Re: NDB - Airspy HF+ DIscovery versus Hermes Lite 2


Exactly dB what. They are a measure of how far down you are from when the front end overloads. With the AirSpy HF+ further calibration is not really possible last I knew. For most other front ends calibration is possible and remarkably accurate and linear.


On 20211223 09:41:40, Gedas wrote:

Tom, I do not own an Airspy so I do not know but when you say below -130 dB what are the units? dB what?

Are they an absolute figure like dBm (which is what you need) or is it a relative number related to ADU etc ?

Gedas, W8BYA EN70JT

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On 12/23/2021 11:15 AM, Tom Seeger wrote:
I wonder if you have both receivers connected to the antenna at the same time? This can cause digital noise emitted from one radio to be received by the other. Another good test is to disconnect the antenna from each radio and replace it with a 50 or 75 ohm resistor and record the base noise. It should be less than -130 dB. I measure about -135 dB on my HF Discovery at 277 kHz with a 250 Hz bandwidth. 
73 Tom

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