VK3YNG Foxhunt Sniffer Instruction Manual. Version 4.0
(Revision history updated Feb 2017)
Please note: This manual is for the latest version of sniffer (V4.0 hardware and V4.0.00 or later firmware).
For pricing and more information look here.
For other versions look here.

The VK3YNG Foxhunt Sniffer is a specially designed synthesised VHF direction finding receiver covering 120MHz and 144MHz bands.

The receiver is designed for quickly finding the direction of beacons or hidden transmitters. Anything from distant weak signals to very close "sniffing" of transmitters running many watts of output power can be pin pointed accurately without suffering "overload" 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 into other equipment or build their own housing.

***Note: A number of features have changed since earlier versions of the sniffer were released. This manual reflects operation of version 4.0 hardware and cannot be used for earlier versions of the MK4 sniffer. For a copies of earlier sniffer manuals please refer to the VK3YNG foxhunt web site.

Differences between V3.x and V4.0
Auto Power Down
Low Battery Indication
Display Brightness
Reduced Functionality mode
Quick Button Reference
    Alternative Key Functions
    Detailed Button Operation
    Mode/Power switch
       Power On
       Mode Selection
       Power Off
       Recall functions
       Store functions
    Sync Button
    D-Set button
       Relative Battery Voltage indication
    Volume Control
    Range Control
       Peak Hold Mode
       Peak range memory
    Frequency Entry
Configuring the sniffer
    Minimum Filtering
    Medium Filtering
    Maximum Filtering
    Peak Extend Mode
    ARDF Mode
    Scan Ready Mode
    Display Brightness

    Reduced Functionality Mode
Maximising Battery Life

Sample antenna designs
Block Diagram
Inside View of Prototype
Revision History


The VK3YNG sniffer is designed to allow quick, easy and accurate determination of the direction of a transmitted signal in either the 120-123MHz or 143-150MHz bands. The sniffer provides enough sensitivity to determine the direction of a signal from many kilometres or miles away. This is useful for ARDF or Radio Sport and general commercial or Civil Air Patrol use. It also provides enough attenuation to accurately determine the direction of signals right up to the source of the signal without suffering from overload or compression effects.

Attenuation (signal reduction) 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 an audible tone that increases in frequency (pitch) with increasing signal level. This is done because the human ear is a much more sensitive to changes in pitch than sound level. There is also no inertia or overshoot problems as tend to occur with signal meters. A special software algorithm ensures that the received signal strength tone does not suffer from “compression” effects that occur at higher signal levels with some designs.

Differences between V3.x and V4.0

The main differences between the two versions are:

1) The IF section of the sniffer has been redesigned to remove the obsolete LA8608 IF chip.

2) The mixer has been redesigned to remove an obsolete GaAsFET mixer. The new mixer has slightly better dynamic (IP3) performance.

3) Attenuation is more consistent between ranges.

4) Morse code is now used instead of varying tones for the "Range Tones Announce" feature.

5) Default display brightess is now programmable.

Other than that operation and specifications are largely identical.

Auto Power Down

The sniffer will automatically power down after 10 seconds if either of the following two conditions are met.
1) There has been no key pressed for at least 10 minutes.
2) There has been no "upward" progression in range for at least 10 minutes.
The sniffer will give five short beeps just before the unit powers down.

Low Battery Indication

The sniffer functions accurately to supply voltages down to approximately 2.5 volts. Below this the accuracy becomes compromised or the sniffer may power itself down.

When power has dropped to 2.5 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 Orange LED is used for the range display. (Display is Red in older versions). In "Auto" mode It has two brightness settings, one for daytime use and a significantly reduced brightness level for night use. A light sensor located immediately above the display automatically determines the brightness level. In version 4.0 the default brightness is programmable. The factory default setting is "Auto" but it can be forced to "Dull" or "Bright" only.

Reduced Functionality mode:

This mode may be useful for children or first time operators. It allows the sniffer to be used in its most basic format and hides all programmability options from the user. This mode is very useful for scout foxhunting for example. For this reason, many refer to this mode as “Scout Mode”.

