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Installation 

Power Connection

:

 

Many modern radios p5v or +8v or +9v at the 

microphone connector – this will power the HF3 directly from the mic socket 

with a single cable to suit your radio (e.g. RJ45 to RJ45).

 

Radios that do not pDC power at the mic socket can still be used - 

in these cases 12 volts can be applied separately to the HF3’s “12V DC”  

external power connector (note that 12v DC power filtering and suitable 

fusing is recommended). Note that the 12V DC connector is NOT protected 

against reverse polarity. 

IMPORTANT:

 

The external 12V DC connector is only for radios that DO 

NOT provide DC power via the microphone.  If you use this external power 

connector, then you must not apply power via the microphone cable as well. 

 

 
How It Works 

The HF3 incorporates the following circuit building-blocks:

 

Voltage regulator:

 

The electronics inside the HF3 runs at 3.3 volts and a 

LP2950 low-dropout regulator provides 3.3v internally and accommodates a 

wide input supply-voltage range of up to 30 Volts DC. Normally, the 

microphone socket on most radios will provide from 5 to 10 volts.

 

Mic preamp and audio equalisation:

 

An MCP602 dual low-noise 

Operational Amplifier provides an audio mic gain adjustment, a low-

frequency boost/cut and high-frequency boost/cut using a Baxandall bass 

and treble tone control circuit.

 

Microcontroller:

 

The low-power microcontroller provides all the timing and 

switching functions associated with: 

 

Detecting a momentary push on the TX switch to start transmission 

 

Illumination of the LED indicator 

 

Activation of the radio’s transmit line (PTT) 

 

Operation of the built-in piezo buzzer to warn impending timeout 

Summary of Contents for SAFE SPEAK HF3

Page 1: ...th 2020 Firmware Revision 7 Radio Communication Labs Trading as Ralph Parkhurst and Associates ABN 31 841 821 803 Ringwood North VIC 3134 AUSTRALIA Telephone 61 0 401 718 265 Email admin radcomlabs com Web www radcomlabs com Copyright 2020 by Radio Communication Laboratories ALL RIGHTS RESERVED ...

Page 2: ...bed in the preceding paragraphs We will not be held liable to you or any other party for any damages that result from the failure of this product Damages excluded include but are not limited to the following lost profits lost savings lost data damage to other equipment and incidental or consequential damages arising from the use or inability to use this product In no event will Radio Communication...

Page 3: ...ght dangerous The HF3 aims to help make operating a two way radio safer by minimising the time your hand is off the steering wheel It also helps to overcome the issue of microphone placement and the inherent acoustic problems within a car and lets the radio easily switch from receive to transmit and back again Why Hands Free Safety keep hands on the steering wheel whilst using your radio Improved ...

Page 4: ... piezo indication to warn of impending timeout o 10 seconds before timeout and o 5 seconds before timeout with a different sound and flash rate Electret microphone included Mounting bracket included No adjustments or modification required inside your radio Designed to work with just about every radio transceiver Works with radios that provide 5v 8v or 9v DC via the mic pins or instead via a 12 vol...

Page 5: ...one cable as well How It Works The HF3 incorporates the following circuit building blocks Voltage regulator The electronics inside the HF3 runs at 3 3 volts and a LP2950 low dropout regulator provides 3 3v internally and accommodates a wide input supply voltage range of up to 30 Volts DC Normally the microphone socket on most radios will provide from 5 to 10 volts Mic preamp and audio equalisation...

Page 6: ...onal DC filtering is required RADIO Provides interface between the HF3 and the radio transceiver RJ45 8P8C modular socket 1 DC Power 5v to 10v typically 2 Not used 3 Not used 4 PTT Transmit 5 Ground 6 Mic Audio 7 Ground 8 Not used PTT Input socket allows an external PTT momentary switch to be utilised 2 5mm mono tip sleeve socket Tip Connect to Ground to transmit Sleeve Ground Use a normally open ...

Page 7: ...ance between all three and what works for you With care you should be able to achieve great results with only a minimal increase in road noise please note that depending on how far your microphone is placed from your mouth and how loud your vehicle is some increased degree of background road noise is inevitable the trick is to make these adjustments carefully to prevent background road noise from ...

Page 8: ...ifier that is clockwise rotation from centre will BOOST the Highs or the Lows whilst anticlockwise rotation from the centre will CUT the Highs and Lows 5 Adjusting the BASS and TREBLE equalisation trim pots will affect the overall gain so you will find a degree of interaction is needed with the MIC GAIN trim pot to compensate Up to 12dB BOOST and CUT is provided by the two equalisation trim pots J...

Page 9: ... faster and the piezo makes a different sound If you want to change the timeout from the default 2 minute period please proceed as follows a Turn your radio off which also turns the HF3 off when powered via the Mic cable b Whilst pressing and holding down the TX button on the HF3 power on the radio This will power up the HF3 and invoke the configuration mode where you can adjust the timeout value ...

Page 10: ...hen approaching timeout Dimensions 90mm x 66mm x 30mm overall Weight 200 grams incl mounting bracket Temperature 0 to 55 C operating Included Mounting bracket electret microphone screwdriver user manual FAQ Q Are there circumstances when the HF3 should not be used A In our opinion yes there are two if you have a very noisy vehicle truck etc or you like to drive with the window down you are probabl...

Page 11: ...io s transmit audio is soft will the HF3 improve it A Possibly In principle it s best to get your FM radio set up correctly first with the standard microphone making sure that radio s FM deviation and internal mic gain are correctly adjusted first the HF3 will NOT correct an under deviating FM signal that MUST be set within the radio However you will have much wider control over microphone gain an...

Page 12: ...12 SCHEMATIC G02082019 Copyright by Radio Communication Laboratories trading as Ralph Parkhurst and Associates ABN 31 841 821 803 ...

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