Wednesday, December 31, 2014

CDM 1550 duty cycle

My good friend Tom KJ9P did some testing of the use of Motorola CDM 1550 mobile radios as repeaters. You can use these as repeater receivers or transmitters, but you will need to add a cooling fan. I also recommend not running higher than 50% of the rated power output.

Here's Tom's results:

At idle, and both receivers on, the power consumed is .4 amps.


At Low Power Transmit (8 Watts out) the power consumed is 2.6 amps.


At High Power Transmit (22 Watts out) the power consumed is 4.0 amps.


Temperature rise after one minute of keydown on either low or high power is two degrees with fan cooling 100% of the time.

Wednesday, December 3, 2014

McLean County Illinois DSTAR Coverage

I've found that there are two site options when you're building a repeater...find a really tall structure (tall relative to terrain) or put up multiple sites. We've not had much luck finding a really tall structure in Bloomington, IL for our DSTAR system. So we've got two sites active right at my farm in Heyworth and one in North Normal at KJ9P's QTH. By having two sites active, we've filled in most of the geography for the county. There are still some spots that are aren't going to be able to use a handheld from downtown Bloomington. But hey, we're amateurs and we're learning!

Tuesday, December 2, 2014

DSTAR Commands - A Quick Guide

Reading through all of the DSTAR documentation can get a little crazy. Here is a quick reference on linking commands. 

There are four callsign settings on your radio that you can adjust. They are:

MYCALL: Should always be your callsign, like KG9DW

RPT1: Should be the callsign of the repeater module you're connecting to, with the callsign in positions 1 through 6, a space in position 7, and then the module letter. The module letter is B for UHF or C for VHF; So for Heyworth, that would be KD9AKF B. For Normal, that would be WX9WX  B. Notice that because Normal is a 2x2 call, you have two spaces between the X and the B.

RPT2: If you want to use the gateway (not have your traffic only stay local) then this should be set to the same as RPT1 but the module letter (position 8) should be G. So for Heyworth KD9AKF G or for Normal WX9WX  G. Almost always, you'll want to use the Gateway.

URCALL: This is where you put the command you want the repeater to do.

The fun is with URCALL:

CQCQCQ means let your voice be heard everywhere.

E in the 8th position does an echotest - it repeats your audio back to you.

I in the 8th position tells you if the repeater is linked, and what it is linked to.

U in the 8th position unlinks the repeater if it is linked.

L in the 8th position, with a callsign+module or reflector name in positions 1-7 links the repeater. For example, REF001BL links the repeater to reflector 001B. KC9YFXBL links the repeater to the Decatur repeater. 

*** IMPORANT *** : After you use the E, I, U, or L commands, switch back to CQCQCQ to carry on a QSO! If you keep sending a link command, the repeater will keep linking or relinking and no one will hear your call!

A typical use of the repeater to link to reflector 001B would be:

1. Key up with I to see if the repeater is linked
2. To link, key up with REF001BL
3. Switch to CQCQCQ and begin your call or QSO

A typical use of the repeater to link to Decatur would be:

1. Key up with I to see if the repeater is linked
2. To link, key up with KC9YFXBL
3. Switch to CQCQCQ and begin your call or QSO

Feel free to leave the repeater linked...linking invites more QSOs and more traffic! If you are working on your radio or want to just play, unlink the repeater so that only local users hear your testing.

Whew, that's a lot to understand. Not to try to confuse you, but you can use DTMF codes with our non-ICOM repeaters as well. This allows you to link without having to program up your URCALL. This is useful when you want to link to an odd-ball reflector. For information on those commands, visit:

Above all, have fun, and let me know if you need help!

73, Michael

Monday, December 1, 2014

Cabling a DVRPTR board to a CDM1550 for a DSTAR Repeater

I'm playing with a couple of CDM1550 radios to be used as another DSTAR repeater. I've had pretty good luck with the Kenwood TKR-820, although it can be very finicky. You're using early 80's technology with the Kenwood, where you're using 21st century tech with the CDMs.

Here's how I've cabled my board to two CDM1550 Motorola UHF radios:

CDM1550 (T=transmitter, R=Receiver), purpose, DVRPTR
T5, tx mod in, 1 red
R11, rx dis out, 4 black
T3, PTT, 3 grey
T7 and R7, grnd, 2 green
R15, cos/rus, 6 blue
T10/R10, ignition sense, connect to 12V

You'll also have to do some programming in the CDM:
1. Turn on the flat tx audio when using the external ptt line
2. Set accessory port 3 to be PTT when low
3. Set the tx power low (I'm using 10 watts, and keyed down for 20 minutes wasn't too hot on the heatsink)
4. Set the transmitter timeout to 180 seconds for each channel
5. Set the on/off to be the front panel button and also the ignition sense wire

You need to take pin 10 to 12V so that if the power supply goes off, the radios will power back on by themselves. Without this pin connected, a power failure will cause the radios to stay off when the power returns!

