Foxhunt VK3YNG Sniffer 4 User manual

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 1
VK3YNGFoxhuntSnifferInstruction Manual
(Updated version for version 2.2 hardware***)
The VK3YNG FoxhuntSniffer is a speciallydesigned synthesised VHF direction
findingreceiver covering 120MHz and 144MHz bands.
The receiver is designed for quicklyfindingthe direction of beacons or hidden
transmitters. Anything fromdistantweak signals to veryclose “sniffing” of
transmitters runningmany watts of output power can be pin pointedaccurately
without suffering“overload”problems that plague other designs. Fullauto-ranging
operation allows theoperator to quicklyand intuitively locate the sourceofa signal
without twiddlingknobs or watchingmeters. Theoperator isfreed to concentrateon
more importantthings such as negotiatingterrain or readingmaps.
The unit is also available in afullytested Board levelformatfor thosewho wishto
integratethe unit into other equipment or build their own housing.
***Note: A number of features havechanged since earlierversions ofthe sniffer
werereleased. This manualreflects operation ofversion 2.2 hardware and cannotbe
used for earlier versions ofthe MK4 sniffer. For acopies of earlier sniffermanuals
please refer to theVK3YNG foxhuntweb site (see theend ofthis manual).

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 2
Introduction....................................................................................................................3
Auto Power Down..........................................................................................................4
LowBatteryIndication..................................................................................................4
DisplayBrightness.........................................................................................................4
ReducedFunctionalitymode:........................................................................................4
Quick Button Reference:................................................................................................5
AlternativeKeyFunctions:............................................................................................5
Detailed Button Operation.............................................................................................6
Mode/Power switch: ..................................................................................................6
Power On: ..............................................................................................................6
ModeSelection:.....................................................................................................6
FM Mute:...............................................................................................................6
Power Off:..............................................................................................................6
Memories...................................................................................................................7
Recall functions. ....................................................................................................7
Store functions.......................................................................................................7
SyncButton................................................................................................................8
ARDF Sync:...........................................................................................................8
Band Scan: .............................................................................................................8
Other functions: .....................................................................................................8
D-Setbutton...............................................................................................................9
Uptimeindication: .................................................................................................9
RelativeBatteryVoltage indication:......................................................................9
Firmwareversion indication:...............................................................................10
Volume Control .......................................................................................................10
Range Control..........................................................................................................10
Peak Hold Mode ..................................................................................................10
Peak rangememory..............................................................................................10
Frequency Entry.......................................................................................................11
Configuring the Sniffer................................................................................................12
Tone (RSSI) Filtering: .............................................................................................12
Minimum filtering(1):.........................................................................................12
MediumFiltering(2): ..........................................................................................12
Maximum Filtering(3): .......................................................................................12
Peak Extend modeFiltering(6):..........................................................................12
ARDF/Scan Mode:...................................................................................................12
ARDF Mode(4):..................................................................................................12
Scan Ready Mode(5): .........................................................................................12
Reduced FunctionalityMode:..................................................................................13
MaximisingBatteryLife..............................................................................................13
Sample antennadesigns...............................................................................................14
Specifications:..............................................................................................................15
Links: ...........................................................................................................................15

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 3
Introduction
The VK3YNG sniffer is designed to allow quick, easyand accurate determination of
thedirection of a transmitted signal in either the 120-123MHz or 143-150MHz bands.
The sniffer provides enough sensitivityto determine the direction of asignal from
manykilometres or miles away. This is useful for ARDF or Radio Sport use. Italso
provides enough attenuation to accurately determinethe direction of signals rightup
to thesource of the signal withoutsufferingfrom overload or compression effects.
Attenuation (signal reduction) is provided automaticallyin steps of approximately
15dB each time a particular signal strength threshold is reached. Thenumber of 15dB
steps of attenuationis shown on an LED display. For example, a displayvalue of zero
indicates maximum sensitivity, whereavalue of 9indicates a verystrongsignal that
requires approximately135dB of attenuation.
Signal strength indication is providedbyan audibletone that increases in frequency
(pitch) with increasingsignallevel. This is donebecausethe humanear is a much
more sensitive to changes in pitchthan sound level. Thereis also no inertiaor
overshoot problems as tend to occur with signal meters. A specialsoftware algorithm
ensures that thereceivedsignal strength tone does not suffer from “compression”
effects that occur at higher signal levels with somedesigns.

