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Author Topic: 2 radios, one antenna.  (Read 1017 times)
AA4PB
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Posts: 12847




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« Reply #15 on: January 24, 2009, 06:32:12 AM »

Why not a simple COAX SWTCH?
----------------------------
Switch in wrong position - buy new radio.
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N3OX
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« Reply #16 on: January 24, 2009, 08:33:31 AM »

"Why not a simple COAX SWTCH?
----------------------------
Switch in wrong position - buy new radio.
 "

I've never had that happen with any of my commercially made radios... sure, a homebrew QRP thing with no SWR protection will blow a final...

But if it's really a concern, put in a *transfer* switch (or transfer relay: http://www.mgs4u.com/RF-Microwave/RFrelays_N.htm) with a dummy load on the other port.

Then you can't hurt anything.

I think having two antennas on two radios on a single vehicle on a single band is as likely or more likely to blow up a radio than accidentally transmitting with one into an open circuit.  But if you have a dummy load instead of an open circuit you can't even do that.

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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« Reply #17 on: January 24, 2009, 09:27:53 AM »

A commercial radio may take the abuse but its a poor design that permits an inexperienced operator to inadvertantly transmit into an open circuit. An inexperienced operator may not even realize the antenna is not connected so he continues to call and call into the open circuit.

Instead of an expensive RF transfer relay and a dummy load, why not just use a power relay in an interlocking circuit that only permits DC power to be applied to one radio at a time. If radio A is turned on then a DC relay removes power from radio B. A DC coax relay connects the antenna to radio A when it is on and radio B when radio A is off. Fairly simple and using relativly inexpensive relays.

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KC8VWM
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« Reply #18 on: January 24, 2009, 09:32:51 AM »

So what happens when the relay fails and you end up transmitting a signal into an open circuit? Smiley
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N3OX
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« Reply #19 on: January 24, 2009, 09:48:11 AM »

"An inexperienced operator may not even realize the antenna is not connected so he continues to call and call into the open circuit.
"

That's true...

"Instead of an expensive RF transfer relay and a dummy load, why not just use a power relay in an interlocking circuit that only permits DC power to be applied to one radio at a time"

Yeah, I think that's a good idea too.. especially given that all the transfer relays are $$$

KC8VWM says:

"So what happens when the relay fails and you end up transmitting a signal into an open circuit? Smiley "

One catastrophic failure at a time, Charles.  One at a time ;-)  Eventually the protection/interlock/relay system becomes expensive enough that you can afford to smoke a radio.

;-)

73
Dan

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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Posts: 12847




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« Reply #20 on: January 24, 2009, 10:20:11 AM »

I can tell you from many years of experience that "operator error" is way more likely to occur than a relay failure. The relay greatly improves the odds of successful communications :-)
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AA4PB
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« Reply #21 on: January 24, 2009, 10:21:24 AM »

I can tell you from many years of experience that "operator error" is way more likely to occur than a relay failure. The relay greatly improves the odds of successful communications :-)
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KC8VWM
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« Reply #22 on: January 24, 2009, 10:32:34 AM »

Your probobly right..

My Best.
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W3LK
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« Reply #23 on: January 24, 2009, 07:52:43 PM »

<< 06 grand cherokee >>

What am I missing here? It's what, ten feet max from the dash to the tailgate?

Simply put an 8' extension on the mike cord and turn up the volume, or put a second speaker in the rear. Curl up the excess mike cable and put it under the front seat for normal use and then pull it to the rear when necessary. I've done this on more than one vehicle.

A second radio and switch and all that are unnecessary, especially since the OP says the rear radio will get little actual use.

What is it that hams always want to make the most complicated solution to a simple problem?

73,

Lon - W3LK
Naugatuck, Connecticut
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KE5PJZ
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« Reply #24 on: January 24, 2009, 08:19:32 PM »

The assumption is, while the operator is on a scene, and therefore needs access to the radio in the rear, that the portable is NOT going to be in the convertacom.

If she needs higher power then what the portable can give her, either to speak to incoming units or a bird, the extra step of taking the portable from the back of the truck, back to the front, docking it in the cradle, and walking back to the rear of the truck where she needs it is more effort then it should be.

If I were doing to do a mic and speaker extension in the first place, then the primary radio would NOT be a portable + convertacom, when we could simply install a radio that can use two faceplates and two mics.

I do agree that everyone is over engineering the solution though.
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W3LK
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« Reply #25 on: January 25, 2009, 11:26:18 AM »

<< I do agree that everyone is over engineering the solution though.>>

No, I mean YOU were over-engineering the solution. It would take your lady friend all of 15 seconds to pop the HT into the cradle and pull the mike to the rear of the vehicle - if she walks slowly.

I think your two-radio solution is a solution in search of  problem. If she's talking HT to Helo, the range should be more than sufficient, assuming  5w HT. I've talked to aircraft just a couple of thousand feet in the air at 25 plus miles with a 5w HT. I've talked air to ground well over 100 miles with the aircraft at 5k feet and hit the repeater solidly.

Personally, considering the scenario that you mentioned, I think a second radio in the rear an unnecessary expense, especially in a POV.

<< when we could simply install a radio that can use two faceplates and two mics. >>

Sorry, that doesn't work in the commercial world, or the amateur world. You can't simply parallel control heads. Been there, tried to do that. I'm curious as to what radio you were planning to put in the rear.

73,

Lon - W3LK
Naugatuck, Connecticut
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