Signál je špatný.

• signál = signal
• je = is
• špatný = bad, poor, not good

So the sentence literally means Signal is bad, and in natural English that is usually The signal is bad or The reception is bad, depending on context.

Je is the 3rd person singular form of the verb být (to be).

Here are a few forms of být in the present tense:

• jsem = I am
• jsi/jseš = you are
• je = he/she/it is
• jsme = we are
• jste = you are
• jsou = they are

Since signál is a singular noun, Czech uses je:
Signál je špatný. = The signal is bad.

Because špatný has to agree with signál.

In Czech, adjectives change their endings to match the noun’s:

• gender
• number
• case

Here, signál is:

• masculine
• singular
• nominative

So the adjective also takes the masculine singular nominative ending: špatný.

This agreement is a very important part of Czech grammar.

Signál is masculine inanimate.

A few clues:

• It ends in a consonant, which often suggests masculine gender in Czech.
• It refers to a thing, not a person or animal, so it is inanimate.
• The adjective form špatný also confirms masculine singular nominative agreement.

So:

• ten signál = the signal
• špatný signál = a bad signal

Czech does not use articles like English a and the.

So Signál je špatný. can mean:

• The signal is bad
• A signal is bad

In real use, context tells you which meaning is intended. In this sentence, English will usually translate it as The signal is bad.

Because signál is the subject of the sentence.

In a basic sentence like X is Y, the subject is normally in the nominative:

• Signál = subject
• je = is
• špatný = adjective describing the subject

Also, after být (to be), the predicate adjective usually agrees with the subject and appears in the nominative too:

• Signál je špatný.
• Voda je studená.
• Auto je nové.

A helpful approximation is:

SIG-naal ye SHPAT-nee

A few pronunciation notes:

• si in Signál sounds roughly like si in see, but shorter.
• á is a long vowel: signál
• j in Czech sounds like English y in yes, so je sounds like ye
• š sounds like English sh
• ý is a long ee-like sound

Stress in Czech usually falls on the first syllable of each word:

• SIG-nál
• je
• ŠPAT-ný

Špatný is a very common and natural word for bad or poor.

So Signál je špatný. is a perfectly normal sentence.

But depending on context, Czech speakers might also use other adjectives:

• slabý = weak
  Signál je slabý. = The signal is weak.
• mizerný = awful/terrible
  stronger and more emotional
• nestabilní = unstable

Difference:

• špatný signál = bad/poor signal in a general sense
• slabý signál = specifically weak signal strength

Yes. Czech word order is more flexible than English word order.

The most neutral version is:

• Signál je špatný.

Other orders are possible, but they change emphasis:

• Špatný je signál.
  This is more marked and sounds contrastive or poetic.
• Je špatný signál.
  Usually not the best choice for this simple meaning unless it fits a special context.

For learners, Signál je špatný. is the safest and most natural word order.

No. Czech does not need a separate pronoun here because signál is already the subject.

English:

• It is bad.
• The signal is bad.

Czech:

• Je špatný. = It is bad. / It’s bad. (if the subject is understood from context)
• Signál je špatný. = The signal is bad.

So if the thing being talked about is already clear, Czech can simply say Je špatný.

You negate je by changing it to není:

• Signál není špatný. = The signal is not bad.

This is the standard negative form of je.

You could also say:

• Signál není dobrý. = The signal is not good.

These are similar, but not always identical in tone:

• není špatný = isn’t bad
• není dobrý = isn’t good

No. Signál is a general word and can mean different kinds of signal, depending on context:

• phone signal / mobile reception
• radio signal
• TV signal
• a general signal or indication

So Signál je špatný. is flexible. In everyday speech, people often understand it as phone signal/reception is bad, but context decides.

Yes, absolutely.

• Signál je špatný. = The signal is bad.
• Ten signál je špatný. = That signal is bad or That particular signal is bad

Adding ten makes the noun more specific or more definite in context. It is not an article like English the, but it can sometimes feel similar in translation.