Satellite Internet forum

Satellite Internet forum
https://www.satsig.net/cgi-bin/yabb/YaBB.pl VSAT technology and installation >> iDirect Forum: hubs and terminals >> RX SNR fluctuates when tx cable connected https://www.satsig.net/cgi-bin/yabb/YaBB.pl?num=1331585452 Message started by dhrisht on Mar 12^th, 2012 at 8:50pm

Title: RX SNR fluctuates when tx cable connected
Post by dhrisht on Mar 12^th, 2012 at 8:50pm

Dear All,

We are using a andrew channel master pointed to Arabsat 5C its a c-band platform on iDirect X3 using iDX 3.0. We have a strange problem. We are having good down snr of 10 dBm but when we connect tx cable, down snr fluctuates and rx gets locked and unlocked. But same works fine on prodelin antenna.

Please advice.

Title: Re: RX SNR fluctuates when tx cable connected
Post by Eric Johnston on Mar 13^th, 2012 at 10:04am

Three possibilities:

If the waveguide transmit reject filter (TRF) is missing between the OMT junction and the LNB then when the BUC transmits the transmitted RF power overloads the LNB and the receive side fails briefly whenever the BUC transmits a burst.

If the outer sheath of the BUC cable is bad connection the DC power supply for the BUC comes back via the LNB cable sheath. This can cause voltage drop and LNB receive problems, either all of the time or whenever the BUC transmits as the BUC takes more DC power whenever it transmits a burst.

The power supply module is inadequate for the type of BUC connected. The power supply volts drops when the BUC is connected or transmission takes place and everything fails.

Best regards, Eric.

Title: Re: RX SNR fluctuates when tx cable connected
Post by dhrisht on Mar 13^th, 2012 at 3:28pm

Thanks Eric for your reply.

We do have Transmit Reject Filter connected. Connectors were replaced on both end. On further troubleshooting, we tested same set-up on different satellite and it also did not work. Engineer suspected the problem with feed and after chaning the feed, site came up on different satellite so now we are testing back on our main satellite.

Thanks and will keep you updated. Possibly transmit reject filter or feed is faulty.

Title: Re: RX SNR fluctuates when tx cable connected
Post by tunde300us on Mar 17^th, 2012 at 3:21pm

Hi,
I think i have the same problem here,in my case i am using a 3100 modem and a 1.8m channel master dish, i have RX SNR of 14.8 and as soon as i connect the TX cable the remote state to say rx lock,rx unlock continously on my telnet page,and when i remove the TX cable the RX stays stable but as soon as i plug back the TX the issue starts again
If i go by what dhrisht say,if i try it on a prodelin dish it will work well,but i do not have a prodelin dish here and ISP is just clueless about the issue.
Please any help will be appreciated.

Title: Re: RX SNR fluctuates when tx cable connected
Post by dhrisht on Mar 19^th, 2012 at 8:10am

Hi,

Try putting a bandpass filter and then check.

What type of Transmit Reject Filter are you using? Is it short or long? Try also changing it with a bigger and see.

When we used bandpass filter on channel master, it works well.

Title: Re: RX SNR fluctuates when tx cable connected
Post by tunde300us on Mar 19^th, 2012 at 9:47am

hi dhrist,

what do u mean by the band pass filter,i can send you my feed picture so that you can see and tell me if i probably have the band pass filter .

Title: Re: RX SNR fluctuates when tx cable connected
Post by dhrisht on Mar 19^th, 2012 at 10:09am

Hi,

Please send me / attach feed picture.

Bandpass filter helps to avoid interference.