[hpsdr] MDS

[Robert McGwier]

John:

I am a 160m lover myself.   The noise floor on 160 is pretty darned 
high.   A typical Beverage has "gain" greater than -20dB.  A K9AY is 
about -20dB and has pretty high angle lobes.   A receive array typically 
has gains up around -6 dB but certainly > -10 dB.   We must also assume 
the noise floor will fall away especially if we use a receive array of 
the type I have designed for a few people (as in almost no high angle 
lobes).   So I think you are probably about right, maybe a little 
optimistic, but close.   It has been my experience that people love to 
have the signal seriously wiggle the meter even when they have not 
increased the SNR (they have just raised the noise floor).   This would 
again argue for having a good NF (good enough to say stand alone on 10m 
or 6m) and then raise the OIP3 with attenuation when required and then 
people can optimize the OIP3/NF for their application.

73's
Bob
N4HY

john_eckert at agilent.com wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Folks,
>
> I haven't been following this too closely, but I would add another angle.
>
> The atmospheric noise level numbers suggest that sensitivities greater 
> than these are a waste. I.E., you can't hear below the atmospheric noise.
>
> There are two cases I can think of where I would want all the sensitivity 
> I can get:
>
> i. When we are at the bottom of a sunspot cycle as we are now. On forty meters during the day I'm limited by my receiver MDS.
>
> ii. On 160 meters I use a beverage and it normally reduces signals by
> greater than 30db and noise by 40db.  So I get 10db better S/N but lose
> 30db sensitivity.  I can hear signals Q5 on the beverage that I can't 
> detect on my dipole.  This is another case where I'm limited by NF(MDS)
> rather than atmospheric noise.
>
> Great job guys!  As always I want more.  More sensitivity and more 
> dynamic range.
>
> 73,
> John
> k2ox
>
>
>   


-- 
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
"You see, wire telegraph is a kind of a very, very long cat.
You pull his tail in New York and his head is meowing in Los
Angeles. Do you understand this? And radio operates exactly
the same way: you send signals here, they receive them there.
The only difference is that there is no cat." - Einstein


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