Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Null Modem Serial Cable or Non-Null Modem Serial Cable  (Read 1673 times)
N8EUI
Member

Posts: 146




Ignore
« on: March 23, 2012, 12:30:54 PM »

Hi all,

When connecting a packet radio system and the TNC needs a cable with a male DB25 connector at one end and a DB9 female at the other, do I use a null modem serial cable or a non-null modem serial cable?

Thanks,
Tom, N8EUI
Logged
W8JX
Member

Posts: 5321




Ignore
« Reply #1 on: March 23, 2012, 12:38:55 PM »

Kinda depends on TNC. It is is a design from 90's or older, you will likely need one. If is is a newer design you will likely not need one.
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
K0JEG
Member

Posts: 622




Ignore
« Reply #2 on: March 23, 2012, 12:44:22 PM »

TNCs are considered Data Communications Equipment (DCE), which have 9 or 25 pin female connectors. Computers are Data Terminal Equipment (DTE), which have 9 or 25 pin male connectors:

http://en.wikipedia.org/wiki/RS-232#Connectors

Straight through, 9 pin to 25 pin cables or adapters will work. A null modem cable is for connecting 2 computers together directly without a modem in between.
Logged
W8JX
Member

Posts: 5321




Ignore
« Reply #3 on: March 23, 2012, 01:01:14 PM »

While it is true that you need a null modem to connect old PC's i do recall needing it for some old modems and TNC's too long ago.
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
N4CR
Member

Posts: 1650




Ignore
« Reply #4 on: March 24, 2012, 02:40:35 PM »

Serial communications require a minimum of three signals to operate. More if you are going to use hardware flow control. If you assume you do need hardware flow control you can't go wrong.

Gnd, Tx and Rx. Get the pinouts of each end and determine if each end is DCE or DTE.

If the ends are different, you need a straight through cable. If both ends are the same (and it doesn't matter which both) you need a null cable. A little investigation of your connections will reveal which cable you need. Look specifically for the Tx and Rx pins.

There is an excellent description here: http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html#anchor242192
Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!