[amsat-bb] "Reverse" bias-tee ??

Ed Krome e.krome at comcast.net
Mon Nov 27 02:37:07 UTC 2017

Of course. If your preamp has a D.C. Blocking capacitor at the output, you can usually extract the D.C. by simply putting a small RF choke on the output pin. You MUST have a blocking cap. Generally, for narrow band use, it's not fussy. ARR suggested a 1 mH RFC. Try it. 
Bias T's get fancy only if you want broad frequency coverage.

Ed Krome K9EK
Sent from my iPhone

> On Nov 26, 2017, at 3:02 PM, Scott <scott23192 at gmail.com> wrote:
> Hi everyone.
> The schematic makes me think "yes", but I wanted to check before making a
> purchase.
> Normally a bias-tee is used to inject a DC voltage onto your coax to power
> a pre-amp.  Since some pre-amps aren't powered off the coax, but rather
> from a separate pair of pins, I was wondering if you can use a bias-tee AT
> THE PRE-AMP to extract the DC voltage off our coax for connection to those
> external power pins on the pre-amp?
> Running a separate cable to power the pre-amp is not the end of the world,
> but it would be convenient if I could turn on the bias voltage available on
> the Airspy or RTL-SDR and then extract it up at the antenna to power a
> pre-amp.
> Thanks for any recommendations!
> -Scott,  K4KDR
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