SDS200 Global Auto Filter

[kb9hgi]

what is the Global Auto Filter for on the sds200? I looked thru a manual don't tell me nothing

 

[doctordialtone]

what is the Global Auto Filter

"Global Auto Filter Sets the filters for Departments, Sites, Custom Searches, CC Mode, and Weather Scan. "

Easier to Read SDS100/200 Digital Scanner Manual auto filter

 

[nessnet]

Briefly.....

Sentinal:
In your profile (main) settings, you can choose (in miscellaneous), your global filter or any of the other selections.
Then, this is the setting used by every favorites list - every system/dept/site, where you have "global" as your choice.

Now, if needed, you can change the filter on individual sites (trunking) or depts (conventional) to whatever...

 

[Markb]

The whole filter thing has been somewhat murky with not much documentation accompanying the feature. As far as I know, no one knows whether they are band pass, high pass, low pass or what.

The best course of action is to experiment and see if you have better receive results using one of the filter settings or none at all. Could vary by band and system that you are listening to as well. If you are having poor receive, intermod or whatever, give the filters a try and see if they are beneficial, along with IF exchange. Some people find that they don't need to use them, for others it has been a helpful addition.
The global filter setting is a default for the entire radio unless you specify a specific filter in your favorites lists, searches, etc...

 

[garys]

From the numerous threads on filters here, this is my understanding.

Normal = High Pass
Wide Normal = Wider High Pass
Invert = Low Pass
Wide Invert = Wider Low Pass.

Auto and Wide Auto cycle through all modes. The caveat is that this slows down the scan rate quite a bit. As noted. Global is a master setting.

It's really a matter of trial and error as to what works best where. I've found that in my area, with a lot of UHF T frequencies in use, Wide Normal has been working better of late. However, on a large 900MHZ MotoTrbo network, Invert has improved reception. Meanwhile on a smaller MotoTrbo network, Normal has been working well.

You just have to play around with it, really.

 

[Ubbe]

As far as I know, no one knows whether they are band pass, high pass, low pass or what.

It's bandpass. It's the high IF filter at around 250MHz that's 10MHz wide.

At the OFF setting it works as any other filter in Unidens scanners and pass frequencies +/-5MHz around the monitored frequency.
NORMAL are an IF frequency shift of +5MHz in reference to the filters bandpass frequency so that it doesn't pass any frequencies, or only a narrow range, above the monitored frequency, but pass all frequencies 10MHz below.
INVERT are the opposite of that and pass everything 10MHz above the monitored frequency and nothing below it.
WIDE NORMAL only switch the IF filter halfways, so it will pass frequencies within 2MHz above and 8MHz below the monitored frequency.
WIDE INVERT are the possite with passband of 2MHz below and 8MHz above the frequency.

So there is no more narrower or more wider filters, the whole passband are just shifted more or less at either side, a common function in shortwave receivers.

What filter setting that works best to use are dependent of where the strongest interferencies are at the current unique location and are often an excersise of trial and error and are also dependent of what frequencies that are monitored. As the filter settings are defined for a whole site, or department, that might have a wide spread of different frequencies, it could be that one single setting does not work to be used for all frequencies at a site or department.

/Ubbe

 

[wa8pyr]

It's bandpass. It's the high IF filter at around 250MHz that's 10MHz wide.

At the OFF setting it works as any other filter in Unidens scanners and pass frequencies +/-5MHz around the monitored frequency.
NORMAL are an IF frequency shift of +5MHz in reference to the filters bandpass frequency so that it doesn't pass any frequencies, or only a narrow range, above the monitored frequency, but pass all frequencies 10MHz below.
INVERT are the opposite of that and pass everything 10MHz above the monitored frequency and nothing below it.
WIDE NORMAL only switch the IF filter halfways, so it will pass frequencies within 2MHz above and 8MHz below the monitored frequency.
WIDE INVERT are the possite with passband of 2MHz below and 8MHz above the frequency.

If I'm setting a filter on a specific frequency, why would I want to pass everything within 2, 5 or 8 MHz? It's a scanner and broad as a barn door, and since the purpose of a filter is to filter out the stuff that's not on the frequency of interest, it seems as though +/-1 MHz would be more than enough.

 

[Kaleier1]

If I'm setting a filter on a specific frequency, why would I want to pass everything within 2, 5 or 8 MHz? It's a scanner and broad as a barn door, and since the purpose of a filter is to filter out the stuff that's not on the frequency of interest, it seems as though +/-1 MHz would be more than enough.

That's my question. When trying to monitor FRS frequencies my SDS200 is worthless because it picks up transmissions and DMR control channels on frequencies 262.5 KHz higher, but my $129 Alinco DJ-MD5T 2m/70cm ham handheld handles FRS frequencies with no problems.

 

[Ubbe]

.....the purpose of a filter is to filter out the stuff that's not on the frequency of interest, it seems as though +/-1 MHz would be more than enough....

Those kind of filters are super expensive. The one used now are the same as used in all Uniden scanners, it's on the shelf and Uniden have probably ordered tens of thousands from the manufacturer.

The finer and narrower filters comes later in the chain, in the lower frequency IF where filters at 21,4Mhz and 10,7Mhz are standard components and have 12KHz and 20KHz bandwidth for NFM and FM mode. The IF DSP in the SDS scanner has programmable bandwidth and works the same as any 10,7MHz filter.

The problem are the RF SDR chip that Uniden choosed to use in the SDS scanner. It has an embedded RF AGC function that reduce it's gain when it encounter a strong signal. Unfortunatly that signal strenght detector are right behind that 10MHz wide filter. If anybody would do a mod to his scanner it would be to change that 250Mhz filter to a much more narrower one. The frequency are only used in Unidens scanners so it has to be specially ordered to that frequency and with as narrow bandwidth as possible. The cost would probably be astronomical to order a single one.

If there's no strong adjacent frequencies then the SDS scanner works fine, as the RF AGC doesn't need to interfere with the RF receivers gain.

/Ubbe