LNB + Dish results


#1

I am looking for SNR data from people here who are using the DC3 with the MK1 LNB and a dish.

Could you please post details about your setup and the SNR improvements you see with the dish (compared to just using the LNB). Please also include the size of the dish being used, and any other factors that might matter.


#2

I’m about 20 miles NE of Los Angeles. Using old DirectTV dish, 20 3/4" x 18 1/4". MK-1 LNB at end of original support for the DirectTV LNB. Setup is on a wood 2" platform on a normal patio table shielded from rain or wind. I have been getting a consistent SNR of + 6 to 6.5. This a bit higher than before you replaced the modem on the uplink awhile back.

Don … W6RWN


#3

do you happen to recall the SNR you were seeing before you added the dish? just the bare LNB?


#4

I really didn’t try just the LNB by itself. At the time there were so many novel cone ideas that seemed to work. I just waited and read about them, but didn’t proceed to build one. I was hoping the Team would manufacture the cone idea of the best design.


#5

This is real general question… Can you be more specific on what you are comparing.
Things like, pointing, coax, dish coating, polarity, skew, weather. trees/leaf interference, local rfi

What is a good snr, or lock, or rssi. I’ve got lot’s of variables that I have changed over the last four months. It is tough to generalize — what is good, better, best.


#6

I am currently using an old “MotoSat” 18" dish with the MK1. Seeing +7 to +8 SNR. Naked LNB at same location runs -13 to -11 SNR.
Both show RSSI at around 80.MotoSatDish


#7

So the difference could be 21 dB between dish and no dish. Very Interesting.


#8

Yes, it is. I purchased the old MotoSat unit from the manufacturer (I was just looking for a dish), but the price was right, and the motors still work, although in this application they are not needed. The unit was designed to be carried atop a motor home or camping trailer, and the dish will lay down level with the mount if desired.

It is not hard to point, using the DC’s screen. Of course, the compass and a protractor can be useful to get a startup fix, then using the DC to fine-tune it. It is working in the position shown in this picture. The MK-1 is sitting at approximately the same position as the original LNB, which did not seem to be in working condition when I connected it. I just took measurements of the position of the original, then mounted the MK-1 as closely as possible to that original position and it worked. The original had no skew adjustment, which is possible with the MK-1 as now mounted, so this helped also.


#9

REVISED New Puzzling Results

(I’m editing this post on 2 Dec to fix an error in measurement I made should someone else read it and wonder what’s going on)

Dreamcatcher connected to Maverick MK1-PLL at base of 80 cm offset dish -

gave an SNR of +9.25 dB and RSSI of - 60 dBm with lock. The Maverick has a spec gain of 60 dB and .5 dB noise figure.

Dreamcatcher connected to FTA Invacom QPH-031 at base of 80 cm offset dish -

gave an SNR of +9.25 dB and RSSI of -65 dBm with lock. My FTA Invacom Quad Polar LNB QPH-31 has a spec gain of 55 dB with a .3 dB noise figure.

I checked my portable (it has a different Dreamcatcher board and Maverick LNB) with just a bare LNB and received an SNR of -11.5 dB with an RSSI of -75 dBm. With my cone cup extended, my SNR went up to -9.5 with an RSSI of -75 dBm.

Inside 500 feet away no longer a puzzle

With the Maverick installed on my 80 cm offset dish outside 500 feet away, I had lock with an SNR of + 5 dB and and RSSI of -95 dBm. With the FTA Invacom LNB my SNR was +3.25 dB with an RSSI of -99 dBm. In both cases, I did not have a DiSEqC or motor drive in the circuit.

I can now account for the RSSI signal drop and reduced SNR due to cable loss from locating the Dreamcatcher 500 feet away inside.

PS I hope I haven’t confused too many people.

Ken


#10

Do you have 6-feet of coax cable so you can place the Dreamcatcher behind the dish or way off to the side?


#11

Yes - - let me do that. I’ll do a variety of lengths. Then I’ll maneuver the Dreamcatcher close to the LNB. Ken


#12

Mea Colpa Forum Members

I made a terrible mistake reading the SNRs with the Dreamcatcher connected at the base of my offset dish. I reported the readings as negative - - they were all positive at +9.25.

Now my inside/outside comparisons make sense. Ken


#13

Ha! Now it all makes sense.


#14

This calculator is interesting:
http://www.rfwireless-world.com/calculators/parabolic-dish-antenna-calculator.html

Example: 80 cm dish, 11.2 GHz, = 37 db gain… Now how to relate this to SNR is
a little more difficult.

But the interesting part is the half power beamwidth (In the example = 2 degrees)

So if you are off by one degree, your ‘gain’ is reduced to 50% (in the example: 37 db * 50% = 18.5 db gain)


#15

You are absolutely right on. When I originally pointed my dish, final alignment was done by tightening/loosening the left or right side nuts on the clamps that held the dish onto the mounting pole. I never could see a one degree shift :joy: but my FTA receiver did. Ken


#16

I’m going to correct and annotate my original post. Ken


#17

My math error… a half power… cannot be calculated as
multiplying the dB values by 50%. this is not correct

But the idea leads similar conclusions… just don’t accept the ‘values’ I listed.

Logarithmic can catch in the details…


#18

Yes, half the power or double the power is always a 3 dB change. Us hams always argue about it :grinning:


#19

I normally see a SNR in the range of +10 to +12, depending on factors like cloud cover, light rain, etc with a 1-meter dish. I also have a fairly long coax run to inside the house, which is about 150 feet.