[amsat-bb] [Video] Preamp test in front of radio / satellite ground station build update

[Hans BX2ABT]

More budget friendly, especially the mini versions: 
http://www.shf-elektronik.de/en/index.htm

Got the Mini 70 and am very satisfied with it. Can also be ordered from 
Wimo in Germany.

Hans

BX2ABT

On 1/29/20 6:50 AM, Zach Metzinger via AMSAT-BB wrote:
> On 2020-01-28 14:56, John Brier via AMSAT-BB wrote:
>> Here is a little update on my satellite ground station build project
>> and a demonstration of a test I did with my Advanced Receiver Research
>> 2 meter preamplifier.
>
> Hello John,
>
> As others have said, FM is not ideal for this testing.
>
> Ideally, you'd want to run SSB and feed that into your rig. Then, take 
> the audio output and put it into Spectrum Lab or similar.
>
> For a weak CW signal (less than 1 S unit), you should see a peak at 
> the signal just above the noise. This ensures that AGC is inactive, if 
> it can't be disabled.
>
> Now, switch in the LNA. The CW tone should jump by the gain of the 
> preamp. Ideally, the noise floor will not change at all. If it does, 
> then the preamp is not a low-noise type or something else (overload) 
> is going on.
>
> Even with low-loss coax, putting the LNA at the antenna is the right 
> way to do it. Use the following calculator to experiment with this 
> lineup:
>
> https://www.pasternack.com/t-calculator-noise-figure.aspx
>
> (Noise-dB / Gain-dB)
>
> Case 1: LNA (1/20) -> Coax (2.5/-2.5) -> Rig (6/90) == 1.2dB
> Case 2: Coax (2.5/-2.5) -> LNA (1/20) -> Rig (6/90) == 3.6dB
>
> You're giving up 2.4dB of NFdB for the convenience of putting it 
> indoors. The numbers above assume LMR-400 at 100' loss.
>
> https://www.rtl-sdr.com/tutorial-on-properly-positioning-a-preamp-lna-in-a-radio-system/ 
>
>
> Local noise sources, unless they are incredible broadband, won't 
> impact the usefulness of a quality LNA. The thing to look for here is 
> linearity, which is indicated by the 3rd order intercept (IP3) of the 
> LNA. Most modern designs have eye-popping linearity and noise figures 
> as compared to the lowly, ancient U310-based amplifier.
>
> https://www.maximintegrated.com/en/design/technical-documents/tutorials/5/5429.html 
>
>
>
> --- Zach
> N0ZGO
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