Boatanchor
Member
- Joined
- Jul 17, 2011
- Messages
- 991
Alternative heading - Supercharge your x96XT scanner
Firstly, let me state that I love the x96XT scanners.
Despite being a few years old now, the XT scanners still have some unique features that were not included in the newer models. It seems a shame then to 'upgrade' when there is little really wrong with the older units - As long as you don't need phase 11 (& simulcast improvement?) capability of course
The one thing that 'did' annoy me somewhat about the x96XT design, was the relatively poor weak signal NFM, AM and P25 receive performance compared to 'real' ($1000 plus) radios and even the older PSR600, in some cases.
This is a problem for me because it has reached the point where 90% of the analogue and P25 comms that I want to listen to are NFM. Standard FM (+-5Khz deviation) is almost a thing of the past now, as virtually all Government and Commercial services adopt the newer Narrowband channels to comply with new government mandates or to reduce spectrum tax in those countries that charge fees based on the spectrum/bandwidth used.
Now, before people pipe up and say "Hey, the x96XT does NFM!, It is an option in the menu for each channel/system that you program in."
Well, the above statement is sort of right, but mostly wrong.
Yes, the option is there to program NFM. However, when you select NFM in the x96XT menu, all you are doing is telling the scanner to add a little extra audio processing to lift the audio level up a little to compensate for the much lower deviation. The scanner is not switching in any narrower filters or changing anything in the RF chain.
The crux of the problem..
The x96XT scanners (unlike the newer x36HP and even the venerable old PSR-5/600 and RS equivalents that both have an FM and a 'real' NFM final IF filter) have only one final IF filter. This 450Khz ceramic filter was chosen as a compromise to pass AM, FM, P25 and NFM. As there is only one filter present, the filter had to have a bandwdth wide enough to pass the widest possible modulation. In this case, standard FM.
The problem is, that the standard 450Khz ceramic filter in the x96XT scanner has a bandwidth that is far too wide for NFM, P25 and even AM. Yes it will work, but adjacent channel rejection and signal to noise ratio will suffer on the narrow modes under weaker signal conditions.
So, what can be done?
Actually, it's relatively simple - Replace the 450Khz final IF filter!
Firstly though, let me state that while I have modded my 996XT, I have not done this mod on a 396XT - Yet!
I see no reason why it couldn't be done, I just haven't had the time to pull the little 396XT apart yet
The original Murata '50E' ceramic filter in the 996XT is not that hard to replace.
Although it is a surface mount device, it can be un-soldered with a fine tipped soldering iron - Carefully!. Ideally, though a SMD rework hot air gun makes the job a quick and simple process.
I chose to replace the stock Murata '50E' filter with a Murata '50G' (+-4.5Khz or 9Khz total BW) filter of the same specification and size.
After replacing the stock IF filter, I have noticed the following characteristics:
* NFM - Weak signals are much, much quieter (less noise, pops & clicks), less adjacent channel interference & improved reception on crowded trunking networks. - BIG improvement!
* AM - Massive improvement in AM aircraft and 27Mhz reception. Less noise, improved weak signal performance etc. (The original filter bandwidth is/was twice as wide as necessary for AM voice reception). Again, BIG improvement!
* P25 - Remember that most P25 modulation is already Narrowband. Replacing the 450Khz IF filter improves weak signal P25 reception and adjacent channel interference for the same reasons it improves NFM performance. If you live in an area where trunking channels are crammed together in narrow portions of the band and you have very strong channels right next to weaker distant channels, this mod is for you!
My 996XT scanner will now decode distant P25 voice at levels so low that the PSR-600 doesn't even know a P25 signal is present (on the same base antenna).
* Standard FM - While the replacement 455kHz IF filter, in theory at least, is a little too narrow for standard (+-5Khz) FM, in practice I haven't noticed any signs of distortion or any signal degradation at all after installing the narrow filter. I have several FM channels programmed into my scan banks including 2M/70CM channels and the odd commercial channel, but I've not noticed any drop in performance on these channels regardless of whether they are very strong or very weak. It is conceivable that there may be very slight audio distortion on voice peaks, if the FM signal is very weak and the deviation of the transmitted signal is right up to or exceeds the +-5Khz level. In most cases though, typical FM signals tend to deviate closer to +-4.5kHz, so you may never even experience this phenomenon.
Overall, I would suggest that if you want optimum performance from your X96XT scanner, this mod is very worthwhile..
Edit -- Oh, one thing I forgot to mention.. After replacing the IF filter, you will still need to select 'NFM' for those channels/systems that use NFM.
As mentioned previously, selecting NFM won't actually change anything in the RF/IF/Demodulation stages, but it will boost the audio level up to the same level as FM, AM and demodulated P25. Of course, you still have the option to adjust the audio gain on a per channel basis as well, if you need to fine tune the levels a little.
Important! If you are not confident in pulling your radio apart, you don't want to void any remaining warranty or you are not comfortable messing with SMD components (even big ones) - Do not attempt!
