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Author Topic: Does an antenna switch create loss?  (Read 3433 times)
K1CJS
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Posts: 6034




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« Reply #15 on: March 31, 2013, 06:41:01 AM »

...Since I was getting such a good signal from the Diamond, I thought that using the switch would cancel one unit totally while the other was in use.  Apparently this is not always the case .  I have decided to buy a cheap external antenna for the scanner and place it high on the tower.  After all, most of my use will be on the transceiver anyway.

Quote from: WB6BYU

That might actually be worse than using a switch, because when you transmit
the scanner antenna is still connected.  Depending on the distance between them,
the scanner antenna can pick up a lot of RF from the transmitting antenna.
Whether or not that is enough to damage the scanner depends on the design of
the radio....

That may or may not be the case depending on the mounting location of the scanner antenna.  If you mount the scanner antenna more or less directly below the transceiver antenna with 8 to 10 feet between them, the scanner should be OK.  Just turn it off when using the transceiver.
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KM3F
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Posts: 504




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« Reply #16 on: March 31, 2013, 09:20:04 AM »

Two items you need to be concerned about.
1. The switch should ground the Scanner line when it's not being used.
2. Any device with a GASFET type front end amplifier will be subject to burn out from cross coupling power one antenna to another no matter if the device is powered on or off.
The protection diodes offered as protection  will not do the job in a cross coupling case because the Gasfet juntion has already burned open 'before' the protection diodes have begun to conduct a shunting path.
Been there a couple times already.
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K1DA
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Posts: 498




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« Reply #17 on: April 04, 2013, 07:35:50 AM »

KM3F has it right.  There are passive components in the front ends of receivers, and active components whose junctions may be exposed to RF whether they are powered up or not.  Just look at the circuit diagrams.   On HF, an antenna switch with good isolation and which grounds the connections not is use is wise.
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KC4YWW
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Posts: 11




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« Reply #18 on: April 06, 2013, 12:10:54 AM »

VE3FMC makes a lot of sence.  I myself have the HF rig right by the 2 meter and so do lots of ham shacks.  The dealers do have multiple rigs hooked up to an antenna via switches.
I'm going to go with the switch and if by a freak of nature it ever blows, well I got it on E-bay for 20 bucks.
Thanks to all the guys that took the time to reply to me.  73's to all
Pete
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