Topband: Bias Tee question

[donovanf at starpower.net]

Dave,

Use a well over rated DC blocking capacitor, this is not an application to save a few pennies by using a marginally rated capacitor.

You should also use a choke to ground with a high current rating to protect your receiver if the capacitor shorts out.  A choke wound with #18 wire on a ferrite core will guarantee that your receiver won't be trashed if the capacitor fails.

Its a good idea to place capacitors in series with all three ports of a "magic-T" 3 dB splitter.  The ferrite cores in commercially made splitters are very small, if even a small amount of 60 Hz AC current flows through the core it will saturate causing intermod problems.  

In a multi-operator station, a bandpass filter should be installed to protect the splitter from strong signal saturation, also resulting in intermod problems.

You can avoid splitter intermod problems by building your own splitter with large ferrite cores, but you can usually avoid that by using bandpass filters and capacitors to protect the splitter from saturation.

73
Frank
W3LPL

---- Original message ----
>Date: Sat, 7 Jan 2012 15:08:48 -0500
>From: "ZR" <zr at jeremy.mv.com>  
>Subject: Re: Topband: Bias Tee question  
>To: "Dave Kirk" <w6mqi at yahoo.com>, <topband at contesting.com>
>
>It never hurts to have a DC block when Murphy is around.
>
>Carl
>KM1H
>
>
>----- Original Message ----- 
>From: "Dave Kirk" <w6mqi at yahoo.com>
>To: <topband at contesting.com>
>Sent: Saturday, January 07, 2012 2:42 PM
>Subject: Topband: Bias Tee question
>
>
>> I’m designing a multi element receive array which
>> incorporates the usual 0 deg hybrid
>> combiner, 180 deg phase inverter, and 2:1 transformer. I’m going to use 
>> pre
>> amps on the antenna elements and need to supply 12 volts to them via the 
>> feed
>> lines through a bias tee. My question is do I need to worry about 12v 
>> being fed
>> back through the combiner, phase inverter, or 2:1 transformer to my 
>> receiver even
>> though their not physically connected or should I put .01 cap on the feed 
>> line going the my receiver for
>> safety.
>>
>>
>> Thanks Dave.
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
>> -----
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>
>_______________________________________________
>UR RST IS ... ... ..9 QSB QSB - hw? BK