Linkstar Transmit Questions

1. Given the high gain of the LNB, low DC current needed by the LNB, a good dish and strong signal from the satellite it is quite credible that you have a good receive signal, even with an excessively long cable. You can check you are on the correct satellite and carrier with tclgets, you should see pcr=true



2. You can alter the drive level into the transmit cable using the transmit attenuator setting to compensate, to some extent, for cable length and to set the required uplink power needed.  I think the setting number is in 0.5 dB steps.

Your cable length may be causing too much DC volts drop when the BUC is connected.  Your length is excessive compared with the image above.  If you use the 4 watt BUC it says you should have an external power supply.  Maybe your internal power supply trips to OFF due to excessive current load ?

If you can get sufficient DC power to the BUC, and if you ask the hub to tell you how to transmit a CW carrier they will certainly be able to detect your signal, regardless of length of cable.   They or you can then alter the drive level in 1 dB steps till the BUC starts to saturate, then back off, say 3 dB.   This will verify that your modem and BUC are not faulty.   Even if the BUC never saturates its output level may be sufficient.

If the output level of the BUC is not sufficient, even with the attenuator at minimum, then I would suggest trying a lower transmit bit rate, if the hub has a suitable burst demodulator.

BUCs have a stated power rating.  This refers to the -1dB compression point.  If you try to increase the power above this the BUC saturates and the signal is distorted, the bit error rate degrades and the transistors may be permanently damaged once the modulation is switched on.  It is like turning the volume up too high on an audio amplifier and blowing the output stage and loudspeaker.

The -1dB compression point is the maximum BUC rating.  The actual level used will normally be lower, set as required to get the level right at the hub.

The NJT5016 is a 2 watt device, needs 37.5 watt DC supply at 15 - 24 V.
The NJT5017 is a 4 watt device, needs 50 watt DC supply at 15 - 24 V.

Be careful never to cross over the cables - you can burn out the LNB power supply.

Send images to me eric@satsig.net or put them on a server somewhere. Read  how to put images into yabb forum.

Regards, Eric.

Talk to your hub.   You need their help with any transmit commands.   They will put your modem on a specific frequency for any CW testing.  Do not transmit without their approval as you will interfere with other peoples' services.

Regarding the return link bit rate, this needs to match the hub burst receiver equipment.  With a shorter cable you will be able to match a wider range of transmit bit rates.  Your actual rate will be determined by the hub.  If your transmit power had been inadequate then I suggested a lower transmit bit rate.

If the modem output level is adjustable -30 dBm to -5 dBm and the attenuator is at 9 dB then the modem output level into the cable is -14 dBm.

The input level to the BUC for max output is -20 dBm

Regards, Eric.