spectrum analyzer IF output signal

I have some problem using spectrum analyzer IF output signal.

I want to extract a received signal with antenna and spectrum analyzer and then capture it with high speed A/D card.

the spectrum analyzer's RBW is 10 MHz.

1- what is the relation of received signal (e.g. in 500 MHz with 10 MHz bandwidth)
and IF output?
2- If the output signal of IF (21.4 MHz) is double side band or single?

3- what is the best usage of an IF uotput of a spectrum analyzer?

thanks for attention.

1. shape of 10MHz RBW filter is not "rectangular", it's gain is not constant over passband and the result is product of your signal bandwidth and the filter response. Your signal will be "weighted".
2. IF signal is single side band.
3. there is no best usage, speaking generally, it depends on what you want.

If the measured signal in 500 MHz with spectrum analyzer was an image signal with BW=6 MHz (-80 dBm),
how can we extract signal from IF output?

I think the following blocks needed.

IF(21.4 MHz) out ==>>> video amp + envelope detector + high speed A/D card

is it correct?

I am not shure what do you want to acheive. IF output signal (with zero span) is your signal. You can amplify it if it is low level, demodulate it or use as it is. All depends on what is your 500MHz signal.
If I make a guess, you have UHF TV signal and you want to receive it.