Uniden SDS filter list for San Diego

Anderegg

Enter text in this field
Premium Subscriber
Joined
Mar 7, 2010
Messages
2,218
Location
San Diego
Messing with optimizing my filters for various systems and bands. So far...

700MHz and 800MHz trunking, SD City, RCS Nextgen, Wide Invert provides the highest signal strength and the lowest ERR rate, tested edge of range and -50dBm high signal.

DoD 14C 380MHz trunking, Wide Normal gets about 3dBm improvement over the next best filter, Wide Invert, and best ERR rate.

Testing CHP right now, 39.8MHz, at a distance, it likes Wide Normal.

Anyone else have filter settings for anything specific, maybe VHF brush or marine band, normal UHF analog etc? Not finding Normal and Invert to really best either of the Wide variants, and in many cases, these filters, or no filter, result in significant signal degradation and ERR rate increases.

Paul
 

Anderegg

Enter text in this field
Premium Subscriber
Joined
Mar 7, 2010
Messages
2,218
Location
San Diego
My VHF testing, Trolley 161MHz and Marine 156MHz FM, are digging Wide Normal...Wide Invert 3dBm reduction in signal strength, similar dip for Normal and Invert.

Paul
 

TailGator911

KF4ANC
Premium Subscriber
Joined
Feb 12, 2005
Messages
2,346
Location
Fairborn, OH
Thanks for this thread. I visit family in La Jolla and Escondido quite often, well used to. Lots of systems to monitor. Filter settings appreciated. Taking notes here ...
 

Anderegg

Enter text in this field
Premium Subscriber
Joined
Mar 7, 2010
Messages
2,218
Location
San Diego
Just FM...WFM is what radio stations and older wireless microphone systems use.

Paul
 

jimbrogers

Member
Premium Subscriber
Joined
Jan 10, 2009
Messages
44
Location
Ramona, CA
I live in Ramona and listen to USFS and State Parks. In Sentinel, I had the modulation at NFM, FM would better?
 

Mike_G_D

Member
Joined
Dec 19, 2002
Messages
1,091
Location
Vista, CA
I live in Ramona and listen to USFS and State Parks. In Sentinel, I had the modulation at NFM, FM would better?
Presuming you are using a Uniden SDS100 or 200 then, for USFS VHF conventional NFM should be the correct choice while for State Parks on conventional 700/800MHz it may more likely be FM but you might want to try both and see what works best.

For the record, this is actually off topic for this thread; the "filters" Paul is referring to are special fixed IF shift choices for moving the IF frequency in the SDS series radios around inside the IF filter passband to attempt to mitigate close-in interference. The choices the radio makes when switching between modes like WFM, FM, and NFM actually (depending on the model) switch between IF filter types in the final IF just before demodulation, really wide for WFM, narrow for handling +/-5kHz deviation for FM and really narrow for handling +/-2.5kHz for NFM. Uniden receivers prior to the 436 and 536 models did not actually change the final IF filter with the changing of the analog FM mode, they just altered the discriminator audio characteristics to compensate for the deviation changes while the 436 and 536 actually do use a separate narrower IF filter for the NFM mode as well as the discriminator audio adjustments. I am unsure about the SDS units as the IF filter is something like 10 MHz wide if I am to believe some of what I have read and there may be some DSP "finangling" going on after that which creates a final pre-demodulation filter - the SDS units are based on a wideband digital TV SDR receiver IC as I understand it so very different in design from the 436 and 536 and all other previous Uniden receivers.

Think of it as selecting a filter choice when changing the analog FM deviation modes while using the SDS filter options is really using one filter but moving the IF center around inside that filter's bandwidth - related but very different operationally.

-Mike
 

Anderegg

Enter text in this field
Premium Subscriber
Joined
Mar 7, 2010
Messages
2,218
Location
San Diego
For some reason, in almost all circumstances (I've tested), seems that filter OFF offers poor reception, low RSSI, high ERR rates on digital...I don't use OFF.


