New LNBF or Bigger Dish???

[greyskies]

Hey guys:

Now that I have been up and running for some time, curious as to whether it would be more effective to first replace .75cm dish with a 1.0 meter dish, or to replace ASC-321 Ku LNBF (Standard - 0.7 db) with an ASC-321S Ku LNBF (Standard - 05.db - 0.7 db).

Please provide your thoughts and suggestions, as I need to improve signal quality and strength to receive channels on various satellites.

greyskies in Sunny (at least until this coming weekend) S.E. Florida (and may be down shortly if Hurricane Frances has anything to say about my house remaining on its lot).

 

[Mr Tony]

I would replace the LNB first

The lower the number (.7, .6) the better it can pick up stuff.

The larger dish would help better with the news feeds and some channels that broadcast at lower quality.

 

[bcwmachine]

A .75 meter dish has aprox. 4.75 Sq. Ft. of surface area to reflect the signal to the LNBF, a 1 meter dish has aprox. 8.45 Sq. Ft. of surface area. (If I did the math right).

 

[PSB]

Math is not my strong point, (I would be amazed if the above is right, its almost double the surface area!) but I would agree a BIGGER dish would be the first thing to change, its all about how much signal you can squeeze into the LNBF, then you can worry about a lower noise LNBF, this is just my opinion.

 

[PSB]

As Tom and others have pointed out the signal differs from receiver to receiver and does not mean a whole lot, I am using the same dish and LNB, so its the exact same amount of signal hitting each box, the manufactures just set the level to whatever they want, a bit like VoOM everyone was complaining they were getting low signal levels so in the next software upgrade they bumped up the signal levels, so someone who was getting a 40 signal now gets 70 (example only) nothing has changed but just lets the customers feel better about their signal.

 

[bcwmachine]

Pi*R^2 (pi times radius squared) for area of a circle.
1 meter= 39.37" = 3.28'
3.28' / 2 = 1.64' radius
1.64 * 1.64 * 3.14 = 8.445 Sq. Feet
.75 meters = 29.53" = 2.46'
2.46 / 2 = 1.23' radius
1.23 * 1.23 * 3.14 = 4.75 Sq. Feet

or in metric
1 meter / 2 = .5 meter radius
.5 * .5 * 3.14 = .785 Sq. meters
.75 meter / 2 = .375 meter radius
.375 * .375 * 3.14 = .442 Sq. meters.
Amazing how much the area of a circle increases with a small increase in diameter.
Bruce

 

[PSB]

The way I wrote that may have sounded cheeky sorry if came across that way : )
I am AMAZED at how much surface area is gained, I did a few of my own calculations that confirmed the above (then had to lie down for a bit), I guess it proves that you just cant beat a BIGGER dish!

 

[sksatellite]

I never see a true 1 meter dish, the biggest one I can get is 39" x 36". According from those dish maufacturers, a one meter dish compared with a 75cm dish, the gain is minimum, but this gain is good enough for weak satellite at most.

 

[bcwmachine]

The way I wrote that may have sounded cheeky sorry if came across that way : )
I am AMAZED at how much surface area is gained, I did a few of my own calculations that confirmed the above (then had to lie down for a bit), I guess it proves that you just cant beat a BIGGER dish!

Peter,
I didn't take it as cheeky. I reran the formula's a couple of times as I wasn't sure I believed it at first. I was amazed at how much more surface area there was when I was checking 10 foot vs 12 Buds. The gain in surface area is not that dramatic at at the 10' size, but still quite a bit.

39" x 36" oval dish. Formula for area of an oval. pi*a*b (from the Machinery's Handbook, 22nd edition. (The machinist's bible)). a is 1/2 the long dimension & b is 1/2 the short dimension.
39" = 3.25', 36" = 3'.
3.1416 * 1.625 * 1.5 = 7.68 Sq Feet. Still quite a jump from a 75 cm round dish.

The actual 'gain' depends a lot on how geometrically correct the dish is.
I have an old round offset dish that is only good for use as a trash can lid. I have an oval (ex starband) that's not very much bigger that works quite well. Theoretically bigger is better, but it depends on how well the dish is made. Case in point,
I have a 10' Patriot solid dish that works about as well on ku as my 'little' oval dish. I'm still tweaking on the Patriot, I think it could be quite a bit better. Ku has to be tracked a lot closer on a bud than C-band. Ku beam width is a lot narrower then the C-band beam width. I can be getting a great signal on C and not even see the Ku side of the sat.

 

[PSB]

How true, setting up a Ku band dish to the Clarke Belt IS a lot harder to do than c-band! I was in mechanical engineering for a long time before I was bitten by satellite so I done a lot of machining : ( And as you say the surface area is one thing then you add the curvature of the dish and it really stars to add up on the surface area, so bigger is not always better its all about quality! Nice thread, thanks for the calculations they have really helped!

 

[bcwmachine]

Peter,
I did it the other way around. Spent the first 22 years of my 'adult' life chasing electrons, the last 20 years as a machinist etc. Wonder what I'll try next .

