In defense of the x36HP's RF performance

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Boatanchor

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One thing I would like to point out in defense of the x36HP scanners, is the adoption of true +-4.5Khz (9Khz wide) NFM IF filters. Such a filter has never been included in a Uniden scanner before to my knowledge, despite 'NFM' being available in previous models for many years.

Thanks to N9JIG (http://forums.radioreference.com/members/n9jig.html), we have some nice close up photos of the interior of the 536HP, showing both the 450E (FM) and 450G (NFM) 450Khz ceramic IF filters sitting side by side.

http://www.carmachicago.com/images/536Ribbon.jpg

Prior to the introduction of the x36HP scanners (x96T & x96XT etc), Uniden only utilized 450E (standard FM) filters despite the NFM channel/menu option. In reality, the only thing the NFM setting did in these older scanners was to add a little audio processing for the lower modulation levels which brought the audio level of NFM signals up to the same level as FM signals. It was a very crude way of doing things. In practice, feeding NFM and P25 signals through the FM filter degraded S/N performance and adjacent channel rejection for both NFM and P25 signals.

With increasing band congestion, narrower channel spacing and very strong signal levels on the LMR and trunking bands, IF filtering performance of these devices was always going to be increasingly important.

It is a little unfortunate that Uniden haven't felt the need to promote or even highlight these positive hardware changes in their designs. So much of the spin around new products nowadays, seems to revolve around software features, while the hardware side of things is either forgotten completely or deemed too 'unimportant' to even mention.

Maybe, some of us enthusiasts would feel a little happier about spending $600 on a receiver if we knew that there were actually some significant improvements being made to the RF performance of these new scanners as well, instead of viewing the x36HP's as simply tarted up x96XT's with a few additional apps.
 

Boatanchor

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And, the BCD996XT for comparison..

As a comparison, here is an internal photo of the BCD996XT depicting the I.F filter and AM / FM demodulator circuit in the BCD996XT.

Note the lone '450E' (FT3) ceramic filter adjacent to the NJM2552 FM/AM demodulator chip.

Actually, there are two 450Khz filters shown here. The second filter (FT2) is the 200Khz wide filter that is selected only when FM Wide / FMB is selected. This is the brown looking unit next to the 10.8Mhz crystal filter. This filter is of no concern when it comes to voice communications though :)

It is interesting that Uniden chose to retain the same NJM2552 AM/FM demodulator chip in the new model.
I guess, if it ain't broke..
 

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Boatanchor

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Only catching up..

And, here's the PRO-196 / PSR-600 showing that in this respect at least, GRE was well ahead of Uniden.

Note that the PSR600 / PRO196 scanners (and their handheld counterparts) incorporated a 'real' NFM IF filter when they were released 7 years ago!

I always new that my PSR600 had a better weak signal S/N performance than the BCD996XT - As long as there were no other strong in-band or broadcast signals around..!

It was a real shame that these radios were let down somewhat by their relatively poor front end filtering performance.
 

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RoninJoliet

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EXCELLENT, im not too smart in this explanation but on the two models I can sure "hear" the difference.....TY
 

garys

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The filtering was the weak spot of the PSR600 and the Pro197. We had the PSR600 in our ambulances and other vehicles and they got killed on 800 Mhz. The ambulances had two 800 Mhz data radios in them and they just hammered the scanners. At times the 800 trunk system we monitored was unusable it was so bad.

The Pro 197 I have at home works fine because it has no nearby strong signals, other than a cell tower about 1/4 mile away. It''s 800 Mhz performance is fine.

I know it's a fine balance that has to be achieved between sensitivity and selectivity, but I have to think that selectivity has to have a slight edge in most scanners.



And, here's the PRO-196 / PSR-600 showing that in this respect at least, GRE was well ahead of Uniden.

Note that the PSR600 / PRO196 scanners (and their handheld counterparts) incorporated a 'real' NFM IF filter when they were released 7 years ago!

I always new that my PSR600 had a better weak signal S/N performance than the BCD996XT - As long as there were no other strong in-band or broadcast signals around..!

It was a real shame that these radios were let down somewhat by their relatively poor front end filtering performance.
 

AZScanner

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Great explanation! I knew there was a big difference between the decoding capabilities of my 436 and my 796 simply because of how much BETTER the 436 works, but I had no idea what hardware changes had made it possible. No doubt these are some of the "hardware upgrades" Paul said was necessary in order to do P25 Phase II. Great job in discovering the goodies "under the hood" on these units.

-AZ
 

XTS3000

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While not a big deal, it is sort of disturbing.
It's hot glue gun material to make sure the ribbon cable doesn't vibrate loose.

I'd rather see Uniden take this approach to secure the ribbon cable (which already has it's own retainers) as a way to further secure that cable to prevent it from ever coming loose. Good job Uniden.
 

Boatanchor

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Yes, ribbon cables have been known to come loose with severe vibration. Hot melt glue is a simple and effective solution to prevent this from occurring.

I'm liking the look of the x36HP RF design, but I would love to see some 'real', detailed performance measurements.
 
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