Quick Button Reference:

The following table gives quick index to key functions in both normal and reduced functionality modes.
Operation in Normal mode
Operation in reduced functionality mode
Recall channel 1 (Hold to store frequency/mode) Recall only channel 1
Recall channel 2 (Hold to store frequency/mode) Recall only channel 2
Recall channel 3 (Hold to store frequency/mode) Recall only channel 3
Recall channel 4 (Hold to store frequency/mode) Recall only channel 4
Recall channel 5 (Hold to store frequency/mode) Recall only channel 5
Recall channel 6 (Hold to store frequency/mode) Recall only channel 6
Band Scan or ARDF mode Start of cycle Synchronisation function.
No function
Range down Delay Set/Display. 1 to 5 seconds. 0=peak hold mode. (7-9 are special functions)
Show relative Battery capacity in %
Volume Down No function
Volume Up No function
Manual Range set/disable No function
Frequency Entry (4 digits follow) No function
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-up Function if pressed during power-up
Filter “A”, Minimum Tone filtering. (fastest response)
Filter “B”, Medium Tone filtering
Filter “C”, Maximum Tone filtering (slowest response)
ARDF mode. Synchronised at power-up. Sync key is used to re-sync the transmitter cycle
Scan mode. Sync key is used to scan for strongest signal between frequency stored in channels 5 and 6.
Filter “D”, Tone Extend Mode. Used for very short duration signals. (New function in V2.1 firmware)
(Reset) Normal operation. Resets all options below to default setting:
Low-Tone mode (RSSI tones at quarter frequency. Resolution slightly reduced at low tone frequencies)
9 G
Mt Gambier mode (10-channel special - New in V3.0)
o,d,b,A Toggle display default brightess level (off*/dull/bright/Auto)
Enable Reduced key functionality mode (“Scout” mode)
Enable auto range change announcement tones. (Morse announcements in V4.0)

Detailed Button Operation

Mode/Power switch:

Power On:

Pressing this button once powers on the unit to the frequency and mode stored in memory channel 1.

Mode Selection:

Pressing this button momentarily while the unit is powered up cycles the unit through its operating modes and briefly displays the selection on the display. The modes cycle through in the following sequence: “A” – AM reception, “U” – Unmuted FM reception, “F” – Muted FM reception and “t” – Signal strength Tone. The cycle then repeats. When headphones are used, one channel is always set 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 noise based) mute that activates whenever the received signal is below the lower range threshold on ranges 1 upward and is always active on range 0.

Power Off:

Pressing and holding the Mode button for greater than 1 second will power down the unit. In reduced functionality mode, the unit will power off immediately when the Mode button is pressed. The mode switch operates only as a simple on/off switch in reduced functionality mode.


Buttons 1 through 6 allow storing and recalling of memory modes and frequencies.

Recall functions.

Pressing any of the buttons 1 through 6 in normal operation mode will recall the frequency and mode stored in non-volatile memory. In normal operation mode, the display will display the last 4 digits of the selected memories frequency in kilohertz. For example, a stored 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
3 through 9

The recalled frequency is not displayed in reduced functionality mode.

Store functions

Pressing and holding any of buttons 1 through 6 will result in the selected frequency and mode being stored in the selected memory. The button must be pressed and held until two short beeps are heard in succession. This confirms that the data has been committed to memory.

The Store function is disabled in reduced functionality mode.

Sync Button

This facility is used to synchronise the receiver for use in international style (ARDF) foxhunting for a one-minute cycle, five-transmitter system.

In ARDF mode this timer is automatically synchronized when the receiver is switched on. Three short beeps are generated as confirmation of this mode.  Pressing the Sync button re-synchronises this timer. Three short beeps are given to confirm this button has been pressed. The sync button should be pressed at the start of transmitter one’s cycle.

At 50 seconds into the cycle, the sniffer will generate three short beeps giving 10 seconds warning that the current transmitter’s cycle is about to end. If the sniffer is currently receiving at range 1 or lower, at four seconds before the completion of the current transmitter cycle the sniffer broadcasts a number of beeps corresponding to the number of the transmitter in the cycle which is about to commence. The pitch of these beeps is set slightly lower than the “50-second” beeps. The display also briefly flashes the number of the next transmitter. If a range down delay (d-Set) of zero is selected and the sniffer is not currently configured for manual ranging, the sniffer will automatically select range zero at the start of the next transmitters’ cycle regardless of the current signal strength.

 The ARDF sync mode is entered by pressing and holding the “4” button during power-up. It is cancelled by returning to Scan mode.

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 or higher to be stored.

