Ramsey Electronics FT146 - Manual (Page 23)

FT146 • 23
"hum-m-m-, that's not a .001 uf where a 100 pf should be is it?"
If there is a problem in getting the modulation working, a scope or audio
amplifier will allow tracing down any problem in short order. The microphone
audio is amplifier by about 350 times in U1:B. You should see at least a volt of
audio at the output (pin 7) of U1:B. A low pass filter follows U1:B, you should
still see at least a volt of audio at pin1 of U1. From there, the audio drives the
varactor diode D1.
How about keying of the transmitter? Check to be sure that the microphone is
switching to ground when keyed. This closure to ground causes PNP transistor
Q7 to turn on, switching +12 volts to its collector. This +12 volts lights the LED
and applies bias to the crystal oscillator.
If you hear a AC hum on the transmitted signal, usual causes are RF getting
back into the power supply or a bad VSWR on the antenna.
These short checks in no way detail any and all problems that can rear their
ugly head, but should get you on the way to solving most errors. We'd like to be
able to forsee a problem a builder may encounter, but the sheer number of
parts and the permutations and combinations of installing them makes an list of
precise, exact solutions impossible. If you run into a roadblock, gather all your
thoughts and information and give a call to the factory for some help. If you
elect to enlist the help of a local expert, great - but be sure the expert is
qualified - no need for having someone lead you down the wrong path!
Remember you may always return the kit for factory service, and there's no
charge if the problem is our fault. See the warranty on the last page of this
manual.
MICROPHONE CONSIDERATIONS
During assembly, the FT146 was jumpered for using an Icom style microphone
plugged into the mike jack J2. You may also use the rear panel 5 pin DIN jack,
P1. If you decide to do so, change the "Audio In" wire jumper to go between A
and B. When this is done, the transmitter cannot be keyed from the microphone
and must be keyed from the PTT pin.