OT: Cordless headphones

Did you check for a shorted cell in the battery?

Cheers

Phil Hobbs

Just two cells (AA). Both are good. Don't appear to be any "loose connections". Shaking doesn't cause the problem, etc.

If it was easily repeatable (e.g., orientation of my head, position in the room, etc.) it would be far easier to Dx!

I will have to make a "project" out of identifying how and when it craps out. Note that these are just brief "drop outs" -- as if the carrier went away due to multipath interference, etc. -- then came back a second (!) later.

[I guess I should also examine the base unit to be sure I am not misleading myself by assuming that *it* is "stationary" -- while the "receiver", OTOH, is moving -- and, thus, couldn't be the problem.]

Or, I could learn to keep a "normal" sleep-wake schedule...

Are there other 900 MHz-ish transmitters in the vicinity? Maybe ones that weren't there when you last used the headphones?

How's the transmitter power supply? Maybe dried-out caps in a wall-wart causing ripple or low DC voltage to the transmitter?

Antenna loose or disconnected at either end?

Matt Roberds

None that *I* control. But a fair number of "unintentional radiators" in the room. I'd have to see what happens if I shut *everything* off.

If something is loose, it would have to be in the headset as the "base" isn't subjected to any vibration, motion, etc. But, even the heaqdset isn't seeing lots of "abrupt" motion. Turn my head and, somewhere between where the rotation started and where it ended, the signal will drop out for a fraction of a second, then return. Repeat the movement in ultra slow motion and it's *likely* to drop out, again -- for the same amount of time. I.e., it's as if there is an orientation in which the headset can't tune the signal. (sounds like tuning an old fashion radio in terms of how the signal is squelched as you move off the carrier; then comes right back if you tune back towards it)

Of course, keeping your head in a repeatable (x,y,z) while changing the direction in which you face is tedious. And, I'm usually in the middle of "work" at the time -- easier to deal with the sporadic drop outs than to drop everything and investigate...

[I'll have to make a point of *just* doing that and see what sort of results turn up. At this point, it's more of an intellectual curiosity than a real problem as I can just opt to replace the things and sidestep the problem entirely!]

I've never seen a digital spread-spectrum device run for longer than 4 years before it has problems with dropouts and lost sync. The transceiver is probably a chip with a crystal and a squiggly copper trace sticking out of it, so I doubt there's anything to adjust. If it's only a few years old, the whole system is likely in one slab of epoxy (RF + IF + DSP + CPU + RAM + flash + audio circuits + LDO regulator).

Just buy a new one. Watch out for older Bluetooth headphones that don't have good codecs.

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But the system *works* -- for the most part!

What causes the "dropouts" which *only* manifest with certain head movements? I.e., I can put the headset in any of a multitude of orientations and *leave* it there and never encounter a problem. Likewise, I can move it SOME ways and also see no problems.

Replacing it without understanding the cause of the problem is a surefire way to chase one's tail...

I was going to add about the possibility of 'nearby' frequency transmitters that swamp the pitiful receiver's antenna AGC, causing a momentary dropout [just not in band soyou don't hear it]. Like everytime a nearby cell phone checks in with the tower by blasting up to maximum RF Tx power. That little spike could cause the gain to go down so far that you get a dropout.

But now you say, the dropout only occurs with an abrupt movement of your head! Now that sounds like a potential intermittent connection inside the headset that opens when you move. But then again, I'm sure you tried tapping on the thing and not found any correlation. Or, used a bit of freeze spray, or a bit of hot air from high temp gun and never got a dropout. If you did, you would have solved by now resoldering connections.

It's not a sporadic/non-repeatable event (like someone keying a phone). It happens with some frequency -- but, only when I change my position or "orientation" wrt the base unit as I mentioned in my OP: I suspect it is related to my position/orientation wrt the transmitter in the base.

Not necessarily "abrupt". Of course, in normal use, I move my head often (and not "overly gently") as I look at a different monitor or move to a different workstation. This is when the problem normally manifests (i.e., if I am focused on a single monitor/workstation and largely immobile, all is well).

If I take the time to explore the phenomenon (instead of *working*), I can usually cause it to repeat by slowly moving through the same trajectory that I had previously undertaken. So, the "abruptness" of the motion is not the problem but, rather, *where* the headset is located and/or in which direction my head is facing.

E.g., I can get up and walk into another room and not experience any dropouts. Or, when *in* that other room, could rotate my head and recreate the problem. But, the head orientation varies with location in the house.

So, I'm not sure whether the problem is related to the relationship between the headset and base... *or*, if there are other "unintended radiators" that are playing a role. These would compound the problem as I move to other rooms in the house (there are usually machines running in several rooms concurrently; as I speak, 5 machines in 4 rooms -- assuming "household devices" aren't a contributing factor).

I will have to do a "proper" experiment to sort out the cause of the problem. I was hoping someone may have been down this path before (I'm not the only soul with wireless headphones and computers!) who could offer some pointers.

not been 'down this road'

Is there any relationship between field strengh and dropouts? For example do you get dropouts a long way away or just close? Could be a change in Tx strength. Where storage time has shifted an analog resonance,

Could it be a standing wave null point in your signal? It could be really unpredictable, since the null may shift with your motion. What happens if you move the transmitter?

I've not tried "leaving the house" to check at longer range (lower field strength). But, within the confines of the house, distance to the base unit doesn't seem to be a factor. Rather, it will be specific locations or "head orientations" in those locations that causes the problem to manifest.

But, as I said elsewhere, I could simply be moving from a bad spot caused by one "unintended radiator" to a bad spot cause by *another* unintended radiator!

I really need to find a time when I can afford to shut down all of the machines, here, and test it in a (relatively) "quiet" field.

It's an amusing problem. And, one that I suspect would plague me even if I opted to replace the headset -- esp if it boils down to too much RFI in the environment!

That sounds like what is called a null when disuccing antennas.

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umop apisdn

That was my initial thought. But, there are too many places (in the house) where it occurs. And, hard to believe that they'd design a device that requires you not to move your head, body, etc.

I don't recall this behavior in the past (before I packed it away due to "lack of need") so i wonder if I've just sited it differently or if there's just way too much RF crud in my current environment for that little receiver.

I guess moving the transmitter is NOT the same as moving the receiver (given that the other RF sources retain fixed relationships to the transmitter if it is left "as is"). I will have to try that when I get back home. It will also be a good opportunity to shut everything down -- before I get "back to working", etc.

(sigh) Too much kit is almost worse than not enough kit! :-/

Yes, but it "has to be" related to other things in the environment. I.e., it's not like I've chosen an unusual location for the base/xmitter (e.g., in the basement, on the roof, behind a lead wall). So, something else in the environment must be interacting.

I'll play with it when I get home (traveling at the moment).