This operation takes some time to complete, especially if there is large frequency difference between channels 5 and 6. The scan function works best for continuous signals and may not properly detect intermittent transmissions. Channel 5 must be lower in frequency than channel 6 and both frequencies must be within the same band (i.e. 120MHz or 140MHz)

The SCAN mode is entered by pressing and holding the “5” button during power-up. It is cancelled by entering ARDF Sync mode. Scan mode is the factory default.

Other functions:

In ARDF mode, if a range down delay (d-Set) of zero is selected and the sniffer is not currently configured for manual ranging, the sniffer will automatically select range zero at the start of the next transmitters’ cycle regardless of the current signal strength.

Holding the “7” key during power-up cancels the Low RSSI Tone mode, Range Change Announcement tones* and the Reduced Key Functionality mode. In this mode the signal strength tones function normally and the maximum signal strength pitch is 8KHz. This mode is set as the factory default. (*Note: this facility operates differently in older firmware versions)

This key is disabled in reduced functionality mode.

D-Set button

Ranging up on the sniffer happens automatically with minimal delay. To implement short term peak detection, there is an intentional delay before the sniffer ranges down. This delay is programmable between 1 and 5 seconds using the D-Set button. For beginners, a value between 3 and 5 seconds is recommended. For more advanced users, 1 or 2 seconds gives better results. When hunting intermittent and very short duration transmissions such as those used on wildlife, 5 seconds or “peak hold” mode (see below) is recommended. The factory default is 2 seconds.

To set the range down delay, press the “D-Set” button. The display will respond by displaying the letter “d”. Pressing buttons 0 through 5 will then set and store the new range down delay.

Pressing the D-set (7) button twice will briefly display the current range down delay in seconds. The display then reverts to displaying the current range.

Setting a range down delay of zero disables down ranging. In this case the sniffer operates in a “peak hold” mode and down ranging 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 Dog Collar, 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 frequencies. In this mode the signal strength tone frequencies are divided by 4. The top tone pitch is limited to about 2KHz and resolution becomes slightly limited at the lowest tone frequencies. (Note: this mode has no effect on the pitch of supervisory beep and tone frequencies)

This key is disabled in reduced functionality mode.

Special note: “Dset 0” in “Scout” mode:

In version 3.0, if peak hold mode (Dset 0) is selected before the sniffer is set up for reduced functionality (“scout”) mode, the peak hold behavior behaves slightly differently. If a strong signal disappears for more than 5 seconds, the sniffer will range down by one range only. As with normal peak hold behavior it will stay there until the range is reset or the channel or frequency is changed.

This operation was added to give beginners a second go at a signal source if they happen “over shoot” it and the signal falls below the current peak range.

Uptime indication:

Pressing the “D-Set” button then pressing “7” will display 4 digits indicating the number of hours and minutes since the receiver was powered up. This can be useful for ARDF events where the user may have forgotten to synchronise their watch.

Relative Battery Voltage indication:

Pressing the “D-Set” button then pressing “9” will display two digits giving an indication of the relative battery capacity in percentage terms. 99% indicates a full battery while 0% indicates the point where sniffer operation is significantly compromised. The sniffer may power itself off before reaching 0%.

Firmware version indication:

Pressing the “D-Set” button and then pressing the “F” button will display 4 digits which indicate the installed firmware version.

Volume Control

During normal operation, the "9" and "0" buttons allow the setting of volume. The display briefly shows the new level and reverts to displaying the current range when the button is released.

These buttons are disabled in reduced functionality mode.

Range Control

Normally the sniffer automatically selects the best range for the currently received signal. In some situations it may be necessary to range the sniffer manually. The range control button can be used for this purpose. This button also controls a number of other features depending on the mode selected.

In auto-ranging mode, pressing this button briefly displays the letter “r” in the display, and then the display reverts to displaying the current range.  Pressing any digit then manually selects the range. The display briefly displays “r” followed by the selected 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 enables announcements of range, frequency and various other functions using morse code. This feature has replaced the "be-bop" style range tones announcements feature used in previous versions. It has been added to better assist blind operators using the receiver. (Note: This is a new feature in version 4 and its operation is subject to change. More information on its operation will be added to the web site soon.) Powering up with the "7" button pressed disables morse announcments. See the section on configuring the sniffer for more information.)

This key is disabled in reduced functionality mode.

