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Uniden Advanced Technical Topics For all threads regarding technical performance of specific models or general higher tier, technically oriented discussion of the technology used in Uniden scanners. Please use the Tech Support forum for all normal questions.

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  #41 (permalink)  
Old 04-28-2014, 6:09 PM
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Just FYI...

Sets of 50G filters was shipped today to 12 different addresses,
most of them in the US. Might, with a bit of luck, be delivered
before the weekend, but maybe in the next week. I know close to
nothing about RF stuff, but it's fun to see these come to a use... :-)

Regards, Jan-Erik.
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  #42 (permalink)  
Old 04-28-2014, 6:26 PM
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I hear ya, its just a spare scanner - wont hurt to pull it (except for my use of hot glue haha) if its noisy..

I am the type of engineer who buy's two of them and learns on one..
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  #43 (permalink)  
Old 04-28-2014, 6:39 PM
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Quote:
Originally Posted by kellykeeton View Post
I hear ya, its just a spare scanner - wont hurt to pull it (except for my use of hot glue haha) if its noisy..

I am the type of engineer who buy's two of them and learns on one..
Lol, me too

After installing the filter in this fashion, with the unshielded wires and switch, you won't really know how well the new filter is working. You won't know how much additional noise is being fed into the 450Khz IF from the cpu and other internal systems.

If you were going to try this, I would simply replace the filter first and get a baseline performance figure on FMN and AM using a service monitor, then and only then, maybe play with different switching methods to see if you can come close to a filter switch that is noise free. It won't be easy unless you have the right test equipment.

I think AM performance will suffer the most since it is inherently susceptible to broadband noise.

Rick
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  #44 (permalink)  
Old 04-28-2014, 7:17 PM
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yea good point there .. sweeden-ebay guy shipped them yesterday so right now its just hanging out.. I have time to pull out my hotglue
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Old 04-28-2014, 7:27 PM
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Quote:
Originally Posted by Bote View Post
Again, it's not related to the squelch threshold, it's the lack of hysteresis on the squelch action AT ANY SETTING. The behavior of the squelch changes when the channel bandwidth programming changes from FM to NFM.

This is notable on just about the only thing left worth monitoring on analog FM, the railroads.
Wonder if the issue is with how the x96XT's implemented a single IF filter and altered the IF level for the different bandwidth?

I have not confirmed this, however, my understanding of what happened with the x96XT series, they did not really have different IF filters, they somehow alter the level with the different IF bandwidth choice. This may be why the squelch is "poppy/choppy"??
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  #46 (permalink)  
Old 04-28-2014, 7:35 PM
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Quote:
Originally Posted by AZScanner View Post
This is so cool - reminds me of the good old days I spent muddling my way (with lots of help) through Bill Cheek's Scanner Modification Handbook. Let us know if you mod that 785. I'm curious if a similar mod might breathe new life into my old 796 which has much of the same hardware inside. I'd be willing to try it since that scanner's going to be pretty much used only for analog stuff once the Phoenix RWC goes Phase II in a couple years.

-AZ
If the 785/6 are anything like the BCD-780XLT, they may even be easier/better to modify than the newer models.

The BCD-780XLT actually had two 450Khz IF filters installed at the factory!
They had a 50D and a 50F installed. Presumably, these were for FM and AM respectively. I can't confirm this, but it is conceivable that FMN was also piped through the 50F filter, along with AM.
If so, there may not be much point in modifying these radios.

The inclusion of the 50F filter is probably why so many people prefer these radios over the newer models for AM reception.

If FMN is not piped through the 50F filter, the radio would certainly benefit from replacing the 50D filter.

R
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  #47 (permalink)  
Old 04-28-2014, 8:05 PM
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Quote:
Originally Posted by Boatanchor View Post
If the 785/6 are anything like the BCD-780XLT, they may even be easier/better to modify than the newer models.

The BCD-780XLT actually had two 450Khz IF filters installed at the factory!
They had a 50D and a 50F installed. Presumably, these were for FM and AM respectively. I can't confirm this, but it is conceivable that FMN was also piped through the 50F filter, along with AM.
If so, there may not be much point in modifying these radios.

The inclusion of the 50F filter is probably why so many people prefer these radios over the newer models for AM reception.

If FMN is not piped through the 50F filter, the radio would certainly benefit from replacing the 50D filter.

R
I also cannot confirm this for certain but from actual testing by ear, I can't say NFM mode does anything over FM mode.
If you ask me, they use the same audio filtering trick when changing modes from FM to NFM in the 780XLT's as they do in the newer digital models.
I had (have) adjacent channel interference that a properly working narrow filter will totally eliminate in an Icom R-7000 thru 9000 but changing to NFM on the same frequency in the 780 results in no noticeable change at all on the 780.
AM mode does appear to use the other filter so that helps for AM reception.