 

[PSB]

Had to read that twice : ) Machining is a hard game just you and a lump of metal, that was the worst part of the job but there is a lot to be said for a check arriving EVERY week "rain or shine" and being part of a team

 

[rjb]

Hi,

I just have some information I would like to share with you...

The antenna gain can be calculated by the expression:

Gain = ? * ( (PI * Diameter) / lambda ) ^ 2

where
? is the antenna efficiency
PI is the well known constant 3.1415...
Diameter is the effective antenna diameter
lambda is the wavelength = C/frequency (Hz)
C is the speed of light in the free space

As you can see the antenna gain is related to the square of the diameter, so
the bigger the diameter, the bigger is the gain.

Now, what everybody wants is to maximize the quality of the signal at the demodulator's input inside the receiver. This is called Carrier to Noise ratio (C/N).

The (C/N) can be expressed by the equation:

(C/N) = (Pt * Gt * Gr) / (k * T * B * L)

where:
Pt is the output power of the transmitter
Gt is the transmitter antenna gain
Gr is the receiver antenna gain
k is the Boltzman constant (1.38 x 10 ^ -23 joule/Kelvin)
T is the receptor noise temperature (related to the LNB Noise figure)
B is the transponder bandwidth
L is the sum of all the losses in the system (propagation, connectors, etc)

As you can see the (C/N) is related to the receptor antenna gain, and the later is related to the square of the diameter, so the bigger the diameter the bigger the relation between Carrier and Noise.

This is the equation to get the Noise Temperature from the Noise figure expressed in dBs.

T = 290 * (10^(Noise Figure/10)-1)

as a sample:

LNB1 ==> 0.8dB ==> T = 59 Kelvin
LNB2 ==> 0.4dB ==> T = 28 Kelvin

If LNB1 is changed by LNB2 the gain in the (C/N) will be

Gain in (C/N) = 59 / 28 = 2.1 (The signal quality will be increased by a factor of 2.1)

If we keep the same LNB and change the antenna:

Antenna1 ==> 0.75 m
Antenna2 ==> 1 m

Gain in (C/N) = (1/0.75) ^ 2 = 1.77 (The signal quality will be increased by a factor of 1.77)

If those were the scenarios and my calculations are correct I will go for the LNB.

I hope this is useful at the time of selecting the LNB and the antenna.

RJB

 

[TBI]

Hey guys:

Now that I have been up and running for some time, curious as to whether it would be more effective to first replace .75cm dish with a 1.0 meter dish, or to replace ASC-321 Ku LNBF (Standard - 0.7 db) with an ASC-321S Ku LNBF (Standard - 05.db - 0.7 db).
).

This review might help.
http://www.tele-satellite.com/TSI/03/09/invacomlnb.pdf

 

[greyskies]

This review might help.
http://www.tele-satellite.com/TSI/03/09/invacomlnb.pdf

I have a two LNBF system, with the ASC321 and a circular DBS LNBF. I use a 22khz switch to access the two LNBFs and had been advised that I need to use a standard KuBand LNBF if I want to use the second LNBF. Do you know whether I can use the universal LNBF you have apprised me of with the switch and the second circular DBS LNBF?

I would definitely switch to a lower noise universal LNBF if I could keep my dual LNBF configuration with the 22khz switch. I eagerly await your advice.

 

[TBI]

I have a two LNBF system, with the ASC321 and a circular DBS LNBF. I use a 22khz switch to access the two LNBFs and had been advised that I need to use a standard KuBand LNBF if I want to use the second LNBF. Do you know whether I can use the universal LNBF you have apprised me of with the switch and the second circular DBS LNBF?

I would definitely switch to a lower noise universal LNBF if I could keep my dual LNBF configuration with the 22khz switch. I eagerly await your advice.

Check your PM I will send you some info.

 

[rjb]

Hi,

I think you cannot use a Universal LNB because it switches between the upper band and the lower band using the 22kHz tone. You can use a DiSEqC switch instead of the 22Khz switch to accomplish that.

RJB

 

[MrMylesG]

Where is a good source

I have about made up my mind to go with a 1m dish. My motor can handle it easily. Looked on Ebay and all I see is 76cm and smaller. Anybody have a source of larger dishes? I especially want to grab T11 in the east. I think my wife would appreciate the Russian channels.

Thanks.

MrM

 

[MrMylesG]

Found source for large dishes

Hi Fellas!!!

I found a site that has 1m and 1.2m dishes for a very good price (1.2 meter Winegard dish $69.95). My motor says it will handle a 1.2 meter dish. That should increase the total signal gathering power quite a bit, especially over my current 76cm dish.

I am ready to place my order with them soon. Here is the site:

http://www.free2air.ca/

Have you folks dealt with them before? The prices for dishes are very good.


MrM

 

[PSB]

Watch out for the shipping charges on these "OVERSIZE" items, I would also ask what happens if it arrives bashed or dented, as very often there is no return on a satellite dish.
Bigger is better but do not expect a huge increase in your signal quality, but it will really help with very weak signals and rain fade.