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
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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