Have You Ever Actually Measured Your Dish Size?

[cyberham]

I have two Ku dishes that I use: motorized and fixed. I've always referred to them as 1-metre (39") dishes. Today I measured them.

The Star Choice motorized is actually 40" x 44" (1760 sq.in.) as I've known for a while. The Digiwave fixed is 35.5" x 40" (1420 sq.in.). But this is 100 sq. inches less surface area than a so-called 39" dish, and 340 sq.in. less than my Star Choice!

If I swap my dish reflectors/LNB arms putting the larger reflector on my fixed, maybe I can actually pull in NBC from 103W and PBS from 125W on my fixed. The satellite signals that I receive on my motorized are not so critical. And the slightly smaller reflector would be easier on my wimpy SG-2100 motor too.

 

[Titanium]

I would be surprised if the FD and offset is identical between the two brands. Most likely the reflector swap using existing LNBF arms and clamp would not produce good results.

The reflected signal will probably not converge at the same point and the LNBF support arms would need to be repositioned, lengthened or cut off to put the feedhorn in the "sweet spot".

Might be a fun experiment if you have equipment to Frankenstein.

 

[cyberham]

Back to kijiji to look for a free 1.2m then...

Added: Or, I could swap complete dishes. The Star Choice has always been too heavy for the motor anyway.

 

[jorgek]

Go ahead and try it. Thats the fun part of this hobby. Simple way to check focus is to place 3 tiny mirriors, top, middle and bottom of the dish, aim at the sun, and see where on the LNB the spots of light land. I've done it to verify FD on my 33" dish.


At the dollar store, I got a 6" Party Ball. Must be at least 100 1/2" square mirrors glued to it. The mirrors peel off easily and you can figure out how to attach them to dish surface.

This is not my idea, Polygver has numerous posts on this easy test setup.

 

[cyberham]

Interesting idea...for the springtime. The main problem now is we have no sun anymore here: it's November. Looked for the eclipse this morning, but there was no sun to check.

 

[jorgek]

Interesting idea...for the springtime. The main problem now is we have no sun anymore here: it's November. Looked for the eclipse this morning, but there was no sun to check.

Nice and sunny this AM. This test works any time as long as you can point the dish directly at the sun. Back to standard time today. Digital clocks are fine but try and remember how to reset them without the instruction sheet.
To bad I don't have a 10 year old around he'd have it done in no time! LOL

 

[xtgold]

if you have a receiver with the signal beep function you can hold the lnb in your hand and move it around until you hear a beep.
I have done that many times.

 

[toucan-man]

Back to standard time today. Digital clocks are fine but try and remember how to reset them without the instruction sheet.

My clocks reset themselves. Unless they can't pick up WWV for some reason. Which adds some doubt to the equation.

 

[FaT Air]

The way to go is "swap complete dishes"
Minimal daylight means less time to 'play frank 'n' stein' with stuff. BUT- No mosquitoes, (which is a good thing)
Then sit back and have a Loaded Dog 'n' a wobbly pop while it/you scans a satellite.(frank 'n' stein)
FWIW- I've noticed some 'rate' their dish size by the measurement of the vertical measurement. Which to me is = to <.3db NF LNBF's. The actual effective area is determined by the offset dish width.

 

[cyberham]

Dish width is the important measurement I think. So my Star Choice is 4.5" inches wider and that's why it might work better. Hey...I'm going to move the whole go#$%@! Star Choice dish and motor assembly to where I now have the fixed Digiwave. Shorter RG-6 by about 150+ feet, easier to work on (even at night), can see the TV through the living room window and it'll work fine...until the leaves grow back in Spring. Spring is 6+ months away! With luck, I can get 83W through 125W on a motor and bigger dish too.

 

[cyberham]

...less time to 'play frank 'n' stein' with stuff. BUT- No mosquitoes, (which is a good thing)
Then sit back and have a Loaded Dog 'n' a wobbly pop while it/you scans a satellite.(frank 'n' stein...

About what I'm doing today due to bad weather. Would rather be "doing the dishes" as my wife refers to my hobby activities.

 

[Anole]

..I've noticed some 'rate' their dish size by the measurement of the vertical measurement.
...The actual effective area is determined by the offset dish width.

This is one of the reasons "equal sized" commercial dishes outperform many hobby dishes.
(as described above, they're not equal size)
...and of course , there are also other reasons.
.

 

[AntAltMike]

From: Math Fun Facts

Area of an Ellipse

The area of such an ellipse is: Area = Pi * A * B


So the area of an ellipse - in the case of a satellite dish, of the elliptical cross section of the received and reflected signals - in the first instance is 40"/2 x 44"/2 x 3.14 = 1381.6 square inches., and in the second instance, is 35.5"/2 x 40"/2 x 3.14 = 1114.7 square inches.

Assuming equal efficiency, the larger dish, which is about 24% larger, will tend to have 24% more gain than the smaller one. A signal increase of 24% is less than 1 dB (about .93dB).

 

[Anole]

Area isn't particularly a factor.
Increase in dish width, results in decreased beam width.
So, less interference from the next satellite over.

 

[Tron]

A 1 meter Channel Master is considerably larger than most stamped metal 36" dishes. The difference is greater than a mere 10 centimeters.

 

[Larry1]

Since the Starchoice dish is an offset dish, it's effective size is 1m. I have posted in the past the measurements for checking your LNBF placement from a fax i received from Winegard.



The Digiwave DWD-90T


Items & spec DWD-90T (93.5CM)
Offset Angle 24.62
Aperture-Short Axis 85.0 cm
Aperture-Long Axis 93.5 cm
Focus Length 51.0 cm
KU-BAND Gain @12.45GHz 39.44dB
Elevation 20-60 / 23-90
Azimuth 0-360
Efficiency 70% min
Finish Polyester Powder
Color Gray/Cool Gray
Mounting Type G/W
Pole Diameter Acceptable 38-48
Ambient Temperature -40°C ~ +60°C
Relative Humidity 0~100%
Net/Gross Weight 8.6kg
Material Steel
http://digiwavetechnology.com/36-in...l-offset-dish-in-bulk-taiwan-digimonster.html

http://www.winegard.com/kbase/upload/X3e_21DF3126.pdf

No matter the size, its the gain spec that is the important number.

 

[cyberham]

My Star Choice is 101 cm wide so it truly is a 1-metre dish. My Digiwave is 90 cm wide by 99 cm high. So it is not a 1-metre dish.

 

[cyberham]

Digiwave DWD-90T
Items & spec DWD-90T (93.5CM)
Offset Angle 24.62
Aperture-Short Axis 85.0 cm
Aperture-Long Axis 93.5 cm

Digiwave: the dish I have and the dish I'd prefer.

 

[cyberham]

...So the area of an ellipse - in the case of a satellite dish, of the elliptical cross section of the received and reflected signals - in the first instance is 40"/2 x 44"/2 x 3.14 = 1381.6 square inches., and in the second instance, is 35.5"/2 x 40"/2 x 3.14 = 1114.7 square inches.
Assuming equal efficiency, the larger dish, which is about 24% larger, will tend to have 24% more gain than the smaller one. A signal increase of 24% is less than 1 dB (about .93dB).

At this point, I'll take the extra 0.93 dB if I can get it. I realize this isn't much, but with digital (unlike analog) if you don't receive the minimum threshold signal then you've probably got nothing. My calculation was based on using rectangular dishes! You must be a school teacher.

 

[chapelrun]

It's not the size of your dish - - - it's how you use it!!!