Topics

Receive FM Radio Station #bitx40

qonita.salimah@...
 

Hello everyone..

Finally my bitx, showing some audio signal, but the sound that I've got is FM Radio, at 89-90 MHz.. Any clue why this could happen?

I didn't attach the DDS.

Thankyou very much

Mike aka KC2WVB <rb5363@...>
 

Well, I don't know what you have done since you first posted having an issue with audio and perhaps microphone but it seems you have audio coming to the headphone jack from the audio amp and that's in general what you want, just not with an FM station providing the audio.

First this disclaimer - I am a math guy professionally, electronics is my hobby -so I am about to wildly guess. It seems that you are in close proximity to a strong commercial FM radio station. I wonder if the wires associated with the radio you are building are behaving like an antenna for the FM signal and allowing the FM signal to be injected into the system. Another possibility is the source of power that eventually feeds the radio is not well grounded and acting as the FM signal's antenna thus allowing the FM signal into your rig.


So, I am thinking - if you give the FM signal an easier path to follow other than through your audio amp will the issue  disappear? Maybe, so how would you do this? I am thinking try these ideas:

Make sure that the source you use for power is well grounded. If you can't do this switch to a battery for power to the rig and ground its negative terminal to a cold water pipe.
If the rig is in a metal enclosure ground the chassis too.

Good luck.

On May 28, 2018 5:55 AM, <qonita.salimah@...> wrote:

Hello everyone..

Finally my bitx, showing some audio signal, but the sound that I've got is FM Radio, at 89-90 MHz.. Any clue why this could happen?

I didn't attach the DDS.

Thankyou very much


David Arthur
 

I have the same thing happening for a local (loud) broadcast FM station. I’m 99% it’s coming in on the audio amplifier stage

On Mon, May 28, 2018 at 8:45 AM Mike aka KC2WVB <rb5363@...> wrote:
Well, I don't know what you have done since you first posted having an issue with audio and perhaps microphone but it seems you have audio coming to the headphone jack from the audio amp and that's in general what you want, just not with an FM station providing the audio.

First this disclaimer - I am a math guy professionally, electronics is my hobby -so I am about to wildly guess. It seems that you are in close proximity to a strong commercial FM radio station. I wonder if the wires associated with the radio you are building are behaving like an antenna for the FM signal and allowing the FM signal to be injected into the system. Another possibility is the source of power that eventually feeds the radio is not well grounded and acting as the FM signal's antenna thus allowing the FM signal into your rig.


So, I am thinking - if you give the FM signal an easier path to follow other than through your audio amp will the issue  disappear? Maybe, so how would you do this? I am thinking try these ideas:

Make sure that the source you use for power is well grounded. If you can't do this switch to a battery for power to the rig and ground its negative terminal to a cold water pipe.
If the rig is in a metal enclosure ground the chassis too.

Good luck.

On May 28, 2018 5:55 AM, <qonita.salimah@...> wrote:

Hello everyone..

Finally my bitx, showing some audio signal, but the sound that I've got is FM Radio, at 89-90 MHz.. Any clue why this could happen?

I didn't attach the DDS.

Thankyou very much



--
David K4DBZ
Unofficial bitx chatroom: https://discord.gg/CrHvWFc

qonita.salimah@...
 

Thank you for your reply,
Sorry if my post seems confusing.

The real thing I tried to do is building bitx40. After I soldered and configured all the component, I tried the receive system.
At first, I receive nothing just a "zzz" sound, because I use the Baofeng speaker.
After I connect to other audio speaker, I heard FM radio broadcast station.

So, it probably because the audio amp stage? The signal didn't even go through the IF amplifier? For power source, I use an adapter with 12V, 2 Amp..
Why I didn't receive the signal from another ham radio? Sorry for asking to many question

Thank you 

Mike aka KC2WVB <rb5363@...>
 

OK,
When near a strong broadcast station you can have it's signal get into an audio amplifier without it going through the expected route. I've heard commercial broadcast stations that were strong and closeby on little stand alone audio amps made from an lm386.

