Heros VLF-LF-MF User Manual

VLF-LF-MF Up Converter

User manual. Rev 2018-01

5kHz-500kHz

3.5MHz-4MHz model 350

4MHz-4.5MHz model 400

VLF LF <5KHz - 500KHz Up Converter

Specifications:

- 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; 3.5MHz or 4MHz, fundamental.

- Power: 12volts/40mA

- Enclosure: Aluminium

- Size: 125mmx105mx55mm ( 4.921x4.133x2.165in)

Since many countries are allocating the 472 kHz to 479kHZ 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 configuration.

The VLF-LF Up-Converter enables reception of VLF mobile maritime communications, aviation and marine navigational aids such as LORAN, 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 effect.

WARNING!

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.

A

B

C

D

1

2

3

4

1

2

3

4

A

B

C

D

Date

Sheet

FCSM No

DWG No REV

Size

Drawn

Checked

Issued

Approvals

Drawing

Scale

A4

JJ de Oñate

I I MMXV

5kHz-500kHz VLF LF Up- Converter

1/12016-02

5kHz 500kHz

Antenna Input

(50Ω)

J1

Gas Discharge Tube

LO

RF

IF

Crystal Oscillator 3,5MHz or 4MHz

Front End section

Amplifier

Local oscillator section

Bandpass Diplexer

Output section

IF BPF

Double Balanced Mixer

Buffer

Mini-Circuits SRA-8

+7dBm

Power Reg

3.5MHz or 4MHz, 7 poles Elliptic LPF

Post-Mixer

LNA amplifier

LNA

IF Output frequency models:

Model 350: 3.5MHz - 4MHz Model 400: 4MHz - 4.5MHz

500kHz 7 poles Elliptic LPF

-100dB IF notch filter

Converter

IF Output

(50Ω)

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, Elliptic 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.

Mixer

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 than

5 dB at VLF LF bands, which is compensate by the post-mixer amplifier. A double balanced mixer has the

advantage

of high port-to-port isolation, which keeps the strong LO signal from degrading the dynamic range of the IF

receiver.

Every effort has been made to terminate the ports of the mixer in a proper 50 Ω impedance to maximize its performance.

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.

VLF LF <5KHz - 500KHz Up Converter

Earth

RX antenna input

RF IF Output

Antenna Input

50Ω Antenna

DC 12V/40mA

+

Generic SW receiver

Optional step attenuator

4.100MHz

VLF LF <5KHz - 500KHz Up Converter

Basic connection to a SW receiver

<5KHz to 500KHz Up-Converter

By-passing the Converter on transmission switch-over

Connection diagram.

Antenna

Generic SDR or Analogue Transceiver

(100W PP max.)

Delayed Transmission/Reception switch over command line.

(68mA active state)

12V DC/ 60mA(Active)

+

-

Port A

Port R

Port B

Port C

* 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.

Input

RF Output

Heros Technology

HF Dual By-Pass relay.

Receiver antenna

Optional step attenuator

IMPORTANT! 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.

4.100MHz

XVRX

RX1 IN

XVRX

Flex 1500

VLF LF <5KHz - 500KHz Up Converter

Connection to FlexRadios

Flex 5000

Flex 15000

IF output

Antenna input

Configure Antenna Selection form

according with your cabling.

PowerSDR Antenna Selection form

Local oscillator offset:

Negative value (-)

- 3.5 for Converter model 350

- 4 for Converter model 400

Local oscillator correction

(if any)

Dial lower frequency

(0 KHz in the picture)

Dial upper frequency

(500 KHz in the picture)

VLF LF <5KHz - 500KHz Up Converter

PowerSDR Configuration

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.

WARNING!

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.

Design

A carefully PCB and shielding design keep feed through signals down to a very low level.

The HF receiver used as IF 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.

Operating

The VLF-LF Up Converter is suitable to work with SDR or Analogue radios.

It can works together active antennas, loop antennas and preamplifiers providing an output impedance of 50 Ω. Beverage antennas, 450Ω characteristic impedance need a matching device.

Using an active antenna, a DC block device must be used in order to asure that the antenna power coupler does not

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.

Adjusting trimmer

Measuremet point

VLF LF <5KHz - 500KHz Up Converter

A

B

C

D

1

2

3

4

1

2

3

4

A

B

C

D

Date

Sheet

FCSM No

DWG No REV

Size

Drawn

Checked

Issued

Approvals

Drawing

Scale

A4

JJ de Oñate

I I MMXV

5kHz-500kHz VLF LF Up- Converter

1/12018-01

5kHz to 500kHz

Antenna Input

(50Ω)

J1

Gas Discharge Tube

GDT

LO

RF

IF

L10

L6

L8

L11

L10

F1

L5

T1

T2

Q1

Q2

Q3

IC1

JP1

Q4

100Ω

L9

IF Output

3.5MHz to 4MHz or

4MHz to 4.5MHz

50Ω

J2

J5

J3

J4

L4

SRA-8+

LPF1

50pF

100n100n

100n

10uF

100n

1uF

250V

100n

1N5817

12.5V/40mA

2K2

100Ω

2N44416

22uF

78L09

10n

10pF

MPF102

2N4401

68pF

XT

Xtal 3,5MHz

or

4MHz

100pF

56pF

100K

470Ω

100Ω

2K2

680Ω

100Ω

1K

500kHz 7 poles Elliptic LPF module

DC-10MHz

Dual Balanced Mixer

220pF

82pF

15pF

4MHz 7 poles Elliptic LPF module

3dB Pi attenuator

Jumper

3dB Pi attenuator

L7

Resettable fuse

10uF chip

22uF/16V

10uF

D1

1N5817

D2

a

c

LPF1

LP2

+7dBm

C1

CV1

C2

C3

C4

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11

R12

R13

R14

CV2

C5

C6

C7

C8

C9

C10

C11

C16

C15

Att 1

Att 2

Att 3

C14

C13

C12

C17

C18

C19

C20

C21

C23

C22

C24

C25

C26

C27

C28

C29

C30

C31

C32

L1

L2

L3

100dB IF trap

C33

C34

C35

Mixer

IF Amplifier

SW1

3K3

to J4 a

to J4 c to J5 a

R15

LED

Switch ON

Font panel module

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.

NOTES:

VLF LF <5KHz - 500KHz Up Converter