As I wrote in the previous post, I concluded that flat structure is preferred based on the experiment.

The next question I had was "can I keep my GPS logger in something?". Even though I know completely uncovered is clearly the best way to operate GPS logger, I would rather prefer keeping it in something like a travel bag for convenience. But I wasn't sure which bag I should choose.

I spent some days to google around, but still I wasn't so sure how much GPS signal weakens with what kind of materials. So, I decided to do some more experiments.

Materials to Test

I picked the following materials simply because they can be my travel companion.

• Business backpack of ballistic nylon
• Hiking backpack
• Shoulder bag
• Pocket of down coat

Below are the photos of them.

Additional Experiment: Vertically Held Receiver

Since controlling or watching GPS receiver's orientation in a bag is nearly impossible, we have to know how the orientation affects on signal reception. So, I evaluated a same receiver in two situations: horizontally held and vertically held, in the following way.

I took the same two GPS receivers to the same 5 minute walking course as in the previous experiments. During every walk, receiver (A) was held horizontally. Receiver (B) was held horizontally in the first walk and vertically in the second walk. SNR values comparisons are below.

(1) B horizontally held

Sat#	A	B	Diff. (B-A)
	Total		15
	Mean		1.1
10	40	42	2
12	44	47	3
13	x	0	0
14	18	21	3
15	38	39	1
18	36	38	2
19	6	5	-1
20	25	25	0
21	x	0	0
24	40	40	0
25	34	36	2
31	3	4	1
32	36	36	0
193	34	36	2

(2) B Vertically held

Sat#	A	B	Diff. (B-A)
	Total		-32
	Mean		-2.5
2	33	32	-1
5	42	36	-6
6	8	0	-8
7	24	24	0
13	38	33	-5
15	40	36	-4
20	36	34	-2
21	26	27	1
24	24	23	-1
28	15	17	2
29	20	20	0
30	36	33	-3
193	36	31	-5

By comparing means, we can tell changing receiver B's orientation worsens SNR by 3.6 ( -2.5 - 1.1).

Main Experiments

Then, I put module B in different materials and compared each with the module A. Since comparisons are always with A, we can summarize all results as below. I put the results above, too.

Means of Diff.(B-A)

Situation	Diff. (B-A)	Diff against ref.
Held horizontally	1.1	-
Held vertically	-2.5	-3.6
Business backpack	1.5	+0.4
Sport backpack	1.4	+0.3
Shoulder bag	-0.2	-1.3
Down coat	-1.3	-2.4

As we can see, all materials have relatively minor effect on signal reception compared to usual signal strengths around 30 dBHz and more.

Honestly, this result was a bit surprising for me. I had naively thought GPS signal is more like light than wave, considering its high frequency (around 1.5GHz), and kept GPS logger outside every time I travel.

But now I can put GPS logger into bag or pocket with confidence.