Firstly, let me state that I love the x96XT scanners.
Despite being a few years old now, the XT scanners still have some unique features that were not included in the newer models. It seems a shame then to 'upgrade' when there is little really wrong with the older units - As long as you don't need phase 11 (& simulcast improvement?) capability of course
The one thing that 'did' annoy me somewhat about the x96XT design, was the relatively poor weak signal NFM, AM and P25 receive performance compared to 'real' ($1000 plus) radios and even the older PSR600, in some cases.
This is a problem for me because it has reached the point where 90% of the analogue and P25 comms that I want to listen to are NFM. Standard FM (+-5Khz deviation) is almost a thing of the past now, as virtually all Government and Commercial services adopt the newer Narrowband channels to comply with new government mandates or to reduce spectrum tax in those countries that charge fees based on the spectrum/bandwidth used.
Now, before people pipe up and say "Hey, the x96XT does NFM!, It is an option in the menu for each channel/system that you program in."
Well, the above statement is sort of right, but mostly wrong.
Yes, the option is there to program NFM. However, when you select NFM in the x96XT menu, all you are doing is telling the scanner to add a little extra audio processing to lift the audio level up a little to compensate for the much lower deviation. The scanner is not switching in any narrower filters or changing anything in the RF chain.
The crux of the problem..
The x96XT scanners (unlike the newer x36HP and even the venerable old PSR-5/600 and RS equivalents that both have an FM and a 'real' NFM final IF filter) have only one final IF filter. This 450Khz ceramic filter was chosen as a compromise to pass AM, FM, P25 and NFM. As there is only one filter present, the filter had to have a bandwdth wide enough to pass the widest possible modulation. In this case, standard FM.
The problem is, that the standard 450Khz ceramic filter in the x96XT scanner has a bandwidth that is far too wide for NFM, P25 and even AM. Yes it will work, but adjacent channel rejection and signal to noise ratio will suffer on the narrow modes under weaker signal conditions.
So, what can be done?
Actually, it's relatively simple - Replace the 450Khz final IF filter!
Firstly though, let me state that while I have modded my 996XT, I have not done this mod on a 396XT - Yet!
I see no reason why it couldn't be done, I just haven't had the time to pull the little 396XT apart yet
The original Murata '50E' ceramic filter in the 996XT is not that hard to replace.
Although it is a surface mount device, it can be un-soldered with a fine tipped soldering iron - Carefully!. Ideally, though a SMD rework hot air gun makes the job a quick and simple process.
I chose to replace the stock Murata '50E' filter with a Murata '50G' (+-4.5Khz or 9Khz total BW) filter of the same specification and size.
After replacing the stock IF filter, I have noticed the following characteristics:
* NFM - Weak signals are much, much quieter (less noise, pops & clicks), less adjacent channel interference & improved reception on crowded trunking networks. - BIG improvement!
* AM - Massive improvement in AM aircraft and 27Mhz reception. Less noise, improved weak signal performance etc. (The original filter bandwidth is/was twice as wide as necessary for AM voice reception). Again, BIG improvement!
* P25 - Remember that most P25 modulation is already Narrowband. Replacing the 450Khz IF filter improves weak signal P25 reception and adjacent channel interference for the same reasons it improves NFM performance. If you live in an area where trunking channels are crammed together in narrow portions of the band and you have very strong channels right next to weaker distant channels, this mod is for you!
My 996XT scanner will now decode distant P25 voice at levels so low that the PSR-600 doesn't even know a P25 signal is present (on the same base antenna).
* Standard FM - While the replacement 455kHz IF filter, in theory at least, is a little too narrow for standard (+-5Khz) FM, in practice I haven't noticed any signs of distortion or any signal degradation at all after installing the narrow filter. I have several FM channels programmed into my scan banks including 2M/70CM channels and the odd commercial channel, but I've not noticed any drop in performance on these channels regardless of whether they are very strong or very weak. It is conceivable that there may be very slight audio distortion on voice peaks, if the FM signal is very weak and the deviation of the transmitted signal is right up to or exceeds the +-5Khz level. In most cases though, typical FM signals tend to deviate closer to +-4.5kHz, so you may never even experience this phenomenon.
Overall, I would suggest that if you want optimum performance from your X96XT scanner, this mod is very worthwhile..
Edit -- Oh, one thing I forgot to mention.. After replacing the IF filter, you will still need to select 'NFM' for those channels/systems that use NFM.
As mentioned previously, selecting NFM won't actually change anything in the RF/IF/Demodulation stages, but it will boost the audio level up to the same level as FM, AM and demodulated P25. Of course, you still have the option to adjust the audio gain on a per channel basis as well, if you need to fine tune the levels a little.
Important! If you are not confident in pulling your radio apart, you don't want to void any remaining warranty or you are not comfortable messing with SMD components (even big ones) - Do not attempt!
Last edited: