SatSig topic:

Cable length and attenuation

(Read 25414 times)

Apr 25^th, 2012 at 7:29pm

Hi all.

I might have to move my two way dish, at the moment have a approx 20mtr cable run for the dish to modem but want to move the dish to another position but its approx more like 35 to 40 mtrs, I have been using WF100 on the 20 mtrs and all is fine and would use the same type on the longer run.
Would this sort of distance be OK for the twoway dish re-position/install of 40 mtrs ish

modem is a surfbeam 2 RM4100

Thanks Spikey

Apr 26^th, 2012 at 12:33pm

50m with good quality RG6. 75 ohm. Double shielded (foil for the RF and braid for the DC power). Min 1mm diameter solid copper centre, prefer 1.2mm. RG6 with copper coated steel centre conductor is no good.

Note the 27mm minimum bending radius so don't pull the cable around a tight corner. It will crack the metalisation layer on the plastic film.

The F connectors are the big challenge. They must match the cable type and be terminated very carefully to assure good contact with the outer conductor sheath and braid. They MUST be sealed against moisture, as damp will spread quickly down the cable for several feet and turn the metalisation to dust and ruin the RF performance. The centre conductor and the spring contacts inside the outdoor unit will corrode, burn, blacken and disappear. Use of axial crimp type F connectors and electronic grade silicone grease is recommended.

Use drip loops on the cable run to avoid water running towards the ends. Use cable clips carefully, avoiding obvious crushing of the cable and don't space the clips evenly.

Tell your service provider so they can check your site after the move.

You might wish to record before and after:
TX IF power
TX RF power
RX power
RX SNR
Cable resistance
Cable attenuation

Best regards, Eric.

Apr 26^th, 2012 at 5:46pm

Thanks Eric.

So the WF100 will be OK because its a better quality than RG6???

Cheers
Sp.

Apr 26^th, 2012 at 6:09pm

Thanks SP

Apr 26^th, 2012 at 7:18pm

Hello again eric.

Just as a average.

What should the copeable readings be on average for the list you mention from TX IF pwr down to cable attenuation., we never recorded these and the dish is down at the moment ready to re-fit.

Rgds
Sp

Apr 28^th, 2012 at 11:06am

Just guessing here, so info for general guidance only. Anyone is invited to send in your results:

RX power -33 to -13 dBm Changes significantly with cable length (higher values with shorter cable). Up to 3 dB higher value if at spot beam centre.

RX SNR 11 to 15 dB. Higher values at spot beam centre, with good pointing, clear sky or larger dish.

Note that the difference between the noise floor and the signal (SNR) remains constant along the cable length. It is only with extreme long cable length (>50m) that a deterioration of the SNR will be detected.

Cable resistance (ohms) 0.5 to 1 ohm (guesses)
Cable attenuation 5 to 15 dB (guesses)
Cable attenuation will depend on the frequency at which is is measured. 1 cable system use 300-800MHz for RX and 1800-2300MHz for TX. Dual cable systems use 1000-1500MHz for RX and 1800-2300MHz for TX. The cable attenuation probably relates to the TX IF frequency and may be the difference between the modem IF output level and the TRIA output level minus the nominal TX gain of the TRIA.

TX IF power -30 dBm This is the L band power out of the modem and will need to increase if the cable is longer.

TX RF power +30 dBm. +30 dBm = 1 W. This will increase if you are near beam edge, during rain or transmit at higher bit rate. The value should not exceed the power rating of the TRIA.

Anyone is invited to send in your results like so:
TX IF power ?
TX RF power ?
RX power ?
RX SNR ?
Cable resistance ?
Cable attenuation ?

Best regards, Eric.

Apr 28^th, 2012 at 11:46am

Quote:

Hello again eric.

Just as a average.

What should the copeable readings be on average for the list you mention from TX IF pwr down to cable attenuation., we never recorded these and the dish is down at the moment ready to re-fit.

Rgds
Sp

If you send us a list of readings you need by email we can send you the info.

Compresion F connector | RG6/WF100 cable | Compression tool and cable stripper(s).

Never use those basic TV connectors.

Use always compression F connectors when installing VSAT systems and RG6 or WF100 cable (unless specified otherwise).

May 2^nd, 2012 at 3:23pm

Quote:

Thanks Eric.

So the WF100 will be OK because its a better quality than RG6???

Cheers
Sp.

we have experiencied many outage problems with good Q. RG6120dB cable german and turkish brand, but after replacing with Hirschmann KOKA799 or Webro WB100 cable length up to and +50 m1 without any problem so far... Webro however is quite expensive, so cost per site can drop using Hirschmann.
(This RG6 cabling up to 10 m1 meter showing no outages, but that seemed to be the max.)

May 2^nd, 2012 at 3:31pm

Quote:

we have experiencied many outage problems with good Q. RG6120dB cable german and turkish brand, but after replacing with Hirschmann KOKA799 or Webro WB100 cable length up to and +50 m1 without any problem so far... Webro however is quite expensive, so cost per site can drop using Hirschmann.
(This RG6 cabling up to 10 m1 meter showing no outages, but that seemed to be the max.)

Please specify cable specifications and prices to get a clear picture. Also type of connectors used.

We have installed more than xxxx VSAT systems in the last 10 years Worldwide and used always RG6 cable 25m sets (in some cases between 50m-75m) without any problems, also in very extreme conditions, NEVER any problems.

Download Tooway KA-SAT install manual click here.

Read Page 18 !

• Maximum cable length about 50 m with good RG 6 cable.
• Centre wire must be full copper min 1mm Diameter.
• Minimum double shielding.

We did some digging in our files and, the photo of a connector already earlier posted (see again below) has been made of the many installations done by an engineer (ex SATdsl installer) in Spain some time ago.

We have replaced about 15 systems last year and they were all installed with the same connectors and in the same way, all users were complaining about a lot of problems they had in the past (unstable systems).

Using the correct cable (length) and connectors (and tools) is one of the most important parts of a VSAT installation a fact that is often underestimated.

Also the proper finishing touches to an install can save a lot of problems. Tidying up cables using cable-ties is not for the sake of beauty, it is to prevent the cables moving around in the connector (caused by friction in the event of strong winds for example) and thus by using cable-ties we ensure a good connection.