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Re: [Discuss-gnuradio] argggg .. WBX Front end issues


From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] argggg .. WBX Front end issues
Date: Thu, 12 Apr 2012 20:19:20 -0400
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On 04/12/2012 08:11 PM, dave k wrote:
blew my second WBF front end after 1 day of wonderfull RX. I don't know how it 
happend. I was using a few different types vhf and uhf omnis and yagi antennas, 
everything seemed to be working fine. Now it can't hear hardly anything and the 
typical strong noise signal in the center freq is back. Is it possible that 
some of the equipment mounted on the antenna mast could be shorting it out? Or 
is the WBX just so sensitive that a strong signal can blow it up? I have 2 
Ubiquiti bulllet2HP's on the roof. One is clamped to the same mast as the UHF 
omni that was connected the to WBX. They are 24V DC over the unused pairs. Im 
really bummed out. Any recommendations or similar experiences ?

_______________________________________________
Unfortunately, LNAs are notoriously sensitive little princesses. The new revs of the WBX have TVS diodes between the RF connector and the LNA, which should reduce this problem, at the expense of a slightly poorer noise figure. If the local field strength of RF on your roof is high, enough can couple in to damage the LNA. In those situations a limiter might be needed, or even a stiff bandpass filter to keep stray RF fields that
  are out-of-band with respect to your application out of the front-end.


There's a company online, summitsource, that sells in-line gas-discharge surge arrestors for CATV/SATV use that I've used for protecting LNAs in the past. Taken local lightning hits and survived, for what it's worth. The arrestors are cheap--under $4.00 apiece as I recall, and
  have 75-ohm connectors.  About 0.3dB insertion loss.

--

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org





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