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Foxhunt VK3YNG Sniffer 4, Instruction Manual, Page: 14 / 15

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Foxhunt VK3YNG Sniffer 4 Instruction Manual Download Page 14

 

VK3YNG Sniffer 4 Instruction Manual (for V2.2 hardware) 

 

© 2004, Bryan Ackerly, VK3YNG 

Rev 2.2a 

Page 14 

Sample antenna designs 

The antenna design is largely a matter of personal choice. For portable use, designs 
vary between two and four elements. More elements give better directivity and more 
precise bearings but are more difficult to carry around. For most situations, three 
elements offer a good compromise. Here is an example of antenna designs for 120 
and 146MHz. 
 

Director

Driven Element

Reflector

Frequency:
Director
Driven Element
Refelector

121MHz

1118
1178
1237

146MHz

930
981

1029

Tap Length

138

115

Element Spacing

373

311

Balun Length

815

680

Tap Length

25mm

(centre to centre)

A

B

Sniffer Mounting Plate
73 x 80mm

Element Lengths from Tip to Tip

All units in Millimetres (divide by 25.4 for inches)

Element Material: 10mm aluminium tubing
Tap lengths are typical and may require adjustement

Typical 3-element Beam Antenna (based on VK3VT design)

Balun
(RG174 coax cable)

BNC Connector

 

 

Summary of Contents for VK3YNG Sniffer 4

Page 1: ...load problems that plague other designs Full auto ranging operation allows the operator to quickly and intuitively locate the source of a signal without twiddling knobs or watching meters The operator is freed to concentrate on more important things such as negotiating terrain or reading maps The unit is also available in a fully tested Board level format for those who wish to integrate the unit i...

Page 2: ... Store functions 7 Sync Button 8 ARDF Sync 8 Band Scan 8 Other functions 8 D Set button 9 Uptime indication 9 Relative Battery Voltage indication 9 Firmware version indication 10 Volume Control 10 Range Control 10 Peak Hold Mode 10 Peak range memory 10 Frequency Entry 11 Configuring the Sniffer 12 Tone RSSI Filtering 12 Minimum filtering 1 12 Medium Filtering 2 12 Maximum Filtering 3 12 Peak Exten...

Page 3: ...eduction is provided automatically in steps of approximately 15dB each time a particular signal strength threshold is reached The number of 15dB steps of attenuation is shown on an LED display For example a display value of zero indicates maximum sensitivity where a value of 9 indicates a very strong signal that requires approximately 135dB of attenuation Signal strength indication is provided by ...

Page 4: ... may power itself down When power has dropped to 2 7 volts or lower the display decimal point is enabled to warn the user that batteries are in need of replacement Display Brightness A high efficiency Seven Segment Red LED is used for the range display It has two brightness settings one for daytime use and a significantly reduced brightness level for night use A light sensor located immediately ab...

Page 5: ...unction F Frequency Entry 4 digits follow No function M Power Audio Mode Select Tone AM FM Hold for power off Power On Off only instant power off Alternative Key Functions The default operation mode of the sniffer can be reconfigured by holding down certain keys while powering up the unit The sniffer will maintain this operation mode for subsequent power up down cycles Button Display during power ...

Page 6: ...et to give signal strength tone while the other channel follows the selected mode This is useful for hunting different continuous carrier transmissions where the transmitters identification is given using either AM of FM modulation FM Mute The Muted FM mode offers a pseudo FM mute function to mute all receiver audio when the sniffer is not receiving a signal This is a signal based rather than nois...

Page 7: ...ored frequency of 147 425MHz will flash up the sequence 7 4 2 5 The first two 100 and 10 megahertz digits are inferred by first entered digit as per the following table Setting of MHz digit Band selection 0 1 2 120 122 995MHz 3 through 9 143 149 995MHz The recalled frequency is not displayed in reduced functionality mode Store functions Pressing and holding any of buttons 1 through 6 will result i...

Page 8: ...ansmitter Band Scan When ARDF mode is not selected the 7 key performs a basic band scan operation where the sniffer hunts for the highest signal between the two frequencies stored in channel locations 5 and 6 The highest signal found is stored in channel 4 The scan will ignore any signals within approximately 10KHz of the frequency stored for channel 1 and the signal must be detectable at range 2 ...

Page 9: ... is disabled Manual ranging is disabled and pressing the range button will reset the current peak hold range to zero This mode is useful when hunting extremely intermittent signals such as wildlife or model aircraft beacons Holding the D Set key during power up causes the sniffer to operate in lower tone RSSI mode This mode may prove useful to those who have difficulty hearing higher audio frequen...

Page 10: ...lected range The sniffer remains in manual ranging mode until defeated by pressing the R button a second time This re enables auto ranging Holding this key during power up toggles the state of the range tone announcement flag When this flag is set the sniffer generates a be bop tone sequence whenever the sniffer ranges up or down The frequency of the tones gives the operator audible indication of ...

Page 11: ...frequency The first digit sets both the 1MHz frequency and the band 0 through 2 sets the 120MHz band 3 through 9 set the 140MHz band Factory default frequencies Memory Frequency Mode 1 145 300MHz Tone 2 145 700MHz Tone 3 144 250MHz Tone 4 146 500MHz Tone 5 121 500MHz Tone 6 146 575MHz FM Note 121 5MHz is used as an international personal maritime and aeronautical distress beacon frequency With an ...

Page 12: ...ilar to that of the VK3TJN XAJ Ultra sniffer While this mode offers the best smoothing of received signals it can tend to blur the definition of short duration pulses Peak Extend mode Filtering 6 This is a special mode for use with very short duration repetitive signals such as those emitted from wildlife or model aircraft transmitters The transmitters used are typically very low power and transmi...

Page 13: ...ife is reduced considerably when using the internal speaker on a high volume level with a continuous signal Use the lowest volume level possible when using the internal speaker or use external headphones The display also operates at a higher intensity level for daytime use that puts more load on the battery Typically night time only operation increases alkaline battery life by about 30 Users who w...

Page 14: ...d compromise Here is an example of antenna designs for 120 and 146MHz Director Driven Element Reflector Frequency Director Driven Element Refelector 121MHz 1118 1178 1237 146MHz 930 981 1029 Tap Length 138 115 Element Spacing 373 311 Balun Length 815 680 Tap Length 25mm centre to centre A B Sniffer Mounting Plate 73 x 80mm Element Lengths from Tip to Tip All units in Millimetres divide by 25 4 for...

Page 15: ...onnector Antenna Connection BNC Headphone Connection 3 5mm stereo Note Battery life is dependant sound level and display intensity See section on battery life VCO PLL Atten RF 2nd L O 10 7MHz 455KHz Detector Regulator CPU Keypad Pwr Supply 5V 3V 3V Batt DAC FM AM Tone RSSI LDR Gain Tune Ant 120 150MHz 120 150MHz VK3YNG Sniffer MK4 Block DIagram 2V5 Links More information on foxhunting and techniqu...

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