We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: Passive Squelch Circuit  (Read 306 times)

Offline RadRoadrunner

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
    • Email Contact
    • Email
Passive Squelch Circuit
« on: March 01, 2019, 0446 UTC »
Hi, I'm currently working on a plug-in squelch solution for radios that do not have a squelch function themselves, such as many of my Tecsun radios. Looking at many of the circuit designs freely available, I have yet to find one that satisfies one of two conditions:
1) Completely passive, requires no power supply whatsoever, besides the 3.5mm input. (Maybe this is a ridiculous notion. Please tell me if it is.)

2) Swaps out its transistors for something more feasible like Diode Resistor logic, making it more suited for low power operation.

Thanks!
« Last Edit: March 01, 2019, 0543 UTC by RadRoadrunner »
Please QSL At:  sansswl@gmail.com

Radios: Tecsun PL-600, Tecsun PL-380
Antenna: 1.25m Coil Antenna + Whip Antenna on PL-600

Offline Stretchyman

  • Sr. Member
  • ****
  • Posts: 349
    • View Profile
Re: Passive Squelch Circuit
« Reply #1 on: March 05, 2019, 0925 UTC »
Had to think about this but yep it's not going to work with low level (line/1V) but may with 'Speaker' level voltages.

You're going to need some power.

Not sure why you want it to be 'Passive'?

It's going to have to break into the circuit anyway so may as well power it from there?

Or were you thinking from the headphone socket??


Str
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline Josh

  • DX Legend
  • ******
  • Posts: 2550
    • View Profile
Re: Passive Squelch Circuit
« Reply #2 on: March 05, 2019, 1801 UTC »
Military radios have a syllabic rate squelch, the king of all squelches.

http://www.naval.com/vos/
http://www.repeater-builder.com/projects/jpl-vox-sq/ssb-squelch.html
https://www.ebay.com/itm/VOS-Voice-Operated-Squelch-Audio-Muting-Kit-Form-/322351942384

The Icom 746Pro has a squelch like these and it works fairly well, wish all hf rigs had one.
Conveniently located near Vincennes Indiana.

Offline RadRoadrunner

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
    • Email Contact
    • Email
Re: Passive Squelch Circuit
« Reply #3 on: March 11, 2019, 2008 UTC »
Stretchyman, I was thinking about designing a squelch circuit that can act as a middle man between the radio's headphone jack and the listening device.

Please QSL At:  sansswl@gmail.com

Radios: Tecsun PL-600, Tecsun PL-380
Antenna: 1.25m Coil Antenna + Whip Antenna on PL-600

Offline redhat

  • DX Legend
  • ******
  • Posts: 1094
  • "It looks like green bacon in the sky"
    • View Profile
    • Email
Re: Passive Squelch Circuit
« Reply #4 on: March 11, 2019, 2018 UTC »
I'm not sure how this would be accomplished without massive distortion, or an external power source.  Most squelch circuits need access to the RSSI or AGC signal of the radio, and based on that level determine what level to open at.  Anything post AGC will be of similar level regardless of signal level, thus defeating the purpose.

+-RH
Somewhere under the stars...
WinRadio Excalibur/305 w/ a chi-town resonant loop, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Offline Stretchyman

  • Sr. Member
  • ****
  • Posts: 349
    • View Profile
Re: Passive Squelch Circuit
« Reply #5 on: March 12, 2019, 0707 UTC »
RH is right as the audio (post AGC) is 'fairly' level and therefore wont 'trigger' anything.

Str.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)