VLF LF <5KHz - 500KHz Up Converter
User manual. Rev 05
(January 2015)
© HEROS technology Limited 2010. All rights reserved
VLF LF <5KHz - 500KHz Up Converter
Since many countries are allocating the 472 KHz band for experimental use by Radio Amateurs, a growing number
of them as well as listeners have become interested on VLF and LF bands.
The fact that few radios are available on the market covering properly frequencies from below 5KHz to 500KHz,
convinced us to provide radio amateurs and listeners with the high-performance receiving VLF-LF Converter
that we introduce here.
The VLF-LF Up-Converter extents the range of any shortwave receiver to below 5 KHz to 500 KHz.
It is connected between the antenna and a shortwave radio receiver. When it is power-on the <5KHz to 500 KHz
band segment is translate to 3.500MHz to 4.000MHz, Model-350 or 4.000MHz to 4.500MHz, Model 400,
allowing the reception of VLF and LF bands.
For example, if a conversion frequency of 4.000MHz - 4.500MHz, Model 400, is used, and the receiver tuned on
4.135.500MHz, you are receiving on 135.500KHz, just ignoring the digit 4 on the dial.
Alternatively most SDR radio control software lets customise by the user the dial, in this regard see below PowerSDR
The VLF-LF Up-Converter enables reception of VLF mobile maritime communications, aviation and marine navigational aids such as NDB and DGPS beacons, DGPS reference stations, NAVTEX, Standard Time & Frequency
stations, LF Amateur bands, European LW broadcast stations, monitoring the sounds of nature created by planet Earth
(Natural Radio) such as sferics, hiss, tweaks, whistlers, Dawn Chorus, other not well known VLF radio atmospheric
sounds, and many more.
It is advisable to use a variable attenuator in front of the converter in order to improve signal to noise ratio. Its use have
more or less noticeable effects depending on local band conditions. If you are living in the country side far away from
noise sources probably you do not need one.
In urban areas in presence of strong signals or noise a variable attenuator avoids saturating the IF receiver. Adjusting
the attenuation to a proper value weak signals buried in the noise can be seen emerging.
In addition better energy transfer is achieved between antenna and converter due the broad impedance matching
If the VLF-LF up-Converter is connected in line to a HF transceiver acting as IF receiver,
take precautions to prevent transmitting any signal into the converter.
- Type: Superheterodyne converter. Double balanced mixer; Quartz crystal oscillator.
- Frequency range: <5KHz to 500KHz.
- IF output: 3.5MHz-4MHz, model 350; 4MHz-4.5MHz; model 400.
- Input/Output impedance: 50 Ω
- Gain: 5 dB
- IF rejection: 110dB typical.
- MW band rejection: 80dB
- Crystal oscillator: Low phase noise; quartz crystal ±10ppm; 3.5MHz or 4MHz, fundamental.
- Power: 12volts/40mA
- Enclosure: Aluminium
- Size: 125mmx105mx55mm ( 4.921x4.133x2.165in)
© HEROS technology Limited 2010. All rights reserved
VLF LF <5KHz - 500KHz Up Converter
Input Filters
Referring to the functional block diagram, the 50 Ω antenna is connected to J1 ,BNC type connector; a Gas Discharge Tube
protects the converter from transients that may
come from the antenna.
Next the input filters section is a combination of a
110dB IF trap and a 7th order, 0.3dB insertion loss,
Low Pass Filter with a cut-off frequency of 500 kHz.
This section provides good performance right up to
the start of the AM broadcast band with a sharp
roll-off, giving
a good rejection to MW broadcast signals avoiding
introducing overload or intermodulation products in
the receiver.
Local Oscillator
Low phase noise, crystal controlled oscillator
provides +7dBm signal level to the mixer.
A good quality quartz crystal of 3.5MHz or 4MHz,
according to the model of converter, is used.
A trimmer capacitor is accessible by the user if fine adjust of frequency is required in times.
A linear fixed voltage IC regulates the voltage applied to the oscillator to enhance stability and avoid drift.
The oscillator is followed by a buffer stage to improve its stability. Next, an amplifier accommodates the signal to the
required level. It connects to a 4 MHz, 7th order, Elliptic Low Pass Filter which cleans up any harmonics and assures
that a pure signal applies to the mixer to minimize spurious responses.
The mixer stage is designed around a Mini-Circuits
SRA-8+ double balanced mixer. It is rated to operate
from 500Hz,
giving and excellent frequency coverage. Designed for
+7 dBm of LO power, it have a conversion loss of less
5 dB at VLF LF bands, which is compensate by the
post-mixer amplifier. A double balanced mixer has the
of high port-to-port isolation, which keeps the strong LO
signal from degrading the dynamic range of the IF
Every effort has been made to terminate the ports of
the mixer in a proper 50 Ω impedance to maximize its
The mixer IF port is most critical in terms of proper
termination, for so, a diplexer circuit provides a 50 Ω
resistive load
to the mixer while passing the desired signal to the IF amplifier, with minimum loss.
