Why would a DECT Panasonic cordless phone keep losing the wireless link?

Sounds like interference.

I recently switched to a high-power router and Wi-Max wireless internet. One or both drove my 2.4GHZ wireless phone crazy. Hardly worked at all, even up close. I powered up the spectrum analyzer. Yep they were right on top of one another. I switched to a DECT phone, which, as I recall, works on different frequencies. Problem got a lot better. I still can't stand too close to the router.

There are three kinds of interference that can happen in this case.

The first is direct interference, where your WiFi unit operates on 2.4gHz and your cordless phone also operates on 2.4gHz. The old 2.4gHz phones did not listen for activity on a channel before transmitting on it, and often would wipe out Wifi.

The newer DCT phones listen, but there is only so many channels and eventually they overlap.

Since 2.4gHz is 1/2 of 5.8 gHz, the second harmonic of WiFi can interfere directly with 5.8gHz phones and so on.

The second is intermodulation, where two signals combine and the difference or sum causes interference. Not likey in this case.

The third is desensitization, where a strong signal on a relatively near frequency overloads the receiver in a device. So a WifI router can cause DECT phones to stop receiving, even though WiFi is 2.4gHz and DECT is 1.7gHz.

That's why you can't talk on the DECT phone near your WiFi device.

It's very likely that the OP is experienceing desensitazation or direct interfernce.

Another thing they can try is to move the base station. Especially if it is sitting next to another wireless device.

Geoff.

This is very useful information, an applicable to the WiFi group as well.

My DECT Panasonic KX-TG6441 phones & handsets apparently operate at

1.9 GHz, according to page 6 of this PDF: "The product operates in the frequency range of 1.92 GHz to 1.93 GHz, and the RF transmission power is 115 mW (max.)"

My problematic Panasonic KX-TG6441 cordless phone is also on 1.9 GHz, as described on page 6 of this PDF:

This makes sense.

What I did today was I pulled the batteries out of the five handsets and pulled the power from the base, and let it sit that way all day.

Then, I performed the re-registration procedure as outlined on p27 of this PDF:

Here's just the Panasonic cordless phone re-registration procedure:

Hopefully, re-registering all five handsets may help with the problem of the Panasonic KX-TG6441 dropping calls after a while:

I'll let you know what happens...

They're on 1.9 GHz ...

That's a great suggestion Jeff.

Maybe these other DECT phones in the same house:

Are causing the problem with this DECT phone:

It might also be the batteries, although you can see in the previous photo that they are fully charged - yet - I charged them today off the Panasonic base:

And, strangely, when I ran the registration procedure, they showed up as being discharged! ?????????

So that makes absolutely no sense. I chalk it up to "confused electronics" at this point - because I can't imagine what happened to make a fully charged battery indicate almost discharged.

Anyway, as a precaution, I ran the re-registration procedure, which is described on page 27 of this PDF:

This is a snapshot of the re-registration procedure:

Since the menus don't show up until *after* you run the procedure, I post below sequential screenshots so others who run the registration procedure can see the cause and effect on the phones:

Press LOCATOR on base 4 sec. Then press OK.

Call from Base: Base regtr'ing

That might be the case Mike, because I know two things.

The batteries were showing fully charged initially:

Then, I removed them and let the phone sit for a few hours:

When I then ran my first re-registration procedure, I was surprised to see that all five phones suddenly showed low battery indications:

That made no sense because pulling the batteries and letting them sit disconnected for a few hours couldn't possibly have discharged them from full to near zero. But it was easy enough to charge them independently on a Ni-MH charger:

Yet, I was again very surprised to see, after 3.5 hours on the charger (the lights stop blinking on the charger to indicate full charge) that, back in the handsets, they *still* said they were low on charge!

Something doesn't add up - but all five handsets acted the same way, even with the four new batteries from the charger put into two of the handsets.

All five phones are now in their respective holders, and, I just checked the charge, and they went from one bar to three bars, so, that's just weird.

It's almost as if they'll only charge from their Panasonic holders, and not from a separate non-Panasonic charger. But, that makes no sense - so - I really don't know what to make of this inconsistent data other than to ignore it.

Don't you have a voltmeter? You shouldn't be depending on the base to inform you as to whether the batteries are actually being fully recharged.

Ummm... was the phone designed to use NiMH or NiCd batteries? I'm too lazy to check.

NiMH batteries can be a problem due to high self discharge and possible overcharging. I suggest that you charge a few of the batteries in the phones for a day and then remove the batteries. Measure the voltage which should be about 1.2V when fully charged. Just let them sit outside the handset for at least 12 hrs (or more). Then measure the voltage again. 1.1V to 1.2V is fairly normal. 1.0V is borderline. Anything less than 1.0V is a problem. What you're measuring is the self-discharge rate, which tends to get worse as the batteries get older. It's particularly bad with NiMH which can lose

1% to 5% per day depending on temperature and age.