Paul
 

Ubbe

Member
Joined
Sep 8, 2006
Messages
5,040
Location
Stockholm, Sweden
Uniden receivers prior to the 436 and 536 models did not actually change the final IF filter with the changing of the analog FM mode, they just altered the discriminator audio characteristics to compensate for the deviation changes while the 436 and 536 actually do use a separate narrower IF filter for the NFM mode as well as the discriminator audio adjustments.
Older scanners didn't even have a NFM mode, just FM and then WFM for broadcast FM. But the old BC780 have an additional NFM filter, that are in series with the FM filter and are bypassed in FM mode and there's circuits for audio compensation and for the different squelch operation when NFM are used. My BCT15 has a seperate NFM filter and the BCT15X schematic show two different 10,8MHz filters. Also the 10 year old HP-1 and even the old GRE design Whistler TRX use seperate filters for FM and NFM. So semi old scanners actually use a seperate filter for the NFM mode.

/Ubbe
 

Mike_G_D

Member
Joined
Dec 19, 2002
Messages
1,091
Location
Vista, CA
Older scanners didn't even have a NFM mode, just FM and then WFM for broadcast FM. But the old BC780 have an additional NFM filter, that are in series with the FM filter and are bypassed in FM mode and there's circuits for audio compensation and for the different squelch operation when NFM are used. My BCT15 has a seperate NFM filter and the BCT15X schematic show two different 10,8MHz filters. Also the 10 year old HP-1 and even the old GRE design Whistler TRX use seperate filters for FM and NFM. So semi old scanners actually use a seperate filter for the NFM mode.

/Ubbe
Nope! Sorry, I'm going to have to disagree with you here. I have a 15. Good all- around analog radio but with one major weakness - final if filter is too broad for now close in narrow FM signals as are prominent where I live.

Firstly, I'm talking about the final 3rd if filter not the 10.7 MHZ 2nd if filter. It's in the 455 kHz range I think or thereabouts. I know for a fact that switching to NFM on my 15 will not reduce the of bandwidth but it will change the audio characteristics either by simple amplifier gain or through discriminator adjustment I'm unsure. Anyway, I also have older GRE gear and Whistler. They are the opposite. They indeed do seem to have a narrower IF filter when the FMN mode is selected but they, unlike the older model Unidens do not adjust the audio or discriminator. I always said that Uniden had the superior front end while the GRE's had the better back end IF section.

Secondly, I was speaking only about the pre- 436 model Uniden not the GRE designs. I didn't want to overly complicate the response so was trying to keep it shorter and simpler. Too late now! As I said, the GRE units did have a separate narrower filter with the NFM setting. Also, I can't speak for much older Uniden models like the 780, etc. I'm just referring to the 396 through 996 units. As far as I know the 15X has the same basic IF design as the 15.

On this site a few years ago there was a nice long thread discussing how to replace the broad final IF filter in older Uniden models. The OP, I think, had a source for exact replacement parts that were otherwise the same but with a narrower passband better suited for use with the new +/-2.5 kHz narrow band deviation and 7.5 kHz spaced VHF- HI channels now mandated in the US. I know during heavy fire season where I am the CDF uses those new tight channels a lot and I can't use the 15 to adequately filter adjacent channels bur the gre units have no problem. I wanted to replace that filter but lacked the facilities to do so though I do have the knowledge and skill. I'm on my phone and rushed right now but if I can find that old thread I will link to it in another message once I have the time and can use a PC.

-Mike
 

Ubbe

Member
Joined
Sep 8, 2006
Messages
5,040
Location
Stockholm, Sweden
Nope! Sorry, I'm going to have to disagree with you here.
And you are absolutly right. The BCT15 have only one last IF 450KHz filter used for both FM and NFM.

The 780 have two 450KHz filters, one for FM and another for NFM. The WFM mode uses a 10,7MHz filter to a seperate broadcast receive chip.

I know that there where a thread about switching out the NFM filter in a modern Uniden scanner, I believe HP-1 or HP-2, and it was the same used in 436/536, to a more narrow one and initially it seemed to improve reception but later it was found it had some negative effects. I think it was the digital demodualtion that got too bad and at the end it wasn't a recommended modification. Older scanners that only have FM mode could be benficial to substitute the filter for a more narrow one that more equals todays NFM filters.

/Ubbe
 

Anderegg

Enter text in this field
Premium Subscriber
Joined
Mar 7, 2010
Messages
2,218
Location
San Diego
And you are absolutly right. The BCT15 have only one last IF 450KHz filter used for both FM and NFM.

