[Heathkit] *** Off topic*** Attack on VHF and UHF

[Jim Vohland]

Well being a ex Navy communications guy: (Info from a navy pub) 
 
 
Duplex 
Duplex   describes   a   communications   circuit designed  to transmit  and  receive  simultaneously.  In such operations, each station transmits on a different frequency  and  both  stations  transmit concurrently.  Both stations are required to keep transmitters on the air at all times and to send a phasing signal at the request of the distant end.
Figure 1-11 shows a diagram of a UHF/HF full-duplex  FSK  (frequency-shift keying)  single-channel teleprinter relay circuit. There are two types of duplex operation: full duplex and half duplex. Full duplex (FDX) refers to a communications  system  or  equipment  capable  of transmitting simultaneously in two directions. Half duplex (HDX) pertains to a transmission over a circuit capable  of  transmitting  in  either direction,  but  only  one direction at a time. Small  ships  traveling  in company  normally use duplex in a task group common net in which they terminate with a larger ship that is serving as net control. The net control ship provides the ship-shore relay services. Ships  traveling independently can use this system for anon-call ship-shore termination to transmit their outgoing messages. 
 
 

Simplex 
Simplex is a method of operation that provides a single channel or frequency on which information can be exchanged. Simplex communications operation is normally reserved for UHF and those ships that do  not  have  sufficient  equipment  for  duplex operation. In some cases, a simplex circuit can be established when equipment casualties occur. Where no HF simplex frequency is indicated or guarded, ships requiring a simplex ship-shore circuit must call on a duplex ship send frequency. The ship must state "SIMPLEX" in the call-up, indicating that the ship cannot transmit and receive simultaneously When a ship requests simplex operation on duplex circuits, the shore station may be required to shift transmitters  prior  to acknowledging  call-up.  If  no  reply is received within 45 seconds, the ship should repeat the call-up procedures. If a third attempt is required, the ship  should  check  equipment  to  ensure  proper operation 
 
 
Semi-duplex 
Semi-duplex   communications   circuits,   used primarily  on task  force/task  group/ORESTES,  are  a combination  of  the  simplex  and duplex  modes.  All stations  except  the  net  control  station  (NECOS) transmit and receive on the same frequency. The NECOS  transmits  and  is received  on  a  second frequency.  The  NECOS  may  transmit  continuously, whereas all other stations must transmit in accordance with simplex procedures.

So Semi-duplex does exist in some situations. Of course any mode is enhanced if Heathkit equipment is used.
 
 
 

> Date: Mon, 30 Apr 2012 17:04:11 -0400
> From: n2ie at arrl.net
> To: heathkit at mailman.qth.net
> Subject: Re: [Heathkit] *** Off topic*** Attack on VHF and UHF
> 
> Yes, I understand the differences in forms of duplex operation. The 
> catch-all term "duplex" doesn't specify which, but I assumed hams would 
> understand which one I meant. BTW, I believe the correct term is 
> "half-duplex", not "semi-duplex", the alternative being "full-duplex."
> 
> Kevin N2IE
> 
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