[R-390] Receiver noise floor needs

[wb5uom at hughes.net]

Thank you Perry -- I love reading this stuff. Guess I was born 10 years 
late.

David /WB5UOM

----- Original Message ----- 
From: "Perry Sandeen via R-390" <r-390 at mailman.qth.net>
To: <r-390 at mailman.qth.net>
Sent: Wednesday, October 19, 2016 6:01 PM
Subject: [R-390] Receiver noise floor needs


> List,
> Wrote: "Noise floor measurements seem to me to be of uncertain value in an 
> RFenvironment where atmospheric noise in "S-6" and above, and anyreceiver 
> induced noise is well below."
> That's probably true. And there are some urban areas where HF SW is a 
> total bust.
> Now for the BUT (A debate that will never end)
> I spent 18 months on 2nd (Swing 3 pm to 11 PM and 3rd shift (Mids 11 PM to 
> 7 AM
> Karmusel Air Station was an intercept base about 100 miles west of 
> Istanbul, Turkey. Besides radio interception the base was a HF radio link 
> between the eastern boarder of Turkey and ENT AFB (USAFSS) in Colorado 
> Springs, CO. Out send power was DISB with three 30KW SSB linear amps 24x7.
> Our part of the link was to receive from eastern Turkey to Croughten (SP) 
> AFB in England. They intern re-broadcast HF to Ft. George Mead in 
> Maryland,USA.
> The 2nd and 3rd shift job was standby maintenance (hardly any) and to 
> maintain reception from the 3 bay Hugh's receiver and the R390A's.
> Now to my point - at last.
> Mother nature does what she wants, when she wants, and as long as she 
> wants.
> Most nites, we easily received rock and roll AM pirate radio ships off the 
> English coast and would feed the audio to the intercept operators and of 
> course our receiver site.
> We had a spare "A" and a rtty converter and teletype printer set up so 
> mainly on the nite shifts we would copy AP, UPI, Reuters, what ever. We 
> went through cases and cases of yellow copy paper.
> On several occasions I could not hear the audio shift side tone of the 
> receiver but the rtty printer kept pumping out plain text.
> Many nites the bands were so quiet we would easily pick up WWV on 10 and 
> 15 MHz (17KM sky-wave I was told) as well as foreign SW broadcasts all 
> over the place.
> For this, having a low noise figure was useful.
> Noise floor numbers aren't the end-all for receivers but they are far 
> easier to measure than IP3, receiver stability drift and audio distortion 
> to name a few. That's why most people will try to measure it.
> The problem is that unless one has a HP, Fluke (I have both) or other high 
> end signal generators and-even-then, true sub-micro-volt numbers are hard 
> to measure with repeated accuracy.
> The noise floor "numbers" are averages but omit the fact that ionosphere 
> can and at times much, much quieter.
> An indirect proof. Look at all the receiver specs of the modern 
> transceivers on the market. Making the receivers that good costs money. If 
> it didn't add value they wouldn't do it.
> So one makes choices that are case specific or "How good can I make this 
> sucker, cost be dammed". My personal choice is the latter.
> Whatever floats your boat.
> Regards,
> Perrier
>
>
>
>
>
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