SDS100/SDS200: SDS 200-global auto filter

[Ubbe]

it says if I use the Normal or Invent for global/site. I'll need some sort of external high/low pass filter.

Scanners almost always benefit from using external filters and SDS scanners very much so as their receiver are very poor.

There are always internal filters in a scanner. First there are bandfilters at the antenna port that let trough a wide band that might be the whole VHF-Hi of 137-175MHz. Then the input signal are mixed with the oscillator signal to produce a third frequency that are followed by a more narrow filter of maybe 10MHz.

That 10MHz where too wide to be used in a SDS scanner but a more suitable narrow one of perhaps 1MHz would be too expensive to Uniden to be used. Instead they added the filter settings that use the 10MHz filter but can push it to either side so that in a normal scanner it is centered at -5MHz and +5MHz but the filter settings in a SDS scanner can make it go up to -1MHz and +9MHz or down to -9MHz and +1MHz.

It's the same filter but its frequency range gets moved and if there where an interfering signal at -2MHz when the filter where set at +/-5MHz it can then be blocked by moving the filter to -1MHz/+9MHz and the receiver will then work much better. But it could instead receive an interference that are at +8MHz that didn't affect reception using the +/-5MHz setting. So you will never know what type, and even if, a different filter setting will help.

The +/-5MHz filter are called Off and Normal are -1MHz/+9MHz and Invert are -9MHz/+1MHz and Wide are half of Normal/Invert to make it -2.5MHz/+7.5MHz and -7.5MHz/+2.5MHz

/Ubbe

 

[JamesBrox]

That's certainly possible. The waterfall functions might help in identifying what the problem signal is. In a rural setting I would not imagine it could be a paging or taxi system, but who knows? Be a bit more specific about what it is you are trying to eliminate.

Mike

Hey Mike. I'm not trying to eliminate anything. I'm trying to figure out how to get the best reception possible on this 100/200. It's a little frustrating to read all these filter options. To the hobbyists, whoever (maybe Upman) put that in there just makes the user curious if he's missing RX because he has the radio on the wrong filter.

 

[JamesBrox]

The filtering is performed by the software/firmware in the scanner. There certainly are physical external filters available for the antenna input, but the filtering choices in the menu system are internal to the scanner. I don't believe there was any reference to external filters in that PDF.

Normal (always use a High Pass Filter)
Invert (always use an inverted High Pass Filter)

Not trying to argue sir but it clearly says if I use the option of Normal/Invert.... I need to use a High /Inverted High Pass Filter....anyways. To me that means an after-market accessory. It says, "always use".

 

[JamesBrox]

Scanners almost always benefit from using external filters and SDS scanners very much so as their receiver are very poor.

There are always internal filters in a scanner. First there are bandfilters at the antenna port that let trough a wide band that might be the whole VHF-Hi of 137-175MHz. Then the input signal are mixed with the oscillator signal to produce a third frequency that are followed by a more narrow filter of maybe 10MHz.

That 10MHz where too wide to be used in a SDS scanner but a more suitable narrow one of perhaps 1MHz would be too expensive to Uniden to be used. Instead they added the filter settings that use the 10MHz filter but can push it to either side so that in a normal scanner it is centered at -5MHz and +5MHz but the filter settings in a SDS scanner can make it go up to -1MHz and +9MHz or down to -9MHz and +1MHz.

It's the same filter but its frequency range gets moved and if there where an interfering signal at -2MHz when the filter where set at +/-5MHz it can then be blocked by moving the filter to -1MHz/+9MHz and the receiver will then work much better. But it could instead receive an interference that are at +8MHz that didn't affect reception using the +/-5MHz setting. So you will never know what type, and even if, a different filter setting will help.

The +/-5MHz filter are called Off and Normal are -1MHz/+9MHz and Invert are -9MHz/+1MHz and Wide are half of Normal/Invert to make it -2.5MHz/+7.5MHz and -7.5MHz/+2.5MHz

/Ubbe

Great information sir. But how would I know I need those filters in the first place?

 

[nessnet]

Filters:
If it isn't broke, don't fix it!
Basically, are you creating a solution to a problem that may not exist?

