One thing that happens when tuning an AM station with a narrow receiver is that you tend to tune off to one side to get more highs and less lows through to make it more intelligible. When you tune off to one side you cut off the other side band and you loose 1/2 of the power. That drops the signal down into the noise on a weak signal.
With a signal that has proper pre emphasis the need to tune off to the side with the narrow receiver is eliminated and both side bands can be received raising the signal strength by 3 db. I have a TS430 with an AM filter in it. I think it is about 5 or 5.5 kc wide. When I listen to a very weak AM station in the SSB mode it is weaker than in the AM mode where I am receiving both side bands. There is less noise in the SSB mode using the product detector and the SSB filter but only 1/2 the audio power as compared to the wider AM filter. The AM filter is centered so that when I switch between AM and SSB I do not re tune the receiver. It is an interesting comparison. It can make the difference of being able to copy and not copy. 73 Gary K4FMX Bill Smith wrote: > Hi, Jeff > > > > Further, I have listened to AM signals from across the country, and usually > not with the TS-440. I will agree a few have been so bassy that they can be > difficult to understand, but overall signals with "50 to 5KHz" modulation > are overall so much easier to hear through noise that one wonders where the > notion of "communications quality" came from. There are some signals that > are so well processed (and frequency limited), and where the noise just > happens to be strong in a different part of the audio spectrum, or the voice > characteristic of the operator happens to overcome noise that such weak > signals cut through. Overall, in my experience, a full-fidelity signal will > be heard in most cases where a "communications quality" signal is torn up by > noise and fading. > > This goes for the receiver as well. The SX-62 is very wide, and the audio > capture from an am signal is obvious when compared with the TS-440. I don't > dislike the '440 at all, and use it all the time, but have observed that > even the wider positions of the Collins R-390 will allow better > understanding of a voice buried in noise. Maybe it is just my noggin, but > Mike Dorrough, K06NM would talk here about "power bandwidth," and Rich > Measures, AG6K would talk about "information bandwidth." > > A > 73 de Bill, AB6MT > [EMAIL PROTECTED] >