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 4
AutoPower Down
The sniffer willautomatically power down if either of the followingtwo conditions
aremet:
1) There has been no keypressed for at least 10 minutes.
2) There has been no “upward” progression in range for at least10minutes.
The sniffer willgive fiveshortbeeps just beforethe unit powers down.
LowBatteryIndication
The sniffer functions accuratelyto supplyvoltages down to approximately2.7 volts.
Below this the accuracybecomes compromised or the sniffer maypower itself down.
When power has dropped to 2.7 volts or lower, thedisplaydecimal point is enabled to
warn theuser that batteries areinneed of replacement.
DisplayBrightness
A high efficiencySevenSegmentRed LED is usedfor therange display. It has two
brightness settings, one for daytime useand asignificantlyreduced brightness level
for nightuse. Alight sensor locatedimmediatelyabovethe displayautomatically
determines thebrightnesslevel.
Reduced Functionalitymode:
This mode maybeusefulfor children or first time operators. Itallows the sniffer to be
used in its mostbasic format and hides all programmability options from the user.
This mode is veryuseful for scout foxhuntingfor example. For this reason, many
refer to this modeas “Scout Mode”.

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 5
Quick Button Reference:
The followingtable gives quick index to key functions in both normalandreduced
functionalitymodes.
Button
Operationin Normal mode Operationin reduced
functionality mode
1 Recall channel 1 (Hold to store frequency/mode) Recall onlychannel1
2 Recall channel 2 (Hold to store frequency/mode) Recall onlychannel2
3 Recall channel 3 (Hold to store frequency/mode) Recall onlychannel3
4 Recall channel 4 (Hold to store frequency/mode) Recall onlychannel4
5 Recall channel 5 (Hold to store frequency/mode) Recall onlychannel5
6 Recall channel 6 (Hold to store frequency/mode) Recall onlychannel6
7 Band Scan or ARDF mode Startof cycle
Synchronisation function. No function
8 Range down DelaySet/Display. 1 to 5 seconds.
0=peak hold mode. (7-9 are special functions) Batterylevel
9 Volume Down No function
0 Volume Up No function
R Manual Rangeset/disable No function
F FrequencyEntry(4 digits follow) No function
M Power/Audio ModeSelect (Tone/AM/FM, Hold
for power off) Power On/Off only (instant power off)
AlternativeKeyFunctions:
The default operation mode of the sniffercan be reconfigured byholdingdown
certain keys whilepoweringup the unit. Thesniffer will maintain this operation mode
for subsequentpower up/down cycles.
Button Displayduring
power-up Function if pressed during power-up
1 n Filter “A”, Minimum Tonefiltering. (fastestresponse)
2 o Filter “B”, MediumTone filtering
3 P Filter “C”, Maximum Tone filtering(slowestresponse)
4 A ARDF mode. Synchronised at power-up. Sync key is
used to re-sync thetransmitter cycle.
5 S Scan mode. Sync key is used to scan for strongest signal
between frequency stored in channels 5and 6.
6 J Filter “D”, Tone Extend Mode. Used for veryshort
duration signals. (New function in V2.1 firmware)
7 H Normal operation. Selects normal tone range and
disables reduced functionalitymode if set.
8 L Low-Tone mode(RSSI tones atquarter frequency.
Resolution slightly reducedatlow tone frequencies)
F S Reduced key functionality mode(“scout” mode)
R t Toggle (Enable/disable) auto rangechange
announcementtones

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 6
Detailed Button Operation
Mode/Power switch:
Power On:
Pressingthis button once powers on the unitto the frequencyand mode stored in
memory channel 1.
Mode Selection:
Pressingthis button momentarilywhile theunit is powered up cycles the unitthrough
its operatingmodes and brieflydisplays the selection on the display. Themodes cycle
through in the followingsequence:“A” – AM reception, “U” – Unmuted FM
reception, “F” – MutedFM reception and “t” – Signal strength Tone. Thecyclethen
repeats. When headphones are used, onechannel is always set to givesignal strength
tone, while the other channel follows the selectedmode. This is usefulfor hunting
different continuous carrier transmissions where thetransmitters’ identification is
given usingeither AM of FM modulation.
FMMute:
The Muted FM mode offers apseudo FM mutefunction to muteall receiver audio
when thesniffer is notreceivingasignal. This is a signal based (rather thannoise
based) mutethat activates whenever thereceivedsignal is below thelowerrange
threshold on ranges 1 upward and is always activeon range 0.
Power Off:
Pressingand holdingtheMode button for greater than 1 secondwill power down the
unit. In reduced functionalitymode, the unit will power off immediately when the
Mode button is pressed. Themode switchoperates onlyas a simple on/off switch in
reducedfunctionalitymode.
M