Peak Hold Mode

This range button also resets the peak range hold function if the down range delay (D-set) is set to zero. In peak hold mode, manual ranging is disabled.

Peak range memory

If the range button is pressed twice in succession, the display will briefly show the maximum range the sniffer has achieved since power up or the last successful frequency change. (In version 3.0 onwards, pressing "Dset" then "Range" also perfoems the same operation).

In ARDF mode, (see Sync button section) the peak range value is automatically reset at 30 seconds into the current transmitter cycle. This is very useful if there is a need to check what range the sniffer got to just before the previous transmitter finished its cycle.

This function is not available when Peak Hold mode (dSet=0) is selected.

Frequency Entry

The sniffer can operate at any frequency in the range 120.000-122.995 and 143.000 -149.995MHz in 5KHz steps. Pressing the “F” button initiates frequency entry. The display confirms this by displaying “F”. The sniffer then expects four digits to be keyed in to set the desired frequency. If an error occurs while entering frequency, the letter “E” is briefly displayed and the sniffer then reverts to the previous operation 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

Note: 121.5MHz is used as an international personal, maritime and aeronautical distress beacon frequency. With an appropriate antenna, the sniffer can be used to locate PLB, ELT and EPIRB emergency beacons. 

For the scan function to work correctly, the frequencies stored in channels 5 and 6 should be in the same band. This is not the case for the factory default configuration.

Direct frequency entry is not permitted in reduced functionality mode.

*Note: Some special versions of the sniffer operate with different frequency ranges to those indicated above. The label on the rear of your sniffer will indicate the frequency range your sniffer covers.

Some special “narrowband” versions also allow 1kHz resolution. In this case the fourth digit entered can be any number from “0” to “9” instead of only “0” or “5”.

2.5kHz resolution can be available for some special builds, such as in the United Kingdom and areas of Europe. In this case “2” and “7” are also valid and correspond to xxx.xx25 MHz and xxx.xx75 MHz respectively.

Configuring the Sniffer

The MK4 sniffer has a number of configurable features. Some of these have already been described in the previous sections. The rest are explained here.

Tone (RSSI) Filtering:

There are four levels of filtering available on the MK4 sniffer. These are selected by holding buttons 1, 2, 3 or 6 when powering up the sniffer. The sniffer will retain this setting until the next time it is changed.

Minimum filtering (1):

This level of filtering is the same as the original MK4. It offers the fastest and most accurate tracking of the received signal level. On transmitters with a high AM component, the tone can become quite “thick” sounding as the tone tries to partially track the modulation. This setting is the factory default.

Medium Filtering (2):

This level of filtering offers the best compromise between response time and Amplitude modulation (AM) filtering.

Maximum Filtering (3):

This mode provides maximum filtering of the received signal and is similar 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 transmit for around 40 milliseconds every second or two. The tone pitch and therefore signal direction can be very hard to determine using the above filtering modes.

This special mode extends the time of the peak level of the received signal so that the user can easily compare the signal level from different directions.

ARDF/Scan Mode:

ARDF Mode (4):

Holding the “4” button while powering up puts the sniffer into ARDF mode. In this mode the sniffer will power up giving three beeps and will synchronise the ARDF timer. For more information see the section on the Sync Button.

Scan Ready Mode (5):

Holding the “5” button while powering up puts the sniffer into scan ready mode. In this mode the sniffer gives a single beep during power up and the sync button executes a band scan function. This is the factory default. For more information see the section on the Sync Button.

Low Tone Mode (8):

In this mode the signal strength tone frequencies are divided by 4. See the description of the “Dset” button for more info.

Gambier Mode (9):

This is a special mode in the V3.0 sniffer for Australian Championships “fox-or” foxhunting. In this case the “7”, “8”, “9” and “0” keys are reallocated as fixed frequency channel recall buttons. The sniffer is set up to recall a set of 10 frequencies that match the transmitters used in the Mount Gambier event. This is done without affecting the frequencies stored in the 6 standard memories and resetting from this mode (by powering up with the “7” key) will recall the previously programmed settings. Note that when this mode is set the functions normally allocated to these buttons (Sync, Dset and Volume) are not available.

