5-Inch Sky Robot
FDM in Vacuum
Custom Discovery Roof Rack
August, 2012 - Sierra Backpacking
July 22nd, 2012 - Hiking in Santa Barbara
July 15th, 2012 - Valley of Fire
May 5th, 2012 - Afton Canyon
April 28th, 2012 - Devils Playground
Convict Creek Trail
January 2012 - Mustangs
January 3rd, 2012 - Heart Lake
August 7th, 2011 - Kelso Dunes
August 5th, 2011 - Lundy Canyon Hike
August 2011, Mammoth Archery
Birds in the garden
June 4th, 2011 - San Gorgonio
May 29th, 2011 - Sequoia National Forest
April 23rd, 2011 - Living Desert
April 2nd, 2011 - Death Valley
March 8th, 2011 - Mountain Palm Springs
February 13th, 2011 - Iron Smelt
November 13th, 2010 - Mojave
October, 2010 - Mammoth
September, 2010 - Mammoth
September, 2010 - Duck Lake Trail Backpacking
Iron bloom forging
August 28th, 2010 - Mt. San Jacinto
OSM Import: US Designated Wilderness
July 25th, 2010 - Mojave Mustangs
July 17th, 2010 - Mojave Exploration
Bloomery furnace iron smelting
Open Street Map: Mojave Project
June 13th, 2010 - Mojave
June 6th, 2010 - El Cajon Trails
Wolf Mountain Sanctuary
March 28th, 2010 - Salton Sea
March 21st, 2010 - South Main Divide
March 13th, 2010 - Anza Borrego Wildflowers
March 7th, 2010 - CSULB Japanese Garden
February 2010 - Mammoth
Dakota and Asha Celebrate Christmas, 2009
November 21st, 2009 - Mojave Road
November 14th, 2009 - Anza Borrego
Exploring The East Mojave: The Afton Canyon Area
Broken flex plate
Remote Image Serving
Astro/night photography in Inyo National Forest
Wild Mustang Sightings
September 26th, 2009 - Night Photography In Frazier Park
August 15th, 2009 - Catalina dive trip
January 24th, 2009 - Mojave Exploration
July 2008 Mammoth Vacation
President Barack Obama!
April 12th, 2008 - Wildflowers and Landmarks
My Grandfather's Alfa Romeo Spider
March 8th, 2008 - Carrizo Plain
Bridge To Nowhere
October 20th, 2007 - Big Bear Camping
October 22nd, 2007 - Fire
Scottish Highlands, Aug 7th, 2006
Scottish Highlands, Aug 6th, 2006
August 5th, 2007 - Duck Lake Trail
May 26th, 2007 - Kelso Dunes
Culloden Battlefield, Aug 5th, 2006
May 20th, 2006 - Irwindale Renaissance Faire
Edinburgh, Aug 4th, 2006
The Clifs of Moher, Aug 3rd, 2006
The Burren, Aug 2nd, 2006
Bunratty Castle, Aug 1st, 2006
May 5th, 2007 - Mojave
Truck Audio/Data Network
2007 - Master Bath Remodel
The Ring of Kerry, Jul 31st, 2006
Victory in 2006!
Blarney and Killarney, Jul 30th, 2006
Dublin and Cork, Jul 29th, 2006
Dublin, Jul 27th & 28th, 2006
What Can I Do?
April 30th, 2006 - Anza Borrego
New desktop: Intel 805 D
Jan 7th and 14th, 2006 - Hiking
Whiting Ranch Hiking
Digital Photography with Linux
September 5th, 2005 - Living Desert
August 19th, 2005 - Mammoth
Hiking and Photography
July 30th, 2005 - Tucker Wildlife Sanctuary
Death, Fright and Photography
May 14th, 2005 - Red Rock
April 2nd, 2005 - Death Valley
Count Every Vote Act of 2005
Linear Logic ScanGuage
November 6, 2004 - Mojave
Super Tuesday, 2004
Canon A80 Camera
Jul 25, 2004 - Death Valley
May 4th, 2004
Landscaping - My Front Slope
Stump Pullin' Yeeee Haw!
Feb 22nd, 2004
Feb 16th, 2004
PostgreSQL Logfile Analysis
Mountains? Desert? Jan 30th, 2004
Jan 28th, 2004
Ceiling Cargo Basket
Front Bumper Version 2
Land Rover Valve Jobs
The Matrix: Revolutions
Greg Davis CDL Linkage
Mom's Turkey Gravy
Julian Pie Company
The KB1DIG 2-meter Halo Antenna
Gardening is hard!