I know one route for the interference to get in is the wires that make up the source of power to the radio. So try a battery instead of the plug in power supply and see if that diminishes the problem.

On Mon, May 28, 2018, 11:57 AM <qonita.salimah@...> wrote:

Thank you for your reply,
Sorry if my post seems confusing.

The real thing I tried to do is building bitx40. After I soldered and configured all the component, I tried the receive system.
At first, I receive nothing just a "zzz" sound, because I use the Baofeng speaker.
After I connect to other audio speaker, I heard FM radio broadcast station.

So, it probably because the audio amp stage? The signal didn't even go through the IF amplifier? For power source, I use an adapter with 12V, 2 Amp..
Why I didn't receive the signal from another ham radio? Sorry for asking to many question

Thank you 

Mike aka KC2WVB <rb5363@...>
 

I just googled the Baofeng speaker. I see it is a combination microphone/speaker that is probably used on VHF portables.

You have to remember impedance matching is everything meaning its like the transmission between the car's engine and its rear wheels. You can have a powerful engine but without a transmission that transfers all of the engine's power to the wheels the car either stalls or wants to tear apart. Likewise, if the impedance-out of the radio does not match the impedance-in of the load, say speaker, it will not work just like the car will not move.

I don't know what kind of microphone is utilized in the Baofeng hand held Mic/speaker but if it is not electret it would fail to work with the radio as designed too.

Again, on the FM interference. If it is coming in the wires leading to the power supply then switching to a battery for power will stop the interference. Otherwise it could be a challenge getting it to stop. One thing you might consider is a metal enclosure for the radio that shields its innards from the FM signal. The hardest part is finding how the interference is getting in. Once that is accomplished the solution may be simple.

On Mon, May 28, 2018, 11:27 AM <qonita.salimah@...> wrote:

Thank you for your reply,
Sorry if my post seems confusing.

The real thing I tried to do is building bitx40. After I soldered and configured all the component, I tried the receive system.
At first, I receive nothing just a "zzz" sound, because I use the Baofeng speaker.
After I connect to other audio speaker, I heard FM radio broadcast station.

So, it probably because the audio amp stage? The signal didn't even go through the IF amplifier? For power source, I use an adapter with 12V, 2 Amp..

Thank you 

Jerry Gaffke
 

I just searched this forum for Baofeng, got dozens of hits from people using it with *Bitx* rigs.
Here's one of many threads:  https://groups.io/g/BITX20/topic/4554574

The microphone element is electret, just like the element suppied with the *Bitx*.
If the Baofeng element doesn't sound quite right, could patch in the one supplied with the rig.
Such a tiny speaker is bound to be a compromise, I wouldn't expect much from that.
The PTT switch arrangement looks pretty good, that alone is well worth $3.
Some of the Baofeng mikes on ebay are apparently even cheaper cones, there are some differences.

There is a bunch of stuff in that mike you don't need.
I'd replace the cable, using one with 3 wires for ground, ptt, and mike into a 3.5mm phone jack.
The ground goes to the ground side of the mike, also to one side of the ptt switch.
And of course the mike wire goes to the other side of the mike, the ptt wire goes to the other side of the ptt switch.



On Mon, May 28, 2018 at 01:33 pm, Mike aka KC2WVB wrote:
I just googled the Baofeng speaker. I see it is a combination microphone/speaker that is probably used on VHF portables.
 

Mike aka KC2WVB <rb5363@...>
 

Well, it shows that if you research the Baofeng microphone/speaker it can be made to work with the rig. It also pays to be careful for the little speaker/microphones that you can buy for handheld 2 meter radios often have to have what radio they are being purchased for specified because of impedance issues. I have one where I specified the radio it was for and MFJ sent the wrong one so yes, it works but you have to turn the volume full up to hear it and yell into the microphone to be heard.

