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Author Topic: 2nd Reciever, near another Antenna RF overload?  (Read 332 times)
K2FR
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« on: September 23, 2009, 12:39:04 PM »

I am looking at picking up a Yaesu FT-817nd, and build a nice backpacking kit.

however I also foresee using it on my radio desk hooked up to my 2nd Dipole.

My setup as of now is both dipoles come into the house at opposite ends Via ladderline,  into the attic near my room,  converted Via Baluns to coax and into the room.  From there into my Auto tuner, which I can switch between.


The dipoles are in an X Configuration across the yard.  140 feet of 10g stranded copper up about 85-90 feet in the clear,

64 feet solid copper, up about 65-70 feet.   They do not touch anywhere nor do the feedlines run down together, I put them each towards 1 side of the house to keep them separate on the way down

If I however have a 2nd radio and put it onto the 2nd dipole, would using the main on the big antenna,  Is there a possibility that the 2nd dipole will pickup alot of RF and fry the little 817?


Thoughts and input appreciated
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WA3SKN
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« Reply #1 on: September 23, 2009, 01:04:59 PM »

Depends on the power you are using!
In the "Good Old Days" we used separate antennas for the transmitter and receiver, and could get away with it at the novice power levels without killing the receiver's input.  75 Watts in provided about 50 watts out.  Note that above that power level we had a relay that shorted the receiver's antenna terminal while transmitting, keeping the RF out.  But you are planning 100+ watts, so I think you will want a better solution... you are probably asking for troubles with the solid-state rigs of today!
Oh, and we also placed diodes across the receiver's antenna terminals to limit the static crashes!
73s.

-Mike.
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N4JTE
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« Reply #2 on: September 23, 2009, 04:40:40 PM »

Why do you need two radios  with two antennas? One evidently for 40 and the other for whatever, are you trying to change directions ? Seems like one radio to either antenna will serve the purpose if I understand your question. If you want quick direction changes from two non resonant antennas, another tuner might be in order.
Bob
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VA7CPC
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« Reply #3 on: September 23, 2009, 06:05:16 PM »

Why take the risk?

A few switches (or a single switch, for one radio) are cheaper than replacing the front end on an FT-817.

I don't see that there's a "diode-based" solution.  Each rig is a _transceiver_, and uses the same connection for "receive antenna" and 'transmit antenna'.

           Charles
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W8JI
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« Reply #4 on: September 23, 2009, 06:28:03 PM »

I would not do that. There is a distinct possibility you could fry a radio even when running just a few watts.

You could measure the cross coupling loss or transmission loss if you had the equipment, but it is going to be pretty low. I'd expect something between a few dB loss up to perhaps 10 dB or so loss between the antennas.

You might get anywhere from 1/20th to perhaps half the transmitter power back into the second receiver. It is not worth the risk.
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