February 22, 2011 - Scope Testing Modulation On the Retro 75 Transceiver
Posted a video of my modulation testing on the Bruce's Bench page.
I was surprised to find that modulation was only possible to 60-70% before distortion occurs.
Perhaps this is the norm with this modulation scheme?
Measuring set up used - Retro 75 transceiver built by W1UJR, Elecraft DL1 Wideband Dummy Load,
Elecraft CP1 Directional Coupler, Elecraft 2T-gen 2-Tone Test Oscillator.
Also used the Elecraft W1 140W Computing Wattmeter and SWR Bridge for initial power measurement and set up.
Power output was good, found power output about 2.5 watts with an unmodulated carrier, does rises to about 4 watts at 60-70% modulation.
Waveforms were recorded on Tektronix THS720A Digital Oscilloscope.
Wonder if anyone has discovered the limiting factor here?
RKW mentioned the LED being used as a limiter, thoughts?
Frankly, does it really matter that much with 2-4 watts of carrier?
Photos and video at -->>
http://www.w1ujr.net/bruce's_bench_2011.htm