I'm making a project which involves the use of two HM-TRP radio modules.

At this time, the only way I can test the strength of these modules is to go out on the street and travel with one unit for about 1km until I see signs of data disconnection (example, led on my board flashing).

What I want to do instead is to make the signal transmission weaker without actually configuring the on-board hardware. I mean if I had an elevator made of solid construction in my house or even a subway station with no service nearby, I'd probably be all setup because then I can put a module in one of those things and test my signal without walking 1km.

Since I have no access to either of those things, the only other things I could think of is to use a sheet of mesh wire or cover even one of my units almost completely with aluminum foil.

The point is, winter is approaching and I don't want to freeze my fingers off while running wireless tests. Am I on the right track with using aluminum foil and mesh or are there better things I can use to make a radio module transmission more difficult?

The modules are set to run at 915Mhz frequency.


You'll find that microwave ovens, aluminum foil, metal garbage cans etc aren't really reliable attenuators.

What you need is a channel model that tells you how much your signal will be attenuated after 1km, but also how bad your multipath will be like, together with a signal model that tells you what effect that has in your reception.

I don't know the devices you're referring to, but usually I'd expect an antenna connector to be present in anything that I'd expect to work over such distances, so instead of an antenna, connect your transmitter and receiver with coax cable and attenuators to emulate the attenuation. It's much harder to emulate the multipath environment and temporal effects like fading, but with your signal model you might be able to calculate an attenuation that would be "just as bad" as an actual multipath channel.

  • \$\begingroup\$ That's a pretty good answer! You hit all the points I could think of quickly and added a reasoned approach. Nice. \$\endgroup\$ – jonk Nov 11 '17 at 18:30

Try putting one of them in a microwave oven. Microwave ovens are designed to function as Faraday cages. You should not turn the the oven on, obviously!

If that blocks too much signal, try leaving the door open. If no oven is available any metal box could help. Aluminum foil would as well. Just make sure that the device does not touches metal directly, to avoid short circuiting it.


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