Channel Key Frequency Channel Key Frequency
144.250MHz 7
144.500MHz 8
144.750MHz 9
145.000MHz 0

These frequencies are fixed. There is no facility for storing different frequencies in this mode. However, selection of a different audio mode (AM/FM/Tone) con be stored permanently by pressing and holding any one of the first six (1..6) buttons.This stored setting only applies to Gambier mode.

When the sniffer is reset (Powering up using the "7" button) it reverts back to the settings stored in the individual channel memories. But if the sniffer is set back to Gambier mode (power-up "9") it will recall the audio mode that was previously saved in that mode. The audio mode setting is NOT cleared by the reset function.

Display (and keypad) LED Brightness (0):

This key is a toggle for the brightness level of the display and keypad channel indication LEDs if this option is fitted.

This button cycles between "Dull" (display "d"), "Bright"  (display "b"), "Off" (display "o") or "Auto" (display "A"). "Off" and "Dull" settings are provided to reduce battery consumption in low light conditions or when the bright display option is not required. The "off" setting only applies to the keypad LEDs if fitted. In this setting the range display operated the same as for the "Auto" setting. The "Auto" setting is the factory default and the recommended setting for normal use.

Reduced Functionality Mode:

In this mode, most of the special features of the sniffer are disabled. This mode is useful when a newcomer or a scout group etc uses the sniffer. (Hence why some users call this “Scout Mode”) Memories can only be recalled and most of the other keys, including volume control are disabled. The power button only acts as a simple on-off and the mode of operation is defined by what is stored for each channel.

To set the sniffer in reduced functionality mode, press and hold the “F” button while powering up.

To cancel reduced functionality mode, press and hold the “7” key while powering up.

Function Reset (7):

This key resets the following modes if set:

1)      Low Tone mode,

2)      Range Tones Announce,

3)      Reduced Functionality (scout) mode,

4)      Gambier Mode

Battery Selection and Maximising Battery Life

There are a number of solutions for extending battery life with the sniffer. The most critical one is the volume setting. Battery life 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 would like to get the longest use between battery changes should consider using Single Use Lithium AA batteries. These batteries have a very long shelf life and capable of providing well over 14 hours of continuous daytime operation.

Zinc Carbon and General Purpose Manganese, or so called “Heavy Duty” batteries are not recommended. The internal resistance of these batteries is too high to get reliable operation from the sniffer.

This version of the sniffer can run off higher capacity NiMh batteries but this is generally not recommended as their terminal voltage (1.2V) is normally too low. The power supply module in V3.0 of the sniffer is capable of operating off NiMh batteries and their use may be considered if the sniffer is used very regularly. But keep in mind that the sniffer will always indicate the batteries as partially depleted, even when fully charged. When the batteries go flat the sniffer will stop operating abruptly with little or no warning. The sniffer also provides no means of charging these batteries. They must always be removed for charging.

The above graph shows the discharge rates of the typical battery options. It shows that the Lithium and 2500mAh NiMh can significantly outperform even the best alkaline batteries.

The lower published per cell terminal voltage of NiMh (1.2V) can become irrelevant as time increases since the voltage is essentially constant. Another downside is that the weight of these high capacity rechargeable batteries is around twice that of Lithium.

NiMh rechargeable batteries are not recommended for infrequent use. The self discharge rate of these batteries will mean that they will go flat after sitting unused in the sniffer for several months where Alkaline or Lithium batteries will maintain their usability for a much longer period.

It is always recommended to remove batteries of any type when the sniffer is not in use for extended periods.

** Note: Rechargable Litium Ion batteries are not suitable for use in the sniffer. Their terminal voltage is too high and using them will damage the sniffer!

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 offers a good compromise. Here is an example of antenna designs for 120 and 146MHz.


 Frequency Coverage   Standard version: 120-122.995MHz, 143-149.995MHz in 5KHz steps
 Channel Bandwidth  16KHz
 Sensitivity  Better than -120dBm
 Maximum signal level  Greater than +30dBm
 Power Supply  3VDC (2xAA Alkaline or 1.5V Lithium penlight cells)
 Battery Life*  Typically 8+ hours (alkaline), 14+ hours (Lithium)
 Memories  6, programmable (stores mode and frequency)
 Receive modes  AM, FM, Signal strength Tone
 Max RSSI frequency  Programmable 2KHz or 8KHz
 Size  76mm(W), 80mm(H), 25mm(D) not including BNC connector
 Antenna Connection  BNC
 Headphone Connection   3.5mm stereo
 *Note: Battery life is dependant sound level and display intensity. See section on battery life.


