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T O P I C    R E V I E W Posted - 10/21/2023 : 08:53:10
Thinking of buying the GMC 800. I have been in the market for and looking at the 600+ but seemed too fragile and has an out of date interface.

The 800's interface and durability seems to be much improved from their other models. However, at only $99, it seems almost too cheap/inexpensive.

I know the 800 does not detect Alpha, however do those of you familiar with gieger counters think this new model is sufficiently accurate and responsive in speed of detection and have sufficient feartures/capabilities?

I am purchasing this mostly for the event of a nuclear related accident, dirty bomb or nuclear exchange between the US and one of the other six or seven nuclear capable nations.
19   L A T E S T    R E P L I E S    (Newest First)
UnstableIsotope Posted - 12/08/2023 : 11:54:54
Interesting. That's what I initially thought, but the 500+, to it's credit, has more stable CPM values than the GC-01 even using the same 10s window. I assumed this was due to a moderate denoising filter.
EmfDev Posted - 12/08/2023 : 11:31:37
Not really, the calculation is straightforward, last 10s * 6 for 10s estimate. As for the GC-01, it may be because of the high voltage that causes some extra counts.
UnstableIsotope Posted - 12/08/2023 : 10:00:39
For grins I ran the GMC-500+ with a 10s estimation window along side the GC-01. They should both just be seeing background of 10-20 CPM.

They weren't that far OFF in the same period
Max CPM 500+ : 61
Max CPM GC-01 : 66

Now, I have seen the GC-01 hit peaks of 96.
I think the GMC-500+ is employing an averaging
filter of some sort that keeps the overshoot down.
UnstableIsotope Posted - 12/06/2023 : 20:06:41
It appears that the GMC-500+ is employing some smoothing filter even when using smaller summing windows like 10s so it still avoids overshoot as badly as the GC-01 which can occasionally hit in the 80's for a background level actually in the normal 10 - 20 range.
EmfDev Posted - 12/06/2023 : 14:01:30
You are right, the GC-01 is using 10 second window.
UnstableIsotope Posted - 12/05/2023 : 16:24:54
Originally posted by EmfDev

The FNIRSI GC-01 is not sensitive. You can see the CPM is multiplied by 6 for every single detection.

I agree the GC-01 is not as sensitive as something like the 500+ which has proper grills next to the tubes. The GC-01 has no openings in the case next to it's J321 tube and so blocks a lot more Beta than the GQ devices. I took the back off mine and the CPM went from 450 to 1450 on the same Uranium ore sample.

The 6,12,18... count issue however is not related to sensitivity, it's because FNIRSI designed the GC-01 to have a fast response time (which is naturally less accurate). Since they are using a 10s sliding summing window to estimate CPM, they naturally have to multiply the current 10s window sum by 6.

If you set the GMC-500+ "Fast Estimate" to 10 seconds, you will notice that it also jumps up by 6 for each incoming event and also over-estimates background because of this fast response.

There's simply no substitute for an accurate measurement though and that means summing counts for a whole 60 seconds before sliding the window forward. The GMC-500+ provides TRUE CPM counts when the Fast Response is set to 60 seconds which is great. Most (nerdy) consumers though want to see their shiny GC react quickly to the new Fiestaware purchase that just arrived from eBay. The GC-01's biggest accuracy fault, aside from lacking a tube grill, is that it provides no "slow" or "real" options for tuning the estimation window.
EmfDev Posted - 11/02/2023 : 15:17:23
You're welcome. I just help with customer support. Posted - 11/01/2023 : 11:13:34
Thank you very much for the insight! You seem to be very knowledgeable in the field. What is your background?
EmfDev Posted - 11/01/2023 : 10:17:26
In a nuclear war event, yes. But its sensitivity will provide you more uses of it. Posted - 11/01/2023 : 07:56:49
One additional question: If I did decide to purchase the GMC 600+ because of its ability to detect Alpha and its other features, solely for use in preparation in the event of a nuclear exchange/war, dirty bomb, or nuclear reactor accident, would it be overkill compared to the GMC 800? Posted - 10/31/2023 : 17:01:55
Thank you! I appreciate it.
EmfDev Posted - 10/31/2023 : 09:30:03
We are sorry for the irrelevant responses. To answer your question, yes, beta, gamma, and x-ray detection with GMC-800 and its features is good enough in an event of a nuclear war. Posted - 10/31/2023 : 09:16:55
Most of the responses consist of arguing of previously made points. Please provide some feedback on my original questions. Also, is the ability to measure Alpha radiation (which this unit is not capable of) important in the event of a nuclear exchange/war? Or is this unit's ability to measure gamma, beta and x-ray sufficient in the event of a nuclear war? I understand that for the price, you will not likely find an Alpha capable Geiger counter. However, I am willing to pay more, but do not like the GMC 600+ due to its outdated display/interface and fragile construction.
EmfDev Posted - 10/30/2023 : 09:54:11
That may work in low radiation. I do not think the GC-01 is fully tested on dose rate higher than 500 uSv/h. If it is possible to lower down the voltage, it may not be able to detect anything on low radiation. That may be why they use higher voltage and *6 on each count to make it seems like it detects more radiation per minute, it is misleading. The overall hardware design is problematic. I do not have much information regarding the patent.
ullix Posted - 10/28/2023 : 01:57:13
That sure is a high voltage, given that the upper operating voltage limit is specified as only 600V, the recommended as 380V, and the plateau at 360...440V (provided these Ali numbers can be trusted

So I did my own check:

I'd say, given the uncertainty around the measuring setup, this is the same result, something 700Voltish.