The 780 have two 450KHz filters, one for FM and another for NFM. The WFM mode uses a 10,7MHz filter to a seperate broadcast receive chip.

I know that there where a thread about switching out the NFM filter in a modern Uniden scanner, I believe HP-1 or HP-2, and it was the same used in 436/536, to a more narrow one and initially it seemed to improve reception but later it was found it had some negative effects. I think it was the digital demodualtion that got too bad and at the end it wasn't a recommended modification. Older scanners that only have FM mode could be benficial to substitute the filter for a more narrow one that more equals todays NFM filters.

/Ubbe
Are you referring to the recomendation by Upman to switch from NFM to FM if experiencing issue with LSM systems?

I will also post my IFX list when I get a chance...there are a lot of 700/800MHz frequencies that are messed up by cell phone towers or whatnot. I only have a list for the West site because the IFX filtering helps most when signals can be knocked off the air by interference. The other sites when testing were like -35dBm so basically, couldn't interfere with that in ytesting.

Paul
 

Mike_G_D

Member
Joined
Dec 19, 2002
Messages
1,091
Location
Vista, CA
Are you referring to the recomendation by Upman to switch from NFM to FM if experiencing issue with LSM systems?

I will also post my IFX list when I get a chance...there are a lot of 700/800MHz frequencies that are messed up by cell phone towers or whatnot. I only have a list for the West site because the IFX filtering helps most when signals can be knocked off the air by interference. The other sites when testing were like -35dBm so basically, couldn't interfere with that in ytesting.

Paul
It's related - when using a narrower filter on analog signals you might experience some distortion if the signal deviation is more than the passband of the filter, etc. But with digital modulated signals the problems can be more severe. Something called "group delay" in the filter characteristics comes into play and can mess up a digital signal's phase and amplitude characteristics. The more narrow the IF filter the more important that becomes relative to the bandwidth of the signal. The cheap and dirty way around that which is what most consumer scanners fall back on is to use a wider filter to avoid the affects of the non-ideal filter characteristics which usually become worse at the filter edges.

So what is a relatively minor annoyance for analog FM signals becomes a big hairy deal for complex digitally modulated signals. Since the 436 and 536, unlike the 396 through 996 models, really DO have two IF filters with the NFM one being the narrower of the two, since those filters were of marginal quality for digital signals but fine for analog, using the wider filter for P25 might improve the decode overall including on tricky simulcast variants. You sacrifice some adjacent channel selctivity for better digital decode - again, cheap and dirty compromise.

If the filters were of much higher quality this would not be as severe an issue but it's a whole lot of stuff, really, in the design, including LO accuracy and phase noise, etc., all of which are a compromise in lower cost consumer scanners, of course.

Again, this is a seperate issue from the "SDS Filter" choices. Different concept and animal. That method involves basically moving the IF signal around in the passband of one of the IF filters, I think Ubbe's description is best and it sounds like it is the second IF filter being 10 MHz wide or so. What you're doing here is trying to move the IF signal away from the center of the filter where it normally is suppose to be so that you get closer to one of the "filter walls" in the hopes that you can move the interfering signal outside the passband of the filter and reduce its negative affects on the desired signal. But, again, when you do this, you start bringing in the negative effects of the non-ideal filter edges affecting your signal. This is why using it can sometimes reduce some signal amplitude of the desired signal but the hope is that you gain more in reducing the interferer level. Again, always a compromise.

And the IFX ("IF Exchange") is another thing alltogether. In the pure superhet models pre-SDS series it basically swapped the LO feed into one or more of the IF mixers from high side to low side injection or vice-versa. What that is supposed to do is relieve problems stemming from IF image issues. It is an effective and clever method that can work for that kind of issue. But IF images are just one superhet receiver bugaboo. There are many others and many of which will not be affected by a high side/low side LO mixer injection swap. I am unsure how this works in the SDS receivers. I assume they are hybrid designs using some superhet up/down conversion at the front end before the sdr portion comes into play. If so, then the IFX LO high side vs. low side mixer injection can work the same way as in pure non-sdr superhet receivers.

-Mike
 
Last edited:

dsefcik

Member
Joined
Jan 7, 2017
Messages
15
Helpful thread for a new SDS100 owner trying to make sense of the new filters, thank you.
 
Top