Aurora Design Newsletter - Product Updates November 2021 #2

Aurora Design Newsletter - Product Updates November 2021 #2

Posted by Brad Dassow on Nov 23rd 2021

Newsletter November 

2021 #2

Product Updates:

FMR3.0.4: The FMR3.0.4 adds some handy new features for setting up a radio. First, the FMR enforces strict bounds checking on the tuner mechanism. It does this to ensure the microprocessor has enough resolution to accurately tune the radio. When attempting to Setup a tuner that doesn’t meet the specifications listed in the Technical Manual, after Step 2 (tune to high end) is performed, the radio will announce “tuner out of range” indicating that the radio does not meet specs and goes back to Step 1.

Because the Worldwide band requires higher resolution than the Americas and Japanese bands, the FMR has always bounds checked to the tighter Worldwide band. This puts a more restrictive check on the Americas and Japanese bands than is actually required. Where this mainly becomes an issue is with potentiometer tuned radios where the rotational travel on the pot doesn’t meet the tighter spec. 

The firmware was updated to relax the bounds checking for the Americas and Japanese bands. Because of this change, the new looser bounds check will be done at Step 2 and if not met will error out and return to Step 1 as it does now. Additionally when selecting the Worldwide region in Step 3, the tighter bounds check will be performed and if not met will error out and return to Step 1.

Next the minimum frequency allowed on the LC oscillator was lowered to allow for twice the maximum inductive or capacitive tuners to be used.

LC tuner specifications: 

  • 395kHz minimum frequency (all regions) 
  • 470kHz minimum bandspread (Americas, Japan) 
  • 700kHz minimum bandspread (Worldwide)

Potentiometer tuner specifications: 

  • 40% of Control Voltage minimum range (Americas, Japan) 
  • 60% of Control Voltage minimum range (Worldwide)

Next the virtual tuner actions have joined the virtual volume/tone actions in they are now adjustable. When the optional Step 6 is invoked in Setup, selecting a higher or lower sensitivity will also affect virtual tuner actions. Also, the default virtual tuner actions have been made slightly more sensitive.

Finally the status LED color during Step 1 and 2 (tune to low end / tune to high end) will change based on the tuner type. If an inductive or capacitive tuner is detected the LED will be red/green as it is now. If a pot tuner is detected the LED will be orange/yellow. In this way you can immediately determine if the correct tuning mechanism has been detected.

Note: Due to required Setup table differences in this firmware, flashing it into an earlier FMR will force a new Setup cycle, therefore the radio will have to go through Setup again after updating.

Bass blocking capacitors:

Sometimes it becomes necessary to insert bass blocking capacitors in series with small speakers that would otherwise rattle with too much bass signal. Typically non-polarized capacitors of 47µF or 100µF are used. This capacitor with the impedance of the speaker create a high pass filter blocking the bass signal. 

The problem with doing this on an FMR radio is the power-on speaker check becomes erratic depending on the residual charge on the capacitor as the radio is turned on. If there is little charge on the capacitor the check will work properly, while if there is substantial charge it may give erroneous results. 

To work around this issue a 150 Ohm 1W resistor can be placed in parallel with the capacitor thereby bleeding off any residual charge.

Always be safe! Never text and drive. Do not become distracted with the radio when driving. Become fully familiar with the operation of the radio before using it on the road. 

©2021 Aurora Design LLC