Leif Asbrink wrote: > > Hi Jose and all, >> 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:-)
Interesting indeed.... >> 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:-) Well, some other authors are including VNA software in their packages. Versatility is good for the users 8-) >> 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:-) It worked very well for me, when all I had at hand was a D'Arsonval multimeter, diode probes, a 1 MHz oscilloscope and a heavily modified HRO-60 (with stabilized oscillator heater, xtal controlled 2nd conversion, mechanical filters, balanced diode product detector, switchable AM / SSB hang AGC). > I can provide a site for upload. OK, I will try to do some "sample fishing". > And they really use it? The cuban short wave station (Radio Habana Cuba) has quite a good audio, using digital links and pulse step modulators. It has a mixed news/comments/music content which may take adventage of the good source quality. It is being copied in Spain and North Africa beaming at 50 degrees from here. Maybe it could be copied in Scandinavia too. Existent transmitters and antennas achieve some 10 MW EIRP. > The original Linrad list was closed long ago. The current list is at > http://groups.google.com/group/linrad > Thanks for reminding me. > > 73 > > Leif / SM5BSZ 73, Jose, CO2JA
