BCD436HP/BCD536HP: UHF Reception Issues due to Noise from Battery Compartment

[jeffm77]

I intended that message for Mule1075, as he stated he doesn't have the problem or even heard of the problem.

 

[bearcat]

Kevin,

Can you post some pictures of your quick tape job, for curiosity sake?

Greg

You are seeing exactly what I found. However in my case aluminum foil did not work. Keep us posted.

Sorry I see you said aluminum tape. That it was I used because I had it. I think the folks with copper may see even better results.

 

[bearcat]

Has any of the testing been done with aftermarket batteries compared to stock batteries?


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My stock batteries are end of life. I have Nuons in mine. I tried Duracell Alkalines no change.

 

[SCPD]

Now to decide on whether copper tape or conductive coating is the better choice.

The coating route is probably best, easier to apply and if done right, more durable.

Anne-britt

 

[KevinC]

I really feel as though I'm missing something and this "fix" is actually a placebo, but I just tried another frequency (analog).

Without the cover lots of noise and barely able to understand, with the cover almost full quieting.

 

[bearcat]

I did a quick measurement with my spectrum analyzer. Around the middle battery the noise floor will rise about 20 dB in the UHF range (it might in other areas also, but I didn't test elsewhere).

You can actually watch the radio power up/down as the noise floor will rise before the "on" beep and stay elevated after the "off" beep.

I didn't test any shielding, so I can't comment on that.

I do not have an SA but thought I would give the Airspy a try. I probed the rear case with a rubber duck attached to the Airspy. I also see 20db increase in the noise floor with the cover off. When I put the shielded cover back on. I still see about 5 - 8 db of noise. So a better tape like copper EMI/RFI may yield even better results. I realized that my method is not very scientific but it does show the change

 

[DataSquid]

I wonder how many people who don't suffer this issue have swapped the stock SD card (for one with better shielding?), stock batteries (for ones that accidentally provide better shielding?), or have turned off the "always on" recording feature.

If I had that spray stuff (and this problem) I'd be tempted to mask off the SD card contacts and give it a good dosing. My guess is the interference is from a harmonic of those cells constantly being written during recording.

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[gonefishn1]

I wonder how many people who don't suffer this issue have swapped the stock SD card (for one with better shielding?), stock batteries (for ones that accidentally provide better shielding?), or have turned off the "always on" recording feature.

If I had that spray stuff (and this problem) I'd be tempted to mask off the SD card contacts and give it a good dosing. My guess is the interference is from a harmonic of those cells constantly being written during recording.

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Nope that's not the source of the noise. The EMI/RFI is traveling into the battery compartment via the battery connections.

 

[darunimal]

With all the dust and debris too, it has free roam to the screen, I noticed that when I had it apart.

 

[bearcat]

I wonder how many people who don't suffer this issue have swapped the stock SD card (for one with better shielding?), stock batteries (for ones that accidentally provide better shielding?), or have turned off the "always on" recording feature.

If I had that spray stuff (and this problem) I'd be tempted to mask off the SD card contacts and give it a good dosing. My guess is the interference is from a harmonic of those cells constantly being written during recording.

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Some people have posted they do not have the issue, but then I come to find they use external antennas. That will solve the problem also. Moving the antenna away from the radio. I turned off the recording and the noise floor still goes up 20db at the center battery when probed. I shielded the center battery and with no joy. Your points regarding SD cards with better shielding is not something I could comment on. I do have two different brands and they both do it. Shielding the opening for the SD card did not help.

 

[bearcat]

I really feel as though I'm missing something and this "fix" is actually a placebo, but I just tried another frequency (analog).

Without the cover lots of noise and barely able to understand, with the cover almost full quieting.

Exactly what I have found. I am hearing tons of things that I never could hear on 436 before this. My comparison was always the 396 or 330 which heard them fine. Looking forward to getting some tape designed for this purpose.

 

[gonefishn1]

The source of noise would not come from the low level digital 1's and 0's being written to the SD card.

 

[bearcat]

Jay since you do not have the problem. Do you have and RTL or Airspy or something to see if your noise floor goes up near the center battery? I put SDR sharp on 460.000 and turned up the gain to where I see signals. Then probe the center battery with a metal antenna on the end of the SDR. Might be interesting since you do not see what some of us see.

 

[Jay911]

Jay since you do not have the problem. Do you have and RTL or Airspy or something to see if your noise floor goes up near the center battery? I put SDR sharp on 460.000 and turned up the gain to where I see signals. Then probe the center battery with a metal antenna on the end of the SDR. Might be interesting since you do not see what some of us see.

I'll see if I can do that tomorrow.

 

[darunimal]

http://forums.radioreference.com/uniden-tech-support/298342-bcd436hp-poor-vhf-performance.html

http://forums.radioreference.com/uniden-thread-archives/283358-bcd436hp-discriminator-teardown.html

 

[DataSquid]

The source of noise would not come from the low level digital 1's and 0's being written to the SD card.

I wouldn't write it off that quickly. See section 4.4 of http://www.ti.com/litv/pdf/snoa382 and consider the harmonics those step functions produce. Ugly.

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[bearcat]

436 Improved UHF Reception

Just for the heck of it I probed the 396xt and found not even the slightest of db increase on SDR sharp in the UHF range. I really believe if we can find the proper shielding or component causing it. We can achieve the same UHF performance as the 396XT

 

[gonefishn1]

darunamil was kind enough to field strip his radio so we can all view the PCB. It seems the main radio guts are very well shielded. So for the average user, shielding the battery compartment from EMI/RFI leakage is probably the best we can do to prevent the noise from hitting the antenna, which is the end result everyone is looking for.

 

[gonefishn1]

Datasquid: Thank you for the good reading material. Remember that harmonics are always lower amplitude than the fundamental freq that creates them and the engineers always attenuate and filter them out. So my thought is the power supply or clocking circuits are noisey (leaking EMI). At this point it doesn't really matter where its coming from as much as it matters to contain it. So the more shielding added the better.

 

[bearcat]

darunamil was kind enough to field strip his radio so we can all view the PCB. It seems the main radio guts are very well shielded. So for the average user, shielding the battery compartment from EMI/RFI leakage is probably the best we can do to prevent the noise from hitting the antenna, which is the end result everyone is looking for.

Exactly what we need. He seems to have a vast knowledge of the components. He may be able to identify the issue. I really think we are on to something here.