Aug 13th, 2003
SQL and Perl
Jul 9th, 2003
Jun 17th, 2003
Some People's Comments
Dakota is a silly dog
The Matrix: Reloaded
Chris' Stage Bottle Harness
April 23rd, 2003
DVD Burning Under Linux
My Satellite Phone
My Near-Death Experience
Laser Cannon Revival
Front Bumper, Version 2
KPC 3 Plus and HTX-252
Moving, moving moving...
New new house
In Truck Dr. Pepper
My Favorite Toilet
Late Thoughts: Dr. Pepper Cooler
265/75-R16 Tires on a DII
George W. Bush
Horses Sep 14 2002
August 17th Yukon Dives
My Custom Front Bumper
Bracketless, Renamable Links
Jul 28 2002 Day Trip
Jedi Group, my T1 and money
A Bumperless Discovery!
My Custom Rear Bumper
Vanessa's 24th Birthday
Jun 30th Dive to Long Beach Canyon
PHP/PostgreSQL String Quoting
Tonsillectomy, Uvulaectomy and Turbinite Reduction
240 Watt CO2 Laser Cannon
The Tulsa Rib Company
The quality of hard disks these days
Email notification of articles
Email notification of comments
erikburrows.com source code
Renisance Faire Jun 9, 2002
Computers hate me, and it is mutual.
Star Wars Sucks!
Horses, Jun 1, 2002
Land Rover Mileage
Insomnia, Robin goes evil.
100 Watt Diode Laser Test Firing 1
2001: A Space Odyssey
TDI Deco Class
Horses, Apr 30, 2002
My Truck Batteries
The Zope Bible
100 Watt Diode Laser
The New www.erikburrows.com
Hunter the Kitty
Matts Desert Pics
|KPC 3 Plus and HTX-252 -   2002/12/09||Viewed 105 times this month, last update: 2004/11/27|
|I've been asked how I wired up my Radio Shack HTX-252 2 meter FM HAM radio to my Kantronics KPC 3+ TNC.|
Actually, I couldn't find out how to do it either, so I kind of had to figure it out on my own. The hard part is that the HTX-252 doesn't detect PTT as most radios do, by shorting PTT to ground. The HTX-252 detects PTT by shorting one of the mic pins to an isolated ground. The specifics of this mechanism are out on the 'net somewhere... I couldn't find it again. Sorry.
The basics are this:
Here's my hand-made diagram:
- Connect the center pin of the HTX-252's audio out jack to pin 5 of the KPC 3+ DB9 connector
- Connect the ground of the HTX-252's audio out jack to pin 6 of the KPC 3+ DB9 connector
- Connect pin 1 of the HTX-252's DIN-8 microphone jack through a 5% 2200 k ohm resistor to pin 3 of the KPC 3+ DB9 connector
- Also connect pin 1 of the HTX-252's DIN-8 microphone jack through a 104k capacitor to pin 1 of the KPC 3+ DB9 connector.
- Open up the KPC 3+ and jumper the J9 center pin to the 'HT' pin.
- Optionally, connect pin 2 of the KPC 3+ to pin 2 of a DB9 connector, and pin 6 of the KPC 3+ to pin 5 of the DB9 connector to connect up to a GPS for position data, to be read from the GPSPORT of the KPC 3+
Click to enlarge
If I were to setup another APRS station, I would not use the Radio Shack HTX-252. It's signal is very noisy, and it's recive quality could be much better. Also, it's display uses quite a bit of juice, so, if I were to do it again, I would use one of the 'data radios' available, which operate at a set frequency and mode, and have no display. (Unless of course, this other radio may be used manually in an emergency.)
Last week, I noticed that every time my radio transmitted a packet, my FM sterio would fuzz. Worse, when I was listening to my CD player via one of the fake-tape doohickeys, it would Fuzz too. Then I noticed that while working in my garage, the FM sterio on my workshelf woulf fuzz. It seems the HTX-252's noise gets worse with age. I've had to turn off my transmitter, since I'm certainly not licensed to transmit into the FM broadcast band!
I need to take back the above. The HTX-252 did not die. It was another casualty of the Death Valley washboard roads. The antenna wire nut got vibrated right off! Yesterday I screwed it back on, and all is well.
William Avery e-mailed me with lots of informational links about the HTX-252:
The HTX-252 Service Manual which you can order from Radio Shack is:
Cat# 12276358, MANUAL SERVICE 19-1127 ; NP Part # MS1901127
This was listed on a partial parts list at:
from the official HTX-252 web-support site:
"Product: Amateur Radios
Question: How do I get a schematic and/or pinouts for my radio?
