Distortion / Loud sound when trying to record from BC898T

[Marauder]

Hi everyone,
I have been trying to get audio from my bearcat to my PC using the LINE output instead of the EXT SP headphone output so I can record/broadcast and listen at the same time and with the line output into my PC, I am noticing it is very hard to hear and cuts off the first and last parts of the audio when the scanner comes across a channel, or even if I lock to one.

When a unit keys up it makes a big pop or loud sound that 'drowns out' the first part of the message for about 1.5 seconds and makes the messages unreadable. Same when they unkey from the mic or someone replies, Takes about 1.5 secs to ungarble and hear a voice.

Please note this is very different from the headphone output, everything is crystal clear on that end. Now I have made sure my audio levels on my receiving PC are not too high or overpowering. I lowered my input device setting to less than 50 percent and nothing changes except the voices are now even harder to hear. Any ideas, ladies and gents?

 

[doctordialtone]

Any ideas, ladies and gents?

You need to use an isolation Transformer.

This one has worked for others here on Radio Reference.

That should fix it!

 

[Marauder]

You need to use an isolation Transformer.

This one has worked for others here on Radio Reference.

That should fix it!

Well... Easy fix I suppose! haha thanks for letting me know about this, what does it do? Basically amp it and give it enough power to come thru without clipping?

Or the opposite and reduce and suppress the distortion?

 

[doctordialtone]

Basically amp it and give it enough power to come thru without clipping?

It isolates the input and output so the grounds aren't tied together.

Google is your friend.

 

[Marauder]

It isolates the input and output so the grounds aren't tied together.

Google is your friend.

Thank you!

 

[pro92b]

The problems with the BC898T line output have been known since 2006. The link below details a modification by James Kondel to get rid of the thumps when the squelch opens and closes.

Wayback Machine

web.archive.org

Further comments on this issue were published by n9ewo and are archived at the link below.

Uniden Bearcat BC898T Scanner Receiver - N9EWO Review -

In addition to what Kondel published about eliminating the thump, n9ewo mentioned a long delay in line out passing audio when the squelch opens. Removing an electrolytic capacitor eliminates the delay. The schematic below shows the changes. The transistors can be almost any small-signal NPN type.

The line out shares a common ground with the rest of the radio so an isolation transformer will not be of benefit in eliminating the problems.

 

[Marauder]

The problems with the BC898T line output have been known since 2006. The link below details a modification by James Kondel to get rid of the thumps when the squelch opens and closes.

Wayback Machine

web.archive.org

Further comments on this issue were published by n9ewo and are archived at the link below.

Uniden Bearcat BC898T Scanner Receiver - N9EWO Review -

In addition to what Kondel published about eliminating the thump, n9ewo mentioned a long delay in line out passing audio when the squelch opens. Removing an electrolytic capacitor eliminates the delay. The schematic below shows the changes. The transistors can be almost any small-signal NPN type.

The line out shares a common ground with the rest of the radio so an isolation transformer will not be of benefit in eliminating the problems.

View attachment 86472

Well I guess I will be canceling that amazon order. The thump and delay between squelch perfectly describes the issues I have on my 898t

Thanks much for the in-depth explanation and diagram, I will give it a try

 

[tvengr]

When a unit keys up it makes a big pop or loud sound that 'drowns out' the first part of the message for about 1.5 seconds and makes the messages unreadable. Same when they unkey from the mic or someone replies, Takes about 1.5 secs to ungarble and hear a voice.

The Record output is line level. If the input level on your computer is set to microphone level, you are overloading the input on your computer. Change the input to line level. It would be a good idea to use the isolation transformer.

 

[pro92b]

The Line Out in the BC898T can be adjusted by setting RT7 to reduce the output voltage.

The line out driver IC is an ordinary class AB power amplifier, not a bridged output. There is no need for an isolation transformer.

The screenshot below shows a test I ran with my BC898T without an isolation transformer and there is no distortion on the scope display.