The best cable is still a killer so let us get organised

[canofan]

The best sat cables cause an attenuation of 21db/100m or 6.5db/100ft. The lesser cables vary from 27 to 36db.
If one uses a 50ft best cable this still represents more than 3db loss.
If we consider that 3db is the extra gain obtained from doubling the surface of the dish which is increasing the dish with a factor of square root of 2 which is 1.414. A 1.2m should be replaced with a 1.7m to compensate for this loss.
An alternate way to compensate losses is to insert line amplifiers.
The usual cheap line amplifiers on the market are useless.
One has to use the specialised ones used for communal distribution; unfortunately this requires the use of quattro LNB's and multiswitches, so, motorised solutions are excluded.
The SAX-44 (MSV 44) from Satrix amplifies the 4 polarities and gives a gain of 9.5db. It is best installed near the dish, and therefore requires weatherproof housing.
Some multiswitches cause 0db insertion loss. Like the PMSE 9/8 HQ T NT.

 

[dxsat]

The kind of loss you're talking about is in signal strength of the intermediate frequency, which is a different frequency entirely from that which the dish is receiving. You'll find signal quality (i.e. integrity of the data) is largely unaffected in runs up to 100m. I did a test once between the cheapest sat cable I could get (aluminium foiled) and one four times as expensive, (Belden with 1.2mm core), there was absolutely no difference at all on a 40m run.
Don't use a line amplifier on a run of less than 100m, and probably never use one at all, they just increase noise.
You don't increase dish size to compensate for loss in cable- it's not necessary.

 

[canofan]

Thank you for responding.
What does the AGC indicator in the dreambox refer to? is it the amplification to compensate for the IF losses?
I still have to assimilate what you said, as cable losses have been accused of deteriorating signals.
Now I notice two types of deterioration:
1- pixelisation
2- plain instability when image and sound start stuttering.
Are these deteriorations both related to degradation of the signal at the dish?
Thank you

 

[Robbo]

What it comes down to, is signal to noise ratio I think.

When a signal is too weak, the SNR is insufficient for the signal to be received properly. Putting a larger dish up, will increase the signal to SNR at the LNB, so that it can be received properly.

Pixelization etc is caused by insufficient SNR at the input of the LNB.

Once the signal has passed through the LNB a small amount of noise is added, the signal amplified and then down-converted. At this point, assuming that only attenuation occurs in the cable, the SNR will remain constant along its length, as both signal and noise are attenuated.

The problem with a really long cable, however is that the signal level falls so much, that it is too low for the receiver to pick-up because of its noise figure. The symptons of this would be the same as lack of signal at the dish.

So cable losses simply reduce signal levels.

Robbo

 

[koansrc]

I'm on a 55m cable run. When I bought the cable I did choose something "better" and looked at the specs etc. As Snap says, signal quality doesn't seem to change. Signal strength is affected. With a cheap inline amplifier I can increase signal strength (by aprox 50%, so from 50% it goes up to 75%) and leave signal quality unaffected. I have however tried two of these inline amplifiers and only one performs well. I'm taking the other one back today and going to ask for a full 5€ refund!. As for positioning the amplifier, the logical place is halfway along the cable. My tests have only been at either end of the run with similar results in both cases. I can't bring myself to cut the cable in half unless I'm absolutely sure it's going to do some good.

 

[canofan]

I shall proceed to-day to SNR measurements on Nilesat. One at LNB and the other at the end of my 55m run including 2 switches that cumulate 8db attenuation.
I shall report back.

 

[canofan]

I have however tried two of these inline amplifiers and only one performs well. I'm taking the other one back today and going to ask for a full 5€ refund!.

What is this amplifier? I tried at least 5 different brands and found them all useless.

I have just received the Satrix SAX44 with 9.5db gain at 2150 MHZ and shall be testing it. This is for cascade inputs and meant for quattro LNB's.

Thread: The best cable is still a killer so let us get organised Reply to Thread

 

[koansrc]

What is this amplifier?

The "good" one I've used is very similar to this one :

http://cgi.ebay.co.uk/Inline-Sky-Satellite-Signal-Amplifier-Booster-F-Plugs_W0QQitemZ270195302362QQihZ017QQcategoryZ4693QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[canofan]

I tested this amp before and it did not improve anything.
I Just tested the SATRIX amplifier. The effect is marginal on SNR:1%. It is useless in my case, but with very long cable runs as in communal distribution, I could see its necessity.
The quality of cables could be appreciated in 2 ways:
1- attenuation, this is an obvious topic.
2- shielding.
Some cables shield up to 90 db, 100db, 120db, 125db and 130db. What is the meaning, practically, of these figures. Prices grow accordingly. Cables do decrease the quality of the signal by lack of shielding.
So the better shielded cable adds less noise in its run, but by how much?
I shall try. Will the effect of using the 130db cable be also marginal?

 

[koansrc]

The cable I have used is "VECTOR DGS 1600". No complaints but also nothing to compare it with. Perhaps with a different cable I'd already be watching 2D

Have a look around their site _www.viokal.gr as they have some interesting info and selection criteria for cables.

 

[dxsat]

More expensive cables have a larger inner conductor, typically 1.2mm.

 

[canofan]

My Satlook was useless trying to measure at the receiver. It does not have an amplifier to compensate for cable loss. It is usable above a threshold.
I made measurements at the LNB and 17m later before the switches. Also after the switches, which cumulate 8db attenuation. SNR was virtually identical. So in order to estimate degradation in the 40M run to the receiver, I used my dreambox to measure SNR in the loft and at the end of the cable. Here again the two SNR readings were identical.
This confirms what SNAP said:

"The kind of loss you're talking about is in signal strength of the intermediate frequency, which is a different frequency entirely from that which the dish is receiving. You'll find signal quality (i.e. integrity of the data) is largely unaffected in runs up to 100m. I did a test once between the cheapest sat cable I could get (aluminium foiled) and one four times as expensive, (Belden with 1.2mm core), there was absolutely no difference at all on a 40m run.
Don't use a line amplifier on a run of less than 100m, and probably never use one at all, they just increase noise.
You don't increase dish size to compensate for loss in cable- it's not necessary."

So big thanks to you SNAP.