Fine Tune Star Receiver
STAR Rx can accept wide range of input signal power i.e. –20 to –60 dBm. However, the STAR Rx must be configured its “stargain” according to the signal power. Stargain controls the amplifier for the input signal. The STAR input signal can be high or low depending on the configuration of the BDC, dividers and other things. If the input signal is high, the stargain shall be set low because of less need to amplify the signal. But if the signal is low, the stargain shall be set high. Adjusting stargain is a balancing act between amplifier clipping and nonlinearity (too high of a Stargain value) and tuner noise (which dominates when the Stargain is set to too low of a value).
- Set up the receiver in Aloha mode. Assign a STAR band (2.11 MHz) frequency to STAR Rx. Make sure that the 2.11 MHz band has no other carriers.
- Unplug data cable from the Rx.
- Force transmit a CB to transmit Aloha packets (full channel e.g. slot mask = ffffffff ffffffff) to a channel of this Rx. Make sure that frequency is calculated correctly.
- Telnet to the Rx. Run “starlog2” in “app” directory. It will display statistics of the Aloha packets being transmitted (see definition of each column in the “STAR Rx User Manual). If everything is set right, the CRC should reach 100 (99.9 is ok also). This mean that the receiver can receive all aloha packets and the CB is sending aloha packets in every available slot in the channel.
- Next we will fine-tune the stargain by adjusting the value up and down by 0.1 dB stepsize. Open another telnet session to the receiver, “cd app” and then “./setstargain” to show the current stargain. Note down the stargain and the avg EsNo value from starlog2
- Change the stargain in upward direction by 0.1 dB step. Wait a few seconds for the stargain to take effect and for the starlog2 to update its measurement. No need to reboot the receiver. If the EsNo at this new stargain is higher than the previous value, adjust stargain +0.1 dB more and check out the EsNo. Continue the procedure. Move stargain up and down to find the stargain that gives the highest EsNo. Here is the example of the result.
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