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Re: Beacon Strength

Alberto,Hilton and all,

I guess I may as well throw in my two cents worth.

A number of years ago, one of the HF RX manufacturers tried to standardize
his receivers with a 6 db increment between "S" units.  There was a lot of
interest in the ham community at the time.  It never worked out. I think
for several reasons.  First he couldn't assembly line produce receivers
that had this quality. Second none of the other manufacturers would go
along with the idea.  Third there was no real benefit to having such a
standard.  But the MYTH of 6 db between "S" meter increments was born.  I
cannot remember which company tried this but Hallicrafters comes to
mind...but maybe not.

Several years ago, maybe ten or fifteen or so, I measured my HF RX "S"
meter units to see how it stacked up. This was a TS-440s.  It was no where
near 6 db per "S" unit.  In fact, it wasn't even constant between units.
Out of curiosity, I decided to measure the 2m section of the FT-736R I was
using on AO-13.  It was no where near 6 db and it was not linear either.
About a year or so ago, in an idle moment, I decided to repeat these
measurements on the same FT-736.  They were essentially the same as
several years ago.  I have not tried this on either the 70 cm or the 1.2
Ghz modules in the 736 but I would suspect I would get different results
on each one.  In fact, I suspect that I could measure two 736 on 2 m and
get different results.  Unless you measure your own "S" meter and know
what the increments mean, comparisons are just not valid.  

Here are the results of my measurements.

    "S" units        db change

      1-2            2
      2-3            2
      3-4            1
      4-5            2
      5-6            2
      6-7            2    
      7-8            3 
      8-9            5

I find this useful now to determine when I am approximately 10 db below
the beacon.

73 and Merry Christmas to all.


Dr. Jim Akers
Dept. of Electrical 
and Computer Engineering
Miss. State Univ. 

On Thu, 13 Dec 2001, ALberto Helmfelt wrote:

> Hi Hilton..
> Your right, One S unit equals 3 db this is doubled power this is the
> reasong for this relation.
> Also I have the same values for noise flor and max beacon S7, my antenna
> 1,6 mtrs and DEMI with squint around 3/5 if there was a biger dish the 
> signal diference will bee grater.
> Best Regards.
> Alberto LU2FGN
> At 01:23 p.m. 13/12/01 +1300, you wrote:
> >For some time I have been observing what would appear to be somewhat
> >extravagant claims for the strength of the AO40 Beacon. It is my
> >understanding that the best level the Beacon can reach above the noise
> >floor is perhaps 27 or 28 dB.  Another source measured this as around 21dB.
> >My question is how can claims be made for S9+ levels when the standard S
> >point unit is 6dB?   I would suggest that a more realistic level claim
> >would be dB above the noise floor if this can be determined. With my modest
> >set-up using an FT847 with attenuator on, pre-amp off and noise floor at
> >under S1 on the meter, the beacon at best reaches S7.  Signals that don't
> >upset Leila are around S4 or 5 which in IMHO would equate to 12 or 15 dB
> >above the noise floor.  The S unit on the FT847 would seem to be 3dB?
> >Regardless of the size of the antenna if you can detect the noise floor you
> >have reached the practical limit of signal level?  I would appreciate some
> >input from more learned persons on this, thank you.
> >Hilton Meyer  ZL2MN
> >
> >
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