10M:28.6Mhz FM transmiter

@July/31, 2015

these days, after building  0.5W Linear push pull PA, i want to use it to build a real transmitter not just stay in lab, like 

27Mhz: AM RX/TX Experiment  or  PA: 27Mhz FM TX Chain Design. 

 it's hard to get a amert band crystal, especially >20Mhz, there are all overtone mode.  it's hard to pull the frequency via VXO.  so the practical way is let the overtone mode crystal work on it's Fundamental band, modulated it and trippler it's frequency. 

i select the miller oscillator cause it's could output around 8 dBm to 50R load. 

the collector tank use a  IF CAN, JET-2740, 3.8uH with a cap 68pF.

i finally found following photo's layout suitable for this VXO than my original design.

JF10ZL use lot's of push push or push-pull to multiply the frequency, it's have a decent performance, get almost same power compare to it's drive.

I disassemble a IF CAN use it's Toroids as input transformer. 15 turns trifilar transformer (0.3mm  magnet wire ),  get a 5uH primary inductor, enough for wide band transformer work above 9Mhz. 

the output DTC does hurt me,  at first time, i use a 1uH primary IF former(5T+5T), and a 33pF capacitor form a tank. the another part of DTC tank use a different IF CAN coil former. my mistake is, not connect secondary tank to ground, no doubt, i get terrible results.

base on calculator, this inductor need a 12pF capacitor, tune to 28.6Mhz(6.8p+2+2 incircuts). actually in the circuits need 8pF~10pF let it resonant at correct frequency. this inductor with capacitor 68p+47p resonant at 9.5Mhz could use as a serial resonant for filter out the baseband frequency. 

i suspect the push push output is wrong, so many 9Mhz band signal left, but check the tank with sweep signal indicated the tank config is good enough. when final filter been connected, output is much better(right photo).