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Al Arduengo wrote:
Carl - w5su writes: snip I'd opt for a 108" steel whip plus a small antenna tuner at the end of the coax by the radio. Where in te heck are these 108" whips? I would like to get it local instead of waiting for mail but all there seems to be are up to 39" whips for CBs. Now, back to the noise problem... snip Out of curiosity, why doesn't this noise show up on my FM/AM that the truck already has? Is it that the noise and its' harmonics lie in the same band as sw? I really need to break out the old college books and refresh my rf theory. Cheers, You've partially answered your own question. Harmonics from the ignition and other electical noise do, indeed, fall within certain spectra. Although these spectra may be quite broad. However, AM/FM broadcast signals are often 10 to 100 times stronger than SW signals, largely masking impulse noise from the vehicle two ways One is simply overwhelming it with signal, the other is the often reduced sensitivity on broadcast bands. If, while listening to your favorite AM station, the carrier drops out, you will likely hear these noises. Even some factory FM receivers will render these noises if tuned to interstation dial positions. SW signals being much lower in amplitude, will not offer the same quieting that a city grade signal will, and will permit some of this impulse noise to be heard. You can experiment with this by tuning between stations. Strong broadcast SW station signals will be less encumbered by vehicle noises, than weaker signals which may be covered up entirely. Good sheilding of the antenna transmission line, as well as effective grounding of the receiver, transmission line and antenna mounts will help reduce much of this noise. Make sure the hood and deck lids are making solid contact with their copper grounding tabs. And ascertain whether the antenna transmission line runs through well shielded areas of the frame, isolated from ignition generated electric fields. My 308 had the antenna cable running through the engine bay right across the ignition cables. But then what do the Italians care about my listening habits. It took quite some effort to re route that cable before my Becker 2340 would render quie3t SW. Once measures were applied, the listening was quite good. |
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