Personally, I run the audio from the speaker/headphone jack of the radio into the line-in RCA inputs meant for audio visual input found on the back of my stereo. The volume is plenty adequate and the bass output is superior to a small speaker.

On the microphone I am hearing that the gain of the amp it feeds which is a 2n3904 transistor based amp with a voltage divider biasing network is too weak. Some of the guys soldered in a resistor parallel to Re in the biasing network to increase the gain with great results. I don't have steady enough hands to make that fix so I am going to see if I can increase the signal into the base of the 2n3904 with an outboard pre-amp for the Mic. I think that I will simulate the circuitry before I assemble anything and I am in no hurry because my listening time far out weighs my PTT time.

Needless to say I am glad you have audio now and again I don't know what to tell you above what I have to solve your FM interference issue.


On Mon, May 28, 2018, 7:02 PM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:
I just searched this forum for Baofeng, got dozens of hits from people using it with *Bitx* rigs.
Here's one of many threads:  https://groups.io/g/BITX20/topic/4554574

The microphone element is electret, just like the element suppied with the *Bitx*.
If the Baofeng element doesn't sound quite right, could patch in the one supplied with the rig.
Such a tiny speaker is bound to be a compromise, I wouldn't expect much from that.
The PTT switch arrangement looks pretty good, that alone is well worth $3.
Some of the Baofeng mikes on ebay are apparently even cheaper cones, there are some differences.

There is a bunch of stuff in that mike you don't need.
I'd replace the cable, using one with 3 wires for ground, ptt, and mike into a 3.5mm phone jack.
The ground goes to the ground side of the mike, also to one side of the ptt switch.
And of course the mike wire goes to the other side of the mike, the ptt wire goes to the other side of the ptt switch.



On Mon, May 28, 2018 at 01:33 pm, Mike aka KC2WVB wrote:
I just googled the Baofeng speaker. I see it is a combination microphone/speaker that is probably used on VHF portables.
 

qonita.salimah@...
 

Thank you for your reply.
I also tried to make the wire connectivity in Baofeng mic and speaker according to the post in this threads : https://groups.io/g/BITX20/topic/4554574

The PTT switch in Baofeng work perfectly, but not for the speaker and mic. I will try to make the modification like you've said.

But what about the RX system? It still not receiving any ham radio signal. I tried to follow the troubleshooting that Asshar Farhan made in https://www.youtube.com/watch?v=R8G8XAwq38A&t=456s
Here is what I've got

C107 (C13 in my schematic) makes noise when it's touched with cable.
C33 (C6) is also make noise
C31 (C9) is also make noise, but not very loud.
C53 (C5) I didn't hear any noise at all. 
C21 (C24) I didn't hear any noise at all. 

I also didn't hear any noise if the cable touched the antenna connector.

I made my own BPF and LPF because I want to make 8.456 MHz frequency as the center frequency.

Here is the schematic. To tell you the truth I didn't buy the kit from Asshar Farhan. I built in from scratch, like from the schematic, the PCB layout, and bought all the component by myself. I come from Indonesia. And this is for my final project. Still learning and this is my first time building a radio

Thank you very much for helping me

 

First check if your VFO and BFO are working correctly.

Put an oscilloscope to C100 and see if you have a good voltage of your BFO frequency. Check the frequency of
BFO with a frequency counter.

Put oscilloscope to Q7 collector and check the amplitude and frequency.

Building from scratch is good and you learn a lot more!

When you reply please do not leave the whole message as groups.io removes it and I dont know to whom
you are replying to. Please delete/remove all the unwanted text and leave the lines that you are sending
a reply.

Raj

At 29/05/2018, you wrote:

I made my own BPF and LPF because I want to make 8.456 MHz frequency as the center frequency.

