RF Diagnostic without Expensive equipment & Hints (Long)

[Scaramouche]

Hi
Like some of you guys, ive been hesitant to work on phones with RF problems due to a lack of a full GSM tester with spectrum analyser. I simply cant afford one of those, and even if i had one it wouldnt pay for itself. So ive been looking & thinking & researching and there are a lot of alternatives for us to diagnose RF problems right under our noses and are underutilised. I hope this helps some people fix RF problems a bit better.

1) NETMONITOR - FREE
Tthis is great! This straight away identified the problem area. In test 01 the first number is the Digital Channel the phone is on & the frequency (900mhz / 1800mhz). If that is not 0, this means your phones PLL has detected a carrier-wave and locked onto that frequency.

The next number is the digital receieve signal strenght. If its 0 your phone isnt receiving the signal strong enough. If its a negative number which changes every second its good, your RX part of the phone is working.

The next number is TX. Usually it is xxx when the phone is not transmitting. When it does transmit a * appears followed by the TX power level. If the asterisk appears but no number usually this means that your TX chain is stuffed.

When you turn on your phone you can see it negotiate using netmonitor. The sequence is RX, followed by TX. So if you have a hardware problem, and when you turn on your phone, and you have network for a second or two and then it goes it away, it usually means RX is OK, but no TX. Whatch the RX & TX in netmonitor.

2) CRACKED WINTESLA - FREE
A lot of people bitch about this, but it works a treat. The "universal" DLL's allow you to use the RF controls.

3) RADIATION STICKERS. - $3
Willy mentioned this. Those crappy anti-radiation sticker make a great but crude TX tester. Use cracked wintesla and set the TX power to about 10 or more, and if they light up your TX chain is functioning.

4) RF COUNTER - $40
I picked up a 1.3ghz one on ebay for $40. It has an antenna & an oscilloscope probe connector. This measures RF & displays the frequency. Again, use wintesla & set TX to max and hold the counter over the antenna. Mine displays a frequency around 900mhz when i do this, so I know TX is working. Also I use the probe in circuit along the TX chain and I can easily find the fault.

5) OSCILLOSCOPE - $200
Mine is only 100mhz. However when i test the 900mhz RF part, i see either fuzzy **** or a small part of a wave depending on the scope setting. Probe the output pin of the PA and use wintesla to increase the TX power level one level at a time. On a working PA the amplitude & shape of the wave increases when power is increased. On a faulty PA it stays the same. Do the same at the Antenna terminals, this checks the Diplexer if its working.

Well, thats all ive come up with for now. Iam still researching cheap RX chain repairs, any advice & suggestions would be welcome. What we need is a RF generator. This generates a RF signal at ~900mhz wheich we feed into the antenna of the phone and test parts of the circuit. All the ones ive seen are expensive. What iam thinking & researching is using another phone to generate the RF signal at the right frequency using Wintesla. Set the phone to TX, and feed the signal it generates into the phone with the RX problem, so we can test the RX chain.

Thats all for now, let me know what you think of these Tips!! Feel free to add.

[mujie]

Great post!!

[fiZ]

super,I become more clever

[genocite]

i can't find that rf counter you mentioned in ebay, could you be more specific about rf counter ?

regards

[olsa]

I heard for low-cost (about 700euros) spectrum analyser +signal generator ATTEN,model AT 5011,works from 0.15-1050MHz.

[Scaramouche]

An RF counter is a device which measures the frequency of an RF signal. It is a near field RF detector. They are mostly used for tuning CB's & radios, but i don't see why they shouldnt be used on mobile phones. RF is RF whether its carrying digital or analog. You hold it close to a cordless phone or a CB or a mobile, and counter will find the strongest radio wave and tell you what frequency it is at. Some have a connector where you can connect a probe and test parts of the circuit directly.

Now, a mobile phone is not transmitting all the time & channel-hopping as well. So how can we use a RF Counter with a mobile? Cracked Wintesla of course!! you use RF controls in testing and turn TX on and leave it on. You should see the frequency displayed. Also you probe along the TX / RX chain and find where the signal disappears, thats your faulty part.

This is an expensive one I have found

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1780722812

This is the one I have purchased, it is made by Radio Shack!!! It is very cheap but i read good reviews on it.

http://cgi.ebay.com.au/ws/eBayISAPI....391278076&rd=1


Where is this 700 euro spectrum analyser????????

[hanoon]

GOOD INFORMATION...




THANKS Scaramouche


try to contact me on icq!




good luck!

[genocite]

Scaramouche : that's a used one and it's only 1 item, where could we find this unexpensive item anymore ?

[Scaramouche]

Looks like I may have been lucky snapping that one up so cheaply I guess just keep looking on Ebay. They also are sometimes called "Bug tracers", as you can use them to find hidden transmitters in your room or office!!!

[gsmsalers]

Hi.
For section 1:If that is not 0, this means your phones PLL has detected a carrier-wave and locked onto that frequency.
Then how I resolve this? Where is problemm ?

[olsa]

Hello my friend! You are talking about measuring with RF-COUNTER???I have RF-COUNTER,and understund you,but it`s funny to me...OK.,profess.equipement-diagnostics measuring instruments(HP;COLLINS;FLUKE;RHODE-SHWARTZ...)are very exspensive,but I traying to be better and better in my job.Here I mean, how you can measure(follow) receiving signal(dbm),RSSI lines,quality inspection of IF FILTERS,ANT.SWITCHER,and whats happening with clock 13.00MHz SAMSUNG 600(phone power on,but NO NETWORK...),SAMSUNG A300/A400 bad VAPC of PA?,RSSI lines ER.T-39/65/68,what kind of signal COBBA send and receive from HAGGAR ...GSM(EUREKA PROJECT)...Wintesla is only for NOKIAS!!!

[flashman]

Hi guys,
I use one simply tool to test PA TX power:
It's like lighting antena - 5 thread of 0.5mm wire - high lighting red LED is connected on start - end on wire with germanium diode. - I U know how much intensive it should lighting - U can say PA is good or bad.

I know it's stupid simply thing, but it can help U..

try it

best regards

[hs_]

Hi,
You say another phone to generate the RF signal at the right frequency and will use like RF generator...
Did you test this method?
Dou you have any experiance???
Pls write me...

Best regarts

[Scaramouche]

HS - This is only an idea!!! i have no idea if it will even work, i have never tried it.

Flashamn - This is EXACTLY what is inside one of those radiation prevention stickers. I cut one open, all it is is a small anetna and a circuit tuned to mobile phone frequencies. You can buy these stickers very cheaply

OLSA - Sorry, i only have experience with Nokias. These are very crude tools iam talking about, they are no way a match for a prof. GSM testing station. What i was sayying is that we are not taking EXACT measurements. a 100mhz scope will not properly display a 900mhz RF signal. What iam saying is, that the displayed signal will CHANGE in amplitude after the PA when we increase TX power in steps. Its a crude, but it works for me!!

gsmsalers - That is a RX problem and i havent investigated them properly yet . A PLL is a syncrhonisation circuit, if the chanel is NOT 0, it means the phone has found a carrier & the PLL has locked onto that frequency.

Another good test for TX i found is your computer monitor. Crank it all the way in wintesla & hold it close to your monitor, if you see interference your TX should be working

[nab]