ARC T-20 VHF Model?

Emil M Dular WD4SCZ at AOL.COM
Thu May 21 18:17:26 EDT 2009

whistle tuning also known as whistle stop tuning. A spotting feature,  
allowed you to zero beat the continuous tune receiver to the transmit crystal  
for simplex operation.  Aircraft receivers of that era often did double  duty 
and were used to receive nav signals  as well as voice.  Also  there were 
standardized calling frequencies like 122.1 mc for Flight Service,  122.5 
standard civil tower, 126.2 standard military tower, 121.9 ground control,  
etc. You would transmit on a "standard" frequency and listen on a facilities  
"discrete" frequency if you didn't have a crystal for the facilities discrete 
 frequency.  An example might be you wanted to talk to say, Louisville 
Tower  whose frequency was 119.8 but you didn't have a 119.8 crystal installed.  
 You would tune the receiver to around 119.8 and listened until you heard  
Louisville tower talk to someone and fine tune that. You would have the  
transmitter set to 122.5 and call Louisville Tower and listen for him on  119.8.
One reason it was still useful and practical to know the light gun signals  
back in the day....................
Emil WD4SCZ   ( N88421 in aeronuatical service)

I will have to read-up on the "whistle tuning"  feature.

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