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Sources of Noise on the HF Bands (read the description)

The noise floor has gradually gotten worse in recent decades, due to the introduction of more and more man-made electronic devices. And this adds to the noise floor generated in the receiver itself. Radio receivers already have an inherent noise floor. One source of noise is due to the the heat generated by receiver components. This cannot be avoided. Another source of noise, predominant in superheterodyne receivers, is caused by something called phase jitter, a phenomenon associated with oscillators. The resultant noise is called phase noise. Newer technology has minimized the noise generated by such sources. With a traditional superheterodyne receiver, each conversion stage adds more selectivity, but simultaneously each stage adds more phase noise. There receivers with three-stage (triple-conversion) and four-stage (quad-conversion) receivers. So we must choose whether to hear the weakest signals (sensitivity) or be able to block stronger unwanted signals (selectivity). Life is all about trade-offs isn’t it? Even with radios. A brief history of receiver design: Some radios in the past featured a preselector to help with selectivity, so a 2-stage (dual-conversion superheterodyne) receive architecture would deliver the sensitivity, while the preselector delivered selectivity. The preselector would allow the operator to favor a particular portion of the band they were tuned to. But the Preselector added cost. Note that a few transceivers on the market today include a preselector. FTdx5000MP, FTdx101D, FTdx101MP, TS-990S, IC-7610, are a few that include a type of preselector. An IF (Intermediate Frequency) filter, often called a “roofing filter”, could be used, immediately following the 1st mixer, to add additional selectivity to the receiver’s first stage. Roofing filters are only available at specific frequencies so the 1st LO (Local Oscillator) must operate at a frequency that mixes with the incoming signal from the antenna to create a resultant 1st IF that matches the operating frequency of the roofing filter. Higher quality roofing filters are available at lower cost if the receiver uses a down-conversion architecture. Down-conversion was in common use until the late 1970s. Down-conversion uses a 1st IF that is generally between 8 and 11 MHz. To save the cost of a preselector, and to keep the 1st IF from preventing full receive coverage from 1.8 to 30 MHz, manufacturers switched to up-conversion, in the late 1970s. This placed the 1st IF at 40 to 70 MHz. The trade-off was the roofing filters. Roofing filters at 40 to 70 MHz are more costly and less effective. In 2003, Ten-Tec introduced the Orion HF transceiver. The Orion reintroduced down-conversion and high-quality roofing filters. Yaesu would follow next, with the FTdx5000. Kenwood followed with the TS-990S. The Yaesu and Kenwood transceivers also include a preselector. Many of the experts in receiver design prefer the dual-conversion (2 stages only) receiver architecture, with the 1st IF at 9 MHz +/-, because it offers a balance between receiving weak signals and blocking unwanted signals. The higher quality receivers today are designed in such a way that the jitter is reduced to a minimum. Many modern transceivers feature a low internal noise floor, thanks to improvements in the components used to create the oscillator circuit and the receiver mixing and amplification components. Back to the main topic: So, while the internal noise floor has been greatly reduced, there is still the atmospheric noise to contend with, which we can do nothing about. I covered the source of atmospheric noise in a video a couple of years ago. Lightning from around the world combines to create a large portion of what we call atmospheric noise. And then there is man-made noise. This we can control to some extent. In this video I point out some of the primary sources of noise on the HF bands and how to investigate the noise source. Note that other sources of noise I didn’t mention in the video are can be garden lamps or the lamps in a greenhouse. I hope you enjoy this video and find it helpful. If you find my channel informative and entertaining, I hope you will consider joining my support group by clicking on: www.patreon.com/N4HNH There are 3 levels of support, including exclusive content. Patreon team members gain insight from our technical discussions and internal polls. They also have the opportunity to view certain videos before they are released for public viewing. N4HNH Radio has a Web site, where you can purchase T-shirts with some of the sayings you might hear in the videos. Some of the more prominent videos are featured there as well as a page geared toward ham radio training. Go to: https://www.n4hnhradio.com Another great way to help support this channel is to click subscribe. 73, de N4HNH