Equipment Review
ChezRadio Procaster 100mW Part 15 Certified AM Transmitter
continuedInstallation:
The Procaster was installed on a fencepost noting some particular observations. Just above us at approximately 20 feet are electrical lines coming from the street pole to the dwelling on the property. You'll note from the picture that a small portion of the antenna is below the top of the fence itself. If this doesn't present another challenge, nothing will.
The transmitter was mounted to the fence and wired to the studio unit with the supplied cable. This was pretty straightforward with the exception it was a little difficult to wire the studio interface as it's a little tight between the wire inlet and the terminal block. Once connected, a clear frequency was selected in the extended AM band (1610 to 1710 KHz) to accommodate both daytime and nighttime testing. In the interest in keeping with the less than ideal installation, the transmitter was grounded to the fence itself.
Besides coming with a well written and detailed manual, the Procaster comes with a single page quick setup guide. The transmitter comes preset at 1610 KHz, but with a local travelers' information service (TIS) station in the area it was decided to use an open frequency in the upper portion of the band. The internal DIP switches enable the operator to change the transmit frequency, enable or disable the on-board audio processing, set the time constant for the processing (slow for voice or talk programming, fast for music programming) as well as enable or disable the treble boost, which works in a similar fashion to the high frequency boost utilized in NRSC-complaint AM broadcasting.
Tuning Up:Since Joe has extensive experience installing similar transmitters, we decided to let him take the plunge and go through the tuning procedure. It's pretty simple, as the only thing that needs to be done is peak the internal meter's reading by adjusting trimmer capacitor C18. The simplicity speaks for itself, as within less than a minute the output was peaked to maximum output. The Procaster includes automatic output control which prevents the unit from exceeding legal power limits as dictated by Part 15 regulations.
Crank Up The Audio:In our tests we opted to put the built-in audio processor through its paces. After setting the studio unit's audio control to the middle of its range we connected the audio test source. We adjusted the audio controls on the transmitter using a test receiver prior to securing the cover. The on-board processing is probably the most outstanding aspect of the transmitter. The audio is crisp and loud. Adjusting the output of our audio source from maximum output to approximately -15db yielded no percievable difference in loudness, thanks to the built-in audio processing. There was no difference observed on our Motorola 1310 C-QUAM AM modulation monitor used as reference. A variety of music genres were sampled and the audio fidelity was most impressive. It was noted that the unit may appear to be a little bass heavy to some, but this may depend on the programming aired. The audio this transmitter produces rivals some of the commercial broadcast transmitters we've had the opportunity to engineer.
Coverage Area:The first mobile test was performed with a Chrysler stock radio. Audio level was good and coverage total was about one half mile, which was what was expected considering the test setup. This was performed in the early stage prior to maximizing the audio settings on both the studio unit's control and the on-board processing adjustments. Once these adjustments were optimized the off-air tests were repeated with a variety of receivers ranging from several walk-about type portables, a Honda factory auto receiver, a Delco receiver and two boombox type portables. Average range was one-half mile with the best range of about three-quarters mile from the transmitter with stellar audio quality and full modulation. While of interest to some, we didn't attempt injecting a 25 Hz pilot tone to open up the response of the C-QUAM equipped Delco receiver. This was partly due to a time limitations with returning the test unit back to its owner.
A comparison was performed with the unit mounted on an elevated mount with similar grounding and audio properties as the city dweller test setup. Coverage jumped up to about one mile during this portion of the test and it's believed that had we spent more time with refining the available ground that this range could have been improved upon.
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