[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:
>Content-Type: multipart/alternative;
> boundary="----=_NextPart_000_002B_01CFF0F8.0E8B4E80"
>Content-Language: fr
>
>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 Dougs 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
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