QRPBuilder Feedline Emission Detector – $35
Detached sensing coil option – $15
During the installation of my antennas, occasionally I have encountered some spurious emissions along the feed lines that caused problems resulting in poor SWR and frequency resonance issues. Sometimes the emissions mask a good antenna but due to the unwanted radiation, results are not ideal. I thought a tool that detected this radiation might be helpful in finding and checking that measures taken, eliminated it. This kit detects the presence of these emissions and quantifies them with a digital display so preventative solutions can be judged. Feed lines are an important part of the whole system, and should not be taken for granted that they are not contributing to problems that can be easily remedied.
Other uses have been suggested for faulty coax or poor connections that emit any RF. Another user plans to use the device to detect the RF variations on his vertical antenna radials that may have corrosion.
The kit is a battery operated, self contained, hand held device. The 1N5811 Schottky detector diode used is sensitive from VLF to well above VHF frequencies, and fed to a TI MCU for processing, driving the three digit led display. There is a sensitivity potentiometer for full range control down to QRP levels. Power to the unit is supplied with a common CR2032 coin battery for many hours of continuous use. It can be turned on via a slide switch or used in spot check mode, with the push button switch.
There is an option available that allows lets you separate the main board from the sensor board giving you more reach (3ft.) and versatility. The enclosed male and female SMA connectors allow you to join the sensor back to the main board if desired, as a single unit without the jumper. Also, this option includes an SMA telescoping antenna so the unit can be used as a field strength meter.
The kit is all on one board 2.0″ x 4.0″ and uses all thru hole components. The tools required are a soldering iron with a small tip, rosin core solder, small side cutters, and can be built in about an hour, depending on your experience. On a difficulty scale of 1 to 5, 5 being the most difficult, this is rated at 2.
Click here for the assembly manual
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