SDS100/SDS200: Filter setting questions

[dgoodson]

I've been experimenting with Filter Settings and have started simple...
I focused on a NOAA weather frequency for a station about 40 miles away which I can receive fairly reliably, but certainly not "full quieting". I set up a special "System" with five different "Departments" and I set the filter option differently for each Department (Off, Normal, Invert, Wide Normal and Wide Invert). Within each department I programmed only one Channel, the same for all, which is the NOAA channel 162.425.
From time to time over the past few days I would monitor the system and manually step through the five different departments to see if I could discern any difference in the audio quality. The short answer is "not really". Then yesterday, for no particular reason, the Department with the filter set to Invert was noticeably better than the others (less background static, better SNR).

So my questions are:

• Should I expect this filter setting to always be best for this frequency, or will the filter performance depend on propagation or other factors?
• Should I expect this filter setting to also work best for other nearby frequencies (i.e. VHF Hi)?

I've tried to read all the posts and articles I can find about the filters and settings but would appreciate a bit more details. For example, if Normal refers to a High Pass Filter, what is the cutoff frequency (fco)? Is fco dynamic, is it proportional to the carrier frequency? Is an Inverted filter a just notch filter? And I guess the Wide Normal and Wide Invert just apply a wider band pass/notch.

Any insight appreciated!

 

[Whiskey3JMC]

There's no "one size fits all" filter setting for frequencies, bands, etc. Everyone's mileage will vary depending on several factors outlined here. Experimentation is key

 

[nessnet]

Here is the simple way to look at it filters.

The SDS radios use a commercially available tuner chip (Rafael Micro R836 or R840, or...?) which have a very 'wide' front end'. Meaning that frequencies close by to the target frequency can interfere. After being on the market for a while, Uniden realized this was a problem and released firmware with these filters as a 'fix'.

First, what filter to use is 100% dependent on if you have a problem in the first place. If there is no interference to your target frequency, leave the filter on normal - or off. You may find that this is the best setting for most.

Now IF you have interference, remember that RFI is not only frequency dependent, it is also very location dependent. Filters are meant to fix problems with induvial frequencies/bands, in certain locations, so filters are not a one size fits all - and they probably will not apply to everything you scan - and not everywhere you may be.

That is why you can apply individual filters to each SITE in on a trunking system, or each department in conventional.
There is also a filter setting in your main profile, which can get confusing. There have been some very good write-ups here on how to test filters and determine what individual items to apply them to. You do NOT want your profile filter to apply to everything in your radio - only on the freqs that they are needed on. Again, off or normal are quite viable options also. Don't make a problem where there isn't one...

 

[Ubbe]

Uniden reused the 10MHz wide filter in their SDS scanner that worked perfectly well in the HP range of scanners but the SDR receiver chip used where suffering from desense and interference much easier from other transmitters in the frequency band. They found a way to offset the filter to one side to block reception to either higher or lower frequencies using the Normal and Invert setting.

That filter are still too wide and only doing an offset opens up the frequency range much more in the other frequency direction. I believe that Unidens latest SDS150 scanner uses a much more narrow and more appropriate filter that doesn't need any extra filter settings to be used.

Filter setting are only decided from what other transmitters that needs to be blocked. Those other transmitters might not be continuously transmitting like it could when it is a digital control channel, but can be different transmit intervals during the day or on different week days. I have a powerplant that usually only gets active with its DMR system a couple of days each month or so when they do maintenance work.

/Ubbe

 

[dgoodson]

Here is the simple way to look at it filters.

The SDS radios use a commercially available tuner chip (Rafael Micro R836 or R840, or...?) which have a very 'wide' front end'. Meaning that frequencies close by to the target frequency can interfere. After being on the market for a while, Uniden realized this was a problem and released firmware with these filters as a 'fix'.

First, what filter to use is 100% dependent on if you have a problem in the first place. If there is no interference to your target frequency, leave the filter on normal - or off. You may find that this is the best setting for most.

