[Moon] [Moon-Net] OFFSET DISH MON NOISE

Edward R Cole kl7uw at acsalaska.net
Sun Oct 26 12:59:46 CET 2014


JJ,

Used current range 384,000 km, so results will 
change with lunar distance.  Probably my notes 
would only be good around perigee.  Usually, I 
find that VK3UM EME Calc will ask if you want to use current lunar range.

A few years ago I evaluated small dish eme 
performance for contacts with OVRO 40m dish and 
lunar noise temp was limiting for the larger dish 
(used 210K for moon temp).  I no longer have that 
link on my website so cannot refer to the math 
that was done.  I did make a lunar path link 
program to use for mw frequencies that took into 
account lunar temperature and beamwidth of 
antennas as system noise temp is affected by the 
Moon for large dishes.  The 1.2m dish would not 
be subject to this as beamwidth is much larger 
than apparent solid angle of the Moon.

Of course many design factors will affect ability 
to see Moon noise.  I used the best fit for a 
f/d=0.5 dish as there is no model of offset 
dishes on VK3UM EME Calc.  So my numbers would be for ultimate performance.

My intuitive guess would be that 1.2m would be 
too small to see Moon temperature, but 0.4 dB is 
detectable with Spectravue.  Not a large value 
but it can be seen.  I resolve sun temp at 0.2 
dB/DIV with Spectravue and can just see 0.1 dB 
change on 1296.  Dish movement is touchy to peak 
the sun at the last 0.1 dB.  Easier to move ahead 
to a known position and allow sun to drift thru a 
peak.  LNA noise temp is only one factor in the 
overall receiver system noise so one should use a 
calculator like VK3UM to incorporate all factors. 
Analysis with a math model is only good to give 
one a reference point to measure against.  But it 
is informational to see what factors make more impact.

On 1296 MHz my 4.9m dish does not see enough Moon 
noise to be useful for tracking.

73, Ed - KL7UW

At 11:37 PM 10/25/2014, JJ Mx wrote:
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>
>GM,
>The distance Earth/Moon has also an impact on 
>this result (ratio between area of the moon to 
>the area of the antenna aperture). So, do the 
>measurement near/around the moon perigee. Ed, did you observe at this time ?
>Serge, there is a small calculator into my 
>SW(EME System). It is not as accurate / complete 
>as Doug’s calculator but it is done to give a 
>rough order of magnitude of the measurements 
>(using “standard” values). LNA is important but 
>side lobes or spillover can quickly/badly  increase the antenna temperature.
>73. JJ F1EHN
>
>De : moon-net-bounces at mailman.pe1itr.com 
>[mailto:moon-net-bounces at mailman.pe1itr.com] De la part de Edward R Cole
>Envoyé : dimanche 26 octobre 2014 00:19
>À : serge; moon-net at mailman.pe1itr.com; moon at moonbounce.info
>Objet : Re: [Moon-Net] [Moon] OFFSET DISH MON NOISE
>
>Serge,
>
>I checked a 1.2m dish with optimum feed and 0.8 
>dBNF LNA*.  Moon noise today would be 0.4 dB 
>over cold sky.  Beamwidth = 1.69 degree, gain = 
>40.31 dB.  I used VK3UM EME Calc for this.  Sun 
>noise/cs = 9.15 dB (2695-MHz SFU=219 is very 
>high today).  VK3UM Calc does not have feeds for 
>offset fed dishes so I substituted f/d = 0.53 and N2UO feed.
>
>0.4 dB moon noise would be just detectable if 
>you use the 0.2 dB/DIV scale on Spectravue.
>
>For comparison my 4.9m dish with W2IMU feed on 
>1296-MHz shows 0.18 dB Moon noise/cs on VK3UM 
>EME Calc, and 18.47 dB sun noise/cs
>
>73, Ed - KL7UW
>
>*0.8 dBNF is typical eme standard on 10-GHz.
>
>At 01:27 PM 10/25/2014, serge wrote:
>
>Using Spectravue what would be the moon noise 
>detectable for a 1M or 120cm offset dish on 
>10368ghz?? I tried to look at VK3UM program & 
>that would generate more questions.
>Thank you
>Serge VE1KG
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>73, Ed - KL7UW
><http://www.kl7uw.com/>http://www.kl7uw.com
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73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
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