As Ubbe said, the 100/200 has a very wide front end.
So, any signals close to your target freq. can possibly cause interference/reception problems.
That is why the filters were put there - to mitigate this interference.
And, whatever filter that works best would be for a SPECIFIC LOCATION, because interference is very location dependent.

But, if you don't have any close signals causing interference, you don't need to worry about filters.
In fact, if you don't have nearby interference, there is an option to turn the global (and site) filter(s) to off.
Which will actually give you the highest sensitivity (best reception) - if you indeed don't have an interference problem.

 

[fxdscon]

Normal (always use a High Pass Filter)
Invert (always use an inverted High Pass Filter)

Not trying to argue sir but it clearly says if I use the option of Normal/Invert.... I need to use a High /Inverted High Pass Filter....anyways. To me that means an after-market accessory. It says, "always use".

When you select normal, you’re telling the scanner to always use its internal high pass filter.

When you select invert, you’re telling the scanner to always use its internal inverted high pass filter.

 

[Ubbe]

just makes the user curious if he's missing RX because he has the radio on the wrong filter.

But how would I know I need those filters in the first place?

That's a problem and you'll probably need another radio/scanner set to the same frequency as a SDS100/200 to notice that you are actually missing something.

If you have a weak reception where signals strength are -95dBm or worse then you can enter that frequency by Channel+Freq+Channel and look at the Digital Error Count for a digital system and go into the menu to Srch/CloCall Opt and Set Filter and choose another filter and do Avoid to come back to the normal display and check if it helped. Then do Fn+7 to activate IFX and try all filters again. You don't try the Auto filter settings as you will not know what they do as Uniden forgot to include a display setting that show what the Auto have selected.

If you find a filter that improve reception then program that to the site.

You can do the same for analog frequencies and use the Noise indication that should be as low as possible but can only be looked at when there's no modulation, no voice from the transmission but still a carrier that opens squelch. Maybe it's best using your ears and listen to the background hiss.

The signal strength indication cannot be used in neither analog or digital mode as the scanner treats interference as a signal and you then might set the scanner to have the strongest interference.

Also if you have signal strengths that are -60dBm or stronger then activate the Attenuator to that frequency or site as you then get a lot less of interference issues that could make it unnecessary to work with the filter settings. Uniden doesn't have a user friendly attenuator system as if you take your scanner with you and use it in your car or at another location, you probably need to disable attenuation and you have to painstakingly go thru the programming to remove the attenuation from frequencies and sites, if you remember which one it was.

Whistler has another system, probably patented, that you can choose to have the attenuation globally off to temporarily disable it on all frequencies in the scanner, or globally on if all frequencies should be attenuated, or normal where only the programmed ones are active. Then you can actually use attenuation as a tool to help you use a scanner. It would also help if attenuation could be selected to be of a half value but no scanner have that option.

/Ubbe

 

[JamesBrox]

Understood guys. Thanks for the patience.

 

[enCrypt]

Scanners almost always benefit from using external filters and SDS scanners very much so as their receiver are very poor.

There are always internal filters in a scanner. First there are bandfilters at the antenna port that let trough a wide band that might be the whole VHF-Hi of 137-175MHz. Then the input signal are mixed with the oscillator signal to produce a third frequency that are followed by a more narrow filter of maybe 10MHz.

That 10MHz where too wide to be used in a SDS scanner but a more suitable narrow one of perhaps 1MHz would be too expensive to Uniden to be used. Instead they added the filter settings that use the 10MHz filter but can push it to either side so that in a normal scanner it is centered at -5MHz and +5MHz but the filter settings in a SDS scanner can make it go up to -1MHz and +9MHz or down to -9MHz and +1MHz.

It's the same filter but its frequency range gets moved and if there where an interfering signal at -2MHz when the filter where set at +/-5MHz it can then be blocked by moving the filter to -1MHz/+9MHz and the receiver will then work much better. But it could instead receive an interference that are at +8MHz that didn't affect reception using the +/-5MHz setting. So you will never know what type, and even if, a different filter setting will help.

The +/-5MHz filter are called Off and Normal are -1MHz/+9MHz and Invert are -9MHz/+1MHz and Wide are half of Normal/Invert to make it -2.5MHz/+7.5MHz and -7.5MHz/+2.5MHz

/Ubbe

Thanks for this Ubbe,
I've been trying to get my head around the filters and now I understand them, awesome!