Goal: send a voice signal on VHF or UHF, receive and record with SDR via RTL dongle

Core Problem and Resolution

An issue may have been a

hardware I/Q Imbalance

 in the RTL-SDR, which suppressed the desired signal, resulting in very low output volume that required excessive manual amplification.

Initial Problem:

 Very quiet, barely audible recorded audio, initially on UHF 433 MHz

Key Discovery:

 An 

I/Q imbalance

 caused a repeating signal "image" in the spectrum,

Frequency Change:

 Switched to the 

VHF 145.500 Mhz

 band,

Gain Override:

To overcome the defect and the failing AGC, gain stages were manually adjusted:

Squelch:

 

Squelch (SQL) was set to OFF (0)

 to prevent the software from muting the quiet, legitimate signal.

Adjusted the final Sound Output/Recording Gain

 on the host OS to match the maximized digital output, achieving audible voice.

Summary of Key Radio and Software Settings

Transmitting Radio (Baofeng UV-5R):

Operation: Simplex (direct radio-to-SDR).

Mode: Narrowband FM (NFM).

Receiving Software (SDR++):

AGC:

 Disabled (Crucial override).

RF/Tuner Gain:

 Adjust (Inject best signal power).

AF Gain:

 Adjust (Produce loudest digital audio).

Squelch (SQL):

 OFF (0) (Prevent muting of quiet signal).

Filter Bandwidth:

 12.5 kHz(Correct setting for NFM).

The ultimate resolution was forcing input and output gain in SDR++ and volume adjustment in Audacity