It has been brought to my attention of how to trouble shoot the GMC-200 for what is believed to be a rare problem with the voltage regulator. I want to stress that I own many GMC-200 units and I have NOT (to date) had this problem with any of my units. In fact, I have extra units so I can easily swap them out and verify that the radiation levels are in fact happening and also that my GMC-200 units are not defective.

If you question your GMC-200 is defective and causing a false rise in radiation levels, please try this test below to trouble shoot it. Also please make sure that your weather forecast does not have any rain in it for the next 36 hours, because the rise that often comes with rain will make it hard to verify this test.

1. Unplug your GMC-200 AC power supply. Allow it to run the internal battery dead, 24 -36 hours.
2. Record the time & date that you unplug the GMC-200's AC power supply.
3. Watch your graph and see if your readings return to what you believe is a normal level.

If your unit does return to what you believe to be your stations normal CPM level, your unit might need to be repaired. Remember that this problem is only believed to happen when the internal battery is fully charged and still connected to the AC. Even if your unit fails this test and is believed to have a bad voltage regulator, when the battery is not fully charged and the AC is plugged in you should not see the problem.

I want to stress again that I have not noticed any problem with any of the several GMC-200 units that I currently own. I just wanted to start this thread to point out this possible problem and also as a Q/A thread for the GMC-200 since NETC recommends and sells this unit.

I should also point out that the manufacture (GQ Electronics) of the GMC-200 has a support forum of their own. Although we can answer some questions about the GMC-200 unit within the NETC forum, we can not answer them all so this support forum from the company is a great resource too:

http://www.gqelectronicsllc.com/forum/forum.asp?FORUM_ID=14

I have 2 of these now and I'm still learning about radiation so here is a question. I want to mount one of them outside, can I basically mount it in something waterproof, ex: a plastic container with a snap on cover, in a 4 inch pvc piece of tubing with end caps and these listed won't have any real effect on the data samples, in other words, these 2 items will work just fine and that radiation passes thru almost anything. I would like to mount one in a 4 inch pvc tube about 5 inches long, put an end cap on each end and get better data results than being inside? I have searched the web for ideas of users to see what they have done to mount it outside, yet protect it from weather elements and having come across much out here... thanks in advance.

@skybug - The GMC-200 detects beta radiation and the more you cover up the unit, the more you will cause less beta radiation to reach the GM tube. The main reason you want to put the unit outside is so you can detect the beta radiation. The gamma radiation is what you detect already with the unit inside the house. The unit is not designed to detect alpha x-ray radiation which is not that big of a deal because outside if there is alpha there would likely be beta outside too. My GMC-200 has been outside in a thin generic sandwich bag on the face of an air purifier since last Winter.

If you didn't remember where to find the thread where you and I already talked in detail about setting up a unit outside, here: https://www.netc.com/bb/viewtopic.php?f=23&t=368

It detects both Beta and Gamma if I'm not mistaken. Yes, I do recall the talks we had and the images some have posted and reference them all the time. Since I am new still, is it the Beta or Gamma that is more important to monitor? The postings of the air units being used is interesting, but what I am looking of is something simple looking without going thru all that. Some way to enclose the unit, if it adds more blockage, then I'll remove it from its original case and install it that way. Looking to just put it in a simple tube of some type, provide some air for it and mount it on a tower leg about 4 or so feet above ground. If I have too and will do, is provide a small fan inside as well to create the airflow past the unit. Trying to keep is small and mountable, so hence, the question on types of material to use in the enclosure that won't impede performance.. thank you

Correct, just beta & gamma



I have found that the beta is more telling and that is why I try to get more people to setup outside units since to detect the beta you need to be outside. The EPA stations that NETC hosts a copy of are all energy channel 5 which has the energy range of cesium 137 or often seen as Cs 137. This is said to be a key indicator in Fukushima fallout or any nuclear plant I believe.



Do your own tests and post what way you found to be best. From my tests, the best results were with my GMC-200 on the face of an air purifier filter. I have a screenshot of my chart (I will try to find it and post here) that shows how my readings dropped when the geiger counter was taken off the air purifier filter. I have found that my air purifier unit helps the GMC-200 greatly to have enough samples to detect a rise in radiation.

I found my outside unit graph that shows the drop in radiation detection when the GMC-200 geiger counter was moved away from the air purifier filter. I focus on rises and not CPM so much.

KC: Would having the meter in a location that is inside, with plywood/stucco walls, and a large number of windows be as good as actually being outside? I have a rec room that matches that description, but I would have to buy the $200 setup sold by Hey to have a detector there. As it is I am probably only detecting gamma radiation where my present detector is located. My only problem with mounting it inside is I have a metal roof on the house. That might affect bete radiation detection. But with all the windows, I was hoping that wouldn't be as great a problem. If I mounted the unit outside, I suspect the only thing I would be detecting would be Fukishima, as I have no nuclear powerplants or other radiation sources nearby.

I believe this video will answer your question. I can not post this short video enough, it helped me early on to understand more about the different types of radiation and their detection. It has been pointed out by a user on this forum, I can not remember who off hand, that the video fails to mention x-rays. While receiving an x-ray, the GMC-200 will not make a sound because it only detects beta and gamma.

http://www.youtube.com/watch?v=TSiNXBLfzK4