A big advantage of the CDMs is the ease at programming the frequencies. With the right software, it is a breeze. The problem, the software isn't cheap. Luckily I have the software available from my work at the fire station. 

For my setup, I put both the transmit and receive frequencies in both radios as simplex channels. That way, if my transmitter finals go bad, I can swap the accessory plugs, change the selected frequency on each radio, and be back on the air. Of course, if the finals go out, it likely is because of an antenna system failure or because I ran the transmitter too hard!

UPDATE: Here's a pdf version of the wiring diagram that Tom KJ9P created. Thanks Tom!

Saturday, November 22, 2014

Disabling internal controller on TKR-820

From Mark, N9WYS:

Remove the internal signaling unit. (I'm looking at the TX/RX Unit in the service manual, Page 83, and the Signaling Unit, Page 76.) Unplug both cables from the signaling unit and add the jumpers to the connector.

On CN6 of the repeater TX/RX Unit, or at the cable connector end for CN1 of the Signaling Unit, apply a jumper to pins 2&3, 8&9, 10&11.
Pin 2  = PTT
Pin 3  = KEY
Pin 8  = AFD
Pin 9  = DET
Pin 10 = AC
Pin 11 = GND

That way, if the external crashes, you can plug the internal back in and still be operational.  If the external controller is wired CORRECTLY to the 15 pin accessory plug, it WILL work properly. 
I've used the solid copper 24g telephone wire to short the connections, secured with black tape.  My personal preference was to insert the jumper wires into CN1 connector at the Signaling Unit end of the cable… to reverse the modification, all one needs to do it remove the jumpers and plug the Signaling Unit back in.

NEVER use the internal controller with an external controller. You are
asking for problems.

DVRPTR to TKR-820 cabling

Here's how I've cabled my board to a TKR-820 UHF repeater accessory port:

TKR, purpose, DVRPTR
3, tx mod in, 1 red
4, rx dis out, 4 black
8, PTT, 3 grey
11, grnd, 2 green
13, cos/rus, 6 blue

Also connect pin 1 to pin 11 on the TKR to disable the internal controller. You also should jumper the controller so that you don't create an unintended audio path.

Kenwood TKR-820 DSTAR LSB-208

I found this service bulletin one time, but I haven't been able to find it online since. I'm uploading it here so others will be able to access it. It is a simple mod for TKR-820 repeaters used for DMR or DSTAR. By removing a capacitor on the display unit, the output waveform to the modem is less distorted. I've seen only minor improvement in error rates, but every little thing helps.

To access the capacitor, you remove the top and bottom covers. Then remove the left and right top screws holding the front face in place. Tilt it down, and you have access to the capacitor. You do not need to take the knobs off, or remove the from face from the unit. Total time is less than 15 minutes to complete.

Good luck!

Tuesday, October 21, 2014

Ham radio with a low power radio

If you've been following my posts lately, you've seen more of a move from the "farm life" to the "ham life"...ham being amateur radio. I've re-kindled my interest in amateur radio. I sold the radio I purchased a year ago on ebay and bought a used Elecraft KX3. This is a truly modern software defined radio. It's quite the to the world with a radio that fits in your hand and an antenna made from 40 feet of wire.

Besides the technology differences between the FT897 I had before and the KX3, there's a shift in operational thinking. The FT897 is a 100 watt, bulky, mainly fixed based unit. Yes, you could mount it in the car and take it camping...but it certainly isn't something you want to pack around for a while. The KX3 is small - it fits in your hand. It is low power - 10 watts or so if you connect it to external power, but it shines running 5 watts or less off of 8 AA batteries.  While I do operate from my home office, I also enjoy sitting on the porch and listening for new people to meet.

In my few weeks of ownership, I've noticed a shift in my operating patterns. I'm spending more time doing CW (morse code). I'm still doing a little PSK. And I've made 3 voice contacts with a piece of wire temporarily strung up to a low tree branch. This weekend I worked a special event station in Georgia after hanging up my wire on my Mom's porch. It was pretty cool...

Sure, I can Skype all over the world. Need to get a message to a friend? Facebook or LinkedIn is probably my first choice. But when it comes to meeting new people, ham radio, and especially low power (aka QRP) operations are the way to go.

Friday, September 26, 2014

UPDATE!!!! Evergreen FS in Bloomington IL - no guns - no Michael

UPDATE 10/17/2014:

I received a phone call from Mr Kendall Miller, general manager for Evergreen FS. They have decided to take down their no guns signs in response to my letter and the many others received from across the area. Thank you Mr. Miller and I'm happy to be able to visit FS FarmTown again!!!!

Original post from 9/26/2014:

Dear Mr Jon Thomas - Manager FS FarmTown -

I've been a patron of Evergreen FS for 7+ years. I routinely buy fuel as I've found your diesel to be of the highest quality. Today I stopped by and purchased propane for the first time this year. I noticed the no guns signs on your doors. I'm disappointed by your decision to post your business in this fashion.

