Paul,
I went back and rechecked everything and I find the am demodulator in the RA6830 a lot cleaner than the diode detector in Steve's mod monitor. I heard distortion just above 100% on the diodes but no problem on the Racal until I clipped or hit the base line. My point was a little audio processing would have sounded better. I can hit 150% positive on the 160 meter rig.
Steve and I both sound better on his rig with audio processing. I never noticed it until I heard him on my rig.
This makes me think I would sound better with a little audio work.
Hi Frank,
The modulation monitor detector is not going to introduce any distortion to the signal
It's way too clean for that. I'm wondering if either something changed, or more likely, the receiver IF is filtering stuff out that we were able to hear in the monitor.
Remember we thought you might have some RF getting in somewhere? Did something change? The problem may have lessoned due to rain/antenna changes/whatever.... We both heard the transmitted distortion that night I was there (and, we could even see it on the 'scope). We did think it might be RF, because of the slope change - almost like feedback, but not quite. It was fairly substantial. From time to time, I've heard that distortion on your signal, on the air, although it was dramatic listening to it using the modulation monitor !
The mod monitor detector is completely linear up to over 200% positive modulation (I never checked it any higher - I don't have any transmitters that will go much over 200% positive) and there is absolutely nothing in the system or detector that would limit, in any way, the proper demodulation of a heavily modulated signal.
You will most certainly be able to hear any distortion
that you might be transmitting while listening to the modulation monitor output - distortion that you might never hear on the air or even through a very good receiver, due primarily to the extremely wide bandwidth of the monitor, and the flat response to above 20kHz. A receiver would need to have a 40kHz bandwidth to reproduce that !!!
Check this out:
Here is a modulated triangle wave and the output from the modulation monitor, demodulating that signal. Note that the output from the monitor is an exact demodulation of the transmitted signal. The output from the monitor is the top trace. The modulation monitor display is also shown:
[img ]http://www.radioassociates.com/mod_monitor_output.jpg[/img]
[img ]http://www.radioassociates.com/mod_monitor_100_percent[/img]
Below, what things look like at 150% positive - output is an exact demodulation of the transmitted signal:
[img ]http://www.radioassociates.com/mod_monitor_150_percent_output[/img]
[img ]http://www.radioassociates.com/mod_monitor_150_percent[/img]
The detector in the modulation monitor is extremely linear! The headphone output is flat from a few Hz to well over 20kHz, and the headphone amplifier in the modulation monitor is absolutely superb (and has lots of output, and a phase switch!). For better or worse, if it's on the signal, you're going to hear it
On listening in a local receiver:
I've got what I consider to be a very good hi-fi receiver. It will go to 18kHz bandwidth, with very shallow slopes on either side, so it's REAL wide. The detector is nice. Full wave, precision rectifiers. But it just does not compare to the modulation monitor when I monitor my transmitted signal and switch between the monitor and the receiver. The receiver is good, but the monitor is much better.
If there's any garbage, distortion, frequency response problems, etc. I hear all of if with the monitor.
I guess the main point of the discussion is, the receiver, by definition, has to color and filter the signal somewhat due to the bandwidth limitations, even if it's really wide
Talk later and Regards,
Steve