[R-390] The OLE receiver sensitivity test revisited

Wed Feb 29 20:16:24 EST 2012

I agree.  Now out here where I live it is not as quiet as it was back 15 
years a go, but  if there are no storms nearby (200-300 miles)
my noise floor will bobble around -128DBm.

I have a splitter/combiner with a hodge podge of receivers tied onto it 
using a common antenna.

I have the 390A sitting on 8942Khz using the 455 output driving the Drake 
R8-B in SSB mode.
I have the  Win Radio 313i here and can ark it on 8942Khz as well and most 
morning really early, I will start
hearing the SELcal  tomes from Manilla Radio and or Toyko Radio on the 390 
before I hear them on the 313i.

Then after a bit I will start hearing tones and voice on both hear  on both. 
And conversely as the sun comes
up and the nosie increase ,the audio on the 390 is the last to fade out. 
usually around 9am local (CST)

I just thought it would be interesting to see how far sown I can actually 
copy a voice signal. I may play this weekend if i dont have to work (again 
arrrgh!)

Off to check out the webpage Todd mentioned.

David WB5UOM

East Texas USA

----- Original Message ----- 
From: "Curt" <cptcurt at flash.net>
To: <r-390 at mailman.qth.net>
Sent: Wednesday, February 29, 2012 7:50 AM
Subject: Re: [R-390] The OLE receiver sensitivity test revisited

> Well, to me, I would like to see it in absolute terms.  i.e., not
> "adjusted" for any arbitrary noise level.  It surely is possible to copy
> CW below the noise level, because noise is random and the human brain
> can do remarkable integration over time,  The EME groups have worked
> this down to a science and can compare good CW ops to digital modes for
> copying into the noise.
>
> Also, I suspect that some of these receivers were used with specialized
> detection that could integrate signals out of the random noise...similar
> to averaging when using a digital scope.  Integrators were standard fare
> back in the 60's for doing weak signal detection at VHF.
>
> I am amazed that the RF seals on some of the older test equipment can
> actually be trusted down to -138.
>
> I am very curious as to what others might add to this as I am really a
> novice in the front-end measurement arena.
>
> Thanks
>
> Curt
> KU8L
>
>
>
>
> On 2/28/2012 10:44 PM, wb5uom at hughes.net wrote:
>>
>> Good point Curt,
>> Ive been sitting here pondering your thought.
>>
>> So, would I use the standard method up to the point of setting the 
>> reference
>> noise level with the line level meter /adjustment
>> and THEN use the actual ssb audio signal from then on
>>
>> OR
>>
>> Do we care because we KNOWwe are never going to actually hear a -138
>> (or -128 ,or -118DBm ) station
>> because we are not (in normal operating conditions) going to have a noise
>> level that low on hf anyway.
>>
>> (although in years gone by my QTH has has some pretty quiet late nights)
>>
>> Just a thought.
>>
>>
>>
>>
>> ----- Original Message -----
>> From: "Curt Nixon"<cptcurt at flash.net>
>> To:<r-390 at mailman.qth.net>
>> Sent: Tuesday, February 28, 2012 7:59 PM
>> Subject: Re: [R-390] The OLE receiver sensitivity test revisited
>>
>>
>>> That is interesting..
>>>
>>> I also have a generator that will go down to -138.  I haven't tried it
>>> but that would be under no noise conditions..only internal noise.  On
>>> HF, it is my experience that for the most part, we are never limited by
>>> the sensitivity or the noise floor of the Rx but the level of QRN 
>>> present.
>>>
>>> Curt
>>> KU8L
>>>
>>> On 2/28/2012 8:07 PM, wb5uom at hughes.net wrote:
>>>>
>>>>    Ok Now that there are some awake from the PING Test:
>>>>
>>>>    I know that there is the 'standard' +30 plus year old method(s) of
>>>>    measuring receiver sensitivity on the R-390.
>>>>
>>>> But, since I took delivery of my AeroFlex 3920 service monitor,
>>>> (primarily
>>>>    for working on P25 digital radios) and after a couple of firmware
>>>> upgrades
>>>>    to get the SSB generate fuction on track with the correct readings, 
>>>> and
>>>> seeing as how it now goes down to -138DBm, I though I could put it to 
>>>> use
>>>> at
>>>> home as well.
>>>>
>>>>    In SSB mode and with a 1000cycle tone, I can hear it all the way 
>>>> down
>>>> to -138DBm on my
>>>>    R-390 (I get down to various levels on my other receivers,but not 
>>>> that
>>>> far,
>>>>    which tells me I could copy a CW signal pretty much down in the mud 
>>>> (If
>>>> I
>>>>    had headphones on)
>>>>
>>>>    My idea is to make a test tape of sorts into a .wav file on the pc 
>>>> and
>>>> play
>>>> it
>>>>    back thru the external mod input on the service monitor
>>>>    to see how far down I can go with VOICE.
>>>> Actually,I thought about recording an actual broadcast of whatever (AM 
>>>> /
>>>> SSB )
>>>> and play that back thru to give me more realism, and crank the level 
>>>> down
>>>> and see how I can go.
>>>>
>>>> What the heck Ive got over $50K in the machine, might as well put it to
>>>> use!
>>>>
>>>>    Thoughts?
>>>>
>>>>    David / WB5UOM
>>>>
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>
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