Can a microfilterless phone disrupt your ADSL signal?

Hi Franc,

Just a wild guess here, but some RF telephone devices, in addition to the normal Voice Frequency line line traffic, they have also been known to generate VHF signaling that can compete with ADSL signals on the copper, and so can compete with ADSL if they are using an unfiltered connection. So effectively the Filter works both ways, protecting the Voice device from VHF signalling and protecting the VHF ADSL side from injected "noise" from the Phone.

Does this make sense?

Cheers.............pk.

Franc Zabkar wrote in part:

Undoubtedly. This is also true in N.America

Some phone may have a tiny low ESR cap across the incoming line. That cap is too small to dampen LF voice, but will soak up some HF DSL. The DSL filter isolates the line.

-- Robert

snipped-for-privacy@iinternode.on.net (Franc Zabkar) wrote in news: snipped-for-privacy@4ax.com:

Perhaps the modem's HP filter is internal, to avoid the possibility of the end user forgetting to install it.

On 07 May 2007 14:14:20 GMT, Bert Hyman put finger to keyboard and composed:

Exactly.

In Australia there is nothing to forget. AFAIK, we don't use central splitters unless we have a back-to-base alarm system. Our telcos supply self-installable ADSL kits which typically include one modem and two phone filters.

- Franc Zabkar

On 7 May 2007 23:18:06 +1300, "Peter" put finger to keyboard and composed:

Why would a phone which is designed to operate on a phone line with a ~4kHz bandwidth generate VHF?

- Franc Zabkar

I think the theory proposed is it's a cordless phone, and generates RF to talk to the handset, and the filtering isn't perfect so some of the RF leaks into the phone wires (or alternatively, the phone wires pass very close to the RF transmitter, and act as an antenna, picking up some of the RF.)

This theory seems reasonable and possible to me, but I'm not an expert. (IANAEE ??)

On Mon, 07 May 2007 14:02:31 GMT, Robert Redelmeier put finger to keyboard and composed:

I've only ever taken apart about a dozen phones (but lots of dialup modems), but IIRC the only caps I've seen were ceramic RF noise suppression caps of the order of tens or hundreds of pF, between each of the tip and ring terminals and circuit ground. Are these the caps you are referring to?

This is a photo of the innards of my ADSL modem:

It bears some rough similarity to a dialup modem's DAA in that it also has the abovementioned caps (C118/C120). RV1 is connected across the line and appears to be a gas arrestor. It is normally open circuit. Are you perhaps mistaking RV1 as your across-the-line cap?

- Franc Zabkar

On Wed, 09 May 2007 01:09:26 GMT, John Santos put finger to keyboard and composed:

Sounds reasonable to me.

FWIW, I used to have two phone lines, one for a dialup modem and one for voice. I once tested my setup by disabling my modem's error correction and connecting to my ISP via a comms app (HyperTerminal). I then rang my voice line. During the ringing, the crosstalk between the two wire pairs was serious enough to flood the terminal window with dozens of spurious characters.

- Franc Zabkar

Franc Zabkar wrote in part:

No. Tip & Ring caps to ground are functionally equivalent to caps in series across. What they soak up is dependant on their size and ESR. An ADSL modem cannot tolerate much, but a phone could. And some would.

-- Robert

The telephone company uses twisted pairs with hundreds of pairs in a bundle in the aerial and buried plant without any problems at all with millivolt level voice signals running directly adjacent to 90 volt AC ringing.

Some possibilities to explain the cross-talk on your installation are:

1) You home has been wired with the old JK inside wire (known as "Jake" to telephone installers) which is untwisted pairs. 2) You are using a lot of 20 or 40 ft flat silver satin non-twisted station cords around your place. 3) Grunge in you wall outlets. 4) You might have low quality multi-line KSUless phones.

Fully agreed. 5-15 thousand feet of tight bundle run to the typical phone. The pairs are carefully twisted and allocated.. Crosstalk happens when pairs are split.

Sure. But quad isn't so horrible for crosstalk if the pairs are allocated on the diagonal.

Flat silver satin isn't great for crosstalk, and very much worse if the pairs are not nested USOC.

Unlikely. But poor (hi resistance) connections might generate noise with ringing current.

Quite possible. Unplug to check.

-- Robert