Next, a Band Pass filter at IF frequency connects to a Low Noise Amplifier to compensate losses, delivering around
5dB of gain to the output, necessary to overcome losses from external cable tails, relays and connectors.
© HEROS technology Limited 2010. All rights reserved
Double Balanced Mixer
Antenna Input (50Ω)
<5KHz 500KHz
500KHz 7 poles Elliptic LPF
-100dB IF notch filter
Mini-Circuits SRA-8
LNA amplifier
Bandpass Diplexer
Output (50Ω)
Output section
Input filtering section
Gas Discharge Tube
Freq. Output:
Model 350: 3.5MHz - 4MHz
Model 400: 4MHz - 4.5MHz
Power Reg
4MHz 7 poles Elliptic LPF
Crystal Oscillator
3,5MHz or 4MHz
Local oscillator section
Drawing <5KHz-500KHz VLF LF Up- Converter
REV 05 Sheet 1/1
Scale FCSM No
Drawn JJ de Oñate
© HEROS technology Limited 2006. All rights reserved
VLF LF <5KHz - 500KHz Up Converter
A carefully PCB and shielding design keep feed through signals of the HF receiving frequency down to a very low
level therefore weak LF signals will not be interfered by strong HF signals on the same frequency.
The HF receiver used should have strong rejection of HF signals through paths other than the antenna connector.
Most HF transceivers and receivers have good performance in this respect, but some SWL receivers do not and may
be used with the addition of filters and shielding.
The VLF-LF Up Converter is suitable for use with active antennas, loops and preamplifiers providing an output
impedance of 50 Ω.
Beverage antennas may need a matching network.
Using an active antenna, a DC block device must be used in order to asure that the antenna power coupler does not
introduces a DC voltage across the antenna input connector that will destroy the converter mixer.
If the VLF-LF up-Converter is connected in line to a HF transceiver acting as IF receiver,
take precautions to prevent transmitting any signal into the converter.
Oscillator calibration
The VLF-LF Up-converter comes calibrated from factory after a burn test of 24 hours. If for any reason you need to
recalibrate the local oscillator proceed as follows:
Remove the four front panel screws and slide gently the lid. You may untie the two upper screws on rear panel.
© HEROS technology Limited 2010. All rights reserved
VLF LF <5KHz - 500KHz Up Converter
Remove the lid from the local oscillator section.
Switch ON the converter. Allow at least 30 minutes of warming time before adjusting
at room temperature.
Measuremet point
© HEROS technology Limited 2010. All rights reserved
Adjust trimmer
VLF LF <5KHz - 500KHz Up Converter
Basic connection to a SW receiver
50Ω Antenna
Optional step attenuator
Antenna Input
RF IF Output
DC 12V/40mA
RX antenna input
Generic SW receiver
© HEROS technology Limited 2010. All rights reserved
<5KHz to 500KHz Up-Converter
By-passing the Converter on transmission switch-over
Connection diagram.
Optional step attenuator
Port B
Port A
RF Output
Port C
Port R
In order to avoid damage assure that your
transceiver provides delayed transmission switch over command.
i.e. derived from the linear amplifier control output connector.
Generic SDR or Analogue Transceiver
(100W PP max.)
Receiver antenna
* Reception state (relay no activated)
- Ports A-B connected
- Ports C-R connected
* Transmission state (relay activated)
- Port A connected to Port R
- Ports B and C are shortcut to ground.
Heros Technology
HF Dual By-Pass relay.
Delayed Transmission/Reception switch over command line.
(68mA active state)
12V DC/ 60mA(Active)
VLF LF <5KHz - 500KHz Up Converter
Flex 5000
Connection to FlexRadios
Flex 5000
Antenna input
RF output
Flex 1500
© HEROS technology Limited 2015. All rights reserved
VLF LF <5KHz - 500KHz Up Converter
PowerSDR Configuration
Dial lower frequency
(0 KHz in the picture)
Local oscillator correction
(if any)
Local oscillator offset:
Negative value (-)
- 3.5 for Converter model 350
- 4 for Converter model 400
Dial upper frequency
(500 KHz in the picture)
© HEROS technology Limited 2015. All rights reserved
VLF LF <5KHz - 500KHz Up Converter
Heros technology Limited disclaims all liability arising from this information and its use.
It is your responsibility to ensure that your application meets with your specifications.
Information contained in this publication regarding device applications and the like is provided only for your convenience
and may be superseded by updates.
Heros technology Limited makes no representations or warranties of any kind whether express or implied, written or oral,
statutory or otherwise, related to the information, including but not limited to its condition, quality, performance,
merchantability or fitness for purpose.
© HEROS technology Limited 2010. All rights reserved
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