Hi Jose and all, > > In your example it would have to be 5 Hz wide. Then the phase of whatever > > signals that passes the filter is used as the carrier for synchronous AM > > and FM with the AM modulation to one ear and the FM modulation to the other > > ear. > > Seems that the instantaneous phase shall be a vector built up with the > superposition of all "carrier contributions". Yes.
> Why did you do that AM in one ear and FM on the other? What are the > adventages? If you have a single local station the FM component will be very close to zero. The two channels AM and FM have separate AGCs that are derived from the detected audio signal. As a consequence the gain in the FM channel becomes VERY high. In case there is another station on the same frequency you will have a reasonable chance to hear it:-) > I see one you may not have thought of...monitoring of homebrew > transmitters. Here it is important. With a good, clean transmitter with > a stable and well isolated VFO the spurious modulation output (either AM > of FM) shall be zero. Oooh! There is a "Transmitter test" option in Linrad:-) > While building my old homebrew heterodyne phasing transmitter back in > 1972, I checked the VFO for pulling listening with a receiver tuned to > the VFO frequency, which should remain stable and unmodulated. Yes. Isolating signals and checking them separately is a very good idea:-) > > > I would be interested in a recording where the ECSS detector has > > difficulties. Linrad currently does not provide the corresponding > > function with a filter to remove one sideband but it would be a fairly > > easy add-on in case it would give any benefit. > > I don't have any at hand now. Such audio files can be large. I can provide a site for upload. > > > > Regarding to the LF response, I would like to have the lowest possible > > > frequency cutoff available, 20 Hz might be a good choice, if it is > > > possible to go that low. > > > Do the BC stations really transmit anything that low (close to the > > carrier)? > > Yes, at least the studio equipment can go down between 20 and 50 Hz. > Whether the studio - transmitter links can support that is another > story. Nautel transmitters chop the large low frequency peaks to avoid > overheating with sustained large peaks. But pulse width modulators and > pulse step modulators can have excellent low frequency responses, almost > impossible to achieve with the old modulation transformers and shunt > feed chokes. And they really use it? > > What is "lowest possible" is determined by where you want the AGC time > > constant. The purpose of the AGC is to remove the variations in signal > > amplitude due to the the interference between signals that travel > > different distances. Sometimes they are in phase and create a strong > > signal, sometimes they are out of phase and nearly cancel out. > > Taking that into account, maybe 50 Hz could be a reasonably low limit, > imposed by the real performance of small subwoofer systems. I have one > of those, and sounds very well. I worked in broadcasting for some years > and quality audio can get to be very addictive. OK. 50 Hz or even 40 Hz seems quite reasonable. > > When carriers are spaced at 5 Hz, the QSB rate will be 5 Hz and to > > make the AGC tune up the gain fast enough during a dip it may be > > reasonable to allow the AGC to absorb a substantial part of the AM > > modulation at 20 Hz. Another thing is that the fading may be selective > > for the amplitude of the entire signal to vary less rapidly or not > > much at all. > > > > I had no responses on the Linrad AM detector so far. I do not know > > whether it is because starting to use Linrad is too difficult > > or whether Linrad does not provide any improvement over existing > > AM detectors. You may download linrad.exe and run it on a wideband > > .wav file under any Windows system. Linrad is free and open source > > and it compiles under Linux Windows as well as under Windows. > > I have not downloaded any recent versions after 2.34. One of the hiccups > of my mail provider seems to have caused the suspension of my > subscription to the Linrad list. Being busy and forgetful is not a good > combination. The original Linrad list was closed long ago. The current list is at http://groups.google.com/group/linrad 73 Leif / SM5BSZ
