Am Mo 29. September 2008 schrieb Andy Green: > Somebody in the thread at some point said: > > | Got around to try it just today. > | The problem for me with testing is that I (too) have a pretty good > | signal where I life (Actually orignating about 300m away ;) ), so that > | if there is buzz it is relatively silent. > | To reproduce it reliably I just went into the cellar and did a longer > | test call. Interestingly the buzz was sometimes pretty loud and > | sometimes hardly present which did not seem to coincide with the signal > | strength. Actually once I noticed the buzz getting louder when the > | signal got stronger oO. What I annoyingly had all the time was a pretty > | loud echo though :(. > > I know what you mean about it coming and going, seemingly disconnected > from what you are doing to the phone. > > I was looking at the VB_SYS rail during the buzz time a couple of months > ago, it seemed to me the buzz came and went according to what I saw on > VB_SYS. But this was an A5 revision.
I will include this to my mail signature: Buzz obviously is related to TRANSMIT-power of mobile. Transmit power is remote controlled by the base station, so the signal BS is receiving meets BS' "taste". There is *no* direct relation between RECEIVE-signal strength as reported by signal meter on mobile, and the way BS decides to set he TX-power of mobile to. Obvious example: when very remote of a strong BS, you might see good signal strength, but transmitter of mobile has to power up to the limit. When close to a BS of a small cell (usual situation in urban areas), you might see weak signal strength, but nevertheless mobile needs low tx-power to reach the nearby BS. Then when BS sees some bad noise spoiling the signal from your phone, BS will decide to level up TX-power of your phone, and buzz increases without any change at all in your test setup. That's also the reason why replacing original antenna with a "piece of wire" doesn't really change buzz situation: BS is leveling TX-power so the "reduced" TX-RF-field is attenuated to be same as before, though transmitter-amp is burning more power to achieve this identical TX-strength - so this "wire-antenna-test" actually is a proof for OTA-injection of buzz, as it has to yield *more* buzz if it was by internal coupling via RF or DC. It's difficult to test in real live, you absolutely can't control the setup. > > | As for the shorted plug: If there is buzz it amplifies it a tiny bit, if > | there is no buzz it doesn't seem to induce buzz, but it definitely does > | not seem to make things better. > > At high frequencies "shorts" with some loop area don't necessarily have > that low an impedence. > > What did you actually short to what, everything to the 0V pin really? The most easy way to short it is to use a copper wire of correct diameter and insert that instead of a plug (don't push it in too far ;-) ). I don't expect this will yield a good result, as our tests to short JK4401:pin6 to GND internally also didn't help. Be aware: this isn't exactly GND plane, but in fact one half of the antenna dipole. RF isn't only at antenna, but spreads all over the device electrical surface. cheers jOERG
signature.asc
Description: This is a digitally signed message part.
_______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
