Re: Elad S3 versus Perseus and FDM Duo


jdow
 

144 MHz and 445 MHz dynamic range around here is simply unreal. LNAs have a wide bandwidth on their input, typically. That means you are receiving some VERY weak signals. Unfortunately pagers still exist. And around here pager transmitters are in the kW region. Having one relatively nearby can periodically desensitize a receiver in addition to creating IMD products. With rtlsdr dongles this is easy to see here with little whips depending on where I am tuned. AirSpy R2 dongles can show it on frequencies too close to the pager frequency.

{^_^}

On 20220330 07:45:07, Brian Morrison wrote:
On Wed, 30 Mar 2022 14:28:27 +0000
"Conrad, PA5Y" <g0ruz@...> wrote:

That is true and unnecessary, perhaps I misunderstand but you seem
to be indicating that I am advocating sub 1dB noise figures on 144MHz.
I am not and Chris Bartram was absolutely right.
I'm not Conrad, you're definitely correct in your earlier statements.
Others seemed to be advocating lower noise figures in general, as you
say there is a breakpoint somewhere above 200MHz where the sky and
reflected ground noise falls off and at 70cm a 0.5dB NF is nice to have
if you put the LNA at the correct place right next to your antenna.

It's interesting that you say the DR needed on VHF is harder to achieve,
but I suppose it must be due to the RMDRs due to the LO being worse at
higher frequency. Stepped attenuators have their place, you just have
to understand their effect which is not particularly difficult as it's
just a normal cascaded NF/gain diagram and calculation.


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