This miniature radio receiver module allows reception in the lower frequency bands up to 2 MHz.
Covers VLF 3 KHz to Ham 120 meters (1.8 - 2.0 MHz), and the AM broadcast band 530 KHz - 1710 KHz.
Features built in RF signal strength meter driver to allow viewing signal strength with a meter, or for chart-recording signal strength over time.
The VLF-101 radio receiver does not have AGC so you get full dynamic signal range without clipping and faithful reproduction of signal strength levels.
Lightning detector mode allows the receive to work as a lightning detector.
Works with the coil or loop antenna you supply, or works with our VLF ready-made antennas.
Easy 4 wire connection: Yellow = Antenna , Green = Audio Output , Red = (+) , Black = (-).
Input and output static and overload protected.
Audio output will drive any audio amplifier, and also will directly drive sensitive earphones.
Operates on 6 to 12 volts.
Part # VLF-101 $ 49.95 + $ 8.00 s/h.
The following diagram shows how to wire the unit to make a radio receiver having many features, including an analog signal strength meter.
The receiver will tune 3 KHz VLF through 2 MHz (120 meters) Ham, and the AM broadcast band: The chosen value of L1 and C1 sets the band received.
The antenna used for reception in the above video.
R1 = 4.7 K-ohm resistor.
R2 = 1 K-ohm resistor.
C1 = Variable Capacitor or fixed-value Capacitor to tune desired frequency range. 47 pF - 0.47 uF typical values range.
C2 = 0.047 uF capacitor.
C3 = 0.22 uF capacitor.
C4 = 0.22 uF capacitor.
C5 = 100 uF capacitor (required for audio decoupling, do not omit).
SW1 = ON/OFF switch.
SW2 = SPST switch.
SW3 = SPDT switch.
VR1 = 10 K-ohm variable control resistor.
D1, D2, D3 = 1N4148 or 1N914 silicon diodes. (sets signal meter zero point).
J1 = phono jack. (audio output).
Meter = 0 - 50 uA meter. (Stormwise part # METER50uA).
FE = Ferrite Rod. 125u value for range of 30 KHz - 2 MHz and AM broadcast band. For VLF 30 KHz and lower use a 2000u rod.
TP1, TP2, TP3, TP4 = Binding posts for connecting antenna, and for signal level DC output.
L1 = coil wound on ferrite rod. See table below. Can be a variable inductor (slide the ferrite in or out to tune, if a variable capacitor is not available).
L2 = coil wound on top of L1. Usually 1 to 10 turns, adjust for best signal and bandwidth performance.
Connect L2 to binding posts TP1 and TP2.
NOTE: If tuning 1 MHz (AM broadcast band) when L2 = 2 turns, this is typically @ 50 ohms. Adding more turns will increase signal level but selectivity (station separation) may suffer slightly.
NOTE: Lower frequencies require L2 to have more turns, 30 turns max for 3 KHz.
NOTE: Adjust antenna turns and coupling for best reception per requred for your application.
NOTE: For tuning the AM broadcast band, C1 should be adjustable from 15 pF - 384 pF.
Connect the J1 audio output to any portable audio amilifier or guitar amplifier's microphone input.
NOTE: You can listen directly thru a sensitive earphone (16 ohms coil or greater) if you don't have an amplifier.
Turn SW1 to the ON position.
Adjust VR1 to the full right position (max gain).
With TP1 and TP2 shorted together (no antenna connected) the signal meter should read 0. If the signal meter does not read 0 when power is applied, add another diode in the meter line.
Connect TP1 and TP2 to your antenna. Accepts tuned antennas of 50 to 300 ohms.
Adjust tuning of antenna to desired station. Rotate antenna for best reception.
If signal strength is too great, adjust VR1 gain control to reduce level.
To receive VLF stations having no audio: Inject into the antenna a low level signal 500 Hz - 1 KHz from from the station's frequency to produce a tone in the speaker. Careful to not slam the meter.
To receive WWVB 60 KHz: reception can be viewed with the signal strength meter as an ON-OFF signal, no need to inject a BFO carrier, unless an audo tone is needed.
Lightning Detector Mode. Set SW3 to select. With receiver tuned to 10 KHz ( VLF band ) or 210 KHz ( LF band ), the static crackling will sound from the speaker, but no other background noise should be present due to the 'squelch' effect of the D1, D2, D3 diode chain.
The lightning detector mode also works when receiving CW (morse code), the background noise is cut down between dit's and dah's, depending on signal strength of the CW signals.
NOTE: Adjusting the TONE switch ( SW2 ) can have a large effect on the signal strength meter reading. For increased signal meter gain, set the TONE switch to 'ON' ( Low ).
Construction and Modification Tips and Notes:
The receiver can be built into a wood, plastic, or metal box. A metal box is best for rejecting out of band signals.
A ferrite EMI sleeve bead is provided. This should be placed on the receiver's cable. 2 loops thru.
Keep all connecting leads short length.
Keep outputs and speakers away from input or antennas.
If using the signal meter, do not omit SW2, C2. C2 affects how the signal meter operates at lower frequency.
Do not omit C5 100 uF capacitor. Feedback squeal will result when adjusting VR1 RF gain.
Reciever will work normally without the signal meter and diodes, if you just want to keep it simple.
Don't want RF gain? Then omit VR1. Receiver will always be at 'max' gain.
The receiver will drive other meters than the 50 uA meter. Adjustment of D1,D2,D3 and R1 will be needed.
Power the amplifier and the receiver thru batteries only for best low noise performance. Power lines are full of noise at VLF and LF frequencies.
Keep antenna away from power lines for best reception.
NOTE: If powering the unit at 6 volts only, you can short D3 for more meter sensitivity.
NOTE: If powering at 12 volts add 1 or 2 more diodes if the signal meter does not read 0 when the antenna terminals are shorted together.
NOTE: Use 3 diodes like shown for highest meter sensitivity when powered at 9 volts.
How to use the VLF-101 as a 120 meter Ham Receiver:
Some fun can be had with this: (and the antenna design can also be used to receive other bands below 2 MHz).
Build 120 meter loop receiving antenna. A 3 foot x 3 foot square-shaped air core antenna will work, made of plastic PVC pipe and fittings to support the turns. Couple out to the VLF-101 with a single turn (more if needed) to make a 50 ohm load or what ever gives best performance. Tune receive antenna to desired operating frequency with a variable capacitor.
A separate HAM antenna should be used for transmitting, placed well away from the VLF-101 and receive antenna.
Short circuit the VLF-101 input -and- de-tune the receive antenna when transmitting to prevent damage. Do not allow more than 100 mW into VLF-101 input.
Loops are bi-directional. Rotate the receive antenna for best reception.
To receive CW, inject a low level beat frequency signal to the VLF-101 antenna to produce a CW tone or to even demodulate SSB.
If out of band RFI is received, add a band filter or RF choke to the coupling loop.
NOTE: The VLF-101 comes with an RF choke bead placed on the cable. If this affects 2 MHz reception, then remove it.