Here is the schematic. To tell you the truth I didn't buy the kit from Asshar Farhan. I built in from scratch, like from the schematic, the PCB layout, and bought all the component by myself. I come from Indonesia. And this is for my final project. Still learning and this is my first time building a radio

Thank you very much for helping me

Mike aka KC2WVB <rb5363@...>
 

What ever the outcome you did great! Most people did not build from scratch and source their own parts.

Too bad my lack of knowing your language may make it difficult to be of much help. However, let me ask this simple question. What are you using for an antenna? If it is not something like a dipole cut to 40 meters or 20 meters or 80 meters...then you may hear nothing but noise and interference on the receiver. 
My version of the radio came to life when I connected a 40 meter dipole to the rig. The 40 meter dipole is two wires each 32.5 feet long connected at one end to either the center conductor or shield of 50 ohm coax cable. The other end of the coax runs to the rig. The feed point of this antenna, I.e. where the wires connect to the coax, is ideally elevated to 1/4 wave length in height or roughly 33 feet.
I could not elevate my 40 meter dipole so I built a compromise dipole. The issue that occurs when the dipole is not elevated to 1/4 wavelength is that the feedpoint impedance becomes terribly low to the point it is far short of 50 ohms and nearly nothing can then be heard. So, I made my dipole as a folded dipole that uses two wires on each leg. This raises the feedpoint impedance of the antenna to such an extent that it is actually spot on 50 ohms when it is barely off the ground. This of course changes the radiation pattern but not enough that I don't still pick up Dave, on or about 7.145 MHz, out of England whenever he keys up.

AgIn good luck, hope you get the bugs worked out.

On Tue, May 29, 2018, 4:12 AM <qonita.salimah@...> wrote:

Thank you for your reply.
I also tried to make the wire connectivity in Baofeng mic and speaker according to the post in this threads : https://groups.io/g/BITX20/topic/4554574

The PTT switch in Baofeng work perfectly, but not for the speaker and mic. I will try to make the modification like you've said.

But what about the RX system? It still not receiving any ham radio signal. I tried to follow the troubleshooting that Asshar Farhan made in https://www.youtube.com/watch?v=R8G8XAwq38A&t=456s
Here is what I've got

C107 (C13 in my schematic) makes noise when it's touched with cable.
C33 (C6) is also make noise
C31 (C9) is also make noise, but not very loud.
C53 (C5) I didn't hear any noise at all. 
C21 (C24) I didn't hear any noise at all. 

I also didn't hear any noise if the cable touched the antenna connector.

I made my own BPF and LPF because I want to make 8.456 MHz frequency as the center frequency.

Here is the schematic. To tell you the truth I didn't buy the kit from Asshar Farhan. I built in from scratch, like from the schematic, the PCB layout, and bought all the component by myself. I come from Indonesia. And this is for my final project. Still learning and this is my first time building a radio

Thank you very much for helping me

Mike aka KC2WVB <rb5363@...>
 

Incidentally, what is your call sign?? I want to listen for you once you have the bugs worked out and the rig up and running.


On Tue, May 29, 2018, 7:54 AM Mike aka KC2WVB <rb5363@...> wrote:
What ever the outcome you did great! Most people did not build from scratch and source their own parts.

Too bad my lack of knowing your language may make it difficult to be of much help. However, let me ask this simple question. What are you using for an antenna? If it is not something like a dipole cut to 40 meters or 20 meters or 80 meters...then you may hear nothing but noise and interference on the receiver. 
My version of the radio came to life when I connected a 40 meter dipole to the rig. The 40 meter dipole is two wires each 32.5 feet long connected at one end to either the center conductor or shield of 50 ohm coax cable. The other end of the coax runs to the rig. The feed point of this antenna, I.e. where the wires connect to the coax, is ideally elevated to 1/4 wave length in height or roughly 33 feet.
I could not elevate my 40 meter dipole so I built a compromise dipole. The issue that occurs when the dipole is not elevated to 1/4 wavelength is that the feedpoint impedance becomes terribly low to the point it is far short of 50 ohms and nearly nothing can then be heard. So, I made my dipole as a folded dipole that uses two wires on each leg. This raises the feedpoint impedance of the antenna to such an extent that it is actually spot on 50 ohms when it is barely off the ground. This of course changes the radiation pattern but not enough that I don't still pick up Dave, on or about 7.145 MHz, out of England whenever he keys up.