It's really a shame Uniden did not add electronic filter switching of wide and narrow filters in the triple conversion and later models.
I'd guess on a mass scale, it would have cost them a dollar for the models that have selectable FM bandwidths already. The signal line is already there to drive a circuit to make the switch.
And doing it with proper circuit traces would eliminate any problems of unwanted noise or signals being introduced at the filters leads as they would still be surface mounted and probably right next to each other with only a diode switch between them.

I noticed that almost all scanners did not really have a narrowband mode long before they announced the narrowband mandate.
I think Uniden is relying upon the fact that the frequency coordinators are not supposed to put a new narrowband channel right next to an old wideband channel unless the stations are seperated by a decent physical distance.
Something tells me that will not remain true in cities with severe bandwidth issues!
Then there is even a future reduction in bandwidth planned in the not far off future. Basically that one will again reduce the bandwidth by half or 6.25 kHz I think. Some radios are already capable of that narrow bandwidth.
I hope that one goes smoother than the current bandwidth reduction did.

I saw a licence app the other day for a town somewhere that was applying for a narrowband change on VHF low band!
Unless there is something in the works to narrowband low band, I think someone was misinformed and does not know that low band does not need to be narrow.
I forget what city or state that was in.
The only thing I could figure is they were using some type of dual band VHF hi and low radios that shared the filters and in order to narrowband their high band frequencies, they also had to narrowband the low band section.
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  #48 (permalink)  
Old 04-28-2014, 8:17 PM
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Quote:
Originally Posted by sodjan View Post
Just FYI...

Sets of 50G filters was shipped today to 12 different addresses,
most of them in the US. Might, with a bit of luck, be delivered
before the weekend, but maybe in the next week. I know close to
nothing about RF stuff, but it's fun to see these come to a use... :-)

Regards, Jan-Erik.
Thanks for the update!
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  #49 (permalink)  
Old 04-29-2014, 2:36 AM
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Quote:
Originally Posted by sodjan View Post
Just FYI...

Sets of 50G filters was shipped today to 12 different addresses,
most of them in the US. Might, with a bit of luck, be delivered
before the weekend, but maybe in the next week. I know close to
nothing about RF stuff, but it's fun to see these come to a use... :-)

Regards, Jan-Erik.
haha I just noticed the name here.. funny stuff.. welcome to the site! thanks for supplying us!
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  #50 (permalink)  
Old 04-29-2014, 6:43 PM
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Anybody have an idea where I can take/send the 396xt to have this mod done considering I don't have the equipment and/or experience to attempt it myself?
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  #51 (permalink)  
Old 04-29-2014, 6:46 PM
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Quote:
Originally Posted by SquierStrat View Post
Shoot me a PM when they arrive.. I'll take one
Me too please.
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  #52 (permalink)  
Old 04-30-2014, 12:23 AM
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Quote:
Originally Posted by davenlr View Post
Since I use my BCT15 almost exclusively for monitor AM Air, Im going to have to take it apart and see if it would be improved by this mod. Less noise on AM Air would be a godsend.
AM is not affected by NFM or FM modulation. I agree with a notch filter add on however...
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  #53 (permalink)  
Old 04-30-2014, 1:15 AM
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Quote:
Originally Posted by scottyhetzel View Post
AM is not affected by NFM or FM modulation. I agree with a notch filter add on however...
AM on the x96XT is also fed through the 450Khz IF filter in the radio, so replacing this filter will also effect AM reception..

That said, if you have high powered FM broadcast transmitters within a few miles of you, then yes, an FM notch filter may help.
Problem is, because the FM broadcast band is so close to the bottom end of the Air band, virtually any FM bandstop or high pass filter you put inline will also attenuate the bottom end of the civilian Air band to some extent as well.

Anyway, following are some test results of the mod.
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Last edited by Boatanchor; 04-30-2014 at 2:16 AM..
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  #54 (permalink)  
Old 04-30-2014, 2:11 AM
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Default Some basic AM/FM sensitivity measurements of the mod.

All of these tests were conducted on a calibrated HP 8921 service monitor.
The same coax patch leads and test configurations were used for both radios.

Radios: 2x brand new 396XT scanners.

For those unfamiliar with dBm, the higher the negative number, the weaker the signal.
-120dBm is a weaker signal than -110dBm.

Most commercial/high end radio manufacturers strive to achieve about -122dBm for 12dB Sinad on NFM/FM and 5% BER on P25.

