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I need to set up to radios with high gain directional antennas to talk to each other within a relatively small distance. The radio in questions is a RADWIN 5000 jet. The max distance I can set them up is about 20 feet from each other. Each antenna has a gain of 20dBi and the lowest power the radios will transmit at is -1dBm. So without attenuation each radio will receive a signal about 1/2W and we have a concern this will damage the receiver. Traditionally we could use a wave guide filter to attenuate the signal before the antenna but since this device is an all in 1 package (radio and antenna in one case) we don't have this option.

So my questions is this: does anyone have any suggestions on type of materials or sets ups I can put between the 2 devices to attenuate a 5GHz signal by say 30dBm?

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If you stick some ECCOSORB in front of the antennas, it should attenuate the transmitted power pretty considerably.

Basically, you want some sort of microwave absorbing attenuator. There's a number of brands, but it's generally colloquially called "echosorb" or something like that. In general, it's a carbon-loaded open-celled foam substance, which attenuates broadband microwave energy.

The downside is it's pretty specialized, and kind of expensive.

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  • \$\begingroup\$ Thank you for the information. I think the ECCOSORB might be my best bet. \$\endgroup\$ Sep 14, 2015 at 15:36
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You don't have to worry about damage. The signal will be strong, but not that strong.

A path loss calculation says that for two 20 dBi antennas 6 m apart, at 5700 MHz, the received power is -23 dB of the transmitted power. So if the transmitter is -1 dBm, the received power will be -24 dBm, or 4 microwatts. This won't damage them, but they may be overloaded and not work perfectly.

Two simple ways to reduce the signal:
Misalign the antennas - don't point them at each other. That will quickly reduce the signal. For example, the front to back ratio of the panel is probably more than 30 dB, so if you turn one around completely, that reduces the received power to -54 dBm, as though you were 200 m away. Or put something in the way of the signal. It doesn't need to be anything fancy, a wall, a sheet of tinfoil will work fine. If you're going to use metal, use a piece at least 3 times the size of the antenna, and keep it near to one antenna. In the middle of the link, the signal will just diffraction around it.

Finally, there's no way you could receive half a watt! If the transmitter power is -1 dBm, that's the most you could ever receive, by conservation of energy. In practice, much less as you see above.

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    \$\begingroup\$ Thanks for the info. I kinda just took what I heard at face value and forgot how to math and physic. I went and did a PL calculation and u are right. I don't think it will damage them I just have to work on convincing someone to test it.... \$\endgroup\$ Sep 15, 2015 at 18:46
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You're really not using the right radios for this. is there a reason you picked these? Can you put a wall between them? How about some anti-static shielding foam?

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  • \$\begingroup\$ I'd bet this is a test-setup for validation, or something. \$\endgroup\$ Sep 12, 2015 at 2:46
  • \$\begingroup\$ You don't know the application so how can you say they are the wrong radios? It is a test set up to characterize these specific radios. \$\endgroup\$ Sep 14, 2015 at 15:34
  • \$\begingroup\$ If it's a test setup, then you might also need to make sure you're characterizing them down near sensitivity, where the BER is measurable. They certainly are the wrong radio's just to set up a comms link across 20 feet. \$\endgroup\$
    – rfdave
    Sep 15, 2015 at 1:27
  • \$\begingroup\$ We are characterizing the SNMP alarm info. As long as we can fade the path enough 20 feet is fine for what we do. \$\endgroup\$ Sep 15, 2015 at 18:42

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