    V2.2 inside  MK4 V3.0 inside  MK4 V3.0 internals
Inside view of V1.3 prototype (Left) and the V2.2/V2.4 unit. In both cases not all components are shown as a significant number of them are on the opposite side of the board. The two images to the right are the new V3.0 unit. The later rev units use fine pitch IC's and 0603 SMD components to give maximum functionality in a small package.

More information on foxhunting and techniques can be found on the Australian ARDF website

Follow this link for Pricing, Availability and other foxhunt projects.

To contact the author:
Bryan Ackerly, VK3YNG

Revision History

Manual Revision
Date (dd/mm/yy)
23 Jan 2002
Initial Release of manual
Hardware release 1.0, Firmware release 1.0
26 Jul 2002
Manual revision 1.1:
- Included quick button reference details and rewritten some button function details.
- Added sample antenna designs, block diagram, tips for extending battery life, links and contact information

Hardware release 1.1:
- Addition of improved VCO module

Firmware release 1.1:
- Added display range display override.
- Display shows range instead of Tx number in ARDF mode if range goes up.
- Added ability to see battery voltage in reduced functionality (scout) mode
- Volume control disabled in reduced functionality (scout) mode.
- Relative battery capacity (0-99%) can be displayed.
- Different tones used for ARDF mode transmitter number announcement beeps. 
- Transmitter announcment beeps now set to four seconds before minute boundary (was 2 seconds)
- Peak range detector added which holds peak range for 30 seconds in ARDF mode.
- Range hold mode simulates the “Green button” on the “YQN” sniffer by using the range button.

28 Oct 2002
Manual updated to release 1.2 to link with firmware revision. No code or hardware changes
02 Nov 2002
Hardware Release 1.2:
- Improved Power Supply noise filtering

Firmware release 1.3:
- Added auto volume reset (limits setting to “5” under low battery conditions)
- Recalling a channel multiple times in the presence of a signal would cause the sniffer to range up each time a button was pressed and not range back down if the channel was recalled more than 9 times in a row. Range is now reset to zero if the received frequency is changed or preserved as is if the same frequency is recalled. Frequency will be displayed if no range up is required.
13 Oct 2003
Hardware release 2.0
- Processor changed to ATMega8. Doubled processor speed.
- Receiver redesigned to remove obsolete Motorola MC13135
- New Rx front end and Discrete MOSFET mixer

Firmware Release 2.0.00
- Port to new processor
- Added uptime counter
- Added Band Scan function on sync key
- Added ARDF sync at power-up
- Added "FM Mute" as 4th audio mode
- Added tone filtering features
- Added some handling for UHF operation
- Changed battery capacity lookup table

Manual Release 2.0
- Manual updated to reflect new hardware and firmware features
- released as pdf only
26 Jun 2004
Manual release 2.1a
- Minor manual update
2.2a 25 Oct 2004 Hardware release 2.2
- Replaced Mux and Audio amp IC's with smaller packages
- Varactors changed
- Replaced MOSFET mixer with GaAsFET part

Firmware release 2.1.01
- Added Filter "D" - peak extend mode for Wildlife and Model Aircraft hunting.
- Improved autoranging functionality and range-up speed.

Manual release 2.2a
- Released as pdf and html versions
- Added documentation for "peak extend" tone filtering mode
2.2a 17 Nov 2004
Hardware release 2.2b
- Changes to 2nd IF osc current for new ref crystals

Hardware release 2.2c
- Improved isolation from reflected PLL noise (mainly affects 160MHz models)

Firmware release 2.1.02
- alignment tuning range span changes (120MHz only models)
2.2a 28 Nov 2004
Firmware release 2.1.03
- Added variable peak extend mode support for 10.7MHz special build (evaluation only).
2.2a 2 Dec 2004
Firmware release 2.1.04
- Minor adjustment to peak extend tone length
2.2a 5 Dec 2004
Firmware release 2.1.05
- Added support for LMX2316 PLL for a UHF version (no change for VHF versions)
2.2a 24 Dec 2004
Firmware release 2.1.06
- Upgraded compiler
- Fixed RSSI filter initialisation (minor bug)
- Added independent range alignments for 120/144MHz bands to improve range 6 overlap on 120MHz.
2.2a 29 Jan 2005
Firmware release 2.1.07
- Added initial LCD support (requires special hardware build)
2.2a 14 Apr 2005
Firmware release 2.1.08
- Fixed bug for scout mode powerdown lockup.
   (Workaround for earlier versions: Do not store "muted FM" mode in memory 1)
- Slight reduction in peak extend time
2.2a 10 Jun 05
Firmware release 2.1.09
- Update for internal use. No change for released version.
2.2a 26 Jun 05
Hardware release 2.2d
- New power supply. Allows operation down to 2.0V giving much greater battery life.

