Comparing the VRF (Variable RF) and mu-tuning preselectors скачать в хорошем качестве

Comparing the VRF (Variable RF) and mu-tuning preselectors

Some of you may recall the strange noise I was chasing down earlier this year. I found it to be our new washing machine, which is computer-controlled, with an AC inverter drive. As it cycles on and off it generates a horrendous noise. The washing machine is on right now, and you can clearly see the noise on the bandscope. The noise is so broad that it spreads from 170 through 20 meters. In this video, I show the difference between the built-in preselector, VRF (Variable RF) and the optional, external, *mu-tuning preselector. The VRF is certainly an effective preselector. Most radios don’t even have a preselector at all. Most only have a fixed bandpass filter. As the name implies, the bandpass filter passes all noise and signals in an entire band. A preselector allows us to narrow the front end of our receiver to a fraction of the width of the band, helping to attenuate broadband noise and interference before it enters the bandpass filter. These “variable preselectors” are high-Q factor (+300) filters that are inserted into the receiver signal chain between the attenuation stage and the bandpass filter stage. They narrow down the amount of RF spectrum allowed to continue to the bandpass filter stage to a mere few dozen kHz, by motor-driving a large 1.1” (28 mm) ferrite core stack through a 2” high (50 mm) coil structure. Both the VRF and the optional mu-tuning preselector are adjustable, so we can decide what portion of the band we want to focus on. In this video you will clearly see how the mu-tuning preselector is approximately narrower than the VRF preselector. But, again, the VRF preselector is no slouch. I hope you find this video informative and helpful. If you would like to help with the cost of this channel, please consider becoming a Patreon by visiting:   / n4hnh   73, de N4HNH