AgIn good luck, hope you get the bugs worked out.

On Tue, May 29, 2018, 4:12 AM <qonita.salimah@...> wrote:

Thank you for your reply.
I also tried to make the wire connectivity in Baofeng mic and speaker according to the post in this threads : https://groups.io/g/BITX20/topic/4554574

The PTT switch in Baofeng work perfectly, but not for the speaker and mic. I will try to make the modification like you've said.

But what about the RX system? It still not receiving any ham radio signal. I tried to follow the troubleshooting that Asshar Farhan made in https://www.youtube.com/watch?v=R8G8XAwq38A&t=456s
Here is what I've got

C107 (C13 in my schematic) makes noise when it's touched with cable.
C33 (C6) is also make noise
C31 (C9) is also make noise, but not very loud.
C53 (C5) I didn't hear any noise at all. 
C21 (C24) I didn't hear any noise at all. 

I also didn't hear any noise if the cable touched the antenna connector.

I made my own BPF and LPF because I want to make 8.456 MHz frequency as the center frequency.

Here is the schematic. To tell you the truth I didn't buy the kit from Asshar Farhan. I built in from scratch, like from the schematic, the PCB layout, and bought all the component by myself. I come from Indonesia. And this is for my final project. Still learning and this is my first time building a radio

Thank you very much for helping me

Mike aka KC2WVB <rb5363@...>
 

Since your building your rig from scratch this will be easy for you to accomplish.

Once everything is working. Modify the amp that the microphone feeds by doing this:

"I lhave changed just R63 so now it is 24 ohm (I added 2 ordinary 100ohms resistors in parallel) as suggested. I confirm it increases the average power to the right level given the stock mic element."

This is the fix people are using to increase the gain. Its the one that I can't do because my hands are not steady enough to pull it off. Hence I am going the route of adding a pre-amp which I intend to make variable. Apparently without this change the audio being mixed into the RF is too weak and one needs to speak rather loudly to be heard on receive.

Good luck and I am rooting for your success.

On Tue, May 29, 2018, 8:07 AM Mike aka KC2WVB <rb5363@...> wrote:
Incidentally, what is your call sign?? I want to listen for you once you have the bugs worked out and the rig up and running.

On Tue, May 29, 2018, 7:54 AM Mike aka KC2WVB <rb5363@...> wrote:
What ever the outcome you did great! Most people did not build from scratch and source their own parts.

Too bad my lack of knowing your language may make it difficult to be of much help. However, let me ask this simple question. What are you using for an antenna? If it is not something like a dipole cut to 40 meters or 20 meters or 80 meters...then you may hear nothing but noise and interference on the receiver. 
My version of the radio came to life when I connected a 40 meter dipole to the rig. The 40 meter dipole is two wires each 32.5 feet long connected at one end to either the center conductor or shield of 50 ohm coax cable. The other end of the coax runs to the rig. The feed point of this antenna, I.e. where the wires connect to the coax, is ideally elevated to 1/4 wave length in height or roughly 33 feet.
I could not elevate my 40 meter dipole so I built a compromise dipole. The issue that occurs when the dipole is not elevated to 1/4 wavelength is that the feedpoint impedance becomes terribly low to the point it is far short of 50 ohms and nearly nothing can then be heard. So, I made my dipole as a folded dipole that uses two wires on each leg. This raises the feedpoint impedance of the antenna to such an extent that it is actually spot on 50 ohms when it is barely off the ground. This of course changes the radiation pattern but not enough that I don't still pick up Dave, on or about 7.145 MHz, out of England whenever he keys up.

AgIn good luck, hope you get the bugs worked out.