Firmware release 2.1.10
- Support for new power supply module
- Added "dead battery" powerdown below 2.0V (was a hardware function with previous supply)
2.2a 5 Sep 2005
Firmware release 2.1.11
- Added support for 150-153 and 173-180MHz version
2.2a 4 Oct 2005
Firmware release 2.1.12
- Added support for 153-163MHz version.
2.2a 17 Nov 2005
Firmware release 2.1.13
- Added support for 10.240MHz reference for 160MHz version.
2.2a 31 Jan 2006
Hardware release 2.3b
- PCB update to integrate rev 2.2d modifications
- Slight improvements to front end amp.

Fimware release 2.1.14
- Range announce display now works on all ranges when manual range selected
- Added initial 243MHz support for trial use.
- Changed default channel 5 and 6 frequencies for 160MHz version.
15 July 2006
Hardware release 2.3c
- Changes to enhance front end stability and simplify alignment.

Firmware release 2.1.15
- shifted keypad voltages for 4V supply version. (LCD version support special)
- Added support for 10m and 6m versions
- added 1KHz resolution support (requires special "narrowband" hardware)
- added stepped range down delay (dependent on DSet) for peak extend mode.
- fixed bug where range would not update immediately after channel recall in "Scout mode"
- fixed flashing "d" segment for "8" display on special LCD build.
- Added support for narrowband 1KHz step version for 2m Indonesia special build.
- Peak range storage in ARDF mode now shows peak from last minute for whole minute, not just first 30 seconds.
21 Sept 2006
Firmware release 2.1.16
- Added support for narrowband standard 2m freq range (NZ AR pulsed beacons)
- Added support for narrowband special 160MHz version (NZ pulsed beacons)
- Fixed bug where ranging would sometimes go nuts when changing channel from an intermittent transmitter being received on higher than range 0.
27 Feb 2007
Firmware release 2.1.17
- Added support for the same PLL for both standard and narrow builds. (Used to require use of different parts)
31 Mar 2007
Hardware release 2.4
- PCB update to include rev 2.3c changes and simplify frequency alignment.
- Lower battery voltage sensing. (Mainly affects LCD build, but also useful to get more life from alkaline batteries)
- Change to first IF filter to improve adjacent channel rejection and blocking performance.