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 7
through
Memories
Buttons 1 through 6allow storing and recallingof memory modes and frequencies.
Recall functions.
Pressinganyof the buttons 1 through 6innormaloperation modewill recallthe
frequencyand mode stored in non-volatile memory. In normal operation mode, the
displaywilldisplaythelast 4 digits of the selected memories frequencyin kilohertz.
For example, a stored frequencyof 147.425MHz will flash up thesequence “7 4 2 5”.
The first two (100 and 10) megahertz digits areinferred byfirstentered digit as per
thefollowingtable:
Setting of “MHz” digit Band selection
0, 1, 2 120-122.995MHz
3 through 9 143-149.995MHz
The recalled frequencyis not displayed in reducedfunctionalitymode.
Storefunctions
Pressingand holdingany of buttons 1 through 6 will resultin the selected frequency
andmode beingstored inthe selected memory. The button must be pressed and held
until two short beeps areheard in succession. This confirms that thedata has been
committed to memory.
The Store function is disabled in reduced functionalitymode.
1
6

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 8
Sync Button
ARDF Sync:
This facilityis used to synchronisethe receiver for useininternationalstyle (ARDF)
foxhuntingfor a one-minute cycle, five-transmitter system.
In ARDF modethis timer is automatically synchronized when the receiveris switched
on. Threeshortbeeps are generated as confirmation of this mode.
PressingtheSyncbutton re-synchronises this timer. Threeshortbeeps are given to
confirmthis button has beenpressed. Thesync button should be pressed at thestart of
transmitter one’s cycle.
At 50 seconds into thecycle, the sniffer willgeneratethree short beeps giving10
seconds warningthatthe current transmitter’s cycle is abouttoend. If the sniffer is
currentlyreceivingat range1 or lower, at four seconds beforethe completion of the
current transmitter cycle the sniffer broadcasts anumber of beeps correspondingto
thenumber of thetransmitter in the cyclewhich is about to commence. The pitch of
these beeps is set slightly lower than the “50-second”beeps. Thedisplayalso briefly
flashes the number ofthe nexttransmitter.
Band Scan:
When ARDF modeis notselected, the “7”keyperforms a basicband scan operation
wherethe sniffer hunts for thehighest signalbetween the two frequencies stored in
channellocations 5 and 6. Thehighest signal found is stored inchannel 4. The scan
will ignoreanysignals within approximately 10KHz of the frequency stored for
channel1 and the signalmustbedetectableat range2 or higher to bestored.
This operation takes some time to complete, especiallyif thereis large frequency
difference between channels 5 and 6. The scan function works bestfor continuous
signals and maynotproperlydetect intermittent transmissions. Channel5 must be
lower in frequencythan channel6 andbothfrequencies mustbewithin thesame band
(i.e. 120MHz or 140MHz)
Other functions:
In ARDF mode, if a rangedown delay(d-Set) of zero is selected and thesniffer is not
currentlyconfigured for manual ranging, the sniffer willautomatically selectrange
zero at thestart of the nexttransmitters’ cycle regardless of the current signal
strength.
Holdingthe “7”keyduringpower-up cancelsthe Low RSSI Tonemode and the
ReducedKeyFunctionalitymode. In this mode the signal strength tones function
normallyand the maximum signal strength pitchis 8KHz. This mode is set as the
factory default.
This keyis disabled in reducedfunctionality mode.
7

