parnass@cbnewsc.ATT.COM (Bob Parnass, AJ9S) (11/23/89)
x
FROM JUNK TO A JEWEL
or How I Listen to My Home Radio Receiver
While Away From Home
by Bob Parnass, AJ9S
One Saturday morning a few years ago, my wife Pam, N9HRZ,
brought home 3 large gray steel relay boxes from a garage
sale. She didn't know what they were, but was sure they
were a "steal" at $5 apiece.
My examination brought disappointment. These 35 lb.
"boat anchors" appeared to be something ripped out of a
factory control system. The outsides were filthy, and
someone had spilled oil inside of them.
Pam sensed my unhappiness with her find, so she offered
to ask her dad, KA9CAI, to sell these boat anchors at a
hamfest so we could get back some of the $15.
For a year, one box sat in my garage, and the other boxes
two sat in my father-in-law's garage.
Junk Reexamined
Each box had a large hinged door, protected against the
weather by a gasket. On the inside was a thick steel
panel with about 8 DPDT relays, a time delay relay, and
several toggle switches.
All relays were made by Potter & Brumfield, a top relay
manufacturer. Each had a 117 VAC coil, 10 amp contacts,
and was in a high quality Amphenol socket. The DPDT
relays were enclosed in clear plastic dust covers, and
had neon bulbs and resistors wired across their coils,
which provided a visual indication of relay activation.
Components were wired together neatly to 2 large Bakelite
barrier (terminal) strips. All interconnecting wires had
terminals crimped on at the ends, so a screwdriver was
the only tool necessary to service the unit.
Now for the challenge:
- I wanted a way to listen to my home radio receivers
while I was away from home. Could this "junk" be
converted into a remote receiver controller?
I dreamed up a remote receiver scheme when back when I
was presiding over our club at Bell Labs which operated
on a poverty level budget. When the club telephone line
rings, our controller:
1. Grabs the phone line by placing a resistor across it
2. Starts a timer
3. Connects the audio output of the remote 2 meter
receiver to the phone line through an old phone
patch
After the timer times out, the controller drops the phone
line.
We had originally thought of modifying a telephone
answering machine to serve as a controller, but our home-
built controller proved cheaper and more reliable.
Time Delay Relay
The plug in time delay relay was a DPDT configuration,
enclosed in a yellow cover. Instructions printed on the
side revealed that the delay time was between 0.1 and 10
seconds, and was determined by the value of an external
resistor.
Older delay relays use a thermal switch, which heats up
over time, making or breaking contact after reaching a
given temperature. Fortunately, my delay relay employed
more modern circuitry. Inside was a printed circuit
board with an actual solid state timer. The current
Newark catalog lists this relay at $45, socket extra.
I wanted a delay adjustable between a few seconds and an
60 minutes. Not having a schematic of the timer, I
applied 117 VAC to the coil and probed the circuit with a
voltmeter. I found the capacitor that, along with the
external resistor, determined the delay time.
A much larger capacitor was needed for long delays, but
wouldn't fit within the relay case. I removed the origi-
nal timing capacitor, and ran 2 wires from its old loca-
tion to an external 220 ufd capacitor through a hole
drilled in the case.
A Controller Takes Shape
I rewired the relays, and mounted a rheostat to set the
timeout delay. The addition of pilot lights, 1/4" phone
jacks, and modular telephone jacks complete the construc-
tion.
The remote receiver controller at IHARC requires use of
an external phone patch to connect the telephone line to
the receiver audio. We currently use a deluxe patch made
by Waters.
Not wanting to tie up a phone patch for my home con-
troller, I brewed up an interface to feed the audio out-
put of a receiver to the phone line. It used a capacitor
and 600 ohm transformer salvaged from a discarded PC
board, and a varistor cut out from a telephone handset.
The varistor clips residual voltage spikes that could
appear on the telephone line from ringing voltage and
damage the receiver.
The 35 lb. receiver controller works well. The only
problem to date is that the timer was unstable. Some-
times it timed out after 10 minutes, sometimes after 20
minutes, sometimes .... I replaced the timing capacitor
with a better grade component.
I use the setup to listen to a home scanner while I'm
away from home. The scanner is powered from an AC outlet
which becomes live when the controller answers a phone
call.
The controller also came in handy for monitoring the NASA
frequencies on shortwave during Shuttle missions. I con-
nected the controller to my Japan Radio NRD-525 HF
receiver and called it up from my office at work.
During Hurricane Hugo, I set up the controller to monitor
the Hurricane Net on 20 meters and gave out my phone
number to coworkers with relatives living in the affected
area. They could call my home and listen to 15 minutes
of hurricane news more current than reports available
from the press.
The "Junk to a Jewel" controller is connected to spare
phone line. I wouldn't connect it to my main telephone
line without adding a circuit that waits for several
rings before grabbing the line.
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Bob Parnass, AJ9S - AT&T Bell Laboratories - att!ihuxz!parnass (708)979-5414