Now IF you have interference, remember that RFI is not only frequency dependent, it is also very location dependent. Filters are meant to fix problems with induvial frequencies/bands, in certain locations, so filters are not a one size fits all - and they probably will not apply to everything you scan - and not everywhere you may be.

That is why you can apply individual filters to each SITE in on a trunking system, or each department in conventional.
There is also a filter setting in your main profile, which can get confusing. There have been some very good write-ups here on how to test filters and determine what individual items to apply them to. You do NOT want your profile filter to apply to everything in your radio - only on the freqs that they are needed on. Again, off or normal are quite viable options also. Don't make a problem where there isn't one...

Thanks, that was helpful

 

[CollinsURG]

The IF bandwidth of the SDS100/200 is 10 Mhz. Way too wide! It was narrowed to 1 Mhz with the SDS150 which greatly improved performance, but is still way too wide than is needed to operate.

In order to try and mitigate interference from adjacent signals and images, the filters were introduced.

When filters are off, the intended programmed target frequency is in the middle of the 10 MHz passband.

Normal shifts the 10MHz filter window to cut off signals lower in frequency, leaving 1MHz below and 9MHz above the tuned frequency.

Invert shifts the window to cut off signals higher in frequency, leaving 9MHz below and 1MHz above.

Wide Normal shifts the 10MHz filter window to cut off signals lower in frequency, leaving 3 MHz below and 7 MHz above the tuned frequency.

Wide Invert shifts the window to cut off signals higher in frequency, leaving 7 MHz below and 3 MHz above.

The problem with this scheme is that, what filter is most effective depends on the interfering signals that are present, which in reality are location and time determinant.

Different locations have different signals present. Different times of day have different signals present.

With AUTO, the scanner tests different filter settings to determine which one provides the best signal. Unfortunately this greatly slows down scanning speed.

 

[dgoodson]

The IF bandwidth of the SDS100/200 is 10 Mhz. Way too wide! It was narrowed to 1 Mhz with the SDS150 which greatly improved performance, but is still way too wide than is needed to operate.

In order to try and mitigate interference from adjacent signals and images, the filters were introduced.

When filters are off, the intended programmed target frequency is in the middle of the 10 MHz passband.

Normal shifts the 10MHz filter window to cut off signals lower in frequency, leaving 1MHz below and 9MHz above the tuned frequency.

Invert shifts the window to cut off signals higher in frequency, leaving 9MHz below and 1MHz above.

Wide Normal shifts the 10MHz filter window to cut off signals lower in frequency, leaving 3 MHz below and 7 MHz above the tuned frequency.

Wide Invert shifts the window to cut off signals higher in frequency, leaving 7 MHz below and 3 MHz above.

The problem with this scheme is that, what filter is most effective depends on the interfering signals that are present, which in reality are location and time determinant.

Different locations have different signals present. Different times of day have different signals present.

With AUTO, the scanner tests different filter settings to determine which one provides the best signal. Unfortunately this greatly slows down scanning speed.

That is super helpful information and exactly the type of info I was looking for. Thanks so much for sharing!

 

[dmfalk]

There's a PDF for this, FYI....

https://wiki.radioreference.com/images/3/31/SDS100_SDS200_Filter_Settings.pdf

 

[Chris0516]

There's a PDF for this, FYI....

https://wiki.radioreference.com/images/3/31/SDS100_SDS200_Filter_Settings.pdf

Is there a way to bookmark, that page. Because, When I went to that page. It wouldn't let me bookmark it.

 

[buddrousa]

I am using EDGE and CHROME and they both will let me bookmark that page.

 

[RandyKuff]

You can also "Download the PDF file" of the filter settings to keep on your computer or print it out...

 

[dmfalk]

Is there a way to bookmark, that page. Because, When I went to that page. It wouldn't let me bookmark it.

It's a link to a PDF file. Just download it.

It comes from here:

SDS100 and SDS200 FAQ Page - The RadioReference Wiki

wiki.radioreference.com