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R: 10 db signal improvement on ao40 - free




----- Original Message -----
From: Malcolm M. Preston <malnp2l@attglobal.net>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, February 21, 2002 12:49 PM
Subject: [amsat-bb] 10 db signal improvement on ao40 - free


> I've been thinking about posting this and was reminded to do so on
> Tuesday's pass when Leila welcomed me for the first time.  What intrigues
> me is the huge difference between the readability of my downlink signal on
> cw vs. ssb.
>
> I run 30w. ssb/40w. cw watts up 45 feet of 9913 to my old KLM 44 el.
crossed
> yagi.  Down link is a bbq dish, UEK3000 converter and another 45 feet of
> 9913 (typical and not exciting).  AO40 was WSW of me and moving slowly
west
> and up.
>
> The cw signal with my 500 hz narrow filter was s8 with transmit power
turned
> down to the minimum of nominally 6 watts.  I worked W0SAT and W0TUP at
this
> level.  There were a few ssb signals on, just above or below my noise
level.
>
> My signal was decreasing as the bird moved away.  I then tried to compare
my
> signal on ssb with cw.  Although difficult to quantify with my equipment
the
> signal seemed to be about 1.5 s units better on ssb as measured through
the
> 2.4khz if filter.  This tells me that there has to be a db gain for a cw
> signal on
> transmit as well as on receive.
>
> As far as I know after discussions with VP2VI and KP2A over the years the
> transmit gain advantage has never been formally quantified.  It seems to
> make sense in that all the rf power is concentraged at one frequency on cw
> while it is spread over the voice spectrum on ssb.  The two cw gurus
agreed
> this gaini must be at least equal to the cw receive gain.  Therefore, if I
> double my ICOM's hypothetical receive gain of about 5db (due to the narrow
> filter) one would
> arrive at 10db or about what I have been experiencing.
>
> If anyone knows of any formal study of transmit gain in relation to
> bandwidth of signal I would be interested.  If not it might be a
worthwhile
> endeavor for someone to do one.
>
> In any it event, it looks like by using cw you can get about a 10 db
signal
> improvement at no cost.
>
> Mal, NP2L
>

Mal,

CW is very efficient because for it you can use a very narrow bandwidth IF
filter of 500 Hz or even less.

The noise power Pn referred to the input of your receiver is Pn=KTB
Were:
K is the Boltzmann's constant = 1.38x10e-23 joule/kelvin
T is the equivalent noise temperature of your receiving system in kelvins
B is the bandwidth of your receiver in Hz

If you are receiving a CW signal using the SSB 2400 Hz filter,and you
switch to the CW 500 Hz filter on the same CW signal you improve your
signal to noise ratio or S/N by:

10 log    2400/500 = 6.81 dB
          10

at no cost for your friend wich is still using the same power on CW

I hope this help

73" de i8CVS Domenico

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