[R-390] The OLE receiver sensitivity test revisited
Curt
cptcurt at flash.net
Wed Feb 29 08:50:48 EST 2012
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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