Amplifier and cable run questions

[marria01]

I'm in a bit of a quandary. I have a dish on the roof of work that is subject to a rather long cable run. It's approx. 120 to 140 meters using CT167 cabling. The dish is a 1.2 meter channel master with feedhorn and C120 Inverto dual LNB. It's pointed at 28E. Currently there is no amplifier anywhere on the run. Down on the ground floor it goes straight into an IRD (Tandberg T1222).

During good weather I get a lock, although the C/N margin is quite low, less than 3dB. However when it clouds over (which it does in Manchester a lot!), the signal will drop to pretty much nothing. Up at the dish I have a very good C/N.

Work is getting a shiny new TV Explorer 2+ next week so I'm going to do some investigation. First off I'm going to double check the positioning of the dish. It would seem putting an amplifier in will help but I'm not 100% sure how I should go about doing it. I've looked at in-line amplifiers which might do the trick, although should I be putting it at the dish end or half-way down the run? I also have access to mains power up on the roof which is terminated in a sealed box a couple of feet from the dish. However I haven't come across a mains powered satellite amp that doesn't require a quattro LNB and four feeders.

Any pointers?

 

[Robbo]

Hi,

I can only give a theoretical answer and that is that the amplifier should go as close to the LNB as possible. However put it too close and with a large dish like yours on 28E, the amplifier could be overloaded.


If you measure the signal level coming from the dish, add on the gain of the amlifier, you must make sure that it does not exeed the maximum amplifier output. If you know the attenuation per m of your cable ( about 22dB per 100m at the highest IF frequency), you would be able to work out how far down the cable you need to put it.

Amplifiers for a single LNB are available with a sloped gain response v frequency. google for LNB amplifier.

 

[satelliteman]

Gain and slope adjustment

26dB loss @ 2Ghz over a 130m run using 167 type coaxial.

 

[rolfw]

I would be inclined to fit the amp about 30m/40m from the dish if possible, as the signal loss will not be massive at that point and the amp will give it a big kick to travel the remaining distance.

 

[marria01]

Sounds good, thanks guys. Think I'll start with a tweak to the dish just to make sure it's absolutely bob on. Once that's done I'll start with putting the amp approx. 5 meters run from the dish (inside that sealed cabinet on the roof), if that yields good results then I might leave it there. If not, I'll look at putting the amp in further along the run once it enters the building riser.

Do you guys have any recommendations on make and model of amp? My local supplier has both the 12dB Triax model that satelliteman mentioned and also a Global one with 22dB they are both of similar price (within a quid or two). I've not been able to find specs on the Triax one.