[Moon] Question RST vs S/N on EME

[Joe Martin K5SO]

Hello Oene,

As K5GW pointed out, using narrow BW dramatically increases S+N/N (by  
lowering the level of the noise floor in receive channel) so your  
selection off 2500 Hz bandwidth reduces the S/N you observe with your  
system compared with what you could observe simply by using a narrower  
bandwidth.

With regard to your question regarding actual meter readings on the  
transceiver during EME QSOs (but not with respect to 2m EME yagi  
operations specifically), I can assure you that I routinely observe  
several of the big guns on 23 cm EME at S-9 meter deflections (and  
even more sometimes, in fact) on the S meter of my HF transceiver when  
using a bandwidth of 250 Hz at my IF frequency of 28 MHz.  Indeed, I  
see my own echoes on 23 cm EME at S-9 signal levels on the S meter.   
When I give an RST report during an EME QSO the S-value that I report  
is the result of observing the S-meter deflection on my rig, not the  
result of an audible evaluation.  I'm certainly not knocking audibly  
derived reports mind you, they're equally valid for reporting signal  
strengths, of course!!  I'm only telling you what I do personally  
during my QSOs.

Of course, and I'm sure you also know this very well, S-meter readings  
cannot be used universally as a particularly meaningful method of  
reporting received signal power levels because such readings vary so  
dramatically among transceivers for a given power-level input due to  
the fact that there is no standard that has been adopted among  
manufacturers  and builders as to how the indicated S-unit on a  
receiver should map to dB-unit power input level changes.  In my  
particular case I have independently determined that a 1 S-unit  
increase in signal level into my transceiver corresponds to an  
approximately 2.7 dB increase in input power level.  In my case, I use  
my transceiver S-meter readings for RST reports simply to be able to  
systematically, at least in a relative sense, keep track in my own  
records as to how signals from stations that I work change from one  
QSO to another with the same station at a later time.  Using S-meter  
readings on my rig helps me keep tabs easily and semi-quantitatively  
on how well my receive system is performing over time (in addition to  
occasionally monitoring sun noise and moon noise for the same purpose,  
of course).

I'm sure that you also are aware that S/N on 23 cm EME is typically  
better than what you typically find on 2m for a variety of fundamental  
reasons, not the least of which is that stations on 23 cm EME normally  
use circular polarization instead of linear polarization.  Use of  
circular polarization eliminates the all-to-often very serious signal  
attenuation that one runs into with linear polarization resulting from  
polarity misalignments of the transmitting and receiving antennas  
associated with geographical misalignment between the respective  
stations on the surface of the earth and Faraday rotation of polarity  
that occurs when the signal passes through ionized regions that lie  
along the signal path.

I have no direct experience with 2m EME signal reports so perhaps what  
I've said here is not particularly relevant to your question as you  
asked it.  Nevertheless I wanted to assure you that if you happen to  
receive an S9 signal report from me on any band it is the result of a  
meter deflection to the S-9 level on my rig relative to a noise floor  
level that has been adjusted to give an S0 reading with no signal  
present.  EME signals on 23 cm from many stations these days are  
frequently VERY impressive and such stations deflect my S-meter  
dramatically!

73,  Joe K5SO

23cm EME
8.6m dish
900w at feed