Can your SIM affect your signal quality?

blunt

blunt

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I'm inclined to think not, but just a query. I recently switched back to Cell C and the shop where I got my sim from had to cut down the sim to fit in my iPhone 5, I do have times where I have full signal but a lot of the time it is on 1 bar. Previously on Cell C (only about 3 months ago) I do not recall having such low signal. The cut sim wasn't the neatest job I've ever seen so I am wondering if it could possibly have anything to do with my low signal?
 
Can your sim affect your signal quality in general, yes.
However the issues you experiencing is just the poor network coverage of your provider, 64k sim or not.
 
I disagree.
There is nothing stored in the SIM that has anything to do with the analog RF part.
Changing the SIM changes the crypto key (Kp) and the ICCID and a few other bits of identifiable digitally stored information.

The SIM speed, i.e. how long it takes to respond to commands/become ready will determine how long the GSM stack takes to camp to a cell. That is the only variable
 
It has nothing to do with signal, if the SIM card was faulty you wouldn't be able to connect to the network at all as this is responsible for the subscriber information.
 
Fudzy said:
It has nothing to do with signal, if the SIM card was faulty you wouldn't be able to connect to the network at all as this is responsible for the subscriber information.
Click to expand...

Ok, this is what I thought initially.

Thanks for the info @ all.
 
Koosi said:
I disagree.
There is nothing stored in the SIM that has anything to do with the analog RF part.
Changing the SIM changes the crypto key (Kp) and the ICCID and a few other bits of identifiable digitally stored information.

The SIM speed, i.e. how long it takes to respond to commands/become ready will determine how long the GSM stack takes to camp to a cell. That is the only variable
Click to expand...

Then why do we need 64k+ simcards for HSPA and LTE phones?
 
Of course sim can affect signal quality. The problem here is that you have a Cell C sim. Try a Vodacom sim, the signal will most likely be better :D
 
Gulio said:
Then why do we need 64k+ simcards for HSPA and LTE phones?
Click to expand...
To store stuff.
I haven't a clue why it needs to be so big. I am doing HSDPA with an 8k SIM

Just so that you know, I designed a GSM engine that does GPRS and EDGE the last few years.
I am now waiting for authroization to design a 3G/HSPA7.2 version of the same thing, using the new Qualcomm chipset I was offered.

So when I say cellphone networks spew sh*t then you better believe me. I know the GSM system backwards, feel free to try me!
 
Last edited:
Koosi said:
I haven't a clue why it needs to be so big. I am doing HSDPA with an 8k SIM
Click to expand...

Speculating here, but I did a few test's a while back to satisfy my own curiosity. Since 3G is not truely diverse and LTE is. I ran some tests using crafted APDU's to get around the restrictive AT abstraction. Found the difference is the inclusion of two logical pipes on the LTE SIM over the non-LTE SIMs. Below you can see the only other major difference is the T0 directive being 9F noted as RX/TX diversity in 3GPP spec TS 25.211.

Other than that they are much the same as below:

MTN 3G 64k
root ~ #
+ TS = 3B --> Direct Convention
+ T0 = 9E, Y(1): 1001, K: 14 (historical bytes)
TA(1) = 96 --> Fi=512, Di=32, 16 cycles/ETU
250000 bits/s at 4 MHz, fMax for Fi = 5 MHz => 312500 bits/s
TD(1) = 80 --> Y(i+1) = 1000, Protocol T = 0
TD(2) = 1F --> Y(i+1) = 0001, Protocol T = 15 - Global interface bytes following
TA(3) = 83 --> Clock stop: state H - Class accepted by the card: (3G) A 5V B 3V
Category indicator byte: 80 (compact TLV data object)
...

Vodacom 64k:
+ TS = 3B --> Direct Convention
+ T0 = 9E, Y(1): 1001, K: 14 (historical bytes)
TA(1) = 94 --> Fi=512, Di=8, 64 cycles/ETU
62500 bits/s at 4 MHz, fMax for Fi = 5 MHz => 78125 bits/s
TD(1) = 80 --> Y(i+1) = 1000, Protocol T = 0
TD(2) = 1F --> Y(i+1) = 0001, Protocol T = 15 - Global interface bytes following
TA(3) = C7 --> Clock stop: no preference - Class accepted by the card: (3G) A 5V B 3V C 1.
...

8ta 64k:
+ TS = 3B --> Direct Convention
+ T0 = 97, Y(1): 1001, K: 7 (historical bytes)
TA(1) = 95 --> Fi=512, Di=16, 32 cycles/ETU
125000 bits/s at 4 MHz, fMax for Fi = 5 MHz => 156250 bits/s
TD(1) = 80 --> Y(i+1) = 1000, Protocol T = 0
TD(2) = 1F --> Y(i+1) = 0001, Protocol T = 15 - Global interface bytes following
TA(3) = 43 --> Clock stop: state L - Class accepted by the card: (3G) A 5V B 3V

Vodacom 128k:
ATR: 3B 9F 95 80 1F 43 80 31 E0 73 36 21 13 57 4A 33 0E 11 31 41 00 B1
+ TS = 3B --> Direct Convention
+ T0 = 9F, Y(1): 1001, K: 15 (historical bytes)
TA(1) = 95 --> Fi=512, Di=16, 32 cycles/ETU
125000 bits/s at 4 MHz, fMax for Fi = 5 MHz => 156250 bits/s
TD(1) = 80 --> Y(i+1) = 1000, Protocol T = 0
TD(2) = 1F --> Y(i+1) = 0001, Protocol T = 15 - Global interface bytes following
TA(3) = 43 --> Clock stop: state L - Class accepted by the card: (3G) A 5V B 3V
 
Interesting. Like I said, my development experience with proper 3G/HSDPA/LTE is about to begin.
Thanks for the info, I am saving this for reference so that I don't have to do same. Thanks for sharing.

Since 3G is not truely diverse
Click to expand...
Very important, remember that.
 
P924 said:
Of course sim can affect signal quality.
Click to expand...
I agree. However your problem might be not related to SIM. Your phone can be stuck to LTE or different 3G frequency picking up distant 2100MHz tower instead of more common 900MHz tower. Try to disable LTE, or disable 3G and compare results.

In addition iPhone is known for poor signal reception due to unconventional antenna placement (on the metal band), no matter how you hold the phone it is always more or less shorted by fingers, unless you put the rubber cover on the phone. Your signal constantly changes depends how you hold the phone.
Did you compare reception with different device in the past or it was the same one?
 
Last edited:
sajunky said:
I agree. However your problem might be not related to SIM. Your phone can be stuck to LTE or different 3G frequency picking up distant 2100MHz tower instead of more common 900MHz tower. Try to disable LTE, or disable 3G and compare results.

In addition iPhone is known for poor signal reception due to unconventional antenna placement (on the metal band), no matter how you hold the phone it is always more or less shorted by fingers, unless you put the rubber cover on the phone. Your signal constantly changes depends how you hold the phone.
Did you compare reception with different device in the past or it was the same one?
Click to expand...

It was also an iPhone 5, but not the same one. Not gonna break the bank to do a sim swap so I think I'll just do that when I have a moment to see if it helps. I know the iPhone has a horrid signal when held in certain ways but my low signal is not always when I am holding it. It just seems to be on one bar more often than anything else - I had a Vodacom sim in this phone before though, and it had very good signal most of the time.

I spend most of my time close to CPT CBD and in the S.Subs where there is very good Cell C coverage.
 
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