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"Poor line condition" means the two fax machines could not hold a clean enough connection to finish the call. "NG" simply means No Good: the transmission failed. The usual culprits are line noise, another device on a shared phone line, or a VoIP connection dropping packets. The fastest test is to plug a handset into the fax jack, dial a number, and listen for static, clicks, or dropouts.
A fax call is a live conversation between two modems trading tones. If the line degrades mid-call, the modems renegotiate to a slower speed; if it degrades too far, the call collapses and the machine reports poor line condition or marks the attempt NG. This is different from a busy signal, a wrong number, or a recipient machine that never picks up: the connection was established, then the line failed the machines. If the error appears on every attempt to every number, the problem is on your line. If it appears only to one number, the problem is more likely theirs.
| Cause | What you hear or see | Fix |
|---|---|---|
| VoIP or digital phone service | Fax works sometimes, fails others, often on long documents | Ask your provider about T.38 fax support, or switch to an online fax service that transmits over the internet |
| Shared line devices | Failures coincide with calls on another phone, credit-card terminal activity, or DSL sync noise | Give the fax machine a dedicated jack or at least unplug other devices while faxing |
| Missing DSL filter | Constant faint hiss or crackle on the line | Put a DSL filter on the jack the fax machine uses |
| Call waiting or other tones | NG errors when someone calls during the fax | Disable call waiting on the fax line (usually *70 before dialing) |
| Worn or long phone cord | Intermittent static | Swap in a shorter, known-good cord plugged directly into the wall jack |
Analog fax was designed for the continuous tone of an old copper phone line. VoIP chops voice into packets, and fax tones do not survive packet loss or jitter well: a one-percent packet loss rate is invisible on a voice call but can kill a fax mid-page. Many VoIP providers support the T.38 protocol, which packages fax data properly instead of treating it as audio, but it has to be enabled and the fax machine or adapter has to support it. Without T.38, faxing over VoIP is a coin flip that gets worse the longer the document is.
Most fax machines have an error correction mode that breaks each page into blocks and re-requests any block that arrives damaged, instead of letting the whole transmission fail. If ECM is off and the line is marginal, turning it on often converts NG errors into completed faxes, at the cost of a slower send. It is worth checking in the machine's settings when poor line condition keeps recurring. If both machines have ECM and the fax still fails, the line itself is the problem, not the settings.
Unplug the fax machine's cord from the wall jack and plug in any regular corded phone. Dial a number you know, such as your own cell, and listen. Clean line: silent except for the dial tone and the other end. Problem line: hiss, crackle, hum, echo, or the call dropping. If you hear noise on a handset with nothing else connected, the fault is the line or the wiring, not the fax machine, and no amount of resending will fix it. That is the point where you call the phone company or move to an internet-based fax method.
If you have tried a direct wall-jack connection, a clean handset test, a dedicated line, and the errors persist, the line is not going to cooperate. Online fax services bypass the analog line entirely: the document travels over the internet to the provider, which handles the phone-side transmission from its own equipment. LetterAgent's fax service works this way, though it is still in testing with US and Canadian numbers only, so treat it as available in testing rather than a guaranteed same-day send.
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