LOW BANDER
Low Frequency SWL
Converter
Ramsey Electronics Model No. VLF1
Tune in on all that low frequency action your rig has been
missing! Get down below 400KHz with an effective and easy-tobuild design.
• Converts 400KHz shortwave up to 4MHz.
• Less than 10dB loss from 10KHz to 600KHz!
• Powered by any 9 - 12 VDC source.
• Uses analog and digital circuitry in a simple, robust design.
• E - Z hookup with built in “feed thru” antenna connections - no
need to disconnect when not in use!
• Uses stable crystal oscillator for drift-free operation!
• Can use 4MHz-10MHz crystal, 4MHz included.
• Complete and informative instructions guide you to a kit that works
the first time, every time.
• Gain valuable experience by winding a three-coil transformer.
PARTIAL LIST OF AVAILABLE KITS:
RAMSEY TRANSMITTER KITS
• FM10A, FM25B FM Stereo Transmitters
• AM1, AM25 Transmitter
RAMSEY RECEIVER KITS
• FR1 FM Broadcast Receiver
• AR1 Aircraft Band Receiver
• SR2 Shortwave Receiver
• AA7 Active Antenna
• SC1 Shortwave Converter
RAMSEY HOBBY KITS
• SG7 Personal Speed Radar
• SS70A Speech Scrambler/Descrambler
• TT1 Telephone Recorder
• SP1 Speakerphone
• MD3 Microwave Motion Detector
• PH14 Peak hold Meter
• TFM3 Tri-Field Meter
RAMSEY AMATEUR RADIO KITS
• HR Series HF All Mode Receivers
• QRP Series HF CW Transmitters
• CW7 CW Keyer
• DDF1 Doppler Direction Finder
• QRP Power Amplifiers
RAMSEY MINI-KITS
Many other kits are available for hobby, school, scouts and just plain FUN. New
kits are always under development. Write or call for our free Ramsey catalog.
VLF1 LOW FREQUENCY SWL CONVERTER INSTRUCTION MANUAL
Ramsey Electronics publication No. MVLF1 Rev. 1.1
November 2002
COPYRIGHT 2002 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.
Ramsey Publication No. VLF1
Manual Price Only $5.00
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR
Low Bander,
Low Frequency SWL
Converter Kit
TABLE OF CONTENTS
Introduction to the VLF1 ........................ 4
VLF1 Circuit Description ........................ 4
Kit Building Tips ......................................5
Parts List ................................................ 7
Parts Layout Diagram ............................ 9
Assembly Instructions ...........................10
Setup and Testing ...............................16
Troubleshooting Guide .........................16
Schematic Diagram ..............................17
Ramsey Kit Warranty ............................18
VLF1 • 3
INTRODUCTION
You have a great setup, tuning in just about everything in the spectrum. You
go up and down, down, down, until...DOH! Your receiver bottoms out. Ever
wonder what was down there just under your rig’s lower limit? You need a
very easy to build and easy to set up frequency converter, so you can delve
in to all the wonders that reside in
cool stuff down there and that’s what the VLF1 is all about: a kit that Ramsey
Electronics is only too happy to provide for you.
You’ll notice that the PC board included with your kit is single sided. It is easy
to assemble and a quick look at the parts list reveals 2 ICs and a handful of
resistors and caps. This kit uses both digital and analog circuitry to step up a
low frequency RF signal to a 4MHz minimum.
VLF1 CIRCUIT DESCRIPTION
Before we begin dissecting the circuit, let’s have a look at the “big picture”
and see what it is that we’re trying to accomplish.
Without getting too much into detailed theory, we need to “mix” the incoming
low frequency signal with a high frequency one to produce an output that
your receiver can use. As shown in the diagram below: the low frequency
input RF signal is added to a high frequency (4MHz) clock producing a high
frequency signal.
=
The Low Frequencies. Well, there’s some
+
VLF1 • 4
Take a quick look at the schematic. The low frequency signal from your
antenna is fed into J1. It passes through a low-pass filter made up of L1, L2,
L3,C1,C2,C3, and C4. The signal then passes through transformer T1 which
produces 2 identical copies of the original signal, with one being inverted.
Next is the magic step that creates the high frequency signal for your
receiver. The 4053 analog switch alternately switches between the input
signal and its inverted version at a frequency of 4MHz. This 4MHz comes
from the crystal oscillator made up of the 7404 and its support components.
The result of this switching is to produce a 4MHz version of your input signal!
That’s it, after being amplified by Q1; this signal comes out of J2 and on to
your receiver.
RAMSEY Learn-As-You-Build KIT ASSEMBLY
There are numerous solder connections on the VLF1 printed circuit board.
Therefore, PLEASE take us seriously when we say that good soldering is
essential to the proper operation of your transmitter!
• Use a 25-watt soldering pencil with a clean, sharp tip.
• Use only rosin-core solder intended for electronics use.
• Use bright lighting, a magnifying lamp or bench-style magnifier may
be helpful.
• Do your work in stages, taking breaks to check your work. Carefully
brush away wire cuttings so they don't lodge between solder
connections.
We have a two-fold "strategy" for the order of the following kit assembly
steps. First, we install parts in physical relationship to each other, so there's
minimal chance of inserting wires into wrong holes. Second, whenever
possible, we install in an order that fits our "Learn-As-You Build" Kit building
philosophy. This entails describing the circuit that you are building instead of
just blindly installing components. We hope that this will not only make
assembly of our kits easier, but help you to understand the circuit you’re
constructing.
For each part, our word "Install" always means these steps:
1. Pick the correct part value to start with.
2. Insert it into the correct PC board location.
3. Orient it correctly, follow the PC board drawing and the written
directions for all parts - especially when there's a right way
and a wrong way to solder it in. (Diode bands, electrolytic
VLF1 • 5
capacitor polarity, transistor shapes, dotted or notched ends
of IC's, and so forth.)
4. Solder all connections unless directed otherwise. Use enough
heat and solder flow for clean, shiny, completed connections.
SINGLE SIDED COMPONENT SOLDERING INSTRUCTIONS:
You’ll notice that the circuit board contains plating on only one side of the
board. This makes soldering relatively easy for even the inexperienced kit
builder. Just take your time and be sure to apply enough heat to the
connections. Don’t be too afraid of overheating a component, most are fairly
hardy and a weak connection will prevent your kit from working properly.
In all RF kits it is a good idea to keep the components as close to the board
as you can and trim off the excess lengths of the component legs. However,
in this kit the highest frequency on the board is around 4MHz, so this isn’t as
critical as it would be in a higher frequency circuit.
VLF1 • 6
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