Topband: bias tee

[Jeff Woods]

If you're switching Beverages, the transformer can serve double-duty as the DC isolation as well as impedance transformation.  75 (or 50) ohm winding in series with the coax center and the relay.  RF bypass capacitor across the relay coil.  

The BN202-73 or -43 cores work well for this application.  Toroids.info has a handy calculator for inductance.

-Jeff W0ODS


>________________________________
> From: "donovanf at starpower.net" <donovanf at starpower.net>
>To: Pete Smith N4ZR <n4zr at contesting.com>; topband at contesting.com 
>Cc: Topband at contesting.com 
>Sent: Thursday, November 14, 2013 8:11 AM
>Subject: Re: Topband: bias tee
> 
>
>Hi Pete,
>
>You can use your MFJ 259 to measure loss through your bias-T setup.  
>
>100 microhenries should be adequate; however, a properly designed bias-T should always have  two inductors at the injection and and two at the far end of the coax cable.   The series inductor isolates the power injection port from the RF path and and an inductor to ground protects the RF electronics (preamps and transceivers) from damage if the series capacitor feeding that port should short.
>
>My bias Ts use simple homebrew inductors, just a few turns of wire on a ferrite core.  Use your MFJ-259 to optimize the inductors.
>
>73
>Frank
>W3LPL
>
>
>----- Original Message -----
>From: Pete Smith N4ZR <n4zr at contesting.com>
>To: Topband at contesting.com
>Sent: Thu, 14 Nov 2013 07:58:47 -0500 (EST)
>Subject: Topband: bias tee
>
>I am using my coax to feed 12 VDC to my remote RX antenna locations, 
>using a traditional bias tee, but am having some trouble with 
>performance. I'm using 100 uH Radio Shack chokes in my bias tee, and am 
>wondering if perhaps that is insufficient inductance for 160 meter 
>operation. If so, what would be an appropriate value?
>
>-- 
>73, Pete N4ZR
>Check out the Reverse Beacon Network at
>http://reversebeacon.net,
>blog at reversebeacon.blogspot.com.
>For spots, please go to your favorite
>ARC V6 or VE7CC DX cluster node.
>
>_________________
>Topband Reflector
>
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>Topband Reflector
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