SDS100: So what exactly are the filters, anyway?

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wa8pyr

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Before I start, I'd like to say the manual that comes with the SDS100/200 is the weakest POS I've ever seen. In a radio with so many advanced settings, one would think the manufacturer would at least put together a PDF manual that explains the basics of what they do and examples of when to use them, so that you have at least an idea what settings do before you use them (rather than the time consuming trial-and-error method we're stuck with).

I've been a ham for 40 years and and public safety communications professional nearly that long. I'm not an RF neophyte; I've built and serviced radios and repeaters, tuned filters and duplexers and have reasonably good knowledge of how they work. If the manual gave a clue I could probably figure it out, but there's nothing; pretty bad for a $700 radio.

Soooo, I've been tinkering around with settings in my SDS100 and 200 and have some questions related to the filters. Going through the menu, I see the following filters listed; they're followed by my questions (making the assumption that we're talking about bandpass filters).

Global - Obviously affects the entire radio, but what does the passband look like?
Normal - Normal in relation to what? Again, what does the passband look like?
Invert - What does the passband look like? What are we inverting? Flipping the filter skirts around 180 degrees?
Auto - Assuming this means it selects the best filter for the situation, but how does it determine that?
Wide XXXX - I'm assuming the Wide settings are all the same as the above but with a wider bandpass.

What is the bandwidth/passband of the Normal setting versus the Wide setting? Even an approximate idea would be helpful.

What does the passband look like? Narrow at the frequency of interest then broadening out to the sides? Broad on one side and narrow on the other side? Or is it a pretty narrow passband on both sides covering only the frequency of interest? Being software defined there's all kinds of neat stuff they can do.

And we've got IFX - IF eXchange. . . but what's being exchanged? I'm assuming it's being shifted from low-side injection to high-side.

These are all things that should have been covered in the manual, but weren't. Mark's Easier to Read manual is a great leap ahead of the POS from Uniden, but his section on Filters is still blank and the section on IFX is pretty basic (although enough to give me a clue as to what might be going on).

Figuring some of you all have been tinkering deeply longer than I have, so someone might have a bit of insight.

Thanks,

Tom
 
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wa8pyr

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  • Intermediate Frequency Exchange - changes the IF used for a selected frequency to help avoid image and other mixer-produced interference on a given frequency.
This is to help with "Birdies"
Right, I know that, but is it changing the actual IF or changing from low-side to high-side injection. Changing the actual IF would be a bit unusual; changing the injection point is more common.
 

nessnet

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Filters:
Basically, no-one knows. Or better put, Uniden has never released ANY specifications concerning the filters. There has been quite a bit of experimentation and conclusions drawn from them, but the opinion has always been that the user needs to tinker and find what is best for them, in their specific RF environment. (Google is your friend)

Global:
You do know that you can set a "global" filter in settings - Global Auto Filter, right? Then, whatever this setting is, it will also be the setting (if global is chosen) for any freq. (conventional) or site (trunking). Or, you can set each freq/site individually, which will ignore what the global setting is.
 

wa8pyr

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Filters:
Basically, no-one knows. Or better put, Uniden has never released ANY specifications concerning the filters. There has been quite a bit of experimentation and conclusions drawn from them, but the opinion has always been that the user needs to tinker and find what is best for them, in their specific RF environment. (Google is your friend)
Been there, done that. I've searched for info on the filters and basically what I get is "try it and find out," but some of the stuff I get interference on is intermittent, and I really don't have time to sit around and wait. In any other radio I'd know the parameters of various filters and would be able to pick one which might be more suitable for a given situation.

Global:
You do know that you can set a "global" filter in settings - Global Auto Filter, right? Then, whatever this setting is, it will also be the setting (if global is chosen) for any freq. (conventional) or site (trunking). Or, you can set each freq/site individually, which will ignore what the global setting is.
Aware of that, thanks.
 

TailGator911

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I have played with and experimented with the filters in both SDS 100/200 from coast to coast, up the AlCan Hwy to Alaska, back thru Canada, the Caribbean, Carnival Cruise ports of call, Mexican resorts, Jamaica and Puerto Rico. My scanners are well-traveled and if there is anything I have learned from them (i.e., scanners and filters) after much trial and error and on-the-job-training, is that each and every geographical location is different and the scanner filters have to be individually tweaked for optimum performance. The filters have to be slightly tweaked or 'dialed in' each time you change any part of the geophysical equation of the scanner. Location. Latitude, longitude, elevation, antenna, etc. It can't be said enough - the SDS filters are individually adaptive and temperamental to their surroundings. Even 2 radios at the same location - each one is very different from the other in terms of filters and settings. In other words, your blues ain't gonna be like mine. My two SDS200s, side by side, both got great reception in San Juan, PR, and the filter settings were so different - night and day - in the same exact location. The best and, IMO, the only way to learn the filter systems in these scanners is by tweaking and trying out the different filters as you go. Find a setting that works and save it for that particular location. That's how I do it, and I am very satisfied with what I am hearing :)
 

u2brent

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It would be OK with me if the filter had a display indication on the details screen.. AFAIK this isn't the case..
This would be mucho helpful when trying especially the Auto setting and viewing what the scanner was currently using at that moment.. (Since there's no way of knowing until you manually try each one, and who knows if it was the same as the auto mode used)