Hmmm. Nevertheless, using this FNIRSI GC-01 with various samples I have available, I always got meaningful results!

In the circuitry I see no option to adjust anything, so the high-voltage cannot be changed? Or does any electric expert can point to such an option?

But EmfDev, given how much effort you put into pointing to issues with this device, I am looking forward to you putting the same effort towards highlighting the superior GMC-800 features!

In particular I am interested for what part of this umpteenth commercial version of a 100 year old technology you claim a "Patent Pending" for?

EmfDev Posted - 10/26/2023 : 14:43:40
I do not know if I can trust this, it is not built correctly. The voltage on the J321 tube is ~715V. And the background CPM reading only shows 4 numbers other than 0 which are 6, 12, 18, 24.

ullix Posted - 10/24/2023 : 23:19:37
While it is odd that the CPM update is done in 6 counts increments/decrements, it may be programmed as such. In any case it is NOT and indication of sensitivity!

Sensitivity is primarily determined by the Geiger tube, and the tube used is from the J brand. Such tubes are also used by GQ, as you will know.

If you are looking for a device solely for some catastrophic situations, then you have many options for the tube choice. What matters far more is that you get a sturdy, relivable device. This is offered by the GC-01, clearly better than with the current breed of GQ housings. I just point to the contact bounce for one of the most annoying problems!

I am curious to see how the new GMC-800 will fare in this respect!
EmfDev Posted - 10/23/2023 : 10:10:39
The FNIRSI GC-01 is not sensitive. You can see the CPM is multiplied by 6 for every single detection. Do you really have the device? If you buy both and compare the UI, you will think the GC-01 is outdated and you can check the CPM, it will go by 6, 12, 18, 24, 30, etc. I wonder why you would recommend such device. The GMC-800 is made by GQ Electronics while the GC-01 is made by who knows, please stop spreading wrong information, they are not made by the same manufacturers. Wrong information will be removed from forum.
ullix Posted - 10/22/2023 : 02:13:29
Oh, this is interesting! I had no idea such a GCM-800 existed. Looks like GQ is pursuing the selling of cheap counters, as I speculated when the GMC-300S series surfaced. The latter, by the way, is now available in Germany for under USD60, incl. all taxes!

The manual for the GMC-800 is here: This device reminds me strongly of another Chinese product, the FNIRSI GC-1. Compare the two:

The company disclosed for making the FNIRSI is Shenzhen FRI NI RUI SI Technology Co., Ltd, located in Shenzhen City, China. And who knows what the difference between them and GQ is (perhaps none?).

The FNIRSI can be had for under USD50 e.g. at Ali

I had the chance to play a bit with the FNIRSI. It is mechanically built very solidly, good buttons, good display, good display layout and access to info on the screen. Quite a bit better than the ususal GQ fare!

What is does NOT have is ability for computer communication and internal memory for preserving history.

This is what the GMC-800 is now claimed for to also offer, and would thereby fall in line with the other GQ counters.

As the current GQ software is said to work with the GMC-800, so my GeigerLog software will also work with it. Only better ;-)

Sadly, GQ can't help their profound lack of understanding of Physics, exemplified e.g. by this specification (from their manual):
Range of gamma radiation energy, MeV 0.1 to 1.25
Range of registered X-ray radiation energy MeV 0.03 to 3.0

Dear folks at GQ: this is utter nonsense!

GQ nowhere tells you what Geiger tube is used in this device. But they no longer talk about "calibration factors", and instead provide a - tada! - Sensitivity! Just as GeigerLog does and the rest of the world.
Gamma Sensitivity Co60 (cps/mR/hr) 22

But why this odd unit of cps/mR/hr, which is deprecated since more than 4 decades(!) ago? I think I know. GQ never measured this sensitivity, and is simply using the specification of the Russian SBM20 tube, which originated in World War II. For more details see chapter "Appendix G Calibration" in the GeigerLog manual (

In today's units this Sensitivity is 132 CPM /(uSv/h). This is exactly the base for tubes like M4011 or J305 (GQ never distinguished between the tubes, despite their differences). So my guess is one or the other is also used in the GMC-800, whichever is cheaper.

Bottom line:

If the hope for a better product quality (mechanical, electrical) manifests itself, and the firmware is at least not worse than so far, the GMC-800 could be an interesting device, despite all lack of understanding of physics.

If, however, you are not interested in GMC-800 specific features, like computer connection and long-term recording, you are just as well off with the cheaper FNIRSI, which I can recommend if the lack of features is ok with you.

(I bet the money goes into the same pockets anyway!)

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