Scope_in_a_Box Feed Characterization

[Alex P]

Has anyone run a curve on the 2.4GHz Feed ?

I have the 1.7GHz GOES Wx satellite variant.

Curves with Feed installed on reflector 

I regressed my system to the stock config and am getting very low HI vs Cold Sky values :  0.35 dB max at  Dec40 RA20:30  (  bright MW region )

( two days of tests = same results )

Thanks,

Alex   KK4VB

[mike....@gmail.com]

I have just been working on a new scope in the box for the local observatory.

This is unmodified grid dish.

[Mike Otte]

Also did a drift scan of the sun. This is normal orientation  with the widest measurement horizontal.  I want to do one at 90 deg orientation but the weather is not cooperating.

This is a standard unmodified scope in the box .  It is aimed at the Sun at about -2 declination and 180 deg az.

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Mike Otte W9YS

[b alex pettit jr]

Try capturing some data + 40 dg Dec, at Meridian, around 10AM-11AM  ( EDT )   ( +-  RA20:30 )

using IF Avg .. 5 min averages gave this as max

Vert Scale  = IF Avg ampl column processed by   20 * LOG10 ( Col Value )  + sufficient offset to make  Cold Sky = 0 dB

Both feeds seem similar ..

Thanks,

Alex

[Marcus D. Leech]

On 17/03/2023 09:18, Mike Otte wrote:

Also did a drift scan of the sun. This is normal orientation  with the widest measurement horizontal.  I want to do one at 90 deg orientation but the weather is not cooperating.

This is a standard unmodified scope in the box .  It is aimed at the Sun at about -2 declination and 180 deg az.

That plot isn't horrible.

A *very* rough calculation indicates that your antenna "should" be seeing a ratio between cold-sky at peak sun of about
  1.47, whereas your graph shows about 1.38.  That's not horrible!

How did I calculate that?   Solar black-body at L-band (on average) is about 100,000K.   You'll only "see" half of that, so
  call it 50,000K.     Now, your beamwidth on the SIaB is about 15deg.  The sun is about 0.5deg.  The area ratio between those
  two is about 900:1.   So, your feed will "see":

50,000 / 900 = 55K

Now, if we assume Tsys is 100K, then this should produce "about" 1.47 ratio between "cold" and "peak sun".  This is necessarily
  somewhat hand-wavy since we don't know the exact Tsys in your system, we don't know how much spillover your antenna
  has, we're assuming 5K for the cold sky outside the Sun, etc.

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[B & MR Randall]

Attached are some measurements from November 1920.  Dish and feed 1 shows poor return loss at 1420 MHz.  Dish and Feed 2 shows good return loss at 2400 MHz.

 

Pattern of feed at 1420 MHz has some reflections from my crude antenna range.   Note narrow E pattern which is not a bad match to dish in the larger direction.  The wide H patrtern is a poor fit to narrow direction on the dish.  This results in ground noise getting into dish and a loss in gain.  Test with a CFL work light around the edges of the dish show high undesired sensitivty at either edge of dish in the small direction. 

 

For scope in a Box this is good enough to get usable results and does not involve a michine shop to make parts.  The very good sensativity of the SAWBird preamp and the FFT signal processing help with the dish weakness.

 

If you search back the Email group.  Alex did a lot of work on this   Alex's ring feed is considerably better than the WiFi feed.  His dish edge extensions lower ground noise a lot.  My attempts at an improved feed were not as good as Alex's.  I will tip my hat to him & refer you to his design.

 

Last 2 photos are inside of WiFi feed.

 

Bruce Randall  

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[Mike Otte]

Here is the CYG area of MW.

observatory is at about 90W longitude

This was a  scope in a box  drift scan of  CYG  and MW

As I showed on the previous post the  HPBW  beam width of the dish is about 1 hour  which would be 15 degs.

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Mike Otte W9YS

[Mike Otte]

oops , i was sending pics , not text

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Mike Otte W9YS

[b alex pettit jr]

AND,

Here is Your data plotted Looks Great .. What I do not understand is why my data is so low ..

This is comparable to the Photo_Umbrella ( post Mar7th )

Alex

=================================================================

[b alex pettit jr]

I can't account for the poor performance via installing the 1.7G feed on the para grid .. but the simple Umbrella looks great.

( Identical Electronics w/ the ScopeBox & Umbrella ... different feeds & reflectors )

SO, your data answers the question of how well the Umbrella  performs relative to the ScopeNBox

Alex

=================================================================

[b alex pettit jr]

Hello Bruce,

Thanks for the photos

I am going to cut this GOES feed to WiFi and see how it performs at 21cm

GOES 1.7GHz

Alex

On Friday, March 17, 2023 at 11:41:14 AM EDT, B & MR Randall <bran...@comporium.net> wrote:

Attached are some measurements from November 1920.  Dish and feed 1 shows poor return loss at 1420 MHz.  Dish and Feed 2 shows good return loss at 2400 MHz.

 

Bruce Randall