For my location the best setting seems to be OFF
 
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TailGator911

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Yeah it can be confusing and somewhat intimidating when trying to set the filters in these SDS scanners. With me it was constant repetition and most times it was better left alone with NO filters! But that's half the fun right there! ;)
 

n1chu

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Filters; Something you tinker with when you think you should be hearing a comm better. I believe the filters are used with trunked systems. I have seen extensive input on filters here, mostly everyone trying to get Uniden to tell us how to use them. Uniden finally did. I’m not sure what possessed them to come up with the filtering but i believe it was to help with simulcast issues? In any event, take a trunked system and try the different filter settings while watching the RSSI value. A value of around -60 is better than a higher value. I receive some trunked systems with a bad RSSI value of -100 but it’s digital, as long as it’s strong enough I hear perfectly. But then I tried different filters and did see improvement, not much but some. As always, your Results may vary.
 

kruser

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I’m not sure what possessed them to come up with the filtering but i believe it was to help with simulcast issues?
The filters were added to try and overcome the poor selectivity of using a cheap TV tuner chip which has a wide open 8 to 10 MHz wide front end.
In a crowded RF urban environment with signals on many available channels, selectivity is needed which the Raphael tuner chip used does not offer.
 

Ubbe

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Steve Halloway did a bandscope for the SDS scanners that uses the information from the subprocessor USB port, probably what Uniden intended to use in some way, and shows what each filter does. He demonstrate it at his facebook page together with a remote head and a frequency lookup device and other cool things, some of them mainly thought for brittish users.

It is an IF shift feature like the same one used in most shortwave receivers but on the SDS scanners it has 4 fixed settings instead of continuosly variable.

SDS scannes use the same 1:st IF filters as in Unidens other scanners. It's 10Mhz wide but unfortunaly there's a signal strenght detector that adjusts the RF gain up to 50dB lower when a strong signal are sensed inside that 10MHz window, it's s permanent non-adjustable part of the SDR receiver chip that's being used to protect it from overload issues that can cause intermod. By using the different filters you are able to move that window so that the Normal filter only sees 1Mhz above your frequency and 9Mhz below it. Invert filter cuts off 1Mhz below the frequency but opens up 9MHz above it. The Wide settings are only shifting halfway, 3MHz at one direction and 7MHz at the other. Having the filter set to Off will let it work as a normal filter +/-5MHz from the center.

The auto mode probably tests all filter settings and uses the one that gives the weakest signal, thus filtering out any strong adjacent frequencies?


/Ubbe
 

sallen07

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Filters:
Basically, no-one knows. Or better put, Uniden has never released ANY specifications concerning the filters.
Paul told us that they were proprietary and no details were going to be released. I'm sure HE knew very well how they work.
 

pro106import

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It would be OK with me if the filter had a display indication on the details screen.. AFAIK this isn't the case..
This would be mucho helpful when trying especially the Auto setting and viewing what the scanner was currently using at that moment.. (Since there's no way of knowing until you manually try each one, and who knows if it was the same as the auto mode used)

For my location the best setting seems to be OFF
You can have the display show the Filter Setting:
Look at the bottom right

85063
 

ra7850

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Steve Halloway did a bandscope for the SDS scanners that uses the information from the subprocessor USB port, probably what Uniden intended to use in some way, and shows what each filter does. He demonstrate it at his facebook page together with a remote head and a frequency lookup device and other cool things, some of them mainly thought for brittish users.

It is an IF shift feature like the same one used in most shortwave receivers but on the SDS scanners it has 4 fixed settings instead of continuosly variable.

SDS scannes use the same 1:st IF filters as in Unidens other scanners. It's 10Mhz wide but unfortunaly there's a signal strenght detector that adjusts the RF gain up to 50dB lower when a strong signal are sensed inside that 10MHz window, it's s permanent non-adjustable part of the SDR receiver chip that's being used to protect it from overload issues that can cause intermod. By using the different filters you are able to move that window so that the Normal filter only sees 1Mhz above your frequency and 9Mhz below it. Invert filter cuts off 1Mhz below the frequency but opens up 9MHz above it. The Wide settings are only shifting halfway, 3MHz at one direction and 7MHz at the other. Having the filter set to Off will let it work as a normal filter +/-5MHz from the center.

The auto mode probably tests all filter settings and uses the one that gives the weakest signal, thus filtering out any strong adjacent frequencies?


/Ubbe
Ubbe,

Do you have any reference information for Steve Halloway's site?
 

kruser

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You can have the display show the Filter Setting:
Look at the bottom right
I may be wrong but I think some users would like to see which filter is chosen when you have either of the Auto filters selected. I think the display just shows which auto filter you chose currently and does not show which it picked.

I can live without that but it would still be nice if we had a single key or function knob press + a key press combo to get into the filter settings for whatever is displayed or scanning so a user can change the filter on the fly. That would probably help a lot of users figure out what works best for them.
 

wa8pyr

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Paul told us that they were proprietary and no details were going to be released. I'm sure HE knew very well how they work.
I'm sure the internal details of how they made it work are proprietary and have no problem with that, but it sure would be nice if they officially said "here's what filter xx does and here's what the passband looks like."

I do like the idea of an icon on the display which graphically shows the filter passband.
 

Ubbe

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but it sure would be nice if they officially said "here's what filter xx does and here's what the passband looks like."
Halloways facebook page has pictures of how the passband actually looks like in a SDS200 and what the different filter settings do to it.

/Ubbe
 
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