Stock 396XT

120Mhz AM (70% mod for 10dB S/N) = 116.0dBm
163Mhz NFM (@ 1.5Khz deviation and 12dB Sinad) = -118.3dBm
420Mhz NFM (@ 1.5Khz deviation and 12dB Sinad) = -117.2dBm
820Mhz NFM (@ 1.5Khz deviation and 12dB Sinad) = -116.8dBm

Modified 396XT

120Mhz AM (70% mod for 10dB S/N) = 118.4dBm!
163Mhz NFM (@ 1.5Khz deviation and 12dB Sinad) = -120.6dBm!
420Mhz NFM (@ 1.5Khz deviation and 12dB Sinad) = -119.9dBm!
820Mhz NFM (@ 1.5Khz deviation and 12dB Sinad) = -118.4dBm!

In theory, the replacement filter should have the same passband attenuation figure (6dB max) as the stock filter. So really, the main thing affecting these sensitivity figures is the reduced noise bandwidth of the new filter. Regardless of the contributing factor, up to 2dB improvement in S/N and/or sensitivity on AM and NFM, is pretty amazing.

Testing on a weak, very noisy P25 signal confirms that the modified scanner locks almost immediately to the control channel and decodes perfectly. The stock scanner either ignores the noisy digital signal completely, or intermittently switches back and forth between digital and analogue mode.

Of course, there will always be some variation in sensitivity between units, but as far as I'm concerned, based on the tests I've completed so far, this is a worthwhile mod.

The Elephant in the room though will be 'Standard FM' EDACS decoding.
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  #55 (permalink)  
Old 04-30-2014, 7:23 AM
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Gang,
like I posted earlier. I can do this mod for folks. I have extensive SMD repair experience for the DoD. If you want to send me your scanner just send me an email at ka3nxn(at)comcast.net. I just ordered eight of these filters and I have 4 of my own scanners to do.
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Old 04-30-2014, 7:38 AM
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Boatanchor,

Thanks for your contribution with actual test equipment and results. Unfortunately I do not have access to test equipment like I used to, so I was planning on testing with 2 scanners and the NOAA weather channel and/or on a few active systems in my area.

Over 2dB improvement in sensitivity along with improved selectivity should hopefully be a good thing overall. As mentioned, EDACS may be an outstanding issue, however, I am also hopeful that the narrower filter may help slightly with Simulcast situations, which is possible, but only field testing and comparison between radios will likely answer that question.

I have at least 6 of my own radios to modify if I plan on changing the filters in all of them.

The other test I have not had a chance to try is program all the NOAA frequencies with both FM and NFM settings and alter the NOAA level into the radio with an attenuator and try and determine what the difference in the radio reception and audio levels may be.
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Old 04-30-2014, 8:56 AM
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Default PRO-106

I don't have a schematic but it looks as though my Pro-106 has two filters on the board. They are designated CF1 and CF2 . One has markings of 455HTU and the other simply says FY. So I wonder if GRE has it set up to switch between the two.filters.
Any thoughts?
Bob
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Old 04-30-2014, 5:48 PM
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Quote:
Originally Posted by pro106import View Post
I don't have a schematic but it looks as though my Pro-106 has two filters on the board. They are designated CF1 and CF2 . One has markings of 455HTU and the other simply says FY. So I wonder if GRE has it set up to switch between the two.filters.
Any thoughts?
Bob

Actually this thread answers my questions:
GRE PSR-600 Fixed Level Audio Output Modification

Does anybody have a schematic they can share of the Pro-106. Unable to get it anymore from RS.
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  #59 (permalink)  
Old 04-30-2014, 6:15 PM
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Originally Posted by pro106import View Post
Actually this thread answers my questions:
GRE PSR-600 Fixed Level Audio Output Modification

Does anybody have a schematic they can share of the Pro-106. Unable to get it anymore from RS.
Thanks for the above link

I wasn't aware that GRE didn't feed P25 through the narrow filter, which incidentally, is even narrower than the one we are fitting to the x96XT. The 'H' model filter in the GRE is only 6Khz (+-3Khz) wide.
It would be a little too tight, even for narrowband P25. .

It would be nice to obtain some circuit diagrams for both the Uniden and GRE scanners.

Does anyone out there have an electronic copy of the Pro-106 service manual/circuit?

R
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  #60 (permalink)  
Old 05-01-2014, 10:33 AM
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Just a minor thing...

ka3nxn wrote:
> I just ordered eight of these filters

Now, *if* you are refering to the filters shiped by me, there are *6* (six) in each lot.
If you are refering to some other "order", please disregard this message... :-)

Jan-Erik.
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