ham Radio Operator, the only HF bands that you have voice privileges on is the 10-meter band (28.3MHz - 28.5MHz).  You can operate CW on a few lower bands, but since I am still in the process of learning Morse Code  (CW), I decided to build an antenna for use where I can talk on voice (using what is called SSB or Single Side Band).

A dipole is a very basic antenna, and very easy to build.  Basically, you need some wire, and something to use as a feedline, such as coax or twinlead.

My Parts List:

• 20' of stranded copper wire
• 1 x 3/4" PVC "T" fitting
• 2 x 2" pieces of 3/4" PVC pic as insulators
• 20' of nylon rope
• 100' of 300-Ohm twinlead from Radio Shack

Time to Completion:

• One hour to measure, cut, solder, mess-up, re-do, and finish.
• One additional hour to hang between two trees.

Here is a quick pic:

Once it was up in the air, I connected it to my radio via my tuner, and was talking to California, Idaho, Montana using SSB on 28.4MHz!

That it for this post, hope you enjoyed it!

73,

Richard, KK4JDO