BCD436HP: UHF Reception Issues due to Noise from Battery Compartment

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bearcat

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This is all done in a portable configuration no external antennas. I probed the case of the 436 and found an excessive amount of noise coming from the bottom rear of the radio. I am not an engineer so I have no idea what kind of noise it is. I applied some RF shielding tape to the inside of the battery case lid. To my surprise the normal hiss/static/noise what ever you wish to call it diminished drastically. I have tested this for a week and the findings are all positive. There are some UHF RF link transmitters in my area that I could not hear. Now I hear them. If I remove the battery cover the signal goes away. Some weaker signals contain a large amount of hiss on the audio, that is hiss is now gone. If I remove the battery cover while they are transmitting the hiss returns. There are some P25 UHF control channels that I could not hear, but now I do. Over all the radio is not quite as good as the 396 but it is a tremendous improvement over what it was. I do not know how many db of noise reduction my tape provides. I have had it for years. I do know that aluminum foil does not work. This was tested on several 436s and the results were the same on each one. I would be interested in how this works for others.
 

pro92b

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What is RF shielding tape? Copper tape? Can you post a photo of the battery cover as modified? Seems like it shouldn't do much unless the shielding tape is grounded somehow.
 

bearcat

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What is RF shielding tape? Copper tape? Can you post a photo of the battery cover as modified? Seems like it shouldn't do much unless the shielding tape is grounded somehow.
My tape is silver sticky on one side shiny silver on the other. I could post a picture but frankly I do not know how. It is not grounded to anything. It can do a lot if it is not letting "noise" into the radio (or out of)
 
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k3fs

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I had tried aluminum foil on the back of the battery door, without much change. I had also tried some aluminum foil shielding under the batteries and that actually made things worse. Tried some better shielding on the back of the battery case, and that seems to work as you said. There are a few stations with not much of a difference on VHF high. But on UHF there is an improvement. I can hear a difference while receiving a signal, and sliding the battery door off and on. Radio in same position with the same antenna, and signal is weaker, or has more hiss with the battery door off. There was no difference with battery cover on or off without the shielding on the battery cover.
 

gonefishn1

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RF shielding tape is indeed copper. Copper shielding prevents EMI/RFI and its used on most electronic devices and emitters in one place or another. Usually surrounding the RF section and LO's of radios. ITs quite a fascinating topic and certainly makes a difference with spurious noise.
 
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darunimal

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What kind of batteries are both of you using or is it straight fed through a power cable and cube.
 

bearcat

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What kind of batteries are both of you using or is it straight fed through a power cable and cube.
I was using NiMH, before I answered you. I put in a set of Durcell Alkalines and the results are the same.
 

gonefishn1

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I was using NiMH, before I answered you. I put in a set of Durcell Alkalines and the results are the same.
The results would be the same. The battery is not causing the EMI/RFI leakage but the shielding is keeping the guts of your radio from leaking EMI/RFI onto your RF input (antenna).

Good job in finding this and for passing it along.
 

bearcat

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So, you're putting the tape on the back (inside) of the battery door?
Yes it is some tape I was given years ago to shield the noise coming from a cheap power supply (which is long gone) but I still had the tape.
 
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darunimal

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Hence why the antenna placed away from the receiver works so well.
 

902

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Interesting!

Most of my stuff is 800 where I currently am, but I go into some parts with UHF trunking, so better sensitivity could be useful.

For the sake of applying some kind of shield to a plastic surface, a metallic tape like HVAC metal tape should do fine. Copper tape is usually for the times where there is contact between surfaces, or where larger amounts of RF might be encountered (like a full duplex product). Industry would apply a thin "metalization" coating inside for shielding.

I haven't taken my 436 apart, but I'd be careful of watching for internal components that might short out.

Wonder if someone with a 3D printer could print up a sleeve that the radio fits into that could have the shielding applied to it. That might be the best bet for a non-invasive solution.

In the meantime, I'm going to try it out! Thank you!
 

bearcat

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Interesting!

Most of my stuff is 800 where I currently am, but I go into some parts with UHF trunking, so better sensitivity could be useful.

For the sake of applying some kind of shield to a plastic surface, a metallic tape like HVAC metal tape should do fine. Copper tape is usually for the times where there is contact between surfaces, or where larger amounts of RF might be encountered (like a full duplex product). Industry would apply a thin "metalization" coating inside for shielding.

I haven't taken my 436 apart, but I'd be careful of watching for internal components that might short out.

Wonder if someone with a 3D printer could print up a sleeve that the radio fits into that could have the shielding applied to it. That might be the best bet for a non-invasive solution.

In the meantime, I'm going to try it out! Thank you!
There is plenty of clearance for the tape, but you are correct watch to make sure nothing is going to contact the battery leads. Believe it or not, but putting the tape on the outside of the battery cover did not yield the same results. I would think it should have.
 

902

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There is plenty of clearance for the tape, but you are correct watch to make sure nothing is going to contact the battery leads. Believe it or not, but putting the tape on the outside of the battery cover did not yield the same results. I would think it should have.
I'm guessing this is from the data bus that reads from and writes to the memory card. It's probably very positional. Wishing I had a spectrum analyzer with a sniffer to quantify where the hot spots are. Did you use copper or aluminum tape, and did you take out the battery retention foam pad?

Wondering if this would work:MG Super Shield Conductive Nickel Coating - 12 Oz. - MG-841-340g. It's kinda pricey, but it can do >29 dB of shielding in the UHF band. Just not sure if it would be appropriate. It would also be permanent.
 

Jay911

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I applied some RF shielding tape to the inside of the battery case lid. To my surprise the normal hiss/static/noise what ever you wish to call it diminished drastically. I have tested this for a week and the findings are all positive. There are some UHF RF link transmitters in my area that I could not hear. Now I hear them. If I remove the battery cover the signal goes away.
You're saying that shielding on the "inside" of the battery door (the part where one side faces the batteries and the other side faces the "outside air" around the scanner) helps reception?

I'm willing to give it a shot, especially considering I haven't been seeing the issues you have. It'll make for a good "control" or comparison.

The one time I do have demonstrable interference/attenuation is when the radio is plugged in to a USB power source while it's receiving. Similar to what you say with regards to the "hissing" - if I plug in the USB charging cable, a noticeable hiss/degradation in reception occurs, but only on a fairly narrow chunk of VHF in the 155 MHz range. All other bands appear unaffected.

Just out of curiosity, have you tried putting shielding on the "other side" of the batteries, i.e. in between the batteries and the SD card?
 

bearcat

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I'm guessing this is from the data bus that reads from and writes to the memory card. It's probably very positional. Wishing I had a spectrum analyzer with a sniffer to quantify where the hot spots are. Did you use copper or aluminum tape, and did you take out the battery retention foam pad?

Wondering if this would work:MG Super Shield Conductive Nickel Coating - 12 Oz. - MG-841-340g. It's kinda pricey, but it can do >29 dB of shielding in the UHF band. Just not sure if it would be appropriate. It would also be permanent.
I used aluminum tape (because I had it) I went over the foam pad. I would love to see the results with some shielding tape that has a known DB reduction. I have no idea what mine is rated at. When I put the shielding over the area where the batteries lay it actually got worse. I also tried behind the batteries and the battery lid at the same time and that was worse.
 
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