[K6BW] Re: standalone TNCs

[Bill Smith]

Regarding digital modes and digital signaling, the question of interface boxes has come up.  This was part of a reply.

One wonders why the devices are so limited in functionality and so expensive.  The Tigertronics is simply a box with cables that allow you to plug your radio into your computer soundcard.  Can you simply use cables without the box?  Yes.  I have cables without any sort of box.  One end of a cable plugs into the radio and the other plugs into the computer.  Another cable plugs into the computer and plugs into the radio (one each for send and receive audio).  A third is used to key the PTT circuit.  They are presently coiled up in a plastic bag and are stored with the laptop.

MFJ, Rigblaster and a bunch of others offer similar products.  They are not TNC's.  They just include plugs which offer to eliminate frustration on the part of the buyer.

A TNC is a "terminal node controller."  It can take audio and turn it into useful digital signals which are used by a terminal to display information.  A TNC doesn't need a computer, in fact they often are designed with CPU's inside them to handle the features they support.  Popular TNC models are PK-232, KAM and MFJ-1278.

A TNC does need a display/keyboard device, such as a "terminal" (old dumb terminals consisted simply of a display and a keyboard, with very limited curser location/screen address processing).  This function can readily be supported by a computer with a program such as Hyperterminal.

Unfortunately, or fortunately if you will, digital protocols have been invented that take advantage of soundcard technology.  They work better than earlier TNC-supported protocols because they are more sophisticated.  Traditional TNC's can't decode these protocols because they don't have any or at least enough DSP (Digital Signal Processing) capability.  Standalone TNC's with sophisticated DSP decoding are not likely to appear because the low cost of computers have made the development of such devices uneconomical.

Software programs take the place of TNC's.  Audio from the radio transceiver is wired to the input of a sound card.  Inside the computer, tones are digitized by the sound card and computer software program.  Additional software provides protocol decoding and terminal emulation.

Same for transmit, the computer and sound card accept data entry from keyboard or disk and generate the digital protocol and generate audio tones. The tone output from the sound card is connected by wire to a radio transceiver.

All you have to do to work with digital communications is load software in a computer, and hook up the wires to your transceiver.  

Well, almost.  You do have to worry about isolation and signal levels.  But experimenting is a big part of the challenge, and a great vehicle to learn something.

73 de Bill, AB6MT
billsmith at ispwest.com

  
  ----- Original Message ----- 
  From: K6 BBQ 
  To: Bill Smith 
  Sent: Saturday, December 04, 2004 4:03 PM
  Subject: standalone TNCs



  Hello Bill,

  Well you hit the nail on the head with my question or dilemma. 
  I don't want or need a packet mailbox and am not going to leave any
  rigs, computers or phone lines on 24 hours a day or even 12 hours.

  I would need something (maybe just the TNC, not sound card box like MFJ)
  portable most likely. The TNCs confuse me as I think that the Tigertronics
  box lets you work all of these modes with stereo cables and the interface box.
  At least with the Tigertronics' SL-1+, I don't need to disconnect my mic because of its use of the back accessory ports on my Kenwood 570. But
  still, the box SL-1+, Rigblaster Nomic, etc.) aren't TNCs most likely.

  Confusing. 

  I think a Kantronics would be overkill for me.

  Gotta go, talk with you later,


  73 

  Rem

  On Saturday, Dec 4, 2004, at 15:42 US/Pacific, Bill Smith wrote:


    For your portable work, standalone PSK31 TNC's look attractive.