I will no longer be patronizing your facility now that you've decided to limit my ability to protect myself. Although your staff has always been friendly and helpful, I am doubtful that they can ensure my security. 

I would never have noticed your signs as I never go inside. But today I did and now I know that you have chosen to restrict my rights. 

I will share your decision with my friends, fellow farmers, and colleagues. Should you chose to revisit your policy, please let me know. I would welcome the ability to provide you with the money I spend each week in diesel.


Wednesday, March 19, 2014

Illinois D-STAR Net

Every week on Wednesday nights at 9pm Central is the Illinois D-STAR Net on Reflector 001B. Normally hosted by Milt, K9QZI of Champaign, the net attracts amateurs from across the state to share the events of the past week. We spend a few minutes each talking about the hobby and just keeping track of each other.  Sometimes 10 people check in and we're done in 30 minutes, and other times it's over an hour!

If you're in Central Illinois, you can catch the net on the W9YR, W9PIA, or KD9AKF repeaters. And if you're using our Heyworth repeater, feel free to move it to REF001B if it isn't already there for the net!

Tuesday, March 4, 2014

How much to put up a D-Star HomeBrew Repeater?

We've got the Heyworth D-Star on the air...and completing the testing. I've gotten a couple of questions about how much it all costs. So to share with everyone, here's what we've invested:

Used Kenwood TKR-820 UHF repeater, narrowbanded $270
Duplexer - notch only, mobile type, donated $0
DVRPTR d-star connection, with cables and enclosure $130
Raspberry PI computer board, with case, with heatsinks, with power supply $70
Coax, donated $0
N-Connectors $12
Power strip with surge connector $15
Coax surge protector  $35
Antenna, donated $0

All together, we have $532 invested in the KD9AKF system. If you were building a comparable system, you would probably spend another $100-$200 on a duplexer, $100 for coax, and then anywhere from $150 to $350 for a quality antenna. Low end, you're looking at $900 for a complete system - high end, you should be under $1400.

We went really quick getting our system up and running - we went from "idea" to "working system" in 60 days. We'll end up having another $100 in labor costs to get the repeater reprogrammed for our final coordinated frequency.

We also have been really fortunate to have a great working relationship with the local grain elevator that is providing us with tower space. We're also getting a free internet connection from the wireless internet provider that is co-located at the elevator. How sweet is that!

Wednesday, February 26, 2014

Heyworth D-Star Ham Radio Repeater

My ham radio adventure continues. I know I haven't written much about life on the farm lately, but since it is so cold not much farm or outdoor stuff is getting done! I have started working a new mode in ham radio - Digital Voice, specifically D-Star! With the help of my buddies K9GUN, KC9REG, KB9GIG, and KJ9P, the Heyworth D-Star repeater is on the air! It's under callsign KD9AKF on 444.2375. You can read more about it on our QRZ page ( This hobby is really, really fun!

Monday, January 20, 2014

APRS digipeater with a Raspberry Pi

For Christmas this year I received a Raspberry Pi. This is one sweet little computer! I also asked for (and got) an TNC-X board that you build and then plug into the top of the Pi. I now have a fully-functional APRS I-Gate and fill-in Digipeater up and functional here on the south side of McLean County. The stats are remarkable...and after some fiddling, filtering, and optimization, I've got it working just like I want. There are a few wide-area digipeaters in the area, but not many I-gates. While digipeaters allow mobile or portable stations to get their packets out to a broader audience, an I-gate takes APRS traffic from the internet and puts it out on the RF. Likewise, it take RF traffic and puts it back on the internet. Using a program called aprx, I'm running a digipeater and I-gate all from the little Pi! A local member of the Central Illinois Radio Club (CIRC) had an Alinco 2m rig he wasn't using anymore. That, along with the homebrew j-pole antenna I built, makes for a pretty good station. I'm only 30' up in the air, but we're on a bit of a rise. I'm copying stations from up to 75km away.

Heyworth UHF repeater update

The KG9DW Repeater in Heyworth is up and running on the Tate and Lyle Grain Elevator! This puts the repeater up at about 200' AGL. I made a trip to Indiana this past weekend and I was able to work it from Champaign. That's a pretty good haul for a kludged together UHF ham repeater. The antenna is a 8 element Decibel antenna, with 9 to 11 DB of gain (depending on who you ask). The antenna was abandoned from a farm operation that moved to Nextel or phones or something. This made the move a near non-event. The only hard part was routing the coax into the pressurized room. The previous coax had been removed, and the hole had been filled in. A little chiseling (without a chisel) and I was in. I've been working guys all over McLean and Dewitt counties, and even some down into Logan county. Give a hollar anytime on 442.825+ 141.3PL.