Bob132
Member
Got it. Thank you for your input.
BCD436HP/BCD536HP: UHF Reception Issues due to Noise from Battery Compartment
- Thread starter bearcat
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I put my trx 1 on 460Mhz and squelch all the way down, from across the room all the way to the trx1 right in the battery compartment of the 436 the background noise didn't change.
I will see if it sounds different when receiving a signal, either way just trying to add some data.
I thought that was a valid test. Maybe I was wrong. I do remember that it would totally wipe out a station with a weak signal on the second radio. I cannot test it any longer as I now have the cap in both of my 436s.
I'll have to pop mine open see what board it has and if anything is missing. Haven't noticed any issues minus a vhf dmr channel, while a system radio programmed to a NM system on vhf was decoding fine the 436 would decode partial then not decode, either noise or as if it wasn't decoding the format. First figured antenna but went all out on that then same result. FWIW the 436 would mute the enc end of whIle the radio decoded fine when secure was used. The tower is a ways down the way but with those mentioning the capacitor issue and other it has got me wondering. Bah. I'll have to pop it open sometime within the next few days. I could do the repair myself no doubt but interesting some shipped with the components while others not same board revision.
BOBRR
Member
Opening unit up ?
Hi,
Guess I'll bite the bullet and take a look and see if the Cap and Resistor are there.
Can someone please point me to the right page here that shows how to do it ?
How easy ?
Potential for damage, etc. ?
Also, the pix(s) that show the resistor and cap: what page ?
Thanks,
Bob
Hi,
Guess I'll bite the bullet and take a look and see if the Cap and Resistor are there.
Can someone please point me to the right page here that shows how to do it ?
How easy ?
Potential for damage, etc. ?
Also, the pix(s) that show the resistor and cap: what page ?
Thanks,
Bob
BOBRR
Member
Warr. ?
Hi
Forgot to ask:
Does opening unit up void (theoretically)
the warranty. ?
Bob
Hi
Forgot to ask:
Does opening unit up void (theoretically)
the warranty. ?
Bob
I do not know if anyone has posted pictures on how to open the unit.
Page 37 msg#727 is a picture of the board with the cap
Page 33 msg#654 is a picture of the board without the cap
I am sure in Uniden's eyes if you open the unit you void the warranty, however if you do not break anything then it is a mute point.
Legally: any access to interior of the scanner by anyone other than authorized technicians or repair persons authorized by Uniden voids warranty unless otherwise stated explicitly in aforementioned warranty. In English. .. Yes you void the warranty if you open the case.
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It would be nice if there were a simple test that people could do to tell if they have the noise problem, and then send the scanner to Uniden and demand warranty service.
Is there a version of shielding people can do safely with household items like aluminum foil and scotch tape just to see if they have the problem? Maybe cover the batteries with a sheet of paper as an insulator and stick some foil inside the battery cover?
prcguy
Is there a version of shielding people can do safely with household items like aluminum foil and scotch tape just to see if they have the problem? Maybe cover the batteries with a sheet of paper as an insulator and stick some foil inside the battery cover?
prcguy
Aluminum foil will not work. There is no simple test unless you have an SDR receiver.
This fix will do nothing for what you are already hearing. It has to do with what you may not be receiving at all. I only became aware of the issue because my 396XT was receiving certain freqs that the 436 could not hear.
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Summary of All BCD436 RF noise issues.
I noticed early on that the 436 could not receive UHF signals in fringe areas. The 396XT had no problem receiving these same signals. I started to experiment and found that a significant amount of RF noise was present near the middle battery positive side. These measurements were taken with an AirSpy Mini, a stubby antenna and SpectrumSpy software set to 200 mhz range with 460 mhz being the center freq. The noise floor on the scope would increase 15 - 18 db when the SDR antenna was placed near the battery compartment. The noise is not a factor if you use an external antenna or remove the batteries and run off of USB power.
July 2016
At this point I started to experiment with shielding. After many different trials and suggestions from others on this list it was determined that a battery case door sprayed with 10 coats of RF/EMI spray and a strip of aluminium shielding over the foam pad was best. Shielding the door with aluminum shielding tape (not aluminum foil) was a close second, while 6 layers of copper shielding was last. They all work to some degree and in all cases the shielding MUST go over the foam pad. I knew there had to be more to this but had to way to find the root cause.
March 2017
I purchased a second 436 and did these same measurements on the new unit. There was no noise present in the battery compartment of the new unit. I decided to see if I compared the circuit boards of the two units that I might get lucky. I noticed very quickly on the display board that a capacitor was now installed near the negative side of the top battery. The circuit board is marked TDO where the capacitor pads are located. My old unit had solder pads but no capacitor. I did some research and found that common filtering capacitors are .01uf and .1uf. I started with a .01uf capacitor and all was good the noise was gone. Maybe a .1uf would be better I do not know.
To recap:
1. You cannot tell by S/N if you have the capacitor, clock issue or backlight issue.
2. Opening the unit will void the warranty
3. The only way to know if you have the capacitor is to look. See #2
4. Soldering in the microscopic capacitor requires expert soldering skills. See #2
This is everything I know about the issue condensed into one page. Many have challenged these findings and many have seen different results. It is my conclusion that if the capacitor is missing the RF noise is present. Please direct those with questions to this page and message number. It will save on repeating messages and give them the total story.
