A master timing address chain is used to address memory sine tables stored in an EPROM. The 19 KHz and 38 KHz signals are added without filtering which would otherwise adversely affect phasing precision. The 19 KHz pilot subcarrier signal is generated by a digital-to-analog converter that is clocked by a crystal timer which is common to both signals thereby to lock the phase of the pilot signal to the 38 KHz signal. The difference component is applied as an input to a double sideband suppressed carrier digital-to-analog converter which is responsive to the synthesis circuit to provide the 38 KHZ carrier signal.
The left and right stereophonic audio signals are applied to operational amplifiers to provide sum and difference audio components. The 38 KHz double sideband suppressed carrier signal is generated in a digital synthesis circuit to provide a stable 38 KHz carrier signal. The phase of the generated 19 KHz pilot subcarrier signal is fixed relative to the 38 KHz carrier signal. Or go for an older used HP/Agilent generator that will cover some ham bands in the future.Įdit: Or look for a good old used service monitor like a Singer FM10C that will not only generate a signal but measure some transmitter stuff.An FM stereo generator for use as a modulator or in a test instrument or the like to provide the conventional 19 KHz and 38 KHz signals. Some names to look for are B&K Precision, Meguro and Logimetrics. There are a number of CB specific signal generators you can get on Ebay for good prices. When using this you have to take the 30dB into consideration when making receiver sensitivity measurements. Usually 30dB is good for this, so you might look for a 30dB power attenuator that will handle 20w or whatever your radios put out. You also want good frequency accuracy.Īlso consider its best to have some attenuation between the radio and signal generator to protect it in case you accidentally transmit into the generator. The Ebay unit will only go down to 1mv, which is over 1,000 X too high. You need a generator that will do built in AM modulation with preferably an adjustable 1KHz and 400Hz tone with a modulation reference level and an accurate RF output down to at least. It does a ton of things you would never use and not much you could use working on CBs.
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