Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[bkenobi]

I have noticed that on rainy days my motion sensors don't all work as consistently as they do when it's nice out.  I'm not sure if that's really due to the water on the roof/siding or if it's something else (my heat pump/furnace are more likely to run if it's raining since it's most likely colder out).  Anyway, I was thinking that there should be a simple approach to determining if there was any transmissions on the +/-310MHz range.  For detecting interference, I know some people use AM radios.  I'm not sure if that would work since 310MHz is not in the AM band.  I'm not looking to decode the signal, just see if anything is actually present on that frequency (EMF from some equipment, RF X10 transmission, etc).

What I was envisioning was some kind of basic antenna -> handheld meter/oscilloscope.  This is just a temporary question that I would answer once so I could fulfill my need for understanding.  I'm not looking to buy a $$$$ piece of equipment or build a RF room to do formal testing.  I saw an instructibles article about using an Arduino and a 3' wire for this purpose, but I don't see how that tunes it for this frequency.  It seems like I should be able to use a 1/4 or 1/2 wavelength antenna and connect it appropriately to either an Arduino or the microphone input to an Android and then use a basic monitoring device (speaker for Arduino, screen for Android, something else?).  I'm willing to spend $0 on this project, so I should be set, right?   

[bkenobi]

Until someone else reads this, I decided to do 5 minutes more research.  I found the following:

http://brohogan.blogspot.com/2010/10/receiving-x10-rf-transmissions.html

This guy used an Arduino and a retuned 315Mhz receiver to listen for RF X10 commands and perform some actions based on it.  Looks like I can simply use a $5 receiver with an Arduino, modify the antenna, tune the unit, and use a version of his script to get more or less what I want.  He actually uses a detecting script to tune the antenna which would probably do pretty much what I want.  The only down side is that this would only sniff at exactly the tuned frequency and not +/- that might be related since X10 antennas will detect close to 310 as well as I understand.

[bkenobi]

HA, full circle in a way.  I read more on a similar Arduino project and found that they are referencing Dave Houston's page for info.  I've read that page before, but forgot that he did microcontroller projects (ZArduino among others).  In other words, Dave already has a lot of info on the topic and I've been there before.   

[dhouston]

If you use a superregenerative receiver, they have a bandwidth of about ±2MHz so you should receive from even those sensors that are poorly tuned. Most of the receivers here qualify...

• http://davehouston.org/modules.htm

There's also this...

• http://www.cdadapter.com/srtune.htm

The RM1SG seems to have a bit more bandwidth than most.

Also, I vaguely recall a web article about some range testing of similar modules on the campus of a university (in Indiana?) where they tested under various weather conditions. Water vapor in the air causes refraction and absorption of the RF beam which results in lower range.

• http://setup-wireless.blogspot.com/2008/11/radio-frequency-behaviors.html

[bkenobi]

That's a very interesting article.  It's obvious that if things worked fine before but they don't work fine now, something has changed.  My high level observations are that when it's rained a lot or is currently raining, 2 of my 3 outdoor MS16A modules seem to flake out.  When I had this issue in the past, I assumed that it was due to 2 things: range issues and moisture inside the motion sensors.  I thought I had corrected all of this with silicone and a set of passive repeating antennas (copper wire stuck behind the modules).  In fact, these units have been very reliable overall, but on adverse weather days, they don't work as well.

The article suggests that moisture in the air can lead to attenuation among other things.  If I were to add a reflector plate of some kind on the side of the module pointing away from the X10 receiving antenna, it seems like that would improve my signal strength since it would act as a very basic wave guide to redirect wasted signal back towards the antenna.  I'm not sure this would help all that much, but it's something that I used way back when I was messing with WiFi antennas.

[bkenobi]

After reading the thread on modding the CM15A to use this same module (RM1SG), I decided to order a few from ebay.  They are cheap and small enough to stash in my junk bin so it's no biggie even if they don't help me.

http://forums.x10.com/index.php?topic=21000.0