SatSig topic:

16watt SSPA Kills RX

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Mar 1^st, 2012 at 10:10pm

Ok, fellow grus...

What would cause a 16watt Mi-Tech SSPA to kill my RX lock once powered on?

Equipment:
iDirect 7000
Prodelin 1.8m
100ft of Dual RG-6

Currently, I have a 6watt BUC on the antenna and the terminal is fully operational(with a minimal amount of data transfer). What I don't get is how can the SSPA saturate my RX, when powered up? As, soon as I disconnect power to the SSPA I get my RX lock back...

Thanks in advance!!

Mar 1^st, 2012 at 11:11pm

The DC power current taken by the 16W BUC may be excessive for the power supply in the modem. Maybe this will cause damage to the modem or or make it overheat or trip off. The highest DC supply current will occur when an L band input is applied sufficient to cause the full 16W output.

The RF output from the BUC may be so high or distorted such that it causes interference into the LNB. The transmit reject filter should stop a high level signal. Try reducing the modem transmit output power so there is no risk of overdriving the BUC.

If the outer sheath in the BUC cable is open circuit the BUC DC power will return via the LNB cable, causing the LNB volts to drop. Check the cable connectors.

You say that with the existing low power BUC you have minimal data transfer. Does this mean you have unsatisfactory low bit rate? If so, you need to investigate why this is so. Test with lower power transmission from the modem, in case it causing the low power BUC to saturate. Ask your hub for advice.

Beest regards Eric.

Mar 2^nd, 2012 at 12:24am

Thanks for your reply Eric

Sorry, should've been more detailed on the SSPA. The SSPA has it's own seperate ODU A/C power supply. The issue started when the breaker the ODU was connected to continued to trip due to the customer connecting a heater to the oulet w/o anyones knowledege.

The SSPA was connected to the feed horn via flex wave guide, I rolled the cables and ended up with the same result...

The intial TX pw was at -28 and immediately after power was supplied to the SSPA I would lose the RX.

The HUB wrote it up as a bad SSPA, but it's just one of those things I could not understand, how is this auctually happening...

Thanks again Eric.

Mar 2^nd, 2012 at 11:41am

If the problem is due to the RF output power from the SSPA causing overload of the LNB then try reducing or turning off the transmit signal at the modem. The LNB should work normally. It is unlikely, as going from 6W to 16W is only a 4.3 dB increase and transmit reject filters, which protect the LNB, usually have far more margin than this.

But, your original symptom was minimal data transfer with the 6W BUC. If this means you have a bad, low bit rate, service, this needs investigating first. All that a 16W SSPA might do is to double your maximum possible transmit bit rate, e.g. from 512 kbit/s to 1 Mbit/s uplink from the remote to the hub.

I wonder if the power injection biasT has been inserted the right way round ? The iDirect modem might not be happy with 48 volts back fed into its transmit port from the external power supply.

You mention use of flex waveguide, so I guess this is probably Ku band with square flanges. Are the waveguides crossed (by mistake) at the OMT so that you are attempting to transmit on the same polarisation as receive ? If so, this would put a thousand times higher signal into the TRF filter and sufficient power would get through to saturate the LNB.

Best regards, Eric.