BCD436HP/BCD536HP: BCD536 Interference

[radar614]

My BCD536 is causing interference to my Kenwood TK-690H that I am using for CHP frequencies. When there is a call on the Kenwood and my BCD536 is on all I get is noise that sounds like static. Is there any way that this could be fixed so that the two radios don't cause problems to each other?

 

[KevinC]

How is the 536 powered?

 

[radar614]

How is the 536 powered?

Both are on 12 v

 

[KevinC]

Both are on 12 v

Ok. No idea then, but I’m assuming CHP low band?

 

[radar614]

Ok. No idea then, but I’m assuming CHP low band?

Correct!

 

[KevinC]

Correct!

Or they sharing the same antenna?

 

[K4EET]

Both are on 12 v

What is/are the source(s) of the 12 VDC? Wall wart on the 536, linear or switching power supply (need manufacturer and model number), etc. Also, when you get static on the CHP frequency, is the 536 scanning or locked on a certain frequency? Does the noise ever occur when the 536 does not have an antenna connected? Finally, how close together are the two radios and have you tried moving them further apart? And WRT @KevinC’s last question, if the radios are sharing the same antenna, how are they connected?

 

[radar614]

12vdc from truck batteries, static when scanning ( didn't think to stop the 536 from scanning, will try), at the same time I will disconnect the antenna. The 536 is on the dash as well as the 690 control head, the 690 is under the seat and they have separate antennas.

 

[radar614]

Or they sharing the same antenna?

Separate antennas.

 

[radar614]

12vdc from truck batteries, static when scanning ( didn't think to stop the 536 from scanning, will try), at the same time I will disconnect the antenna. The 536 is on the dash as well as the 690 control head, the 690 is under the seat and they have separate antennas.

Sane thing when not scanning, same when antenna is disconnected. Tomorrow I'll try moving the 690 control head away from the scanner.

 

[K4EET]

@radar614, by any chance, do you have a 200 MHz oscilloscope to do a little “probing” around on some of the wires?

 

[Ubbe]

Sane thing when not scanning, same when antenna is disconnected. Tomorrow I'll try moving the 690 control head away from the scanner.

If I remember correctly the BCD536 have extra shielding plates inside it. Take the cover off and re-seat those plates to get a good ground and then when the cover are back on you can try and run a ground wire from its chassi to ground in your vehicles chassi.

What frequency are affected? It could be that a BCD536 are using a 45MHz IF and maybe a final IF of 450 or 455KHz, that would make an oscillator be that much offset from 45.0MHz.

As it is a constant interference regardless if scanning and switching frequencies it has to be an oscillator with a constant frequency, either to the CPU or the reference oscillator or IF oscillator for the radio frequencies. You would want to have good shielding grounds and also look in the Kenwood if its shielding looks okay, as it isn't entering through its antenna. I would suspect the remote head kit to have the cable input decoupled from RF at both ends, as it is LOW-VHF that would easily transmit into the cable. So I would be surprised if any weak RF signal are following that cable into the radio unit.

/Ubbe

 

[radar614]

If I remember correctly the BCD536 have extra shielding plates inside it. Take the cover off and re-seat those plates to get a good ground and then when the cover are back on you can try and run a ground wire from its chassi to ground in your vehicles chassi.

What frequency are affected? It could be that a BCD536 are using a 45MHz IF and maybe a final IF of 450 or 455KHz, that would make an oscillator be that much offset from 45.0MHz.

As it is a constant interference regardless if scanning and switching frequencies it has to be an oscillator with a constant frequency, either to the CPU or the reference oscillator or IF oscillator for the radio frequencies. You would want to have good shielding grounds and also look in the Kenwood if its shielding looks okay, as it isn't entering through its antenna. I would suspect the remote head kit to have the cable input decoupled from RF at both ends, as it is LOW-VHF that would easily transmit into the cable. So I would be surprised if any weak RF signal are following that cable into the ra

Thank you for the info, The frequencies in the radio are spread from 39 mhz to 45 mhz and the radio is only being used as a monitor/scanner for the highway patrol channels.

 

[Ubbe]

The frequencies in the radio are spread from 39 mhz to 45 mhz

So you get interference from the BCD536 on all frequencies between those two frequency limits?

/Ubbe

 

[radar614]

I found the problem and it wasn't anything I thought could be doing it. I have a DVR camera attached to my rear view mirror and the failing power supply to the camera was causing the interference. When I noticed the interference was gone I also noticed that the DVR wasn't working. When I attached a new power supply to the camera there was no more interference. Thanks for all your help out there.