sakki ha denpa ga warukute, eki de haha ni denwa dekinakatta ndesu.

は is marking さっき as the topic or time frame: as for earlier / earlier on.

In this sentence, さっきは helps set up the situation the speaker is explaining. It can also carry a slight contrast, something like earlier, at least, the signal was bad—which can imply that things may be different now.

Without は, さっき would still work, but さっきは sounds more like the speaker is specifically talking about what happened at that time.

Here, 電波 is the thing being described as bad, so が marks it as the subject of 悪い.

So:

• 電波が悪い = the signal is bad
• 電波は悪い would sound more contrastive, like the signal, at least, is bad or as for the signal, it’s bad

Since さっきは is already the main topic, 電波が is the natural way to say what was bad during that time.

Literally, 電波 means radio waves, but in everyday Japanese, especially with phones, it often means signal or reception.

So 電波が悪い is a very common way to say:

• the signal was bad
• reception was poor

It does not usually mean the speaker is talking scientifically about radio waves here.

悪くて is the て-form of the い-adjective 悪い.

The て-form connects this part to the next clause:

• 電波が悪い = the signal is bad
• 電波が悪くて、電話できなかった = the signal was bad, so I couldn’t call

In this kind of sentence, 〜て often gives a reason or cause. So 悪くて here means something like:

• because it was bad
• and since it was bad

で marks the place where an action happens.

Since the action is 電話できなかった = couldn’t call, the station is the location where that happened:

• 駅で = at the station

By contrast, に is more often used for:

• destination: 駅に行く = go to the station
• existence: 駅にいる = be at the station

Because calling is an action, で is the correct particle here.

With 電話する, the person you call is often marked by に.

So:

• 母に電話する = call my mother
• 友だちに電話する = call a friend

That is why the sentence uses 母に.

English uses call someone directly, but Japanese often uses the pattern someone に 電話する.

This is the past negative potential form.

The base expression is:

• 電話する = to call / to make a phone call

Its potential form is:

• 電話できる = can call / be able to call

Past negative:

• 電話できなかった = couldn’t call / was not able to call

So the sentence is saying the speaker was unable to call, not simply that they chose not to.

When talking to other people about your own mother, Japanese usually uses 母.

• 母 = my mother, when speaking to outsiders
• お母さん = mom / mother, often when addressing your mother directly, or when referring to someone else’s mother more politely

So in this sentence, 母 is the normal choice because the speaker is talking about their own mother.

んです adds an explanatory or background-giving tone.

The sentence without it:

• 電話できなかった = I couldn’t call

With んです:

• 電話できなかったんです = It’s that I couldn’t call / The reason is that I couldn’t call

It often sounds like the speaker is explaining the situation, giving context, or responding to an unspoken why?

So this sentence feels like:

• I couldn’t call my mother at the station, because the signal was bad earlier.

Yes. Japanese often leaves out subjects when they are clear from context.

In English, you would normally say I couldn’t call my mother, but in Japanese the I is often omitted if it is obvious.

So the sentence does not explicitly say 私, but the listener naturally understands that the speaker is the one who couldn’t call.

さっき usually means a little while ago or earlier, not necessarily just a few seconds ago.

It is a casual, everyday word for a recent time in the past. The exact time depends on context. It could mean:

• a few minutes ago
• a short while earlier
• earlier today

So in this sentence, さっきは means something like earlier or a little while ago.