K6QE Jim Gilliam

K6QE NHRC REMOTE SYSTEM

     The NHRC controller is a very versatile. It functions well, not only as a repeater controller, but it also functions well as a remote base controller. As seen from the photograph of the K6QE ham shack the, controller sits proudly above all the other equipment.

     It may seem a bit extravagant (my wife says too damned expensive), two of the 706's (and duplexer) comprise the UHF repeater. They are connected via an interface box and RF filter to the NHRC controller. The third ICOM 706 has dual functionality. It not only interfaces through the NHRC for HF remote base operation, but is also connected through another interface to the computer sound card so that one may link to Echolink. The computer "talks" to the Internet through a wireless router attached to a high speed cable modem. At one minute I can talk to some one on 40 meters, or, just punch up a few DTMF codes and be talking to some one thousands of miles away through the Internet.

     The Hamtronics is used as a remote link receiver to turn the system off and I mean completely off. Through a special DTMF decoder, the system is put to sleep by switching off all the A/C power to the system. This is accomplished by deactivating an opto-coupled relay on the main A/C power strip. During dormant operation the repeater will only draw 100 ma until the "wake-up" command is invoked.

     The interface box is used for various switching functions including powering the ICOM HF remote "ON" and "OFF" as well as providing antenna switching to the various high frequency bands. This interface box is controlled directly from I/O transistors located in the NHRC-10 controller box.

The K6QE repeater system consists of (from top to bottom),

the NHRC-10 controller,

a home-brew relay interface box,

rack-mounted muffin fans, a linksys router and ICOM-AT180 auto tuner,

three ICOM 706's,

a Hamtronics link receiver,

a 430 MHz. Duplexer,

750 MHz. PC operating windows 98 S.E,

an A/C power strip, and a heavy-duty Astron power supply.

There is also associated interface circuitry mounted behind the 706 radios.

These are 2 pictures (top outside, bottom inside) of a relay box which is powered by the NHRC-10 8 channel digital output board. Jim has built two of these to turn off and on higher powered appliances.

This is the first RF filter box that Jim made which goes between the controller and the repeater.

The filter box seen in the photograph is used to eliminate that pesky RF distortion that is generated when the remote base is transmitting on the high frequencies. The RF gets into the audio amplifiers, which changes the biasing and causes the amplifier to operate non-linearly. Getting rid of RF is like trying to fix a leaky roof. It can get in anywhere and is almost impossible to track down its source of entry.

Rather than analyze the problem to find its source, it is sometimes better to just "squash" the problem. This remedy is what the RF filter box accomplishes. Each one of the conductors that connects between NHRC and the remote radio are run through a Pi filter. This filter consists of two feed-through capacitors and a torroid coil. This coil actually is not inductive but resistive at the RF frequencies. The iron-core material of which the coil is wound is very lossy at RF frequencies and can be modeled as a resistor. When the RF "hits" the filter, most of it is shunted to ground through the very low impedance of the feed-through capacitors. What is remaining is dissipated as loss in the coils. This filter box appears to have solved the RF distortion problem very nicely.

This picture shows one of the early controllers
that Jim Gilliam built to control an HF radio.

Text to follow.