Besides dubious batteries, I'm beginning to suspect you may have multiple problems. Two independent but incompatible DECT systems, on the same frequency, are going to cause mutual interference. The reason the problem is intermittent is that both bases have be on the same channel in order to cause mutual interference. With 5 (US) channels to use, you're chances are 1 in 5 of having a collision. Unplug one base and see if the probleem goes away.

Part of the DECT standard is that a device listens before it transmits. If the channel is in use, it changes the channel. What happens when all channels are busy I have no idea.

What you describe was the problem with the old 2.4gHz cordless phones. They just picked a channel and transmitted on it. The later ones were spread spectrum, so as far as WiFi was concerned, it interfered on ALL of channels.

Or in plain English, when my upstairs neighbor's phone rang, my WiFi crashed.

DCT phones work the same way as DECT phones, but on the 2.4gHz or 5.8gHz band. Again, what they do when all channels are busy I do not know.

This is also why cell phones do not need to be licensed. They only transmit when asked to by a cell, which in most places is licensed.

If for example, you were to bring a 1900mHz GSM phone to Europe, or a

900/1800mHz EU GSM phone to the US, it won't start transmitting and interfere with whatever is using those frequencies.

Geoff.

I was remiss in not mentioning that I tested the voltage with my fluke but the problem, as always, with testing open circuit no-load voltage is that without a load, a battery that tests good isn't necessarily good.

However, all the handsets are now reading full bars in battery voltage, so, I'm inclined to assume that the battery-charge indicator on the handsets isn't really a voltage indicator - but some sort of integrator.

The good news is that it hasn't happened since re-registration; but I also haven't been on the phone a lot either. I will report back in a few days to let you know if the problem is solved by the re-registration or not.

Hi Jeff, The batteries are the original, and, they're all Ni-MH batteries. I noticed a set (white paint) was of a different amperage, so, I reassembled all the sets with like-amperage batteries (to prevent reverse voltage situations).

I ran that from yesterday, Jeff, and they came back at 1.2 volts. So, I must tentatively conclude that the phone itself has a summative charging icon, where it might be "timed" in the charger, rather than checked at the battery.

All five handsets, with the same batteries that read nearly dead after charging, now read full. I haven't extensively tested yet, but, all seems well now (tentative assessment).

This might be the reason for the intermittence!

What I *should* do is buy a DECT system with 9 handsets instead of two DECT systems for a total of 9 handsets.

I don't believe it. The phones look at least 8 years old. If the NiMH batteries were that old and left on continuous charge, they should be nearly dead by now. I have a discharge tester (West Mtn Radio CBA-II) that can test them. Send me one cell and I'll run a test (time permitting).

Ok, the batteries are not totally dead.

Dunno. I've used a few Panasonic handsets around the house. The one with individual cells ate batteries about every 3-5 years.

Offhand, I would say a bad battery or charger connection. The chrome plated connections on both the handset and charger base don't make a reliable connection and must be cleaned carefully. Same with the internal battery contacts.

Just buying some additional handsets for your existing base might be a better and cheaper idea. The data sheets list the maximum number of handsets a base will accomodate. I know of one system with 12 handsets. This might help: Oops. Looks like Panasonic is limited to 6 handsets.

Hi Jeff, The phones *are* old. I agree.

And, those yellow Ni-MH AAA batteries are the originals. So, I must have done the voltage test wrong.

Let me explain what I did, so we can see what I did wrong.

1. Here are four of the handsets, with full battery indicators:
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1. Flipping them over, only two currently have original batteries:
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2. Opening one, I find the battery open-circuit voltage is 1.4VDC:
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1. Likewise, the other battery is 1.4VDC, with no load on it:
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2. Yet, putting them back, the phone now indicates a low battery:
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Conclusion? A freshly charged battery (hot off the phone cradle), reads good; but the phone charge indicator reads full at first, and then almost empty after merely removing and then replacing the batteries.

1. Similar voltages were found for the other handset batteries:
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1. The replacement batteries read slightly higher voltages:
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2. Yet, all read low when immediately put back in the handset:
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I'm not sure what to make of this data ...

Danny,

Did your problem show back up again? I am having the same problem with my Panasonic kx-tg764 series 6 handsets. It doesn't make any difference which handset I use, I eventually experience the dropped call. It was a refurbished "new" set to start with. and worked great for about 6 weeks before the problem started. Tried troubleshooting for almost a month. Finally Panasonic switched them out for another "new" refurbished set. These worked for about 1 week and the same thing started. Panasonic told me it was normal for the handsets to think the batteries were low when putting the fully charged batteries into the "new" handsets. And the batteries do not show low when they lose their link and drop the call. And since all the phones were registered individually again when the base was replaced I can't see doing it a third time but am at a loss on what can be going on. Panasonic of course denies any knowledge of this type of problem being an issue but Googling it now seems it has been going one since

2008. Thanks, Cindy