rsingl wrote:
Dave Doughty wrote:
Quote:
Tube receivers will have better dynamic range (generally speaking) and do not have the phase noise
synthesized receivers do.
What does phase noise sound like? Both my Icom IC-R70 and Kenwood R-2000 PLL receivers have what sounds like fast cooking popcorn in the background of extremely weak signals. The RF-4900, while it can have a quiet hiss behind the same weak signal, is much easier to listen to. It has a conventional analog front-end with a tuning cap. The digital display is a frequency counter with IF off-set looking at the local oscillator through a buffer. The SP-600 doesn't have this noise either. All are connected to the same longwire antenna through a selector switch. Is the popcorn sound on my two PLL receivers phase noise.
Dave,
I wonder if that "fast popcorn" sound you are hearing is another defect in these two receivers? Does it disappear when the antenna is disconnected? Some receivers will make some interesting noises from AGC bus issues when there isn't enough signal to create some AGC bias.
Rodger - Thanks for the explanation of what causes phase noise. Maybe "fast popcorn" was not the best description. Perhaps a very low level crackling sound behind an extremely weak signal would have been better. It is not there when there is no signal, just a low level hiss (probably better described as a hush). It is there on the R-2000 only in the narrow IF mode. (The R70's IF is a fixed, narrow bandwidth.) On the RF-4900, noise is a smooth background hiss (hush) that gives me the feeling that it has a lower noise floor and, therefore, more sensitive. Noise drops considerably when the antenna is disconnected so maybe it's just how the detectors deal with noise from the antenna when combined with a weak signal. Admittedly, the narrow IF mode on the 4900 isn't as narrow as the other two radios. I'm probably just being too picky. I'm impressed with the overall performance of all three radios. As with any radio, each have their own personalities.
Edit added: After comparing the three solid state radios again, I think the sound I am hearing on the R70 and R-2000 has more to do with the shape of the "communications style" (accentuated upper midrange) audio response than any internally generated noise. The RF-4900 just sounds so much better. When I turn the bass control fully CCW and the treble control fully CW, it sounds pretty much the same as the other two radios. Also, the R-2000 not only narrows down the IF bandwidth considerably in the "narrow" mode but seems to restrict the bass response as well, giving it two, distinct personalities.
Dave
