receiving antenna question

[Nashua Area Radio Society]

I just finished watching the video on receiving antennas for 160 and 80 meters by frank Donovan. Great video. My question is would a receiving antenna for 40 and 20 meters work? why dont you hear about those and do you need one?

[Hamilton]

Hello Michael,

Reception on 80m and especially 160m is dominated by atmospheric noise including distant lightning. Antennas like a Beverage excel because they reject a portion of this noise more than the signal improving the signal to noise ratio (SNR).

On 40m the atmospheric noise is considerably less so cable losses, and antenna gain become more important. Unless you have a huge yagi or other high gain antenna the signal plus noise is still higher than the minimum detectable signal (MDS, sometimes called noise floor) of the majority of receivers. In most cases a Beverage would reduce the atmospheric noise to below the MDS while also reducing the signal. Unlike on 160m and 80m the SNR would be reduced which is not good.

By 20m and above cable losses, antenna gain and receiver MDS are dominate. A preamplifier is often used to improve the receiver’s MDS on 20m and above.

There are receive only antennas that work well on 40m and above. But unlike the low band Beverage it is not directly related to atmospheric noise. The goal is to improve the antenna’s gain while reducing losses. These antennas include arrays and are often at 75 ohms due to reduce cable losses. Decades ago I supplied equipment to a ITT HF station near San Fransisco. The receive array was almost a square mile.

73

Hamilton K1HMS

[Nashua Area Radio Society]

thanks so much for the explanation and fast response Hamilton. 🙂

[Author]

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