Hi Pete,
You have the right idea, but instead of a 1 mh choke, you should use a few
turns of #18 insulated wire on a small ferrite core. The required number of
turns depends on the ferrite core you have available. Use your MFJ-259B or
other antenna analyzer to select to correct number of turns. My chokes use
only 7 turns on a 1/2 inch diameter ferrite core.
Your Bias Tee should use two chokes and one .01 uF capacitor. The capacitor
blocks the DC to the receiver. One choke couples DC power to the feedline, and
the other choke runs from the receiver input to ground to protect it if the
capacitor fails.
73
Frank
W3LPL
---- Original message ----
>Date: Wed, 15 Feb 2012 15:16:09 -0500
>From: Pete Smith N4ZR <n4zr@contesting.com>
>Subject: Topband: ZJ Electronics Beverage Box and Power Supply - Help Needed
>To: Topband@contesting.com
>
>I am trying to repurpose a ZJ Beverage Box's DC power coupler to support
>a Beverage hub with remote preamp, and have run into a problem. The DC
>supply is extremely "un-stiff." With no load, it delivers close to 25
>volts, while under minimum load it quickly drops to only about 9 volts.
>Add a little more load (one relay) and it goes to 7volts and relays
>start not actuating.
>
>I looked inside the box and find a 240 ohm 1-watt resistor in series
>with the 12 VDC wall-wart supply, and a 2200 uF electrolytic from the
>output side of the resistor to ground. There is an additional 22ohm,
>1/4 watt resistor in line before the DC gets to the antenna port.
>
>I thought that the two crucial components of such a "bias tee" were a
>capacitor to keep the DC out of your receiver and an RF choke to isolate
>the RF signals from the DC supply. The cap is there, but there is no RF
>choke, and if Dr. Ohm was right, the big resistor is dropping the output
>voltage much too much. I'm guessing maybe ZJ put it in there to protect
>the antenna-end electronics by dropping the voltage as soon as any load
>was applied, but it seems like a sloppy way to do it.
>
>I'm thinking of substituting a little regulated Radio Shack 12v supply
>for the wart, deleting the big resistor, and feeding the DC to the
>antenna port through a 1 mH RF choke. Any reason not to do that? Is
>the big capacitor still indicated?
>
>--
>73, Pete N4ZR
>The World Contest Station Database, updated daily at www.conteststations.com
>The Reverse Beacon Network at http://reversebeacon.net, blog at
>reversebeacon.blogspot.com,
>spots at telnet.reversebeacon.net, port 7000 and
>arcluster.reversebeacon.net, port 7000
>
>_______________________________________________
>UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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