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Author Topic: Coax Switch  (Read 1025 times)
W7NMC
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Posts: 8




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« on: October 15, 2002, 12:12:16 AM »

Hello. I know a coax switch is normally used to switch multiple antennas between one rig. But, can a coax switch safely be used to switch one antenna between two rigs? I have a Heathkit coax switch, a wafer type, that grounds the unused terminals. I want to switch two Icom rigs and a G5RV.  My concern is introducing RF to the antenna input of the rig not switched to the antenna, despite the antenna input being grounded. Thanks. Howard
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N8CDN
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Posts: 20




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« Reply #1 on: October 15, 2002, 07:54:40 AM »

I have two rigs in which I use a Diawa two position antenna switch to switch between the two rigs. So far I have had no problems at all. I am not sure if the Heathkit switch will work, But the Diawa or simular two position switches are not all that expensive ( under $30.00). I hope this helps


Terry N8CDN

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AC5E
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Posts: 3585




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« Reply #2 on: October 15, 2002, 09:34:21 AM »

Hi Howard: I use an Alpha Delta switch to switch one antenna between two rigs - and it works FB. However, I would recommend you make sure the switch "grounds" the coax to the "other rig," instead of letting that connection float.

Most solid state rigs front ends won't take much RF without damage - and a shorted coax should hold any leakage to a mininum.

73  Pete Allen  AC5E
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NB6Z
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« Reply #3 on: October 15, 2002, 10:50:13 AM »

If the input to the "unswitched" radio is truely grounded then you are truely safe. I would be careful that your coax switch makes a "possitive" connection each time you switch it, so that you don't accidently end up in a in-between state with both radios connected together.
Note: Even if your unswitched radio input were not grounded, I think any properly designed radio would not be damaged by the small amount of coupling that would occur.
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WB2WIK
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Posts: 21753




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« Reply #4 on: October 15, 2002, 10:51:33 AM »

I do this all the time, and have for many years, at high power levels, using reasonably good switches.

It doesn't really matter if the unused port is grounded or not, but it does matter what the isolation is!  I've found many switch designs that do NOT ground the unused positions and have >40 dB port-to-port isolation at 30 MHz, sufficient to knock a 100W signal down to 10mW, a perfectly safe input level for any receiver on the planet.

I've also found some switch designs that DO ground the unused positions, and have <30 dB isolation.  

Which is why I measure that parameter first, and then proceed to use (or not) the switch!

The Bird coaxial switches, like my Model 74's, have >120 dB isolation port-to-port, even at 1 GHz, but then, they are not ordinary switches, they are a rotating line section.

73,

WB2WIK/6
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N6AJR
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Posts: 9930




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« Reply #5 on: October 15, 2002, 07:21:04 PM »

One point to remember, if you use a B & W or a diawa or other "expensive" switch you will get good seperation and probably grounded outlets for the switch not in use.  If you buy the $9.99 special with a 3 position knoib and a small tin case, you will probably have a bit of cross over to the other rig, and possibly enough to damage it, so if you are using anything over qrp level be aware of the type of switch you use.

I typically bring 3 antennas into one of the cheepie switchws then run the selected one from there to a "good " switch to select my rig.  safer that way.  the cheepies have their uses , but be aware of their limitations... 73  tom N6AJR
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