On Tue, May 29, 2018, 4:12 AM <qonita.salimah@...> wrote:

Thank you for your reply.
I also tried to make the wire connectivity in Baofeng mic and speaker according to the post in this threads : https://groups.io/g/BITX20/topic/4554574

The PTT switch in Baofeng work perfectly, but not for the speaker and mic. I will try to make the modification like you've said.

But what about the RX system? It still not receiving any ham radio signal. I tried to follow the troubleshooting that Asshar Farhan made in https://www.youtube.com/watch?v=R8G8XAwq38A&t=456s
Here is what I've got

C107 (C13 in my schematic) makes noise when it's touched with cable.
C33 (C6) is also make noise
C31 (C9) is also make noise, but not very loud.
C53 (C5) I didn't hear any noise at all. 
C21 (C24) I didn't hear any noise at all. 

I also didn't hear any noise if the cable touched the antenna connector.

I made my own BPF and LPF because I want to make 8.456 MHz frequency as the center frequency.

Here is the schematic. To tell you the truth I didn't buy the kit from Asshar Farhan. I built in from scratch, like from the schematic, the PCB layout, and bought all the component by myself. I come from Indonesia. And this is for my final project. Still learning and this is my first time building a radio

Thank you very much for helping me

Jerry Gaffke
 

If you don't have a scope, perhaps you have or can borrow a receiver that can tune those oscillators in.
The oscillators are an unmodulated carrier, so best if the receiver is in SSB mode so you can year a tone.
But an AM receiver can be used, it should go quiet as you get near the signal.

If you have a 12mhz crystal filter for the IF, the BFO should be 2 or 3 khz below 12mhz.

Jerry



On Tue, May 29, 2018 at 01:34 am, Raj vu2zap wrote:
First check if your VFO and BFO are working correctly.

Put an oscilloscope to C100 and see if you have a good voltage of your BFO frequency. Check the frequency of
BFO with a frequency counter.

Mike aka KC2WVB <rb5363@...>
 

Sorry, I forgot you probably had yet to tune the IF section. It did not dawn on me that might be the issue.

I have not scratch built SSB radios with IF sections but I did build one AM receiver which used IF sections as part of its structure. I did not have the test equipment at the time and I kind of remember that I  tuned the IF section by ear using a stand alone IC oscillator that put out a 1000 KHz signal. 

The receiver used analog tuning. Once I had the variable cap adjusted then it was simply a matter of backing off on each adustment, finding the 1000KHz signal and then working my way sequentially through the adjustment points until I had my 1000KHz signal sounding its best.

The SSB receiver is a bit more complex so I am uncertain if anything from above is of help but its nice to remember that when a dependable receive signal is needed for tuning purposes those easy to set up IC oscillators are easy to come by.


On Tue, May 29, 2018, 1:13 PM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:
If you don't have a scope, perhaps you have or can borrow a receiver that can tune those oscillators in.
The oscillators are an unmodulated carrier, so best if the receiver is in SSB mode so you can year a tone.
But an AM receiver can be used, it should go quiet as you get near the signal.

If you have a 12mhz crystal filter for the IF, the BFO should be 2 or 3 khz below 12mhz.

Jerry



On Tue, May 29, 2018 at 01:34 am, Raj vu2zap wrote:
First check if your VFO and BFO are working correctly.

Put an oscilloscope to C100 and see if you have a good voltage of your BFO frequency. Check the frequency of
BFO with a frequency counter.

ajparent1/kb1gmx
 

Just a wild guess....

There is enough pickup die to leads to hear the station at the input of the 45mhz mixer and 
its second harmonic 90mhz plus DBMs make very good phase detectors (that means
they also can detect frequency changes).  I'd bet you are not far from the station.

IF the input low pass filter is right this should not happen but if you have wire loops 
you can get around the back of the filter.  Shielding is your friend.

FYI I grew up in the shadow of a AM BC station and everything I did picked it up
even ma bells telephones!

Allison