Answer: For schematics or pinout information, you would need to reference the Service Manual for the radio. Service manuals can be ordered by contacting either your local RadioShack store or by calling RadioShack.com at 800-241-8742"
The second quote is from a more up-to-date-site at:
Additional Support is listed on:
The HTX-252 Microphone Pinout is at:
The commercial unit called "RASCAL GLX" with a HTX-252 cable, which is for
TNC/sound card use, is available at:
There is a site which sells Ham Manuals, including the HTX-252 (#19, for $16.00), at:
A free source of manuals is at:
http://www.hamanuals.com/miscmans.html , where the Owners Manual is at:
And the 50 page Service Manual (for Albrecht AE-540, which equals R.S. HTX-252):
Finally, the Microphone Manual is available separately from the Service Manual at:
There is a site which has a few related comments on HTX-252 modifications:
There is a neat description of one man's efforts to make an interface, described in a newsletter called Smoke Signals [ http://www.qsl.net/k3smd/smok1001.pdf ], and the last article by Don Munson, W4GFQ, called "HOMEBREWING, A LOST ART?", has a link to another effort by Stephen A. Smith, WA8MLF, at:
http://members.aol.com/wa8lmf/ham/tonekeyer.htm with 3 designs documented there.
KD7PLU / trooper (2003-01-23): Yes- KPC3+ and HTX-252 was a great idea on paper. But the HTX-252 radios are not worth the effort. I was dumb enough to buy six of them on close-out for 99 bucks each. Two of them worked, three didn't. Alinco just came out with an inexpensive TNC-integrated radio, and the Vertex VX-150 with a 4-pin to standard Spkr/Mic adapter makes an ideal APRS radio if you're usually close to some kind of Wide node.
Rich/N2ROW (2004-01-14): Can you email me the mic wiring for the htx-252. Thanks email@example.com
k1lwi (2004-10-12): looking for a schematic diagram htx 252 can you help 73 wen k1lwi e mail firstname.lastname@example.org
Erik (2004-10-13): Sorry, I don't know where you could get the full diagram for the htx 252.
anonymous (2005-09-12): My HTX-252 transmitts OK, but the receiving side seems to have a problem with the squelch opening. I get NO audio on regular signals, but a strong repeater in the local area open the squelch OK. Is there a control someplace inside the unit to rectify this condition?
Erik (2005-09-13): W6ORS, you're saying your squelch is not opening enough? Maybe it's just the potentiometer, which can be replaced, if you're careful. Are you using this radio for APRS? If so, you can probably just short the squelch open, and let the TNC pick out the signals itself.
N0YXV (2007-10-17): APRS no longer uses 'WIDE' for digi's. To reduce QRM APRS now uses WIDEn-N in place of WIDE. To use WIDEn-N effectively you would replace the N's with a number between 1 and 3. (i.e. WIDE3-3). In place of RELAY APRS now uses WIDE1-1. Mobile paths are usually set with two settings WIDE1-1, WIDE2-1. I live in a sparcly populated APRS area and even a path as small as WIDE2-2 easily covers 200-300 miles.
Brian KJ4AGA (2008-11-21): Do you know where I could find another microphone for the htx252?
KB1GVR (2008-12-21): I've had my HTX-252 on APRS/PKT wired to an MFJ-1274 since 2001 and got the schematics from my local RS dealer.
BJ452 (2009-02-25): IS anyone still interested in the 252 - I bought one for $40, soldered a spare wire into the microphone plug to allow both Mic and TNC use. The Mic line has 5v so I let the PTT line form TNC ground it through a 2.2K resistor wiht a .02uf cap to decouple - works a treat for may packet stuff.
Don Keyes (2009-02-25): Will some please help!!! I have the PK-232 and HTX-252 radio to use for packet. Is there a mod or wiring for this? Don N7OTO email: email@example.com
Joe N4SP (2010-04-12): Approximatly what levl should the audio out be set to to run into the APRS TNC?
Erik (2010-04-13): Joe,
I've found that the KPC isn't too picky. Some experimentation may be worthwhile, but I found "somewhere in the middle" works well. If you live in a high traffic area, just watch the "Rx" light on the KPC as you manipulate the volume knob on your radio.
Bill (2011-01-23): i have a problem with my htx232 when i add offsets to my radio
then i transmit an e shows after i try to save in memory
Paul (2012-11-15): I have an HTX-252 and a KPC-9612+. I'm trying connect the two, but I don't have any resistors or capacitors on hand. Will it brick the radio if I wire it up like you have it and don't use any resistors or capacitors?
Erik (2012-11-15): Paul, I don't know if building this circuit without the capacitor and resistor would fry your radio or TNC, but I'm pretty sure the circuit would not work, so it's probably not worth trying. I suggest going down to your local Radio Shack to get the proper components.
See also: APRS