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Airspy
HF+ Discovery and external preamplifier -- loser's strategyr
It is just going to empty your pocket Joanne (jdow) on io.groups: For that antenna there is one major use for a preamp, emptying your pocket. I learned that the expensive way as a teenager in about 1960. The cost of a DowKey preamp I bought REALLY REALLY hurt when the performance improvement I got was basically zero. Arguably there was some anti-improvement present. That was big money to a teenager. And it left me REALLY annoyed. It hangs on through today. When I was in college I visited the local radio parts store and noticed a book on their rack. It was about "Noise Figure". Reading that explained to me what went on. I think it had the HF noise plot you can find on Wikipedia as well as how noise figure works, also on Wikipedia. Those are good articles for amateurs in electronics and may even help somebody studying engineering to understand the course material better. About the only two things that should be put immediately in front of a Discovery are an antenna or an antenna followed by an AM broadcast band attenuating filter. Seriously, all that noise is present in the EM fields around you. The noise at HF is coming from the atmosphere as long a your radio has a noise figure lower than the antenna's noise level. That is between an effective noise figure of over 30 dB at 80 meters to maube 10 dB at 10 meters. The Discovery is well below that. A beam antenna will do you FAR more good than a preamp. Um, it will cost a bunch more, too. But the "gosh wow!" factor seems enormous beyond the mere engineering numbers. The beam nulls local noise sources at the same time it improves reception from the front. The latter is important. [February 2024, an edited discussion from "Airspy" on io.groups] |
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