Rising Sun Member Forums  

Go Back   Rising Sun Member Forums > Other Hobbies > Ham & CB Radio Corner

Reply
 
Thread Tools
  #11  
Old 01-17-2008, 03:52 PM
DaveInDenver's Avatar
DaveInDenver DaveInDenver is offline
Hard Core 4+
 
Join Date: Jun 2006
Location: Larimer County
Posts: 6,586
Default

No, it's sort of duplex (called half duplex). Duplex means that the channel is two directional at the same time. Like your telephone, you both can talk and hear at the same time. With a repeater, you have an input frequency and a retransmitted frequency. But when you key the mic, you can't hear anyone else on the repeater. So you are picking between one or the other half of the duplex channel. If you have a dual VFO radio, then you could tune both sides to the repeater output (say 145.145) and when you transmit on one side, the other would still listen. This causes feedback, though, if you have the volume up. But if you wore headphones, then you could hear your transmission and would be in full duplex with the repeater (not with everyone else using the repeater, though). The whole system, input freq., output freq. and all the gear comprises a duplex repeater. But each user station is only a half duplex since it must chose to either TX or RX and can't do both at the same time (with the exception of the two tuner radio example).

The reason you have two frequencies is that for the repeater to both TX and RX in real time it must transmit on a difference frequency than it's listening. If the repeater used the same frequency, then in real time it would always hear itself. Even with a shift you still have to isolate one side from the other to keep from causing problems. This is done with a duplexer with a single antenna.

It is possible to do a single frequency repeater (called technically a simplex repeater). This is usually done with a time delay. So the repeater listens until you are done talking, recording your transmission, and then rebroadcasts it after you are done. These are often also called parroting repeaters. These are used often for GMRS repeaters more than ham.
__________________
'91 Toyota Pickup
'09 Kawasaki KLR650
'12 Gunnar Rockhound 29

“Anyone who believes in indefinite growth in anything physical, on a physically finite planet, is either mad or an economist.” -- Kenneth E. Boulding
Reply With Quote
  #12  
Old 01-17-2008, 03:59 PM
Uncle Ben's Avatar
Uncle Ben Uncle Ben is offline
Rising Sun Member
 
Join Date: Aug 2005
Location: Louisville, Colorado
Posts: 13,162
Send a message via AIM to Uncle Ben
Default

DaveinDenver =
.......but the really spooky part is I'm starting to understand what he's saying!
__________________
KØUBN
Kevin
TLCA #3007
Northside!

Colorado Trail Patrol
Stay on the Trail!
I'm the God-fearing, gun-toting, American flag-waving, conservative you were warned about!
Quote:
Originally Posted by AxleIke View Post
I need an FJ40....
Quote:
Originally Posted by Red_Chili View Post
Cruisers are superior
Reply With Quote
  #13  
Old 01-17-2008, 04:11 PM
DaveInDenver's Avatar
DaveInDenver DaveInDenver is offline
Hard Core 4+
 
Join Date: Jun 2006
Location: Larimer County
Posts: 6,586
Default

Quote:
Originally Posted by Uncle Ben View Post
DaveinDenver =
.......but the really spooky part is I'm starting to understand what he's saying!
I figure I've learned a ton of gearhead junk from you guys, might as well not pull any punches and give you the straight dope. I could just say "The whizbang transmit thingie doesn't play nicely with the gizmo receive doohicky", but what good would that do? You're no worse off if it all goes over your head and probably just a little smarter than your average ham if some of it makes sense.
__________________
'91 Toyota Pickup
'09 Kawasaki KLR650
'12 Gunnar Rockhound 29

“Anyone who believes in indefinite growth in anything physical, on a physically finite planet, is either mad or an economist.” -- Kenneth E. Boulding
Reply With Quote
  #14  
Old 01-17-2008, 06:38 PM
Groucho's Avatar
Groucho Groucho is offline
Rising Sun Ham Guru
 
Join Date: Aug 2005
Location: Arvada, Colorado
Posts: 1,651
Default Duplex vs. Simplex

Quote:
Originally Posted by Uncle Ben View Post
Soooooooo...since I was playing hookie during Groucho's first class I now seek on-line education.

Right now when I key up on lets say 145.145 (tone set at 107.2), the transmit frequency jumps to 144.545. Does this mean I'm running Duplex? If that is true then if I wanted to stay Simplex is it just a matter of disabling the freq shift?

*EDIT* I started this at 2:17 and got called away, then finished it before realizing all the other posts!

Silly billy! The class is in February, not January!

In order to utilize one antenna for the actual repeater site on the mountain, the radios there use what is called a duplexer. This is a device that, simply put, makes it so that the electronics don't fry in the repeater receiver when the transmit is transmitting.

Most of the repeaters in use that are not linked to other repeaters(we'll go over all this in the class) operate on what is called "full duplex". Full Duplex is a communications mode in which a radio can transmit and receive at the same time by using two different frequencies. This difference in frequency is called a "shift". Standard VHF shift is +/-600 KhZ, depending on where the frequency is in the band.

The opposite of this is what Chris was saying, Simplex. It uses no offset "shift ", so all transmitting and recieving has to be done separate of the other. Simplex is what is used on CB(AM).

Got it?
__________________
--Choose Wisely--
Reply With Quote
  #15  
Old 01-17-2008, 06:44 PM
Groucho's Avatar
Groucho Groucho is offline
Rising Sun Ham Guru
 
Join Date: Aug 2005
Location: Arvada, Colorado
Posts: 1,651
Default

Quote:
Originally Posted by Hulk View Post
It wouldn't interfere with the repeater operation unless you were broadcasting the tone anyway.
Correct, it wouldn't interfere with the repeater operation, however, folks near to your location will hear you and the repeater and it might be a little confusing.
__________________
--Choose Wisely--
Reply With Quote
  #16  
Old 01-17-2008, 07:02 PM
corsair23's Avatar
corsair23 corsair23 is offline
Rising Sun Member
 
Join Date: Jul 2006
Location: Littleton
Posts: 8,698
Default

Quote:
Originally Posted by Uncle Ben View Post
DaveinDenver =
.......but the really spooky part is I'm starting to understand what he's saying!

Glad you do...My head hurts now...
__________________
Jeff Z. (the "not quite as skinny" one)
TLCA #17037
'97 LX450 - aka "The Whale"
'97 FZJ80 Antique Sage AE #267, stock
12/74 FJ40, 2F, SM420, 4" Lift, ARBs, 33" MTRs

:

"...anything else i can do for you guys, how about i wash your car or mow your lawn while you figure out your firewall system? I am now boarderline insane/unibomber." Kipper

"That assumes I'm even capable of pulling and stabbing..." Jacket

"I really like having a detachable unit." Beater
Reply With Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


All times are GMT -6. The time now is 02:52 AM.


Powered by vBulletin® Version 3.7.1
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.