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Bitx 20 microphone problem

Nigel G7luo
 

Hi I purchased a built bitx20 from ebay a couple of years ago, which I have been using as a portable station on holidays. The microphone that was supplied with it was an old CB hand microphone. This has worked well but when I got the bitx out of storage to use this summer the microphone will not key the radio. The radio still receives as usual but will not key to transmit. I have dug out one of my old CB radio's ans the microphone will key this radio. Does anyone have any idea what could be going on with the bitx. None of the microphones I have to hand will work with it. Any ideas suggestions would be much appreciated.

Thanks Nigel G7luo

Evan Hand
 

I would suggest that you verify that the BITX20 will go into TX by jumpering the pins on the mic/PTT jack on the radio temporarily.  If that works, then the problem is in the mic.  If it does not go into TX then you have an issue in the radio.

Looking at the schematic, I see that the PTT line is keying K1.  If the problem is in the radio, then I would first trace the wires and be sure the jumper did not get disconnected in the move.  If the wiring is OK, then you will probably need to change out K1.  This all assumes that the Raduino is not used in the PTT line.  There are mods that added CW and other functions through the Nano on the Raduino add on from the original.

I do not have either a BITX20 nor a 40, so the above are just suggestions.  Details of the rig, including any modifications done would be needed to provide any other suggestions.  Since it worked before, was put into storage, and now does not work, my best guess is the wiring was dislodged.

73
Evan
AC9TU 

Nigel G7luo
 

Hi Evan
            Thank you for your reply I took the case of the Bitx this afternoon on the circuit board it says Hendrick's QRP Bitx version 1.3. The mic socket has two green wires and two black wires going to it. Both black wires go to pin 4 one green wire to pin1 one green wire to pin 2. one green wire goes to PTT TS and one black wire goes to PTT GRD on the circuit board. one green wire and one black wire goes to mike in on circuit board. If I short out pin 1 and pin 2 the radio clicks but nothing else happens. If I short out pin 1 and pin 4 the radio clicks the green RX led turns red and there is 888 displayed on the read out. All the wires look secure.

Thanks Nigel

On Monday, 18 May 2020, 15:17:30 BST, Evan Hand <elhandjr@...> wrote:


I would suggest that you verify that the BITX20 will go into TX by jumpering the pins on the mic/PTT jack on the radio temporarily.  If that works, then the problem is in the mic.  If it does not go into TX then you have an issue in the radio.

Looking at the schematic, I see that the PTT line is keying K1.  If the problem is in the radio, then I would first trace the wires and be sure the jumper did not get disconnected in the move.  If the wiring is OK, then you will probably need to change out K1.  This all assumes that the Raduino is not used in the PTT line.  There are mods that added CW and other functions through the Nano on the Raduino add on from the original.

I do not have either a BITX20 nor a 40, so the above are just suggestions.  Details of the rig, including any modifications done would be needed to provide any other suggestions.  Since it worked before, was put into storage, and now does not work, my best guess is the wiring was dislodged.

73
Evan
AC9TU 

Evan Hand
 

The Green wire going to the PTT TS (Push To Talk Transmit Switch)  is the PTT line.  It goes to ground (PTT GRD) when the PTT switch is pushed on the mic, assuming all is working correctly.  So when you short that Green wire from the PTT TS to ground the rig should go into transmit mode (which it seems like you described).  That would point to the mic wiring as the issue.

One thing that concerns me is the 888 on the display.  Was that the way it worked before?  I would not have expected that.  That is a possible indication that when the rig goes into transmit mode, it is pulling the power supply voltage down.  That could be caused by a power supply that does not have enough current capability or a short somewhere in the transmit circuit.  I cannot find any information on the display circuit.  I would assume that it is a frequency counter of some sort, or the rig was modified to have a microcontroller of some kind, maybe similar to the uBITX Raduino.

Here is the documentation that I found online:
http://www.qrpkits.com/files/BITX20_Assembly_Manual.pdf

Based on this, you have a variant of the HF Signals version.  This means there are fewer people with direct experience with this version.  It is close enough that the mic and PTT switching still look similar, using a replay that the ground connection is completed when the mic switch is pressed.

Not sure how much more I can help, it is all guesswork for me beyond this.

Good Luck and 73
Evan
AC9TU

Nigel G7luo
 

Hi Evan
             Thank you for you advice and help, I will persevere and see what I can come up with.

thanks Nigel

On Monday, 18 May 2020, 18:35:36 BST, Evan Hand <elhandjr@...> wrote:


The Green wire going to the PTT TS (Push To Talk Transmit Switch)  is the PTT line.  It goes to ground (PTT GRD) when the PTT switch is pushed on the mic, assuming all is working correctly.  So when you short that Green wire from the PTT TS to ground the rig should go into transmit mode (which it seems like you described).  That would point to the mic wiring as the issue.

One thing that concerns me is the 888 on the display.  Was that the way it worked before?  I would not have expected that.  That is a possible indication that when the rig goes into transmit mode, it is pulling the power supply voltage down.  That could be caused by a power supply that does not have enough current capability or a short somewhere in the transmit circuit.  I cannot find any information on the display circuit.  I would assume that it is a frequency counter of some sort, or the rig was modified to have a microcontroller of some kind, maybe similar to the uBITX Raduino.

Here is the documentation that I found online:
http://www.qrpkits.com/files/BITX20_Assembly_Manual.pdf

Based on this, you have a variant of the HF Signals version.  This means there are fewer people with direct experience with this version.  It is close enough that the mic and PTT switching still look similar, using a replay that the ground connection is completed when the mic switch is pressed.

Not sure how much more I can help, it is all guesswork for me beyond this.

Good Luck and 73
Evan
AC9TU