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Pages: 1

IDirect with Short Cable Run

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Ex Member
Ex Member

Mar 6th, 2017 at 7:43am  
I have an iDirect installation that is giving a bad headace.
LMR400 cable less than 30m
And the iNOC says our error rate is of concern.
We've checked all cable connections and realigned the antenna many times with the iNOC
No improvement.
My concern is that moving the modem to the roof top and using the cable before the protector, the modem blinks Green and amber.
Why will the modem not work on shorter cable?
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Reply #1 - Mar 6th, 2017 at 10:00am  
Putting the modem on the roof with a short cable will cause negligible improvement in the receive performance at the modem, assuming the cable was already less than 30m.

So I presume your measured errors were detected at the hub and refer to the burst transmissions from the remote site to the hub.

It is possible to get high errors on the bursts if the remote modem output is too high level, causing the BUC to overload and send out very high power, but badly distorted signals.

This could happen if the hub has increased the remote modem output power. This can happen automatically or manually. Suggest that the hub reduce the output power from the remote modem in 2 dB steps till it is 20 dB lower and measure burst error rate and burst level at each step.

When a site is first installed the hub should carry out a -1 dB compression test on the BUC to determine the maximum level the modem should be ever be allowed to output. Read more: http://www.satsig.net/cgi-bin/yabb/YaBB.pl?num=1279904226

Ideally a site's nominal BUC output power in clear sky will be 6 dB lower than the -1dB compression point.  This allows the transmit power to be increased by up to +6dB during rain. In normal operation the hub will tell the remote to increase or decrease its power to keep the burst level at the hub correct. This will not work properly if the hub has the the -1 dB compression upper limit set wrong. Once you are above the -1 dB compression point increasing the BUC power further just makes errors worse.

Other possibilities are: Weak power supply to the BUC. Poor connections on BUC cable. High DC resistance cable - must have solid copper inner wire and no corrosion in sheath. Pointing error - the transmit beam is narrower than the receive beam and if you have a very strong receive signal it is difficult to point the dish accurately as you get a false impression that you are perfectly pointed.  Make sure you are in the true middle of the beam by mispointing each way to the same degraded level and then halving the distance between the two positions.

Please say if you get it to work better and what was the fix. Thanks.
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Ex Member
Ex Member

Reply #2 - Mar 7th, 2017 at 11:49am  
Can the NOC see the errors on the outbound or inbound?
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