Direct questions to Page 39 msg# 772
I noticed early on that the 436 could not receive UHF signals in fringe areas. The 396XT had no problem receiving these same signals. I started to experiment and found that a significant amount of RF noise was present near the middle battery positive side. These measurements were taken with an AirSpy Mini, a stubby antenna and SpectrumSpy software set to 200 mhz range with 460 mhz being the center freq. The noise floor on the scope would increase 15 - 18 db when the SDR antenna was placed near the battery compartment. The noise is not a factor if you use an external antenna or remove the batteries and run off of USB power.
July 2016
At this point I started to experiment with shielding. After many different trials and suggestions from others on this list it was determined that a battery case door sprayed with 10 coats of RF/EMI spray and a strip of aluminium shielding over the foam pad was best. Shielding the door with aluminum shielding tape (not aluminum foil) was a close second, while 6 layers of copper shielding was last. They all work to some degree and in all cases the shielding MUST go over the foam pad. I knew there had to be more to this but had to way to find the root cause.
March 2017
I purchased a second 436 and did these same measurements on the new unit. There was no noise present in the battery compartment of the new unit. I decided to see if I compared the circuit boards of the two units that I might get lucky. I noticed very quickly on the display board that a capacitor was now installed near the negative side of the top battery. The circuit board is marked TDO where the capacitor pads are located. My old unit had solder pads but no capacitor. I did some research and found that common filtering capacitors are .01uf and .1uf. I started with a .01uf capacitor and all was good the noise was gone. Maybe a .1uf would be better I do not know.
To recap:
1. You cannot tell by S/N if you have the capacitor, clock issue or backlight issue.
2. Opening the unit will void the warranty
3. The only way to know if you have the capacitor is to look. See #2
4. Soldering in the microscopic capacitor requires expert soldering skills. See #2
This is everything I know about the issue condensed into one page. Many have challenged these findings and many have seen different results. It is my conclusion that if the capacitor is missing the RF noise is present. Please direct those with questions to this page and message number. It will save on repeating messages and give them the total story.
Direct questions to Page 39 msg# 772
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ChrisABQ
...
Foil DOES work in my situation. It's the difference of receiving traffic or not, it's that simple. To tell other people that foil does not work is incorrect. Everyones situation is different. I will tell you that I will not buy a second unit just to test whether a change has been made in another unit.
Which "RF/EMI spray" did you use? Do you have a link to it? I have two BCD436HP's, one is 3800 series and the new one is 68005xxx series, both are having issues with UHF receive. The 3800 series has been to Uniden for everything, the 68005xxx one is brand new from Amazon.com last week. I've yet to open it, but that's going to happen this weekend to see the differences between the two boards. The 3800 series one that has been back to Uniden for everything has the pad available but the capacitor is absent. I'll report back on the 68005xxx one later this week. Thanks for all the information and updates.
There is no difference between copper or aluminum foil when discussing the same size and placement for shielding. The only problem with aluminum is it might be more difficult to electrically connect to something because you can't use conventional solder.
If there is a certain size of foil in a certain place that makes contact with something that noticeably reduces the noise, then it should be repeatable by anyone as a test for the noise problem.
prcguy
If there is a certain size of foil in a certain place that makes contact with something that noticeably reduces the noise, then it should be repeatable by anyone as a test for the noise problem.
prcguy
https://redirect.viglink.com/?forma...j12ea8q8-8405bb0a-e4ad-42ec-a95c-263e2de2d986
Link to the spray I used. It may be cheaper to install the caps at this point.
Link to the spray I used. It may be cheaper to install the caps at this point.
There is no soldering involved. The shielding just lines the inside of the battery case door. It prevents the RF noise from leaving that area and getting to the antenna. There are differences in the way materials shield RF, but in this application if appears that you have more than one option.
Those are my results only. That is exactly why I said others have seen different results. I think a picture of your door and the brand of aluminum foil you used and how you attached it to the door. You probably can help a bunch of folks out.
I did not buy another one to see what they changed. I just wanted a second radio. I even had another shielded door ready to go. The lack of noise actually caught me by surprise. I am happy that we now know they made the change, but I never expected it.
k3fs
Member
The best test is to tune another scanner to a weak UHF signal. One with a constant carrier such as a control channel or input link is the best. A very busy weak signal is also usable.
Turn on the 436, and have it scanning. It does not need to be receiving a signal. While the other scanner is receiving the weak UHF signal move the 436 slowly closer the the antenna of the other radio. You will notice an increase in static, and in some cases the signal will totally drop out. Move the 436 away and the signal comes back, and the noise decreases. There will be no effect on strong or very strong signals. Very weak, and weak signals are best for testing.
You may hear some noise moving another scanner, next to the antenna of another one in that manner. With the 436 the noise is significantly increased, and starts from a greater distance. In some cases, bringing the 436 within 4 inches of the other radio was enough to totally eliminate the station I was receiving.
Thanks to Bearcat who has put in a good amount of effort to track this issue down, and for sharing his results.
Turn on the 436, and have it scanning. It does not need to be receiving a signal. While the other scanner is receiving the weak UHF signal move the 436 slowly closer the the antenna of the other radio. You will notice an increase in static, and in some cases the signal will totally drop out. Move the 436 away and the signal comes back, and the noise decreases. There will be no effect on strong or very strong signals. Very weak, and weak signals are best for testing.
You may hear some noise moving another scanner, next to the antenna of another one in that manner. With the 436 the noise is significantly increased, and starts from a greater distance. In some cases, bringing the 436 within 4 inches of the other radio was enough to totally eliminate the station I was receiving.
Thanks to Bearcat who has put in a good amount of effort to track this issue down, and for sharing his results.
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