UPMan: 20dB Attneuation

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KD4UXQ

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UPMan,

For as long as I can remember, it seems that the standard attenuation option on scanners is 20dB and remains so. This amount of attenuation is mostly useless in helping with interference issues. 10db would be much more useful. What would be extremely useful would be at least 3 levels as options. 6dB, 9dB and 15 dB. It is really helpful that it is possible to option attenuation by site, but at 20dB it is enough to kill reception instead of helping with interference. One can just use a lower gain antenna, but of course that affects everything.

I expect the attenuation just inserts a fixed resistance somewhere in the RF path of the scanners, but if it is lowering gain of an amplifier by some controllable bias, it would be nice to have a firmware update to at least change it to 10dB. 3 levels would be outstanding.
 

jonwienke

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The attenuator is hardware, not software, so it can't be changed with a firmware update.
 

KD4UXQ

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The attenuator is hardware, not software, so it can't be changed with a firmware update.
I expected it was only hardware, would have been nice if it were adjusting gain on an amplifier. I would love to know if the attenuator is a discrete component and not internal to an IC. If it were an identifiable discrete component I would really like to change it. I have read you can't get schematics for the BCD436HP. I would modify mine after warranty coverage.
 

Ubbe

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All schematics I've seen uses resistors for the attenuator, right after the filter section.
So it is most probably covered in that black hard resin that is poured over the front-end section.

/Ubbe
 

KD4UXQ

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All schematics I've seen uses resistors for the attenuator, right after the filter section.
So it is most probably covered in that black hard resin that is poured over the front-end section.

/Ubbe
I have not looked inside yet. Even looking at the PCB, it could be very hard to trace the signal path as I am sure it is a multilayer board. But it would be nice to identify the attenuator resistor and change it out.
 

KD4UXQ

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Yea, not sure who came up with 20dB!!!

This is pretty much useless operationally.
Very useless. If they are going to give us just one, I would want 6dB. That is usually enough to cut down on signal to solve some interference issues.
 

jonwienke

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I have not looked inside yet. Even looking at the PCB, it could be very hard to trace the signal path as I am sure it is a multilayer board.
In the case of the 436, the front circuit board has 6 layers.
 
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