Palomar (Hamcrafters) VLF-A, VLF-B VLF Converter

Object/Artifact

-

Radio Alpha

Image: Chuck Penson, WA7ZZE, hamfest

Image: Chuck Penson, WA7ZZE, hamfest

Name/Title

Palomar (Hamcrafters) VLF-A, VLF-B "VLF Converter"

Description

VLF Receiving Converter

Category

Receiving Converter, VLF

Made/Created

Manufacturer

Palomar Engineers, Hamcrafters

Date made

1981 - 1982

Dimensions

Height

2 in

Width

4-1/4 in

Depth

4-1/4 in

General Notes

Note

QST, Dec 1981, p. 224. QST, Jun 1982, p. 181. Converts from 10 to 500 kHz. VLF-A converts to 3510–4000 kHz VLF-B converts to 4010–4500 kHz There isn’t much to the Palomar VLF converter and that is one of its strong points. This little box is designed for the easiest installation possible. You connect your antenna to the SO-239 input, then attach a coaxial jumper between the converter output connector (another SO-239) and your radio. There is one switch on the front panel labeled ON and OFF, along with a green LED to indicate the ON state. The Palomar converter is simple on the inside as well. Incoming signals are first subjected to a 3-stage low-pass filter, which is essential to block overload from nearby AM broadcasters. After the low-pass filter the VLF signals reach a mixer stage composed of a mixer IC and a crystal-controlled oscillator designed around an MPF102 transistor. Around 2010, Hamcrafters bought the full rights and design for the converter from Palomar. For a while, the units were still sold with Palomar branding or as "Palomar by Hamcrafters," but when Palomar Engineers was sold to new owners who focused on other products (like baluns and RFI kits), the converter fully transitioned to the Hamcrafters name. Both the Palomar and Hamcrafters versions use a balanced mixer (the MC1496 IC) to up-convert VLF signals to the 4–4.5 MHz range (or 3.5–4 MHz on "A" models). Later Hamcrafters versions (specifically the Rev B) moved to surface-mount (SMT) components because the original through-hole ICs became nearly impossible to find. Original Palomar units were powered by a 9V battery. Hamcrafters updated the design to include a 12V regulator to make it more stable for use with modern SDRs, though many still retain the internal 9V battery clip. ARRL Lab Measurements: Palomar VLF-B Converter Current consumption: <20 mA L.O. Accuracy: 6.9 kHz error Conversion gain: 0 dB to –14 dB (loss), frequency dependent Conversion gain over frequency: Frequency (kHz) Gain (dB) 10 –7 20 –5 50 –4 100 –2 150 0 200 –2 250 –5 300 –9 400 –12 500 –14