Firmware release 2.1.18
- Modified battery voltage sensing due to resistor value change on rev 2.4 hardware.
- Fixed problem with range 2+ on frequency boundary with band split (eg 121/144MHz) hardware.
Workaround: Only affects 143.000MHz. Avoid using this freq or use 143.005MHz for older firmware versions.
- PLL version now handled by compiler switch. Simplifies updates for hardware prior to rev 2.4
- Fixed frontend alignment bug. Has no effect for end user.
- Fixed range alignment sweep timing above range 1. Has no affect for end user.
12 Aug 2007
Firmware release 2.1.19
- Added support for switchable IF filter
- Improved range up handling (overcomes transient selection of uncalibrated "range 10")
- Filter forced to 0 during alignment (no affect to end user)
- Default atten range now selectable by build type.
- 151/173 build units default atten range shifted from 6 to 7
19 Mar 2008
Firmware release 2.1.20
- Range beep now cancelled by "7" key during power-up (Upgrade to manual v2.3 needed)
- Removed the "toggle" for range beep tones selection
- "Simple" mode added for Bigboar build only:
- "Advanced" modes enabled using power up "9".
- "Standard" default modes re-enables using power up "0". (Also restores factory default settings)
31 Aug 2008
Firmware release 2.1.21
- Removed range "10" from manual ranging unless the build type requires it.
14 Nov 2008
Firmware release 2.1.22
- Added support for 118-123, 143-148MHz special CAP build (However, scan function doesn't work across the 120MHz boundary)
26 Nov 2008
Firmware release 2.1.23
- Added support for 155-165MHz Kiwi tracking version
11 Mar 2009
Firmware release 2.1.24
- Added support for 150-160MHz narrowband for Sweden
16 Oct 2009
Firmware release 2.1.25
- Added support for illuminated channel button display
- Peak range now displayed using Dset-R
- In scout mode only when using dset-0, the range can only go back 1 range from peak hold value unless frequency is changed or channel is recalled. (useful to stop sinffer going "Dead" when an inexperienced user walks right past the signal source.)
- Untested support for manual range keypad LED and button brightness on ADC7 input.
18 Nov 2009
Firmware release 2.1.26
- Added support for 2.5kHz step for standard UK model.
11 Nov 2010
Firmware release 2.1.27
- Added support for 2.5kHz step for Italy version.
- Added range 10 support for narrowband version 151/173MHz.
17 Feb 2011
Firmware release 2.1.28
- Added support for 146-156MHz build.
15 Dec 2010
Firmware release 3.0.00
- Initial V3.0 Test version
30 Aug 2011
Firmware release 3.0.01
- Release version
1 Sept 2011
Firmware release 3.0.02
- Production alignment update. No affect on end user.
9 Sept 2011
Firmware release 3.0.03
- Added support for 2.5kHz channel spacing version.
2 Mar 2012
Firmware release 3.0.04
- Added support for special 10-LED channel indication keypad.
- Fixed bug where sometimes channel 1 ended up with "FF00" as the stored frequency. Only occurs when batteries are removed before power is turned off.
3.1 25 April 2012 Firmware release 3.0.05
- Improvements to production alignment. No change for end user.
- Changesd range IF offset from 2dB to 1dB per range to improve saturation problems at higher ranges with heavily AM modulated ARDF transmitters.
21 Nov 2012 Firmware release 3.0.06
- Improvements to production alignment. No change for end user.
6 Jan 2013
Hardware release 3.1
- Minor PCB update. Changes to display drive bit order.
Firmware release 3.1.00
- Support for V3.1 hardware.
22 Jan 2013
Firmware release 3.1.01
- Added support for special order version to report RSSI values as serial data.
5 April 2013
Firmware release 3.1.02
- Changed low battery reading to once a second to avoid "noisy" operation tone near low battery threshold. (When display decimal point comes on) Issue is new to version 3.1 hardware. It doesnt affect older versions. Units from serial 1057 onwards are Rev 3.1 hardware despite some being incorrectly labelled as V3.0. This issue applies to these units. Best workaround is to use Lithium (or possibly NiMh) batteries which are largely depleted once the decimal point lights.
31 Sept 2013
Firmware release 3.1.03
- Added support for 6m special build.
- Note: for some reason this build cannot support 2.5kHz channel step due to code space restrictions from a new compiler version. 2.5kHz channel step versions will stay at version 2.1.02
23 June 2015
Firmware release 3.1.04
- Added battery level check on eeprom storage to guard against setup corruption. Factory alignment requires hardware strapping to write RF block parameters
- Added battery level check on "9" key in scout mode.
- Brownout detect set to higher level. (Sniffer now takes slightly longer to power up)
7 July 2015
Firmware release 3.1.05
- Extension of v3.1.04 to support 2K5 channel step version.

Firmware release 3.1.06
- Trial version to change "low tone mode" to modify range thresholds to get around "range-up" problems with non compliant Chinese ARDF transmitters. Not fully beta tested.
19 Aug 2016
Firmware release 4.0.00
- Changed processor from ATMEGA88 to ATMEAGA168. Version 3.x only had a few bytes left which restricted ability to add new features.
- New version for rev 4.0 hardware using SA615 IF chip. (Superseded obsolete LA8608V)
- Display brighness and low light levels now software defined and user selectable.
- IF gain and RF gain now independantly controllable. Results in more constant range to range accuracy. Previously the two were directly tied in hardware.
- "Range tone announce" "be-bop" option now replaced with Morse Code code ident support for range and mode selections. Much better for blind operators.
- New design allows more RSSI headroom to get around problems with wideband signals and non-compliant Chinese ARDF transmitters.

2 Feb 2017
Firmware release 4.0.01
- Updated high brightness level for "Rohm" brand black background LED displays.