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 9
D-Set button
Rangingup on the snifferhappens automatically with minimaldelay. To implement
short term peak detection, there is an intentionaldelaybefore the sniffer ranges down.
This delay is programmablebetween 1 and5 seconds usingthe D-Setbutton. For
beginners, avaluebetween 3 and5 seconds is recommended. For more advanced
users, 1 or 2seconds gives better results. When huntingintermittentand veryshort
durationtransmissions such as those used on wildlife, 5 seconds or “peak hold” mode
(seebelow) is recommended. The factorydefault is 2 seconds.
Tosetthe rangedown delay, press the“D-Set” button. The displaywill respond by
displayingthe letter “d”. Pressing buttons 0 through 5 will then set andstorethe new
range down delay.
PressingtheD-set(7) button twicewill brieflydisplaythe current range down delay
in seconds. Thedisplaythen reverts to displayingthe current range.
Setting a range down delay of zero disables down ranging.In this casethe sniffer
operates ina“peak hold” modeand down rangingis disabled. Manual rangingis
disabledand pressingthe “range”button willresetthecurrentpeak hold range to
zero. This mode is usefulwhen huntingextremelyintermittent signals suchas wildlife
or model aircraftbeacons.
Holdingthe “D-Set” keyduring power-up causes the sniffer to operate in lower tone
RSSI mode. This modemayprove usefulto thosewho havedifficultyhearinghigher
audio frequencies. In this modethe signalstrengthtonefrequenciesare divided by4.
The top tonepitch is limited to about2KHz and resolution becomes slightlylimited at
thelowest tonefrequencies. (Note: this mode has no effect onthe pitch of supervisory
beep and tonefrequencies)
This keyis disabled in reducedfunctionalitymode.
Uptimeindication:
Pressingthe“D-Set” button then pressing “7” will display4 digits indicatingthe
number of hours andminutes since thereceiver was powered up. This can be useful
for ARDF events where theuser mayhave forgottentosynchronise their watch.
RelativeBatteryVoltageindication:
Pressingthe“D-Set” button then pressing “9” will displaytwo digits giving an
indication of therelativebatterycapacityin percentageterms. 99% indicates a full
batterywhile 0% indicates the point where sniffer operation is significantly
compromised. The sniffer maypower itself off before reaching0%.
8

VK3YNGSniffer 4 Instruction Manual (for V2.2 hardware)
© 2004, Bryan Ackerly, VK3YNG Rev2.2a Page 10
Firmwareversion indication:
Pressingthe“D-Set” button and thenpressingthe “F” button will display4 digits
which indicatethe installed firmware version.
Volume Control
During normal operation, the “9” and“0” buttons allow the settingof volume. The
displaybrieflyshows thenewlevel and reverts to displaying the current rangewhen
thebutton is released. These buttons are disabledin reduced functionalitymode.
Range Control
Normallythe sniffer automaticallyselects thebestrange for the currentlyreceived
signal. In somesituations it maybe necessaryto range the sniffer manually. Therange
control button canbeused for this purpose. This button also controlsanumber of
other features dependingon the mode selected.
In auto-rangingmode, pressingthis button brieflydisplays theletter “r”in the display,
andthen the displayreverts to displayingthe currentrange. Pressinganydigit then
manuallyselects therange. The displaybrieflydisplays “r”followedbythe selected
range. The sniffer remains in manualranging mode until defeated by pressingthe “R”
button a second time. This re-enables auto-ranging.
Holdingthis keyduringpower-up toggles thestateof the“rangetone announcement”
flag. When this flagis set, the sniffer generates a “be-bop” tonesequencewhenever
thesniffer ranges up or down. The frequencyof thetones gives theoperatoraudible
indication of thecurrentrange and thedirection of thechange. When this flagis
cleared, range changes happen without announcement.
This keyis disabled in reducedfunctionalitymode.
Peak Hold Mode
This range button also resets thepeak rangehold function if the down range delay (D-
set) is set to zero. In peak hold mode, manual rangingis disabled.
Peak range memory
If the range button is pressed twice in succession, the display will brieflyshowthe
maximum range the sniffer has achieved sincepower up or thelast successful
frequencychange.
In ARDF mode, (see Sync button section) the peak rangevalue is automaticallyreset
at30 seconds into the current transmitter cycle. This is very usefulifthereis a need to
check whatrange thesniffer got to just beforethe previous transmitter finished its
cycle.
This function is not available when Peak Holdmode(dSet=0) is selected.
R
9 0