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: One Speaker 3 rigs  (Read 293 times)
K3SZY
Member

Posts: 31




Ignore
« on: April 19, 2008, 09:41:53 AM »

I have 3 rigs that I want to connect to the same speaker without an an A/B/C switch box. This is an original Am-Com Clear Speach speaker.  I am concerned about upsetting the impedance of the speaker if I do this. Will this cause any problems and if so what can I do so I don't run into any problems.

Thanks
Logged
K3GM
Member

Posts: 1815




Ignore
« Reply #1 on: April 19, 2008, 10:37:05 AM »

This item is currently on my list of "must haves".  Note that each radio's input is isolated and is amplified to drive a loudspeaker, not headphones.

http://www.fleetradioproducts.com/htm/model201.htm

Tom Hybiske K3GM
Logged
AC5UP
Member

Posts: 3891




Ignore
« Reply #2 on: April 19, 2008, 10:47:25 AM »

There is probably a fancier way of doing this, but there are plenty of audio mixers and signal combiners / splitters that use a resistor network to mix inputs or share a load.

You should be able to tie the ground side of all three rigs together then run three 4 or 8 ohm resistors from the hot side of all three speaker jacks to the hot side of the common speaker. 2-5 watts should be plenty for the resistors, although I do wonder if the audio coming back to the unused rigs might cause some damage.

It's not unusual to bridge power amp outputs together in PA applications but the amps are rated as 'bridgeable' and they're running in phase. One or more of your radios might not be as forgiving...

For another idea, an Arcnet passive hub uses four 93 ohm resistors in a diamond arrangement with the center pin of a BNC at each of the four resistor junctions. Common ground on all outer shells. Visualize the same thing with 4 or 8 ohm resistors and you'd have three IN and one OUT. Doesn't matter which point is considered IN, it's balanced either way.

You will lose signal through either setup, but without a switch I doubt there's a way to avoid that.

?
Logged

Never change a password on a Friday                
OBSERVER11
Member

Posts: 657




Ignore
« Reply #3 on: April 19, 2008, 11:04:07 AM »

30 years ago, I built a mixer using LM741 opamps. I am still using it. You can probably find a schematic on the internet or buy a kit or built item from someone such as PartsExpress.
Logged
NU0R
Member

Posts: 408




Ignore
« Reply #4 on: April 19, 2008, 03:16:45 PM »

I don't see how a 3 way switch could alter the Z in any way. Get a switch that only makes contact with one set of contacts (+ and -) at a time. The other two are not in line at all under such circumstances.
Logged
K3GM
Member

Posts: 1815




Ignore
« Reply #5 on: April 19, 2008, 04:55:39 PM »

"I don't see how a 3 way switch could alter the Z in any way. Get a switch that only makes contact with one set of contacts (+ and -) at a time. The other two are not in line at all under such circumstances."

You're right.  This is all about mixing all 3 radio's outputs so you can have all of them going at once.
Logged
K0BG
Member

Posts: 9878


WWW

Ignore
« Reply #6 on: April 19, 2008, 05:14:24 PM »

Actually, it isn't all that difficult. The input to the speaker is essentially an op amp, and you can sum the three inputs easily. If you don't understand how that's done, You might want to check the ARRL handbook, or look for the Ward Silver article on summing amps that appeared in the pages of QST some months back.

Alan, KØBG
www.k0bg.com
Logged

N6AJR
Member

Posts: 9910




Ignore
« Reply #7 on: April 19, 2008, 09:12:27 PM »

you could use almost any 3 position switch.  for example use a nice 3 position coax switch, run one side of all the speakers to the shell ( shield or ground side) of the switch and the 3 hot leads into the 3 centers.  bingo, isolated inputs and only obne switch.  
Logged
KA1MDA
Member

Posts: 543




Ignore
« Reply #8 on: April 20, 2008, 06:23:57 AM »

<<use a nice 3 position coax switch>>

Using a coax switch is a bad idea- especially if it's a high quality type that GROUNDS THE UNUSED PORTS. Shorting the speaker output of a solid state amp to ground is a very bad idea! Before using any type os switch, make sure the unused ports or poles are not grounded.

73, de Tom, KA1MDA
www.ka1mda.org
Logged
KL0S
Member

Posts: 132




Ignore
« Reply #9 on: April 20, 2008, 09:37:33 AM »

There's a little pricey solution:

http://www.ncsradio.com/m_rx.html

I've been using one of these in the shack for several years and it works great....allows up to six receivers simultaneously AND with two speakers allows you to send each audio to the left, right, or "middle".  Makes it real easy to tell which radio is talking without looking.

Dino KL0S/4
Logged
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!