Re: Elad S3 versus Perseus and FDM Duo


jdow
 

Of course, when you are up at 2 meters and above (perhaps even 6 meters to a lesser degree) putting the LNA at the antenna feed point gives you a "free" dB of noise figure reduction. There is also a potential TX gain for putting the PA up there, too.

{^_-}

On 20220330 07:28:27, Conrad, PA5Y wrote:
Hello Brian 

Yes sub 1dB noise figures definitely cost dynamic range. 
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 said, earlier in the thread.

....... dynamic range is certainly not optional. I put systems together based upon total system analysis which includes both noise figure and dynamic range. On 2m with a 1dB NF which is a little better than needed for terrestrial operation in my semi-rural location. I use the free AppCAD program for system noise figure and dynamic range analysis, although a spreadsheet also works fine.

I think that a system noise figure of 1dB on 2m is better than needed. I agree that 2dB is good enough for terrestrial use and even then only for the very fortunate. 1dB is slightly better than 2dB. For most people who are not on EME,  these days 3-4dB is adequate for terrestrial use on 144 MHz due to manmade noise. Also in EU contests (including the UKAC) you are better off prioritising dynamic range much of the time. 

Which is why I use a step attenuator after the first LNA stage, I can adjust it extremely quickly depending on conditions. Try it, you will find that is optimal for the EU VHF DXer who suffers from high station density. 

By the way sub 1dB noise figures on 432MHz and above are very worthwhile and certainly not that difficult to achieve these days. 

73

Conrad PA5Y



-----Original Message-----
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Brian Morrison via groups.io
Sent: 30 March 2022 14:52
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Elad S3 versus Perseus and FDM Duo

On Wed, 30 Mar 2022 11:22:30 +0000
"Conrad, PA5Y" <g0ruz@...> wrote:

Yes sub 1dB noise figures definitely cost dynamic range.
Back in the day (i.e. about 1979/80) Chris Bartam G4DGU of muTek determined that 144MHz system noise figures of less than 2dB for terrestrial signals were unnecessary due to the total noise at the antenna from sky and ground sources. The well-known muTek preamps were designed to have a NF of ~0.9dB (using a BF981 or 3SK88 FET with noiseless feedback) and then to allow a further 1dB contribution from the rest of the receiver to minimise any reduction in dynamic range. If you had the complete replacement muTek front-end which had a high-level diode-ring mixer, class A LO amplifier chain and post-mixer high IP3 IF amp then this DR reduction was much less but many of us had far less money then :(.

I would not expect these external limitations to have changed in this regard over the intervening 40+ years, although the radios have become more expensive their performance has improved quite a bit in other respects.


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