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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

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